Question

4) RNA interference (RNAi) can be used to silence specific genes in specific tissues. You inject various RNAi constructs into Drosophila embryos. in each of the following cases? (3pts) What effect on phenotype would you expect a) One gap gene silenced b) Bicoid silenced c) One Hox gene silenced

Answer 1

a) Gap gene is silenced

Gap genes were so named because large areas of the normal cuticular pattern are deleted in individuals with mutant phenotypes. The three wild-type versions of the gap genes Krüppel+, hunchback+, and knirps+ regionalize the embryo by delimiting domains of homeotic gene expression and affect position-specific regulation of the pair-rule genes runt+, fushi tarazu+, even skipped+, paired+, and odd-paired+. All three gap-gene products contain DNA-binding domains.

The gap genes interact to produce sharp boundaries. The establishment of stable domains by the gap genes is a two-step process: 1) a differential response to graded levels of maternal determinants, 2) followed by mutual repression leading to the generation of stable boundaries between adjacent domains.

If one gap gene is silenced further segmentation will not happen pair rule genes will not express.

b) The Drosophila gene bicoid functions at the beginning of a gene cascade that specifies anterior structures in the embryo. Its transcripts are localized at the anterior pole of the oocyte, giving rise to a Bicoid protein gradient, which regulates the spatially restricted expression of target genes along the anterior–posterior axis of the embryo in a concentration-dependent manner. Biocid is important for head and thorax development silenceing it will hinder the anterior part formation.

c) Hox genes are the homologs of the homeotic genes of the fruit fly Drosophila. The Drosophila homeotic genes were first identified through mutations that caused the transformation of a particular segment of the fly body into the likeness of another, hence the term homeotic from the Greek word homeo, which means similar.

Truncated protein expression at wings and limbs associated with perfect regulation of mRNAs for the protein expression in cranio-caudal ( head -tail ) axis.