Molecular functions of Mrhl lncRNA in mouse spermatogenesis.

Proliferation and meiotic division of spermatogonial stem cells are highly regulated biological processes that occur during spermatogenesis. In addition to protein coding genes, mammalian genome encodes thousands of lncRNAs which are spatio-temporally expressed and play key role(s) in cellular differentiation and development. Mrhl lncRNA is one such mono-exonic polyadenylated non-coding RNA encoded within the 15th intron of the mouse Phkb gene. Mrhl lncRNA is expressed in mouse testis amongst other tissues. The RNA is nuclear localized and predominantly bound to chromatin in GC-1 spg cells (derived from B type spermatogonia). It regulates multiple genes belonging to different biological processes including Wnt signaling. Wnt activation of GC-1 spg cells downregulates Mrhl lncRNA expression, in turn activating the expression of meiotic marker genes and downregulating stem cells markers. We have mapped the genomic loci bound by Mrhl lncRNA and identified 37 genes to be regulated by its physical association. Sox8 gene, one among these, is regulated through its interaction at its promoter through RNA: DNA: DNA triplex structure and chromatin looping mediated by the architectural proteins CTCF and YY1. Here we summarize our major findings on this novel lncRNA starting from its discovery to biological function(s) particularly during meiotic commitment/initiation in mouse spermatogenesis.