Lovers of fine science and admirers of the wonders of nature will not be disappointed by a publication in biology, from the Collège de France, the Institut Curie, Sorbonne-University, the CNRS and the Weizmann Institute of Science. (Israel). “It’s a discovery! », summarizes without detour Marie-Hélène Verlhac, head of the team and director of the Interdisciplinary Center for Research in Biology at the College de France. The discovery refers to one of nature’s deepest mysteries, that of the origin of life.
More prosaically, this work reveals a new mode of cell functioning, brought to light on oocytes. The latter, essential to the perpetuation of the species, are more akin to an unleashed mixologist in a bar than to a vulgar balloon filled with water, proteins and chromosomes. In other words, without frantic agitation, the oocyte would not be ready to be fertilized by sperm. This daring image well deserves some details, precisely provided in the nineteen extremely rich pages published in Nature Communications August 29.
A mouse oocyte, approximately 80 micrometers in diameter, takes around ten days to become mature, that is to say ready to divide in order to carry only one set of chromosomes to fuse with a male gamete. It is composed, like any cell, of a membrane enclosing the cytoplasm, in which is the nucleus which contains the DNA. Within this nucleus, regarding 30 micrometers in diameter, are made the strands of RNA and the proteins necessary for the maturation of the oocyte and its division.
These are the last two days of this very delicate machinery, which the researchers studied. During this phase, reactions take place between proteins, enzymes, RNA… But not anywhere in the nucleus. They take place in compartments without a membrane, the nuclear bodies or condensates, which are like droplets of vinegar in oil. But everyone knows that, to create these drops, well-felt fork strokes are necessary. After agitation, the small drops move and stick together to form larger ones. In the nucleus, these condensates, of which there are regarding ten types (speckle, nucleolus, Cajal body, etc.), see, during the maturation of the oocytes, their number decrease and their size increase, as observed by the researchers. .
Nuclear membrane massage
This effervescence comes from the “massage” of the flexible membrane of the nucleus which is modeled from the outside by sorts of molecular fingers… These fingers are actin filaments which move forward and backward, like pistons, and form a kind of skeleton in the cytoplasm. Furthermore, these cytoplasmic forces place the nucleus pile in the center of the cell, in order to optimize the stirring process.
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