Morphogen gradient
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Morphogens are signals that form concentration gradients to specify multiple cell types during development. Cells respond to different morphogen thresholds to activate distinct gene expression. Bicoid is a transcription factor that acts as a morphogen gradient in Drosophila, turning on different genes in different embryo regions based on its concentration. It forms a gradient from anterior to posterior, with high concentrations specifying head structures and lower concentrations specifying more posterior structures. This gradient establishes the basic body plan of the fruit fly embryo.
Morphogen gradient
- 1. Morphogen gradients By Mrs Sanchita Choubey (M.Sc., PGDCR, Pursuing Ph. D) Assistant Professor of Microbiology Dr. D Y Patil Arts Commerce and Science College Pimpri, Pune
- 3. science-img.com **Morphogenesis is the outcome of correct pattern formation
- 4. •A morphogen is a signal (usually secreted from a subset of cells) that elicits different cellular responses at different concentrations. •A morphogen specifies more than one cell type by forming a concentration gradient, ie- it diffuses from its site of synthesis to become progressively less concentrated farther from the source of its synthesis. •Cells respond to different, or threshold, concentrations, of the morphogen by activating expression of distinct sets of genes. •Thresholds can represent the amount of the morphogen required to bind to receptors for activation intracellular signaling, or concentrations of transcription factors required to activate certain genes
- 5. *The very first step in patterning the embryo of the fruit fly, Drosophila melanogaster, is a good example of pattern formation by a gradient. *Bicoid is a transcription factor which turns on different genes in different levels - acting as a morphogen gradient.
- 6. The four genes shown in part A (tailless, empty spiracles, hunchback, and kruppel) are found in different locations within the Drosophila embryo, as a result of the amount of Bicoid protein at a particular location in the embryo.
- 7. The empty spiracles gene is necessary for proper head formation Kruppel :Termed as gap gene .. Meant for development of Centre of embryo Hunchback are the maternal effect genes that are most important for patterning of anterior parts (head and thorax) of the Drosophila embryo Tailles : Posterior part
- 8. After fertilization, bicoid mRNA from the mother fly begins to be translated into Bicoid protein in the Drosophila zygote. image B shows how the Bicoid protein diffuses through the egg forming a gradient. High concentrations of Bicoid protein are shown in white on the left (anterior) end of the zygote, and low concentrations are shown in blue on the right (posterior) end.
- 9. Image C shows Bicoid protein in the nuclei of a Drosophila embryo after a number of rounds of mitosis. The nuclei in the anterior end (left) have more Bicoid protein than those in the posterior end (right)
- 10. Image D shows Kruppel protein in orange and Hunchback protein in green. The region where the two proteins overlap is yellow. The colors come from fluorescent dyes attached to antibodies that bind specifically to these proteins.
- 11. studentreader.com •The asymmetric segregation of cytoplasmic determinants is due to asymmetric localization of molecules (usually proteins or mRNAs) within a cell before it divides. •During cell division, one daughter cell receives most or all of the localized molecules, while the other daughter cell receives less (or none) of these molecules. •This result in two different daughter cells, which then take on different cell fates based on differences in gene expression. •The localized cytoplasmic determinants are often mRNAs encoding transcription factors, or the transcription factors themselves.