(181) Polypyrimidine tract-binding protein 1 (PTBP1), an RNA-binding protein, regulates oviductal function during early pregnancy in the mouse.

1.Departments of Comparative Biosciences¹,  University of Illinois at Urbana-Champaign, Urbana, IL
    2. Department of  Mol & Integrative Physiology², University of Illinois at Urbana-Champaign, Urbana, IL



Abstract Text:

Polypyrimidine tract-binding protein 1 (PTBP1) is a critical regulator of RNA splicing and post-transcriptional gene expression, with emerging roles in male reproductive physiology. However, its role in female reproductive functions remains poorly understood. Our recent studies revealed that PTBP1 is dynamically expressed in the oviduct during early pregnancy, suggesting a potential role in regulating the maternal environment for successful embryo transit. To elucidate the function of PTBP1 in the oviduct, we utilized the Cre-Lox technology using progesterone receptor (PR)-driven Cre and generated conditional knockout mice (Ptbp1 ^d/d) in which Ptbp1 gene is deleted in tissues expressing PR. We conducted a six-month breeding study, which showed that Ptbp1 mutant females are severely subfertile. Further analysis indicated that while ovulation was not affected in the absence of PTBP1, the majority of the developing embryos were retained in the oviductal ampullary isthmus junction of Ptbp1-null females on day 4 of pregnancy. Oviductal flushing on day 4 of pregnancy indicated that a significant number of embryos had failed to develop into the blastocyst stage in Ptbp1 mutant females, indicating developmental retardation of preimplantation embryos. Thus, mice lacking Ptbp1 in the oviduct exhibited impaired fertility, characterized by defects in preimplantation embryonic development and transport through the oviduct. To elucidate the molecular mechanisms underlying these reproductive defects, we next performed RNA sequencing on oviductal tissues from control and Ptbp1 mutant females. Transcriptomic analysis revealed a notable upregulation of several genes associated with fibrosis and extracellular matrix remodeling. Consistent with these results, the isthmus from Ptbp1 mutant females exhibited elevated Picrosirius Red staining of collagen fibers, commonly used to assess fibrosis and changes in the extracellular matrix. These results suggest that loss of PTBP1 may contribute to oviductal structural abnormalities, causing muscle stiffness and contractile dysfunction and impairing its ability to support embryo transport. Interestingly, we also noted that in Ptbp1 mutant oviducts, there is a significant downregulation of PKM2 (pyruvate kinase M2), a key metabolic enzyme implicated in cellular energy homeostasis. Further studies showed that PTBP1 controls alternative splicing and shifts expression from PKM1 to PKM2 in normal oviduct by preventing the inclusion of exon 9 in the Pkm2 transcripts. Unlike other pyruvate kinase isoforms, PKM2 has unique regulatory properties that allow it to function in a conformation promoting the accumulation of glycolytic intermediates, which are used to synthesize nucleotides, amino acids, phospholipids, and other macromolecular biological substances through the pentose phosphate pathway. Thus, it is plausible that PKM2 regulates the metabolic environment in the oviduct by providing essential nutrients and signaling molecules that support early embryo development. Disruptions in this environment, caused by the downregulation of PKM2 in Ptbp1 mutant oviducts, impair embryo quality and compromise pregnancy outcomes. Taken together, this study provides novel insights into the post-transcriptional regulation of reproductive tract function and demonstrates that PTBP1 is indispensable for normal oviductal function during pregnancy.
Supported in part by NIH R01 HD090066 (ICB, MKB).