The ability of bicoid to activate hunchback with a sharp pos

The ability of bicoid to activate hunchback with a sharp posterior boundary involves both the strength of the binding sites for bicoid in the hunchback regulatory region, and the cooperative binding of bicoid to the DNA. Cooperative binding is outside the scope of this course, but let\'s think about the effect of binding site \"strength\". If you were to use genetic engineering techniques to design a gene to contain several very strong binding sites for bicoid protein, where would you predict this gene to become expressed in the embryo? Now picture a gene with only one, very weak binding site: what might its expression pattern be? Review the gradients of bicoid, caudal, and dorsal proteins in the early embryo; all are transcription factors. How might you design a gene to be expressed at the anterior pole, broadly in the posterior of the embryo, or on the ventral surface in a narrow region along the midline?

Solution

Bicoid protein is localised in anterior region and leads gradient diffusion towards posterior part however nanose present on the posterior diffuses towards anterior. Bicoid promote expression of hunchback (responsible for anterior axis formation) were as supress the caudal protein (responsible for posterior axis formation). Nanose has the opposite expression effect to activate caudal protein and supress the hunchback protein. So presence of both gene is require for proper anterior and posterior axis formation.

If strong multiple binding site of bicoid is created by genetic engineering, it promote more protein formation of hunchback and also very little protein required to promote hunchback. This cause more hunchback present in posterior region also which further responsible for suppression of posterior region and promotion of anterior region. So if the amount of nanos is low this is possible to make only head and abdomen and absence of tail.

If single weak side is present for the bicoid it produce insufficient hunchback which leads to no head formation because more nanose (as compare to hunchback) supresses the hunchback.