Induced sterility in aquaculture species has significant value. It can be used to prevent early maturation during grow-out, protect proprietary genetics, eliminate the risk of gene flow from genetically improved populations, and prevent establishment of feral populations.

We describe a transgenic approach driving apoptosis specifically in germ cells of developing embryo. This technology has been demonstrated in a zebrafish model, and here we report results on transfer of this approach to the commercially important tilapia.

We used synthetic tilapia bax:nanos 3'UTR RNA to demonstrate targeted germ line ablation in injected embryos; we identified and characterized tilapia oocyte specific promoters, generated all-tilapia transgenes, and investigated their functionality in 16 stable tilapia lines. Similar to zebrafish, we found that 1) transgenic MSC-females produced offspring that were completely or partially sterile, depending on the line; 2) the severity of this "grandchildless" phenotype directly correlates with the level of maternal transgene expression; and 3) the transgene exerts its sterilization activity by ectopic activation of apoptosis in primordial germ cells (PGCs), resulting in embryos with absent or dramatically reduced PGC number. Finally, embryos lacking PGCs developed into adults with threadlike gonads containing no detectable germ cells. We measured a 20-36 fold reduction in gonado-somatic index associated with a 30% improved growth performance in the 7 months old sterile and substerile progeny of an MSC female. We believe, selection of a more sensitive genetic background can further improve the penetrance of sterility and performance, as energy not spent in gonad development is diverted toward somatic growth.

Finally, in contrast to MSC-females, MSC-males produce fertile offspring, allowing propagation of the line and the possibility to stack sterility to any transgene of interest (see illustration below).

 Model: MSC can be microinjected into embryos to establish first generation transgenic MSC lines that remain fertile, and subsequent MSC generations can be propagated through the male (MSC-male, left panel). Transgenic females carrying at least one copy of the MSC (MSC-female, right panel) can be crossed with transgenic homozygous male to produce embryos that lack germ cells. Progeny produced from these females are a sterile generation, a so-called "grandchildless" phenotype (right hand panel).