Synopsis6 - Katherine Avanesyan, Brittany Eldridge,...

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Katherine Avanesyan, Brittany Eldridge, Anneliese Arno, Jeremy Greeter Synopsis (Limblessness in Pythons) The python ancestor likely had complete forelimbs and hindlimbs. The first major morphological change was the complete loss of forelimbs and the expansion of the thorax. Loss of the hindlimbs came later, leaving limb rudiments and pelvic rudiments in some snakes. Pythons have over 300 vertebrae. All of those anterior to the hindlimbs have ribs, except the atlas (C1). Anterior vertebrae have both ribs and ventral hypopheses, which are thoracic and cervical features, respectively. It is necessary to define the terms of the paper to understand its purpose. SHH is a protein located in the polarizing region that uses a diffusion gradient to regulate the development of limbs and digits and specifies anteroposterior limb patterning. FGFs include many specific types of growth factor proteins, such as FGF2 and FGF8, which interact with proximal molecules, such as SHH; however, they share the common ability to promote proliferation and differentiation in a wide variety of cells. In this experiment FGFs were monitored and intentionally misexpressed in pythons in order to test their involvement in limb formation/repression. Somites are masses of mesoderm distributed along the two sides of the neural tube that are highly involved in rib formation. HOXC6, HOXC8, and HOXC5 were found to be expressed in these somites. The study of the expression of HOX genes in somites is important because they’re the precursors for limb formation. Other important regions involved in limb formation are the Zone of Polarizing Activity (ZPA) and the Apical Ectodermal Ridge (AER). The AER is a layer of cells located in the ectoderm of a budding limb. The ZPA is an area of mesenchyme that conveys signals to the budding limb to form along the anterior/posterior axis. The ZPA and the AER are dependent on each other and are closely related due to interactive signaling pathways. The AER expresses FGF8, which induces SHH expression, which goes on to induce FGF4 to be expressed. FGF soaked beads can mimic the AER and that
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This note was uploaded on 10/24/2010 for the course BIOL 514 taught by Professor Goldstein during the Fall '10 term at UNC.

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Synopsis6 - Katherine Avanesyan, Brittany Eldridge,...

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