Benny Jeong
bennyjeong218@gmail.com
Sunday, March 27, 2011
Healthy Vitamins?
On page 50, it was found out that when a certain concentration of vitamin A at the right stage in embryonic development affects the growth of digits. The effect of vitamin A is to make a mirror-image duplication of the digits on the hands. The affected patch of tissue is known as the zone of polarizing activity. Why is it that vitamin A specifically affects the development of digits? How does the composition of vitamin A affect the tissue? What specific effects does vitamin A have?
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Vitamin A specifically affects pattern duplication. Pattern duplication is when the developing limb bud mimics the effect of the zone of the polarizing activity and causes the anterior-posterior duplication of the limb such that a second limb develops as an anterior mirror image of the primary limb (Tickle, Alberts, Wolpert, & Lee 1982). Vitamin A can cause a dose-related inhibition of the regenerative outgrowth (Scadding, 1983). In other words, if there is too much vitamin A targeting a specific area then this same vitamin has the potential to cause malformations including both skeletal additions and deletions. Too much Vitamin A is not good for the body; therefore, it is toxic to ingest too much.
ReplyDeleteIn the book, Shubin injected vitamin A into a chicken embryo and let it to continue and develop. This, in turn, caused the ZPA to develop the “pinky side” to be different from the “thumb side” -- or digits. Besides the fact that vitamin A in a large dosage is dangerous, the concentration gradient of vitamin A is what causes the different structures of digits. “In areas close to the ZPA, where there is a high concentration of this molecule, cells would respond by making a pinky. In the opposite side of the developing hand, farther from the ZPA so that the molecule was more diffused, the cells would respond by making a thumb” (Shubin 51). From what Shubin described, vitamin A in the chicken embryo seemed to stimulate the ZPA and turn it “on.”
-Michelle Layvant, mlayvan2@students.d125.org
I think Shubin doesn't elaborate enough about the specific functions of Vitamin A. Vitamin A is the primary source of retinoic acid, which is known to control differentiation of pluripotent cells. We know it causes a dose-related inhibition of regenerative outgrowth, but the reason it is used by Shubin to prevent pattern duplication is because it "enters the nucleus and directly binds to target genes via nuclear receptors." (Duester, 2009) By just injecting Vitamin A, retinoic acid can bind to specific genes and repress several growth factor signaling pathways like a horomone flowing through the blood stream. To answer Benny's question as to why it affects the development of digits, retinoic acid is a cofactor to numerous retinol-binding proteins that are involved in "the differentiation and continuing growth of epithelium, osteoblasts and osteoclasts, and many other cells." (Bowen, 1999) I disagree with Michelle's statement that vitamin A in chicken embryo stimulate ZPA. Rather, it suppresses the surrounding cells from producing a large thumb, so the pinky forms instead. That is why no pinky is formed at all when increased vitamin A concentration is added.
ReplyDeletehttp://www.vivo.colostate.edu/hbooks/pathphys/misc_topics/vitamina.html
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2632951/?tool=pmcentrez
Troy Glickstern
cleverstar8@comcast.net