Effects of vitamin D3 on embryonic development, transcripts of genes encoding reproductive hormones, and its active metabolism in common carp (Cyprinus carpio L.)

Vitamin D 3 (VD 3 ) is a pleiotropic hormone with diverse physiological functions, but its role during early embryonic development in fish remains poorly understood. This study investigated the effects of aqueous VD 3 exposure on embryonic survival, hatching, and the expression of the kiss1, kiss2, gnrh3, foxr1, and hsp70 genes in common carp ( Cyprinus carpio L.). We also examined the hypothesis that common carp embryo is a site of VD 3 non-genomic action and its metabolism, evaluated by measuring 25-hydroxyvitamin D 3 (25OHD 3 ) levels and confirmed by immunolocalization of VDR, PDIA3 as well as CYP24A1 and CYP27B1. The eggs (obtained from 6 females) were fertilized and incubated in water containing VD 3 at concentrations: 0, 1, 10, 50, and 100 ng/mL. During early embryonic development (24, 48, 72 h post-fertilization – hpf), VD 3 did not reveal developmental abnormalities and mortality in common carp but increased larvae hatching rate at the highest tested concentration. Furthermore, early life exposure to VD 3 has shown no alteration in kiss1 , kiss2 , gnrh3 , foxr1 , hsp70 gene expression in newly hatched larvae. Crucially, VD 3 exposure altered embryonic 25OHD 3 concentrations. This finding, alongside the immunohistochemical localization of VDR, PDIA3, CYP27B1 and CYP24A1 in the tissue of common carp embryo, indicates the possible genomic and non-genomic action of VD 3 as well as its active metabolism (synthesis and inactivation) at early life stages of this species. These findings encourage further studies to better understand the role of VD 3 in reproduction and early life stages in cyprinids.