In a Toll null mutant in which cells will Dorsal protein be

In a Toll null mutant, in which cells will Dorsal protein be localized to the nucleus? Why? What is the resulting phenotype?

Solution

In a toll null protein Dorsal protein is found in the ventral cell nuclei. The protein that actually distinguishes dorsum (back) from ventrum (belly) is the product of the dorsal gene. The RNA transcript of the mother\'s dorsal gene is placed in the oocyte by her ovarian cells. However, Dorsal protein is not synthesized from this maternal message until about 90 minutes after fertilization. When this protein is translated, it is found throughout the embryo, not just on the ventral or dorsal side.

While Dorsal protein can be found throughout the syncytial blastoderm of the early Drosophila embryo, it is translocated into nuclei only in the ventral part of the embryo

In the nucleus, Dorsal binds to certain genes to activate or suppress their transcription. If Dorsal does not enter the nucleus, the genes responsible for specifying ventral cell types (snail and twist) are not transcribed, the genes responsible for specifying dorsal cell types (decapentaplegic and zerknüllt) are not repressed, and all the cells of the embryo become specified as dorsal cells.

The resulting Phenotype - Dorsal-ventral axis formation in Drosophila is supported by analyses of mutations that give rise to an entirely dorsalized or an entirely ventralized phenotype In those mutants in which all the cells are dorsalized (as is evident by their dorsal cuticle), Dorsal protein does not enter the nucleus in any cell. Conversely, in those mutants in which all cells have a ventral phenotype, Dorsal protein is found in every cell nucleus.