Early embryology; controls over development patterns (Introduction)

by David Turell , Thursday, July 23, 2020, 20:39 (1584 days ago) @ David Turell

Certain proteins from the mother control patterns of development in teh egg:

https://phys.org/news/2020-07-complex-developmental-patterns-surprisingly-simple.html

"Proper embryonic development of the fruit fly Drosophila melanogaster is governed by patterns of protein activity bequeathed to the fertilized egg by its mother. While the embryo is still a single cell, the maternal cells surrounding it deposit certain proteins inside it at specific locations. This establishes protein gradients that direct the development of embryonic features along its anterior-posterior and ventral-dorsal axes. Later, the embryo receives another round of maternal information, called terminal patterning, that guides the development of its head and tail.

"Terminal patterning is driven by a protein called Torso that is made by the mother and deposited throughout the embryo. Torso is stimulated by binding to other proteins that are also produced by the mother, but present only at the embryo's anterior and posterior ends. Torso stimulation kicks off several signaling cascades, including one called the Ras/ERK pathway, whose activation directs the expression of genes crucial to embryonic development. Mothers lacking Torso or the proteins to which it binds are sterile because their embryos fail to develop head and tail.

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"Much of terminal patterning is driven by two genes whose expression is controlled by the Ras/Erk pathway in response to Torso signaling. In normal embryos, the expression of these two genes occurs in different cells at different times. In light-stimulated OptoSOS embryos lacking Torso signaling, however, expression of the two genes overlapped more in both space and time, suggesting their precise expression patterns are not required for development.

"The authors next investigated whether different aspects of the developmental program are triggered at the same or different stimulus thresholds. To do this, they monitored embryonic development after varying the intensity and duration of light stimulus in OptoSOS embryos lacking Torso signaling.

"'We found that the terminal pattern appears to work as a series of switches, where successively longer light pulses trigger a predictable sequence of body parts being 'rescued' one by one," explains Toettcher.

"Together, these data suggest that for terminal signaling, what appears to be a very complex developmental program is actually under the control of a relatively simple system that depends on different thresholds of Ras/Erk signaling."

Comment: Bit by bit we are learning how embryological systems work, by design.