Biologists determine microRNA activity is suppressed in mouse ovum

Feb 03, 2010

Biologists at the University of Pennsylvania studying oocytes in mice, the immature egg cells necessary for sexual reproduction, have demonstrated an unusual behavior in microRNA, or miRNA, activity that may be the first event in reprogramming the differentiated oocyte into pluripotent blastomeres of the embryo. MicroRNAs are a member of the family of small RNAs, the so-called dark matter of the biological world.

MicroRNAs imperfectly pair with untranslated regions of RNA and mediate translational repression and mRNA degradation -- hallmarks of the process. The Dicer enzyme, which generates small RNAs in the miRNA and pathways, is essential for meiotic maturation of mouse oocytes.

The scientists found that the mRNA population in oocytes lacking Dicer was not enriched in miRNA binding sites, implicating a weak impact of miRNAs on regulating mRNA stability. To explore further this possibility, the scientists injected a reporter transcript, a message RNA that is not a normally present in the oocyte but contained sequences that would interact with miRNAs in the oocyte. In , such a message would be degraded and suppressed by micro . However, in oocytes, there is minimal translational repression and no degradation of the message. The finding that this pathway does not operate in oocytes is most surprising because miRNAs are implicated in controlling cell differentiation.

The data, according to researchers, presents a puzzling paradox. "Although mouse oocytes produce miRNAs, their mRNA targets are poorly repressed," said Richard Schultz, associate dean for the natural sciences and the Charles and William L. Day Distinguished Professor of Biology in Penn's School of Arts and Sciences. "Reducing miRNA activity during oocyte growth may have two roles.

First, the low activity of miRNA-mediated mRNA degradation, perhaps linked to the absence of P bodies (structures that are implicated as sites of miRNA-mediated mRNA degradation) may contribute to mRNA stability and accumulation of mRNA in growing oocytes. Second, down-regulation of the miRNA pathway may be required for oocyte-to-zygote transition."

Explore further: Researchers find protein necessary for fertility performs different roles in sperm, eggs

More information: The study, appearing in the journal Current Biology, was conducted by Schultz, Jun Ma and Paula Stein at Penn; Matyas Flemr, Radek Malik and Petr Svoboda of the Institute of Molecular Genetics, Academy of Sciences of the Czech Republic; and Philipp Berninger and Mihaela Zavolan of the University of Basel and Swiss Institute of Bioinformatics.

Related Stories

Researchers Identify microRNA targets in C. elegans

Jan 10, 2010

MicroRNAs (miRNAs) are non-coding RNAs that impact almost every aspect of biology. In recent years, they have been strongly implicated in stem cell biology, tissue and organism development, as well as human conditions ranging ...

Researchers discover how microRNAs control protein synthesis

Jul 09, 2007

While most RNAs work to create, package, and transfer proteins as determined by the cell’s immediate needs, miniature pieces of RNA, called microRNAs (miRNAs) regulate gene expression. Recently, researchers from the University ...

New location found for regulation of RNA fate

Jul 30, 2009

Thousands of scientists and hundreds of software programmers studying the process by which RNA inside cells normally degrades may soon broaden their focus significantly.

Tiny genes may increase cancer susceptibility

May 23, 2007

New evidence indicates that small pieces of noncoding genetic material known as microRNAs (miRNAs) might influence cancer susceptibility. Differences in certain miRNAs may predispose some individuals to develop cancer, say ...

Recommended for you

In a role reversal, RNAs proofread themselves

Jan 29, 2015

Building a protein is a lot like a game of telephone: information is passed along from one messenger to another, creating the potential for errors every step of the way. There are separate, specialized enzymatic ...

Growing functioning brain tissue in 3D

Jan 29, 2015

Researchers at the RIKEN Center for Developmental Biology in Japan have succeeded in inducing human embryonic stem cells to self-organize into a three-dimensional structure similar to the cerebellum, providing ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.