RNA-based Sex Determination?

Researchers find that microRNAs may play a role some of the sexual differences seen in fruit flies.

By | August 20, 2014

WIKIMEDIA, MR. CHECKERCertain microRNAs (miRNAs) play important roles in determining the sexual characteristics of fruit flies, both during development and through adulthood, according to a study published last month (July 31) in Genetics. The miRNAs—specifically a cluster of miRNAs that include one called let-7—regulate proteins that act as sex determinants in developing flies as well as those that function in germ cell behavior differently in male versus female flies. “We found that the differences in miRNAs are important in shaping the structures that distinguish the two sexes," Cold Spring Harbor Laboratory biologist and lead author Delphine Fagegaltier said in a press release.

By conducting a genome-wide survey to pinpoint differential expression of miRNAs in male and female flies, Fagegaltier and colleagues identified the let-7-C cluster as a primary modulator of the sex determination hierarchy. They then reduced let-7 levels in some flies and charted the sexual changes. “In a sense, once they have lost this miRNA, the flies become male and female at the same time,” said Fagegaltier. “It is amazing that the very smallest genes can have such a big effect on sexual identity.”

“This is probably just the tip of the iceberg," Fagegaltier added. “There are likely many more miRNAs regulating sexual identity at the cellular and tissue level.”

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August 20, 2014

Re: The "tip of the iceberg"

"Small intranuclear proteins also participate in generating alternative splicing techniques of pre-mRNA and, by this mechanism, contribute to sexual differentiation in at least two species, Drosophila melanogaster and Caenorhabditis elegans (Adler and Hajduk, 1994; de Bono, Zarkower, and Hodgkin, 1995; Ge, Zuo, and Manley, 1991; Green, 1991; Parkhurst and Meneely, 1994; Wilkins, 1995; Wolfner, 1988). That similar proteins perform functions in humans suggests the possibility that some human sex differences may arise from alternative splicings of otherwise identical genes. (p. 337)"

Excerpted from: From Fertilization to Adult Sexual Behavior (1996)

The likelihood that cell type differentiation occurs via conserved molecular mechanisms that link the epigenetic landscape to the physical landscape of
DNA in the organized genomes of all species from microbes to man does not seem to have entered the perspectives of serious scientists -- even those who have learned about the imporatance of the microRNA/messenger RNA balance to cell type differentiation in all cells of all individuals of all species.

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