Term
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Definition
| German who tied hair loop between developing tadpole cells and showed that not always equivalent cells |
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Term
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Definition
| activation of a relay by a receptor on a cell receiving an initial cellular signal |
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Term
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Definition
| the process in which a signal evokes a cellular response |
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Term
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Definition
| that which binds to or is tied to a receptor |
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Term
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Definition
| ligand is secreted and enters the circulation |
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Term
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Definition
| ligand is secreted but remains in the locality to affect nearby cells |
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Term
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Definition
| ligand secreted to act back on the signaling cell itself |
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Term
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Definition
| traces lines of descent. Unequal division of cytoplasmic material can explain differences between related cells |
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Term
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Definition
| Examines the neighboring cell populations. Autocrine and paracrine signaling can influence cells. Variations in temperature, UV light, ion concentration, etc. |
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Term
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Definition
| maternal effect factors derived from mother's genetic information - transcribed or translated and then stored in eggs |
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Term
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Definition
| entire embryo and fetal placenta |
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Term
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Definition
| all the embryonic structure |
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Term
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Definition
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Term
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Definition
| oogonium - primary oocyte - secondary oocyte - ootid - ovum |
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Term
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Definition
| spermatoonium - primary spermatocyte - secondary spermatocyte - spermatids - spermatazoon |
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Term
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Definition
| female secretions that make sperm viable |
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Term
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Definition
| acrosomal filament - protein binding - species specific |
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Term
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Definition
| still have 2 separate pronuclei in egg |
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Term
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Definition
| support cells that provide sperm testosterone |
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Term
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Definition
| support cells that provide nutrients to sperm |
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Term
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Definition
| give rise to sperm and eggs, migrate to gonads, not originally formed there. |
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Term
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Definition
| the developing primary oocyte enters the extended prophase of the first meiotic division, it is exceptionally large, with a very prominent nucleus often called the germinal vesicle |
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Term
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Definition
| The nucleus of the egg from the two divisions of meiosis is called female pronucleus - it contains only one of each chromosome type and is haploid. |
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Term
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Definition
| Germ cells and their associated accessory cells line the perimeter of connective tissue tubes called seminiferous tubules. |
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Term
spermiogenesis
- histones replaced by protamines (dense packing of chromatin) |
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Definition
| spermatids undergo reorganization and transition from spermatid to spermatozoon near the center of the seminiferous tubule |
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Term
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Definition
Take any cell and put it into an activated egg. It will produce a new cloned organism.
Genomic (nuclear) equivalence – Each cell has the same complement of DNA
Nuclei from differentiated adult cells are able to give rise to all embryonic tissues
This new embryo can become an adult – usually stays as tadpole
Gurden, et al.
1-Culture frog skin cells
2-Break membrane by drawing the cells into a narrow pipette
3-Take an activated frog egg and functionally remove the nucleus, i.e. UV light to inactivate nucleus.
4-Inject cells into enucleated egg
5-Cleavage occurs
6-Tadpole forms - shows nuclei are totipotent
7-Rarely get adult - something else happening. Also done with insects & Dolly the famous sheep |
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Term
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Definition
Each cell has the ability to form the entire embryo plus fetal placenta
Totipotent stem cells can form embryo and fetal placenta |
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Term
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Definition
form the embryo
Pluripotent stem cells – Each cell has the ability to form all the embryonic structure |
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Term
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Definition
Can give rise to subsets of cell types
Committed stem cells can give rise to subsets of cell types, i.e. hemangioblasts - blood vessels, blood cells and lymphocytes |
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Term
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Definition
are precursor cells. They have some level of differentiation. They do not divide into progenitor cells, i.e. Myeloid progenitor cells - can generate all different type of blood cells.
Progenitor (precursor) – no longer stem cells – give rise to very specific types of cells yet can still be considered general |
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Term
| Nonequivalent cell division |
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Definition
Mother cell can change mating type
Daughter cell cannot
Divide a Frog egg at 2 cell stage. Sometimes get two embryos. Sometimes get one embryo and one poorly differentiated entity.
Mouse Embryo
Outer cells can form extra-embryonic tissue
Inner cells form embryo
16 cell stage mouse embryo
A Cells - placenta - therefore committed cells
B Cells - embryo - therefore pluripotent cells
These A and B cells are nonequivalent |
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Term
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Definition
traces lines of descent. Unequal division of cytoplasmic material can explain differences between related cells
Lineage traces lines of descent cytoplasm and subcellular organelles shared by offspring. Not necessarily equivalent. |
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Term
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Definition
Examines the neighboring cell populations. Autocrine and paracrine signaling can influence cells. Variations in temperature, UV light, ion concentration, etc.
Position Information obtained from neighboring cells or environment in which cell is located. |
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Term
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Definition
Lose a body part
Neighboring cells dedifferentiate
area expands and cells redifferentiate
Blastema forms
The nuclei of cells are equivalent yet cells have specific fates depending on environment.
During regeneration the cells dedifferentiate and start to follow a different path.
Sever a limb from a salamander, the stump heals and a mound of cells called the blastema form under the epithelium and over the stump. Get cell division, migration, redifferentiation and a new intact limb.
Note: Differentiation is when cells become specialized. Some genes are active and others inactive in a specific cell type. |
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Term
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Definition
Environmental influences internal Vs external, i.e. signaling from outside, influences internal environment. Maternal effect factors (distribution of factors) influences different regions of the embryo.
As we will find out later even the site of sperm penetration causes environmental changes. |
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Term
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Definition
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Term
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Definition
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Term
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Definition
Organs for reproduction
Ovary – egg formation
Testis – sperm formation
Primordial germ cells (PGC’s) |
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Term
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Definition
Formation of gametes (sperm and egg). The gametes are formed in the gonads. The gonads are the ovaries and the testes. An ovary produces eggs and a testis produces sperm
Primordial germ cells (PGC’s) are the precursor to the germ line. PGC’s do not arise in gonads but migrate to developing gonads.
Most animals have a clear separation of germ cells and somatic cells early in development. This helps to keep the germ line safe.
For other animals and plants this is not the case. For example in jellyfish (cnidaria), sea squirts (tunicates) and flat worms the somatic cells can become germ cells even in adults. |
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Term
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Definition
Oogonia
PGC’s within ovary
Stem cells in frogs
Not stem cells in humans
Accessory cells
Contribute to egg development
Support cells
Produce hormones
Produce shells
Release egg from ovary
Extensive growth
Germinal vesicle formation
Meiosis
Equal karyokinesis
Unequal cytokinesis
Oogenesis is characterized by extensive growth, i.e. chicken, reptile – single cell but lots of yolk.
Germinal vesicle formation. Some organisms form a germinal vesicle. This is when the developing egg stops after it undergoes Meiosis I. Frog oocytes have germinal vesicles.
Pronucleus formed. Other organisms form a pronucleus. This occurs when the 2nd Meiotic division is completed. Humans form a pronucleus |
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Term
| The first step in gametogenesis |
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Definition
get PGC to genital ridge as gonad is forming (both male and female)
PGC in ovary called oogonia In humans these are not stem cells. A single oogonium will mature into a Primary oocyte. In Frogs these are stem cells. Each season the oogonium will divide via mitosis into 1000’s of Primary oocytes
Accessory cells - contribute to oogonium .
Support cells produce hormones, make shells, and release the egg from the ovary. |
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Term
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Definition
| Accessory cells - contribute to oogonium |
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Term
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Definition
| Supporting cells - produce hormones, make shells, and release the egg from the ovary |
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Term
| Germinal vesicle formation |
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Definition
Some organisms form a germinal vesicle. This is when the developing egg stops after it undergoes Meiosis I. Frog oocytes have germinal vesicles.
Xenopus laevis |
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Term
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Definition
| Other organisms form a pronucleus. This occurs when the 2nd Meiotic division is completed. Humans form a pronucleus |
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Term
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Definition
Stores vast quantities of material
Yolk assembled into organelles called yolk platelets – unevenly distributed to vegetal side (animal side less yolk)
Pigment granules, if present, may or may not be evenly distributed. The frog has pigment granules in its animal hemisphere to protect from UV light.
Female pronucleus (or germinal vesicle) is usually near the periphery.
Cortical granules near surface.
Cortex - Peripheral cytoplasm – has different cytoskelatal structure than internal cytoplasm.
NOTE: Parts of egg very differently, therefore future mitotic cells will have different environments. |
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Term
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Definition
is the production of sperm from Primordial Germ Cells.
PGC’s arrive at genital ridge
Incorporate into sex chords
At maturity-sex chords hollow – seminiferous tubules
Epithelium differentiate into Serotoli cells
PGC’s become type A1 spermatogonium
Leydig cells - testosterone
In male vertebrate
PGC’s arrive at genital ridge. They became incorporated into sex chords and stay there until maturity. At maturity the sex chords hollow to form seminiferous tubules. The epithelium of the seminiferous tubules differentiate into sertoli cells (accessory cells). These cells nourish and protect developing sperm cells.
PGC’s become type A1 spermatogonium (stem cells). These are smaller than PGC’s and are characterized by ovoid nucleus.
A1 Spermatogonium are found adjacent to outer membrane of sex chords.
During fetal development Interstitial Mesenchyme cells of testes differentiate into leydig cells (support cells) which produce testosterone
A1 spermatogonium divide-Produce A1 (stem cells) and A2 spermatogonium
A2 spermatogonium divide producing 2x A3 spermatogonium
A3 spermatogonium divide – each producing 2x A4 spermatogonium (still stem cells)
A4 spermatogonium divide
New A4 spermatogonium
apoptosis
Intermediate spermatogonium (committed stem cells)
Undergoes mitosis – 2x Type B spermatogonium
Undergoes mitosis – 2x Primary spermatocyte
Undergoes meiosis yielding spermatid
A4 - New A4 Spermatogonium
Or Apoptosis
Or Intermediate Spermatogonium
Intermediate Spermatogonium – Committed Stem Cell
- Type B Spermatogonium 1 Spermatocyte
- Type B Spermatogonium 1 Spermatocyte
1 Spermatocyte Undergoes Meiosis (yielding Spermatids) |
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Term
| Fate Maps and Lineage Diagrams |
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Definition
Trace cell lineage
Cell – Cell interaction
Lineage and position play a role in determination.
Fate maps are prepared by tagging cells and then observing the location of the descendents in the adult. These can be displayed as a lineage map which outlines the descendents of the original cells and their final structure within the adult |
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Term
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Definition
| rapid mitotic division after fertilization |
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Term
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Definition
isolecithal (limited or no yolk) and mesolecithal (moderate amount of yolk) eggs
Entire cytoplasm of Zygote is partitioned into cells. Seen in species with low to moderate yolk content |
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Term
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Definition
| Echinoderms and amphibians (mesolecithal - displaced radial) |
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Term
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Definition
| Annelids, mulluscs, and flatworms |
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Term
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Definition
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Term
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Definition
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Term
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Definition
are maternal effect genes which produce maternal effect gene products. By definition - Morphogens – substances (proteins) that in influence development by their presence, absence, and in between concentration (gradients)
There are 34 Morphogens in Drosophila
12 Anterior – Posterior (9 of these are Posterior)
6 Extreme ends, Acron & Telson
16 Dorsoventral |
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Term
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Definition
| Simultaneous narrowing and lengthening of a sheet of cells. Brought about by intercalation of cells. |
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Term
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Definition
| Migration of individual cells from surface layer to the interior of embryo. |
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Term
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Definition
| Movement of a sheet of cells into the interior of the embryo, forming a pocket which has an opening to the surface. |
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Term
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Definition
| Folding of a sheet of cells under itself. The sheet then spreads over the internal surface of the cells that remain on the outside. |
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Term
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Definition
| Spreading of a sheet of cells to enclose underlying layers. It is brought about by increase in cell numbers (cell division) flattening of cells or intercalation of subsurface cells into the surface layer |
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Term
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Definition
| Splitting of a layer of cells into 2 layers |
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Term
| Four extraembryonic membranes |
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Definition
Chorion – outer layer of protection
Allantois – Highly vascularized
Yolk sac – highly vascularized
Amnion –inner layer of protestion |
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Term
| Spemann Organizer (Dorsal lip of Blastopore) |
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Definition
A) In older view - induces the nervous system
B) In current view - inhibits cells from becoming epidermis. Therefore the default structure is neural tissue.
Ventral portion of the embryo’s ectoderm produces BMP4 (BMP family of growth factors).
Dorsal ectoderm releases Noggin and Chordin. Chordin is an antagonist to BMP4. Noggin and Chordin form concentration gradient in gastrula phase. Therefore the organizer tissue in the dorsal midline have higher anti BMP concentration and lower BMP concentration. This prevents prospective neural plate cells from becoming epidermis. They form neural tissue by default.
Not sure what causes differentiation between brain and spinal chord. We will discuss this more later in the semester. |
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Term
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
| Stem above the cotyledons |
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Term
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Definition
| Stem portion between cotyledon and root |
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Term
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Definition
| Junction between main stem and leaf |
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Term
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Definition
| regions of cell division. They are embryonic like throughout the life of plant. The meristems are constantly generating new plant organs. |
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Term
| Plants cell fate - position vs. liveage |
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Definition
| In plants position not lineage determines cell fate |
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Term
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Definition
Growing Tip of Shoot and Root
The center is the Central Zone and consists of cells with lots of small vacuoles that renew the meristem – slow cell division.
Peripheral Zone – surrounds the Central Zone – is the morphogenetic region. It contains cells that form the organs – rapid cell division. |
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Term
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Definition
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Term
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Definition
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Term
| Chimeric plants can be used to study final destination of cells. |
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Definition
The destinations are as follows:
L1 – Epidermis
L2 – Bulk of leaf and flower
L3 – Central portion of organ and stem |
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Term
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Definition
position of leave on the stem. Involves communication among existing and newly formed leaf primordium.
Phyllotaxy may change as the plant matures (i.e. spiral Whorled) or by external manipulation (cut the meristems) |
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Term
| Leaves arranged as spiral or whorls |
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Definition
| Whorls can have one leaf, 2 leaves or 3 leaves (leaves/node). The nodes are alternating (180). This is due to chemical and physical interaction and constraints. For instance maize is normally 1 leaf alternating but the mutation abphyl (aberrant phyllotaxy), gives a very large meristem with 2 leaves instead of one. |
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Term
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Definition
allow for cell elongation or expansion. This causes cell wall expansion leading to change in organ pattern.
Class of hormones. |
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Term
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Definition
Leaf axil is the junction between leaf & main stem. Axillary meristems are found in leaf axils and produce axillary buds.
SAM displays apical dominance – suppress axillary meristems get Christmas tree appearance.
Remove SAM get bushy appearance |
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Term
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Definition
| forms from surface cells on stems and leaves get bushy appearance even without SAM |
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Term
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Definition
| cambrium layer causes increase in width of plants or production of bark. |
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Term
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Definition
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Term
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Definition
| is the meristematic region just below the root cap |
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Term
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Definition
| is where the cells elongate |
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Term
| Zone of Cell Differentiation |
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Definition
| is where cells differentiate into Xylem and Phloem as well as where lateral roots and root hairs form |
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Term
| Quiescent Center of Root Meristem |
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Definition
| contains slowly dividing cells |
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Term
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Definition
Ancestral angiosperms are believed to have formed a terminal flower directly
from SAM. Modern angiosperm – variety of flowing patterns where axillary buds
are inflorescent – Inflorescent meristem shift from making leaves to making
flowers. The change to making flowers probably arises from centroradiulus
(cen) gene (in snapdragon). CEN prevents terminal flower formation – CEN
suppresses Floricaula (Flo) (specifies floral meristem) however, FLO stimulates CEN |
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Term
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Definition
| Some flowering is regulated by day length |
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Term
| Where two cortex cells meet |
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Definition
will be root hair (Epidermis forms root hairs)
or atrichoblasts
Root hairs absorb water, allow bacteria to enter, grows in zone of differentiation from epidermal cells. |
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Term
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Definition
– all epidermal cells make root hairs
Hairy roots, no hair on stems. |
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Term
| Normally atrichoblasts produce gl2 |
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Definition
| which produce atrichoblasts |
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Term
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Definition
Trichoblasts (hair precursors) and are structurally different than atrichoblasts (non-hair epidermal cells).
Cortical cells provide signal. Hair cells are next to 2 cortical cells whereas non-hair cells are next to one. |
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Term
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Definition
Hair on leaves & stems
gl2 mutants produce trichomes on leaves which are small compared to normal
and the plant has hairy roots. |
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Term
Transparent testa glubra (ttg) mutant
Why? |
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Definition
no trichomes on leaves, lots of hair on roots.
ttg stimulates gl2. No ttg then no gl2 |
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Term
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Definition
| expressed in non hair cells (root) are required for differentiation. |
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Term
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Definition
| is expressed in the epidermal cells of leaf and are required for trichome formation. |
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Term
| In root, wer, and in leaf, gl1 |
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Definition
| are needed to stimulate gl2 |
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Term
Asymmetrical division yields
Stomata Formation |
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Definition
guard mother cell (GMC)
Adjacent cells undergo asymmetric division, smaller ones close to GMC called subsidiary cells
GMC divides symmetrically producing guard cells
Stomata formation occurs in both monocots and dicots, The stomata is an opening surrounded by photosynthetic guard cells. When the guard cells are actively photosynthesizing (daytime) the stomata is open. It is closed at night. |
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Term
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Definition
Abscisic acid
Auxin
Brassinosteroids
Cytokinins
Ethylene
Giberillins |
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Term
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Definition
| Stomata closure, maintenance of dormancy. Prevents germination. Soak seeds leach out ABA get germination. |
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Term
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Definition
| Apical dominance, cell elongation, phototropism, geotropism, fruit development. Xylem regeneration in wound healing, adventitous root formation. |
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Term
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Definition
| Cell elongation, cell division. Produces steroid reductase enzyme (in humans this enzyme would reduce testosterone). If mutated get short plant. If replace with wildtype or human gene get plan of normal height. If overexpress the gene get large plant |
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Term
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Definition
| cell division yielding shoot formation in culture, delay of leaf senescence, release of apical buds |
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Term
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Definition
| Induced by auxin causes fruit ripening, root hair growth, abscission, senescence, |
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Term
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Definition
| cell elongation, floral induction, seed germination. |
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Term
**Numb
Sensory Organ Precursor Cell (SOP)
neuron
sheath cell
Hair Cell
Socket cell |
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Definition
differentiated - glial mother cell (gets all of Numb)
neuroblast cell gets none of Numb
Body of adult fruit fly is covered with sensory bristles, each composed of a peripheral neuron, a hair cell, a sheath cell and a socket cell. These were derived from a sensory organ precursor (SOP) cell located in the surface epithelium of the pupa.
During pupal development the SOP undergoes 2 asymmetrical cell divisions. Numb goes to one of two daughter cells
IIb gets numb – divides into a sheath cell (no numb) and neuron (numb)
IIa does not get numb – it accumulates numb and divides into hair cell (gets numb) and socket cell (no numb). |
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Term
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Definition
A cell is destined to adopt a neural fate (has numb) it sends out inhibitory Information (delta and serrate). Through paracrine signaling to inhibit other cells. These cells have a notch receptor and are therefore prevented from being neural. Presence of Numb prevents the “neural fated” cell from receiving information in its notch receptor.
Homozygous notch mutants lethal all epidermal cells become neuroblasts |
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Term
Overview Segmentation
Hunchback, Nanos (inhibit hunchback - posterior), bicoid (anterior), Oskar |
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Definition
GAP genes – (mutations – large gaps in segments in Flies) are expressed just prior to cellular blastoderm stage. All encode transcription factors MRNA’s proteins unstable short lived. Large areas anterior to posterior are specified. Then pair rule genes are expressed (early zygotic genes) specify 7 broad stripes.
Next get segment polarity genes (expressed during gastrulation) to subdivide 7 regions into 2 each. Therefore 14 narrower stripes, each with clear anterior and posterior polarity. Some transcription factors, some ligands, some receptors.
Finally homeotic genes, (homeotic selector genes) – type of homeobox genes specify the identity of the different segments |
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Term
Gap genes - Encode Factors Transcription
7 broad areas of the embryo
Turned on by zygote |
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Definition
| Outlines the distribution of the Zygotically active gap genes; tailless, huckebein, giant, hunchback, kruppel, knirps. Gap genes establish 7 broad stripes in embryo; get very specific regions of gene expression. The genes may influence each other in complicated ways, i.e., bicoid (anterior) + hunchback anterior. Hunchback inhibits giant and therefore giant is found more posterior (no hunchback). However, bicord (anterior) is positive regulator of giant therefore even though hunchback is present still get giant |
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Term
| Pair Rule Genes - Transcription factors |
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Definition
There are 8 pair rule genes – encode transcription factors
There are 3 - primary pair rule -> runt, hairy, eve (even skipped)
There are 5 – secondary pair rule -> ftz, opa, odd, slp, prd |
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Term
| Regulation of Eve Expression |
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Definition
Early promoter for eve is influenced by gap genes and turns eve on in strips 2,3, & 7 (represented by sites E3, E7 and E2)
Maternal genes bicoid and hunchback activate and gap genes.
kr and gt repress
Eve expression -> Relationship determined if early enhancer eve is active. Hairy, runt, and eve needed to activate late enhancer to get eve expressed in other stripes and maintained in all. |
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Term
Segment Polarity Genes
Transcription Factors – Ligands Receptors |
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Definition
Segment polarity genes divide 7 regions from pair rule into 14 parasegments
4 key segment polarity genes engrail (en), naked (nkd) patched (ptc) and wingless (wg) (won’t discuss others)
Each is expressed in one cell of the 4 cell wide parasegment.
Pair rule gene eve positively influences engrail
Pair rule gene Ftz positively influences engrail |
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Term
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Definition
Expression of engrail (anterior of parasegment) stimulates hedgehog (Hh) production.
Engrail stimulate more engrail
Active Hh interacts with patched and smoothened (PTC-Smo) receptors on the adjacent cell (posterior end of earlier para segment) PTC inhibited wingless except when Smo is also stimulated therefore wingless (wg) is expressed.
Wg binds frizzled (a receptor on en expressing cell) stimulating En expression.
infulences itself and HH, which binds to both PTC and SMO, turns on WG. WG influences |
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Term
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Definition
Bithorax complex (Bx-C) -> 3 genes ultrabithorax (ubx), abdominal A and abdominal B (abdA & abdB). Null mutation Bx-C lose all abdominal segments and 3rd thoracic segment replaced by duplicated 2nd thoracic – lethal. UBx null mutation – T3 and A1 become T2 (flies with 4 wings) Ubx and AbdA, AbdB contain homeodomains which binds DNA (transcription factors). Mutations in homeobox -> homeobox mutations) (Not all homeoboxs are homeotic). Each gene has alternative promoters and splice sites -> very complicated regulation. Why? -> these genes repress anterior genes such as ant C complex genes
Gene complexes - must be expressed linearly in the embryo |
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Term
| BX-C and ANT-C Complexes, continued |
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Definition
Arrangement Bx-Complex. If put Bx-C to another location get normal development. Rearrange order major mutations. For some reason order is important in regulating those genes or their function.
Ant-C’s genes are arranged linearly, labial (lab), deformed (dfd-maxillary), sex comb reduced (scr) T1, and antennapedia (antp) T2, also gene pb (proboscipedia) all structures have T1 morphology – acts only in adults.
Null mutation – Labial parts of mouth become legs. |
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Term
| 7 segments into 14 parasegments of 4 cells |
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Definition
| Gap rule genes influence Primary pair rule genes which influence segment polarity genes which influence homeotic selector genes |
|
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Term
| BX-C and ANT-C Complexes, more |
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Definition
Gap genes -> stimulate pair rule gene expression -> stimulate homeotic gene expression
4 Homeotic genes -> Antp (from Ant-C) and the 3 BX-C genes are shown.
Posterior gene products prevent transcription of the more anterior genes (Blue Lines) and the proteins of these genes (red lines) allowing appropriate development. |
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Term
| Anterior-posterior Patterning of Drosophila Wing |
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Definition
Wing development. Posterior wing cells express engrail proteins which stimulates (regulates) Hh and Hh is secreted. Anterior cells with patch and (partnered with) smoothened receptors bind Hh.
Stimulates Dpp (decapentaplegic) expression just anterior. Dpp diffuses anteriorly and posteriorly and organizes posterior and anterior portions of the wing. |
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Term
| Dorsal-Ventral Patterning of Drosophila Wing |
|
Definition
D/V interactions in wing development.
Apterous (Apt) and fringe (Fng) is 1) expressed dorsally and 2) Apt stimulate signal cascade between D & V compartments by stimulating dorsal cells to express serrate (membrane bound) ligand for the notch receptor.
For secreted protein fringe. Fringe and notch form a complex making notch less sensitive to serrate and increasing sensitivity to Delta (another ligand of notch) Localized expression of Fng binding to notch allows wingless to be expressed at the D/V border. Therefore, dorsally fringe secreting cells upregulate production of serrate due to Apt and lower sensitivity to serrate.
Ventrally -> sensitive to serrate. Activating notch at D.V. border stimulating wingless transcription which is needed for wing development. Wg gene produces WNT protein (wingless). |
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Term
| Dorsal_Ventral Patterning of Drosophila Wing |
|
Definition
The wingless protein (wnt) is activated by porcupine (porc) and binds to receptor family (frizzled)
Frizzled -> inhibits the destruction of Beta catenin.
Beta-catenin -> stimulates WNT response gene -> wing structure. |
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