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Vocababble: Embryonic Limb Development

QUIZ YOURSELF
1. What is the first major tissue of the limb to differentiate?
2. How do myotomal cells find their way from the somites to the limb to become muscle?
3. What kind of neurons are formed from neural crest cells?
4. What kind of cells migrate medially from the axis to form vertebrae and ribs?
5. What does AER stand for?
6. What (the heck) does the AER do and why?

1. bone
2. they follow the tendons
3. sensory neurons
4. schlerotome cells
5. apical ectodermal ridge
6. thank god for wikipedia;
The Apical Ectodermal Ridge (AER) is a critical component in vertebrate limb development. The AER is an ectodermal structure overlying and inducing the developing limb bud of the vertebrate embryo, and will eventually give rise to the skin covering the limb. Initial formation of the AER is induced by secretion of the fibroblast growth factor FGF-10 from the somatic layer of the lateral plate mesoderm. This initial induction is believed to result from the activity of Hox genes. The AER then secretes FGF-8 back into the mesoderm, stimulating its proliferation and the formation of the progress zone. Continued secretion of FGF-8 by the AER sustains limb formation throughout the process of development. The AER also signals to the Zone of Polarizing Activity (ZPA), which establishes the anterior-posterior axis (thumb versus pinky finger) in the limb bud.

cranial-caudal axis = head to tail axis? anterior-posterior axis? thumb to pinkie axis?

amelia = absence of a limb (can you imagine naming your daughter Amelia?)

meromelia = absence of limb segments (Ocoee Ed has shortened forearms, could have had meromelia if things had gone a little differently)

phocomelia = a kind of meromelia---absence of proximal segemtns but with normal distal segments

polydactyly = extra digits

syndactyly = webbed digits

Thalidomide = drug for nausea that was given to pregnant women causing birth defects. Disrupts cell adhesion in the limbs by down-regulating cell surface adhesion receptors (integrins, selectins) or by inhibiting angiogenesis.

angioblasts = mesodermal vasculoformative cells

marginal sinus = in embryo, becomes cephaic and basilic veins

central artery (in fetus) becomes brachial and interosseus arteries, radial and ulnar branch from brachial

paraxial = on either side of the axis of a skeleton

homeobox = one of various similar homeotic genes that are involved in bodily segmentation during embryonic development

somite = A segmental mass of mesoderm in the vertebrate embryo, occurring in pairs along the notochord and developing into muscles and vertebrae.

sclerotome = One of the bony, cartilaginous, or membranous partitions which separate the myotomes. Becomes vertebrae and ribs. Forms from somitic cells when Shh from notochord and neural tube induce Pax (1,9) genes which convert somitic cells into cartilage producing cells.

dematome = 1. zone of somitic cells that becomes dermis 2. skin served by one spinal nerve: an area of skin that has nerve fibers coming from a single spinal nerve

myotome = becomes muscles of back and limbs, formed when Wnt genes transform dorsal somitic cells into dermatome and myotome

Shh = sonic hedgehog. The best studied ligand of the hedgehog signaling pathway. It plays a key role in regulating vertebrate organogenesis, such as in the growth of digits on limbs and organization of the brain.

Wnt = wingless type, a segment polarity gene, Body axis specification: Injection of Xenopus eggs with Wnt inhibitors is involved in the development of a second head. Wnt is extensively involved in formation of the posterior nervous system and are released by tail "organizers". Morphogenic signaling: Wnts produced from specific sites, such as the edge of the developing fly wing or the ventral edge of the neural tube of the developing vertebrate, are distributed throughout adjacent tissues in a gradient fashion. The Wnt pathway becomes activated to different degrees in cells of these tissues depending on how close they are to the production site, leading to subtle but crucial differences in the level of genes regulated by the Wnt pathway.

limb bud = embryonic beginning of arm or leg, derived from somatic lateral plate mesoderm. Limb develops from these cells and also tissue that migrates from the somites, including migrating muscle & dermal cells.

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