Small RNA-mediated regulation of gene expression is believed to contribute to essentially all genetic pathways in animals, yet detailed biological examples are few in number. MicroRNAs (miRNAs), the best understood class of small RNAs, are non-coding, regulatory RNAs that post-transcriptionally repress gene expression by targeting specific mRNAs for repression. The importance of miRNAs is well illustrated by mouse models: many miRNA loss-of-function or overexpression lines exhibit overt phenotypes, including developmental defects, lethality and susceptibility to disease, including cancers. However, few studies have defined the specific mRNAs targeted by miRNAs in normal mouse or human developmental pathways. In addition to miRNAs, there are other classes of related small RNAs, including endogenous siRNAs (short-interfering RNAs) and piRNAs (piwi-interacting RNAs); the different classes of small RNAs employ a diversity of mechanisms, but all function to regulate gene expression. Several studies have suggested that germline development and function require small RNAs, implicating roles for miRNAs, siRNAs and piRNAs in the germline. Studies by members of the Cornell CRG are directed towards understanding the relative roles of these small RNA species in the germline and extrapolating these functions throughout the reproductive system. Our projects include:
1. Defining the regulatory functions of small RNAs in male germ cells of the mouse, led by Dr. Andrew Grimson.
3. Elucidating the roles of mammalian Argonautes (AGO3 & 4) in meiotic prophase I, led by Paula Cohen
PILOT: CRISPR-mediated mutagenesis of microRNA clusters in the mouse, led by John Schimenti.
Figure 1. Localization of microRNAs (red) to the XY body in prophase I spermatocytes from wildtype (WT) and Ago4 mutant males. From Paula E. Cohen and Andrew Modzelewski.
Copyright Paula E. Cohen, 2015
A new study from Andrew Grimson's lab, in collaboration with Paula Cohen's lab, has identified a key pathway required for maintenance of sex chromosome telomere integrity. Using conditional knockout mice for Dicer and Dgcr8, two key enzymes required for small RNA processing, Modzelewski et al (2015) show that loss of small RNAs during prophase I leads to telomere fusion events specifically involving the X and Y chromosomes. For further information, see the May edition of Journal of Cell Science
A recent publication by Dabaja et al (2015) has identified key cell:cell interactions that are necessary to establish normal profiles of one key microRNA, miR202-5p, in Sertoli cells. This is the first example of a germ cell regulatory interaction that is necessary for miR expression in neighboring somatic cells of the testis
The lab of Center member John Schimenti recently identified the DNA damage checkpoint pathway responsible for culling oocytes that fail to repair double stranded breaks (DSBs) that occur during meiosis or which arise in a female's oocyte pool (Bolcun-Filas et al, Science 343:533-536, 2014). Using combinations of mutants involved in recombination and DNA damage responses, they found that this pathway involves signaling of checkpoint kinase 2 (CHK2) to both p53 and p63. Disruption of this checkpoint pathway restored fertility to females that normally would be deficient of all oocytes due to defects in meiotic recombination or exposure to radiation. This discovery opens the way to using available CHK2 inhibitors to protect the oocytes of women undergoing cancer therapy that would normally cause infertility.