MicroRNAs (miRNAs) are single-stranded, small non-coding RNAs which are critical for gene regulatory networks by directing the translational repression or degradation of complementary target mRNAs. They can be divided into two subclasses: canonical and non-canonical miRNAs. Canonical miRNAs are produced from long primary transcripts by sequential complex events in which RNA III enzymes such as Drosha and Dicer and accessory factors such as DGCR8 and Argonautes work cooperatively. DGCR8 is a RNA-binding protein that assists Drosha to process canonical miRNAs in the nucleus. To understand function of canonical miRNAs in uterine physiology, we have characterized uterine phenotypes of uterine-specific DGCR8 knock-out mice (uDGCR8 KO, DGCR8flox/flox; PRcre/+), and hormonal regulation of expression profiles of major factors working for miRNA biogenesis in the uterus. Gross morphological and histological analyses, immunohistochemistry, PCR and realtime RT-PCR were performed. While DGCR8 and Drosha do not seem to be regulated by ovarian steroid hormones, expression of Dicer, Exportin 5 and Argonaute 2 was transiently increased by E2 but not by P4. Combination of E2+P4 did not have any additional effects on their expression profiles. Genomic DNA PCR analyses showed that while DGCR8 gene is not completely deleted in the uterus, DGCR8 is specifically deleted in the uterus where PR is strongly expressed. uDGCR8 KO females bred with fertile males did not produce any offspring, suggesting that these mice are infertile. Vaginal smear analyses provided evidence that these mice do not undergo estrous cycle. Whereas gross morphology and histological analyses of uteri of 3-week-old uDGCR8 KO mice is similar to that of DGCR8flox/flox mice (control), uteri of 5- and 8-week-old mice are extremely thinner and shorter than those of control mice. These results were supported by significant decrease in uterine weight/body weight of uDGCR8 KO mice at 5-week-old age onward. Interestingly, this phenotype is reflected by significant increase of PR expression in the uteri of 4-week-old mice. Expression of DGCR8 and Dicer is significantly increased after birth. BrdU incorporation experiments showed that cell proliferation governed by ovarian steroid hormones does not normally occur in these mutant mice. Furthermore, artificial decidualization does not occur in these mice. Collectively, these results conclude that canonical miRNAs plays critical roles in normal uterine development and steroid hormone-dependent uterine function.

• Yeon Sun Kim(Department of Biomedical Science, CHA University)
• Hye Ryun Kim(Department of Biomedical Science, CHA University, Fertility Center of CHA Gangnam Medical Center, CHA University)
• Jung Ah Yoon(Department of Biomedical Science, CHA University, Fertility Center of CHA Gangnam Medical Center, CHA University)
• Haengseok Song(Department of Biomedical Science, CHA University, Fertility Center of CHA Gangnam Medical Center, CHA University)