\"The graded nuclear location of the transcription factor Dorsal along the dorso

Question

"The graded nuclear location of the transcription factor Dorsal along the dorsoventral axis of the early Drosophila embryo provides positional information for the determination of different cell fates. Nuclear uptake of Dorsal depends on a complex signalling pathway comprising two parts: an extracellular pro- teolytic cascade transmits the dorsoventral polarity of the egg chamber to the early embryo and gener- ates a gradient of active Spätzle protein, the ligand of the receptor Toll; an intracellular cascade down- stream of Toll relays this graded signal to embryonic nuclei. The slope of the Dorsal gradient is not deter- mined by diffusion of extracellular or intracellular components from a local source, but results from self-organised patterning, in which positive and neg- ative feedback is essential to create and maintain the ratio of key factors at different levels, thereby establishing and stabilising the graded spatial infor- mation for Dorsal nuclear uptake." Curr Biol 15:R887.

Article: http://www.cell.com/current-biology/fulltext/S0960-9822(05)01226-1

1) How do morphogens induce different levels of transcription of target genes in cells depending on the distance of the cells from the source of the morphogen?

Explanation / Answer

Ans- these processes are always dependent on the signaling of the morphogen. These are chemical substance which lead to morphogenesis. When there is a gene which should be transcribed at a specific level then the morphogen produce the signal of corrosponding intensity. The receptors determine the signals and according to their strength the specific gene is transcribed. The signal intensity may be weak or strong which is responsible for the different levels of transcription.

The distance of the cell also play crucial role in this signaling as the nearest cells get strong signal while distant cells may get weak signals. So to overcome this problem the morphogen provide some substance which become such specific that they may work on the targeted gene of one specific cells only. By above method the morphogen induce different levels of transcription.

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