The Dynamics of miR-449a/c Expression during Uterine Cycles Are Associated with Endometrial Development

SIMPLE SUMMARY: The human endometrium is a highly dynamic tissue. Increasing evidence has shown that microRNAs play essential roles in human endometrium development during the menstrual cycle. Here, we applied small RNA-sequencing to demonstrate that miR-449a/c and their sequence variants (isomiRs) may participate in the genetic control of human endometrial receptivity. Stem-looped RT-qPCR analysis of miR expression at four time-points of the endometrial cycle verified the increased expression of the miR-449a/c family members in receptive endometrium, among which the 5′ isoform of miR-449c–miR-449c.1 was the most strongly up-regulated. Moreover, we found in a case study that the expression of miR-449c.1 and its precursor (pre-miR-449c) correlated with the histological assessment of the endometrial phase and patient age. We believe this study will promote the clinical investigation and application of the miR-449 family in the diagnosis and prognosis of human reproductive diseases. ABSTRACT: The human endometrium is a highly dynamic tissue. Increasing evidence has shown that microRNAs (miRs) play essential roles in human endometrium development. Our previous assay, based on small RNA-sequencing (sRNA-seq) indicated the complexity and dynamics of numerous sequence variants of miRs (isomiRs) that can act together to control genes of functional relevance to the receptive endometrium (RE). Here, we used a greater average depth of sRNA-seq to detect poorly expressed small RNAs. The sequencing data confirmed the up-regulation of miR-449c and uncovered other members of the miR-449 family up-regulated in RE—among them miR-449a, as well as several isoforms of both miR-449a and miR-449c, while the third family member, miR-449b, was not identified. Stem-looped RT-qPCR analysis of miR expression at four-time points of the endometrial cycle verified the increased expression of the miR-449a/c family members in RE, among which the 5′ isoform of miR-449c–miR-449c.1 was the most strongly up-regulated. Moreover, we found in a case study that the expression of miR-449c.1 and its precursor correlated with the histological assessment of the endometrial phase and patient age. We believe this study will promote the clinical investigation and application of the miR-449 family in the diagnosis and prognosis of human reproductive diseases.