POU1F1/Pou1f1 c.143-83A > G variant disrupts the branch site in pre-mRNA and leads dwarfism.

POU Class 1 Homeobox1 (POU1F1/Pou1f1) is a well-established pituitary-specific transcription factor, and causes, when mutated, combined pituitary hormone deficiency in humans and mice. POU1F1/Pou1f1 has two isoforms, alpha and beta isoforms. Recently, pathogenic variants in the unique coding region of beta isoform (beta domain), and the intron near the exon-intron boundary for beta domain were reported, although their functional consequences remain obscure. In this study, we generated mice carrying the Pou1f1 c.143-83A > G substitution that recapitulates the human intronic variant near the exon-intron boundary for beta domain. Homozygous mice showed postnatal growth failure with average body weight 35% of wildtype littermates at 12 weeks, which was accompanied by anterior pituitary hypoplasia and deficiency of circulating insulin-like growth factor 1 and thyroxine. The results of RNA-seq analysis of the pituitary gland were consistent with reduction of somatotrophs, and this was confirmed immunohistochemically. Reverse transcription PCR of pituitary Pou1f1 mRNA showed abnormal splicing in homozygous mice, with decrease of alpha isoform, increase of beta isoform and emergence of exon-skipped transcript. We further characterized artificial variants in or near beta domain, which were candidate positions of the branch site in pre-mRNA, using cultured cell-basis analysis, and found that only c.143-83A > G produced transcripts comparable to the mice model. Our report is the first to show that the c.143-83A > G variant leads splicing disruption and causes morphological and functional abnormalities in the pituitary gland. Furthermore, our mice will contribute to understand the role of POU1F1/Pou1f1 transcripts in pituitary development.