Interactive role of Wnt signaling and Zn in regulating testicular function of the common carp, Cyprinus carpio

Abstract

Wnt signaling is conserved among all species and plays a significant role in various cellular processes including reproduction. The present study identified significant involvement of wnt4a, wnt5b, and wnt8a signaling in the testicular growth of common carp,Cyprinus carpio. Predominant expression of wnt4a, wnt5b, and wnt8a was found in the gonads and Wnt4a was localized in spermatocytes and interstitial cells. Ontogeny and testicular phase-wise analysis signified the importance of wnt isofoms analyzed in this study. Specific pathway activation of Wnt signaling revealed that Wnt4a and Wnt5b act through non-canonical while Wnt8a prefers the canonical pathway. The Wnt signaling regulates several steroidogenic enzyme and testis-related genes which was confirmed by the Wnt blockade experiments. Incidentally, zinc (Zn) is an essential trace element involved in the progression of spermatogenesis in teleosts. In adult male carp, a single administration of Zn at different doses elevated the expression of Wnt and Zn transporter genes and a single-dose (30 μg/g body weight [BW]) of Zn treatment elevated steroidogenic enzyme and testis-related genes which coincided with elevated androgens. Conversely, single-dose administration of Zn chelator to the Zn administered (30 μg/g BW) fish reversed the effects emphasizing a prominent role of Zn in the testicular function perhaps through Wnt signaling. Similar effects were observed in the in vitro experiments using the Zn chelator. Bioaccumulation of Zn and histological analysis revealed the importance of Zn in progression of spermatogenesis and sperm motility. Various assays related to cell viability and proliferation exhibited the role of Zn in promoting spermatogenic cell progression. Flow cytometric analysis confirmed Zn-induced elevation of Wnt and Zn transporter genes in germ and supporting cells. Furthermore, the effects of Zn are dose-related in carp. Taken together, it seems wnt4a, wnt5b, and wnt8a play an important role in testis and exposure of Wnt inhibitor, canonical as well as non-canonical activators, and Zn confirmed that Zn regulates Wnt signaling vis-à-vis promoting spermatogenesis in the common carp.