BIOL 030 Lecture Notes - Lecture 25: Apoptosis, Neutrophil, Valine
16 Sep 2020
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Document Summary
Zone of polarizing activity (zpa) cluster of cells at caudal border of limb that establish the cranio-caudal polarization (proper location of digits etc. ) Produces retinoic acid which initiates expression of sonic hedgehog. Absence of shh causes regression of aer (why???) As limb grows the zpa moves distal to keep up with the aer. Dorsoventral axis regulated by bmps in ventral ectoderm. Bmps cause expression of engrailed on ventral side, which represses stuff that is secreted by dorsal side. Influenced by combinations of shh and others. Apoptosis in specific parts of aer creates separate ridge for each digit. If cell death does not occur syndactyly (abnormal digit formation, too many or too few) Apoptosis also important for separation of radius/ulna & tibia/fibia & axilla. Digit specification - bmp concentration is highest between digit 4&5 and this causes digit 4 to be digit 4. Bmp concentration is lowest between 1&2 and this causes 1 to become 1.
