The oocyte cumulus complex regulates mouse sperm migration in the oviduct

Abstract

As the time of ovulation draws near, mouse spermatozoa move out of the isthmic reservoir, which is a prerequisite for fertilization. However, the molecular mechanism remains unclear. The present study revealed that mouse cumulus cells of oocytes–cumulus complexes (OCCs) expressed transforming growth factor-β ligand 1 (TGFB1), whereas ampullary epithelial cells expressed the TGF-β receptors, TGFBR1 and TGFBR2, and all were upregulated by luteinizing hormone (LH)/human chorionic gonadotropin (hCG). OCCs and TGFB1 increased natriuretic peptide type C (NPPC) expression in cultured ampullae via TGF-β signaling, and NPPC treatment promoted spermatozoa moving out of the isthmic reservoir of the preovulatory oviducts. Deletion of Tgfb1 in cumulus cells and Tgfbr2 in ampullary epithelial cells blocked OCC-induced NPPC expression and spermatozoa moving out of the isthmic reservoir, resulting in compromised fertilization and fertility. Oocyte-derived paracrine factors were required for promoting cumulus cell expression of TGFB1. Therefore, oocyte-dependent and cumulus cell-derived TGFB1 promotes the expression of NPPC in oviductal ampulla, which is critical for sperm migration in the oviduct and subsequent fertilization.

The Mature COC Promotes the Ampullary NPPC Required for Sperm Release from Porcine Oviduct Cells

“…Thus, TGFBs, especially TGFB1 from mature COCs, promote NPPC expression in the ampullae. This is consistent with our and others’ studies which found that TGF-β signaling promotes NPPC expression in various cell types [ 19 , 23 , 33 ]. Additionally, the mRNA and protein levels of TGFBRs and their downstream molecules were significantly higher in the ampullae at corpus rubrum phase (after ovulation) than those at follicular phase (before ovulation).…”

“…EGF, cooperation with oocyte paracrine factors, promoted TGFB1 expression in cumulus cells of COCs, consistent with our recent report in mouse [ 33 ]. EGFR signaling-activated cyclic adenosine 3′,5′-monophosphate (cAMP) response element-binding protein (CREB) in mouse cumulus cells, together with oocyte paracrine factor-activated SMAD2/3, induce expansion-related gene expression and consequent cumulus expansion [ 38 ].…”

“…The sequence of peptide NPPC is highly conserved [ 17 ]. NPPC promoted porcine sperm release from the oviduct isthmic cell aggregates, consistent with our recently study that NPPC promotes mouse sperm migration from the isthmic reservoir to the ampulla for fertilization [ 33 ]. This suggests that the function of NPPC may be highly conserved in mammals in promoting sperm release from the isthmic reservoir to the ampullae for fertilization.…”

“…Generally, EGFR signaling-induced cumulus cell gene expression requires the participation of oocyte paracrine factors [ 33 ]. We found that EGF could not increase TGFB1 mRNA and protein levels in porcine cumulus cells of oocytectomized (OOX) complexes ( Figure 6 B,C), suggesting that oocyte paracrine factors are required for EGF-induced TGFB1 expression in cumulus cells.…”

“…On the other hand, the increase of p-SMAD2 in the porcine ampullae was not detected, possibly due to the time limit of sample collection. In mouse, ovulated COCs promote NPPC expression in the ampullae by binding cumulus cell-derived TGFB1 to TGFBR in the ampullary epithelial cells, which is critical for sperm migration for fertilization [ 33 ]. A similar mechanism may exist in pig: mature COCs induce NPPC expression in the ampullae via TGF-β signaling, and then NPPC diffuses to the isthmus for sperm release.…”