Zone of polarizing activity (zpa), Biology

Zone of Polarizing Activity (ZPA)

The A-P axis is the 1st axis to be fixed in the presumptive limb mesoderm at a very early stage. On the basis of results of a series of current experiments on chick embryos it has been recommended that determination of the anterior-posterior pattern of wing parts is apparently within the control of a small block of mesodermal cells located at the posterior junction of the wing bud along with the body wall. This mesoderm has been termed as the Zone of Polarizing Activity (ZPA). The usual chick wing has three digits numbered II, III and IV in this anterio- posterior order. In stage 18 or little older embryos an extra ZPA was transplanted within the ectoderm on the anterior side of the bud near or in contact with the AER. This resulted in the creation of a duplicate set of digits in reverse order on the anterior side so the digital formula anterio-posteriorly turns IV, II, II- II, III, IV.

The second set was a mirror image of the original. The normal polarity was kept even in this set as the usually the most posterior digit IV was still nearest to the transplanted ZPA. It was recommended that ZPA secretes some type of substance, a morphogen, whose diffusion creates a gradient of decreasing concentrations along with the A-P axis. The digit IV may be formed in response to the highest concentration and digits III and II in response to in succession decreasing levels of this morphogen. A second such gradient would be established in reverse direction by the morphogen produced by the ZPA transplanted on the anterior side and hence the second set of digits in mirror image of the original set the above suggested role of ZPA is not generally accepted by most biologists. Identical additional set of digits in chick wing is induced by transplantation of mesoderm from another body regions, several different tissues, transplantation of an additional AER and as well by applying retinoic acid (a derivative of Vitamin A) to the anterior side of the bud. Furthermore, removal of ZPA from the posterior side of the bud does not prevent the creation of the normal set of digits while in an experimental situation ZPA does produce a polarizing effect, this role of ZPA in the normal development whereas it is in its usual posterior position in the wing bud is seriously doubled.

Posted Date: 1/30/2013 5:24:36 AM | Location : United States







Related Discussions:- Zone of polarizing activity (zpa), Assignment Help, Ask Question on Zone of polarizing activity (zpa), Get Answer, Expert's Help, Zone of polarizing activity (zpa) Discussions

Write discussion on Zone of polarizing activity (zpa)
Your posts are moderated
Related Questions
Explain about Phytopinax written by Caspar Bauhin? A significant contribution to taxonomy was made at this time by Caspar Bauhin. His 'Phytopinax' (1596) described 2700 species

What are angiosperms, the flowering plants? What is the major feature that distinguishes them from the gymnosperms? Flowering plants have flowers and seeds (phanerogamic plants

Insulin, insulin syringe and insulin devices Insulin is the hormone used to treat diabetes mellitus. Insulin is given in the form of injection, because the gastro intestinal tr


Some relatively simple eukaryotes, like the adder's tongue fern, may have many more chromosomes than a more complex eukaryote, like a mammal. What might this suggest about the size

How does the swim bladder of fishes work allowing fishes to control their depth under water? From Hydrostatics it is called that an object does not sink if its density is equal

What type of athlete would have a above average reaction time please explain.

Energy Input in Ecosystem Survival and functioning of ecosystem is dependent on the input of energy. Continuous availability of energy is essential for supporting diverse ecos

Stress - Responses of Plants to Stress Let us recall what happens within the natural communities occupying the same habitat. The relative location of two plants may place them

Define Sporangiophore - Types of Hyphae? Sporangiophore - Tufts of special, erect unbranched, hyphae growing in air arise from stolon just opposite to rhizoids. These are s