Abstract
MicroRNAs (miRNAs) are small non-coding RNAs of ~22 nucleotides which can regulate gene expression mainly at post-transcriptional levels. MiRNAs are generated through a multi-step enzymatic process, which requires an RNaseIII endonuclease Dicer. Dicer-null mutant mice cannot develop beyond embryonic day 7.5, precluding the study of roles of Dicer in postnatal testes. In order to study the function of Dicer in spermatogenesis, we generated a male germ cell-specific Dicer knockout mouse line by crossing Stra8-cre mice with a floxed Dicer conditional line. A reporter mouse line mTmG was crossed with Stra8-Cre to confirm the expression pattern of Cre recombinase. EGFP was observed in a portion of undifferentiated spermatogonia at P4 and later appeared in all spermatocytes and spermatids, and no expression in cells other than developing male germ cells within the testis. In Stra8-Cre-Dicerlox/lox males, Dicer was inactivated by Cre recombinase at ~postnatal day 3 (P3) in undifferentiated spermatogonia. Stra8-Cre-Dicerlox/lox males are completely infertile when bred with WT females. Stra8-Cre-Dicerlox/lox testes show normal development until P14, undistinguishable from control heterozygotes. However, from P14 onward, drastic spermatogenic disruptions were detected in Stra8-Cre-Dicerlox/lox testes. Spermatocytes and spermatids were severely depleted, leading to significantly reduced testis size. Few spermatozoa are present in the epididymis with abnormal morphology and impaired motility. Although Dicer was already inactivated in a subpopulation of undifferentiated spermatogonia, the number of differentiated spermatogonia and their morphology appeared to be normal, suggesting Dicer may not be required for the transition from undifferentiated to differentiated status. TUNEL assays revealed massive germ cell apoptosis starting at ~P14. Our data suggests that Dicer is required for the meiotic and haploid phases of spermatogenesis. Supported by NIH grants HD050281 and HD060858to W.Y. (poster)
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