Micro-RNAs Regulate Oogenesis

Investigators from two U.S. universities have recently found that a group of molecules called microRNAs (miRNAs) play a significant role in regulating oogenesis, the process in which females produce eggs.

miRNAs have been found to silence genes by attaching to genetic components called messenger RNAs and prevent them from producing new proteins, the molecules mainly responsible for cell activity. Whereas earlier studies had identified various miRNA targets, scientists do not yet know how they influence developmental processes.

"We found the first evidence that miRNAs are involved in oogenesis, and this adds an extra layer of complexity that needs to be explored if we are to understand how development is regulated,” noted Dr. Jonathan Minden, associate professor of biological sciences at Carnegie Mellon University (Pittsburgh, PA, USA), and one of the study's authors. The study was published online August 8, 2005, in the Proceedings of the [U.S.] National Academy of Sciences.

"If miRNAs are missing from a developing egg, then it fails to develop to term, and the net result is infertility,” stated lead author Dr. Richard W. Carthew, professor of molecular biology at Northwestern University (Evanston, IL, USA). "It is intriguing to think that miRNA dysfunction might be at the root cause of certain forms of infertility. We already know that miRNAs are involved in cancer and stem cell biology.”

Researchers were first amazed to find that miRNAs affected just a small proportion of expressed genes within a maturing egg. On closer evaluation, they discovered that the genes affected by miRNAs shared common roles as regulators of protein production or turnover. These findings suggest that miRAs closely control the large quantity of proteins throughout the process of fertilization and oogenesis.

Utilizing a proteomics technique developed by researchers at Carnegie Mellon, they compared maturing fruit fly eggs. One group of eggs was missing a gene essential for making miRNAs, while another group of eggs had normal miRNA production. (All animals and plants have the gene, DICER, which produces miRNAs; the scientists used a genetic technique to produce DICER-less eggs.)

By comparing overall protein production between these two groups, the investigators found that the miRNAs halted the production of a small group of major proteins, including ones that make ribosomes. These structures make up the cell's protein-producing mechanisms, and their shutdown would result in cells not being able to produce new proteins.

The researchers discovered that miRNAs seem to ease protein turnover. They hypothesize that this function may allow a developing egg to gather large amounts of certain proteins necessary to propel the remarkable structural alterations evident in embryogenesis.



Related Links:
Northwestern University
Carnegie Mellon University