Translocations/genes in Premature Ovarian Failure

Aging

Investigators

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Abstract

About 1-3% of all women undergo precocious menopause, either never going through menarche or stopping menstruation by the mid-30's, rather than reaching the standard reproductive lifespan of about 50. A fraction of such instances of early-onset "premature ovarian failure (POF)" is genetic. A single locus on chromosome 3 is implicated in several families and in several isolated individuals with translocations or deletions that interrupt the DNA in that region. In collaboration with the group of Dr. G. Pilia, we isolated the gene, FOXL2, in which mutations cause POF and an eyelid malformation, and are analyzing its function; it appears to function as a rheostat, determining the number of follicles by the level of its function. We have recovered the mouse orthologue, Foxl2, and have generated a knockout to create a mouse model. We are beginning to characterize the resulting phenotype, which seems to mimic eyelid and ovarian features seen in women lacking one allele of FOXL2. A much larger group of translocations on the X chromosome, centering on a critical region of the long arm, have been associated with POF. We have prevously shown that based on the physical map we had constructed, there are at least 35 distinct X chromosome loci at which translocations can produce POF. We have begun further molecular analyses of the sequences spanning translocation breakpoints. Three have been analyzed in detail at the sequence level, and two of these fall outside of any gene, in regions of repetitive sequence elements. This increases the possibility that some X translocations act by interrupting chromosome dynamics during meiosis, whereas others may cause POF by the interruption of specific genes involved in follicle formation or stability. To help understand the failure of follicle formation and maintenance in POF, we analyzing the normal ovarian development in mouse using 15K cDNA microarray (the NIA array developed by the group of Dr. M. Ko (LG)), to assess the gene cohorts involved in ovary formation. We have thus far compared the profile of genes expressed in nascent ovary, from newborn mice in which ovarian follicles are just starting to be formed, with mature ovary, in which follicles are fully formed and compared them to those expressed in testes. Marker genes expressed in follicle cells only at birth, or in oocytes of nascent or in mature mice have been recovered for further functional studies. These will be analyzed along with genes whose function is sharply affected in hereditary POF, using the mouse model generated with disrupted Foxl2. In that model, the point of interruption of programmed and coordinated gene function will be assessed by determining the target genes under the control of Foxl2.