Heterogeneous nuclear ribonucleoprotein L orchestrates alternative splicing critical for primordial follicle...

The development of germ cells, from PGCs to the formation of primordial follicles, is tightly regulated by post-transcriptional AS. However, the underlying splicing dynamics, key regulatory factors, and precise mechanisms remain poorly understood.

This study aims to elucidate the dynamic landscape and functional significance of AS during the transition from PGCs to primordial follicle formation.

Analysis of scRNA-seq and bulk RNA-seq datasets revealed the dynamic landscape of AS during the transition from PGCs to primordial follicle formation and identified hnRNPL as a key regulatory factor. A conditional Hnrnpl knockout mouse model was employed to examine the physiological significance of AS and demonstrated that its deletion leads to POI. To elucidate the underlying mechanism, we employed an integrated multi-omics strategy combining immunofluorescence, RNA-seq, RIP-seq, and IP-MS to identify hnRNPL-associated spliceosomal components and their target mRNAs.

scRNA-seq and bulk RNA-seq analyses identified a critical peak of AS activity at E16.5-E18.5, encompassing 6,766 differentially spliced junctions and 3,625 differentially spliced genes. We screened for splicing regulators active during this critical developmental window. hnRNPL emerged as a leading candidate and was selected for in vivo functional validation by generating a germ cell-specific Hnrnpl cKO mouse model. Hnrnpl cKO in mice resulted in female sterility, reduced primordial follicle formation, and POI, accompanied by meiotic synapsis defects and unrepaired DSBs. Hnrnpl cKO ovaries exhibited 1,891 (E18.5) and 2,698 (P1) aberrant AS events. Mechanistically, hnRNPL interacts with PTBP1 and SRSF10 to regulate the splicing of genes essential for meiotic progression.

This study demonstrates that hnRNPL-mediated alternative splicing is critical for primordial follicle development, and its loss leads to POI, nominating hnRNPL as a potential POI biomarker.