Question

2) Why is the Dorsal protein critical to development in drosophila? Describe in detail.

Answer 1

In the embryonic stage of drosophila the Dorsal protein accumulates only in nuclei of ventral cells. The maternal effect genes, especially the Cactus gene, are responsible for the development of the ventral arrangement of cells. The Toll gene regulates the allocation on dorsal protein to the nuclei in cells of ventral zone nuclei by removing the effect of Cactus in ventral zone that inhibits the nuclear transportation of Dorsal protein. Toll gene also triggers the activity Dorsal protein trough sending stimulation by Tube and Pelle genes in cytoplasm. The major activity of Dorsal protein is to perform as a transcription factor. The allocation of Dorsal protein in different concentration in different cells creates a nuclear gradient. The gradient is regulated mainly by Toll gene and the allocation of Dorsal protein is highest in the nuclei ventral zone and reduces through nuclei of lateral zone of embryo continuously up to dorsal region where its nuclear concentration is minimum. The effect of the Dorsal protein gradient is highly important in the developmental process of drosophila embryo. Some important effect of the gradients are-

The dorsal ectoderm development is initiated by low concentration of Dorsal protein. High concentration leads to development of mesoderm in ventral region by activation of Snail and Twist genes and inhibiting the activity of non-mesodermal genes .The genetic expression in neurogenic ectoderm increases with decrease in concentration of Dorsal protein. Hence dorsal protein is important of these three primary embryonic tissue development. These primary tissues later develop in several other tissues and organs throughout the embryonic development process. E.g.- mesoderm develops in to muscles, gonad etc.