The transition from an egg to a developing embryo is one of life’s most remarkable transformations. Yet little is known about it. Now Whitehead Institute researchers have deciphered how one aspect—control of the all-important translation of messenger RNAs (mRNAs) into proteins—switches as the egg becomes an embryo. That shift is controlled by a beautiful mechanism, which is triggered at a precise moment in development and automatically shuts itself off after a narrow window of 20 to 90 minutes.
As an egg develops, it stockpiles mRNAs from the mother because it will not have time to create new mRNAs during the rapid development of a very early embryo. When fertilized the egg becomes an embryo, the stashed maternal mRNAs are pressed into service for a brief window before the embryo starts transcribing its own mRNAs. This change occurs very early; in humans, only two to four cell divisions occur before this transition is executed. Whitehead Member Terry Orr-Weaver studies the control of translation of maternal mRNAs in the model organism Drosophila, or the fruit fly, because its developmental strategy offers experimental advantages. More.
A reader writes to note that the “beautiful mechanism” is described as a
negative feedback loop,” with the same function as those designed in engineering control systems: Furthermore, the activity of PNG kinase leads to the destruction of GNU, and this feedback loop limits this kinase’s activity to the narrow window of time in which it is needed.
“Active PNG leads to decreased GNU protein levels. This makes a negative feedback to shut down PNG kinase activity, thereby ensuring PNG kinase activity is constrained to the short developmental window of the oocyte-to-embryo transition
Another reader who forwarded this item points out that the authors let in the “d” word (and I don’t mean “Darwin”…. ):
The design of this transition could tell scientists more about how human cells work and embryos develop. For example, the switch could be a model for how cells massively and globally change mRNA translation. Also, similar kinase activity during early development has been noted in worms, which may mean that a comparable approach is used in other organisms, including humans.
Well, if the researchers’ careers take a beating for mentioning design, they will need to join the Free the Universities movement. After a while language Stalinism starts t collapse from its own uncommunicativeness and one must peak clearly again.
See also: Cells communicate to navigate a crowded embryo