R‐spondin 2 and wnt/ctnnb1 signaling pathways are required for porcine follicle development and in vitro maturation

Abstract

The secretion of oocyte‐derived paracrine factors, such as R‐spondin2, is an essential mechanism for follicle growth by promoting the proliferation and differentiation of cumulus cells around oocytes. In the present study, we aimed to identify the effect of R‐spondin2 during follicular development. First, R‐spondin2‐related factors (R‐spondin2, CTNNB1, LGR4, and LGR5) were identified through immunofluorescence in porcine ovarian tissue. CTNNB1 was expressed in oo-plasm, and CTNNB1 and LGR4 were expressed in granulosa cells. In addition, R‐spondin2, LGR4, and LGR5 were expressed in the theca interna. These results imply that these proteins play a major role in porcine follicular development. In addition, the effects of R‐spondin2 on the in vitro maturation process of porcine cumulus oocyte complexes and subsequent embryonic development were confirmed. A treatment of 100 ng/mL R‐spondin2 in the in vitro maturation (IVM) process increased nuclear maturation and increased the expression of EGFR mRNA in cumulus cells. The EGFR‐ERK signal is essential for oocyte maturation, ovulation, and luteinization. R‐spondin2 treatment also increased the expression of CTNNB1 and EGFR in primary cultured cumulus cells. In conclusion, RSPO2 and WNT/CTNNB1 signaling pathways are required for porcine follicle development and are predicted to be involved in the EGFR‐ERK signaling pathway.