Hypoxia impairs primordial germ cells (PGCs) development in zebrafish (Danio rerio) embryos

Abstract

Primordial Germ Cells (PGCs) are germ cell precursors. They become gametes during gametogenesis upon sexual maturation in animals. Therefore, alteration of PGC development could impair reproduction. PGC development has been studied in many organisms. In zebrafish, vasa and nanos1 are two well known PGC marker genes, and they are both essential for PGC development. By using whole mount in situ hybridization with vasa and nos1 riboprobes to label PGCs, two approaches have been adopted to test the hypothesis that hypoxia causes a reduction of PGCs in terms of number and volume. Direct cell counting showed fewer numbers of PGCs in hypoxic stressed embryos (21.8 +/- 5.4) when compared with the control (30.6 +/- 5.2). Confocal microscopy also revealed a reduction in the volume of PGCs in embryos exposed to hypoxia (20874 +/- 4603μm3), as compared with the control (31142 +/- 1831 μm3). GFP nos1 3’UTR-injected embryos exposed to hypoxia showed mis-migrated PGCs in cranial regions, dorsal caudal regions and yolk cell extension. Real-time PCR showed that expression of igfbp1 was up-regulated; suggesting that igfbp1 induction under hypoxia may be the cause of the observed PGCs migration defect. Over-expression of HIF-1 α resulted in hypoxia-induced PGC migration defect and it could be rescued by IGFBP1 morpholino. For the first time, evidence has been provided that hypoxia induced IGFBP1, which suppresses IGF signalling and results in PGC migration failure, leading to fewer numbers and lower volumes of PGCs in the genital ridge.