Tetraspanin Cd9b plays a role in fertility in zebrafish

In mice, CD9 expression on the egg is required for efficient sperm-egg fusion and no effects on ovulation or male fertility are observed in CD9 null animals. Here we show that cd9b KO zebrafish also appear to have fertility defects. In contrast to mice, fewer eggs were laid by cd9b KO zebrafish pairs and, of the eggs laid, a lower percentage were fertilised. In vitro fertilization (IVF) was used to demonstrate that factors such as courting behaviour, adult size and mate choice were not causing the unexpected decrease in clutch size. The decrease in egg numbers could be rescued by exchanging either cd9b KO partner, male or female, for a wildtype (WT) partner. However, the fertilisation defect could only be rescued by crossing a cd9b KO female with a WT male. Our results indicate that Cd9b has several roles in fish fertility, affecting both clutch size and egg fertilisation. Highlights cd9b mutant pairs lay fewer eggs and of the eggs laid, fewer are fertilised. Mutation in cd9b does not affect primordial germ cell number or migration. Reduction in number of eggs and fertility is not due to courting behaviour, fish size or mate choice. cd9b mutation in either gender affects the number of eggs laid. Mutation of cd9b in the males affects fertilisation efficiency but mutation of cd9b in the females does not.