Repressible Transgenic Sterilization in Channel Catfish, Ictalurus punctatus, by Knockdown of Primordial Germ Cell Genes with Copper-Sensitive Constructs

Repressible knockdown approaches were investigated to manipulate for transgenic sterilization in channel catfish, Ictalurus punctatus. Two primordial germ cell (PGC) marker genes, nanos and dead end, were targeted for knockdown and an off-target gene, vasa, was monitored. Two potentially copper-sensitive repressible promoters, yeast ctr3 (M) and ctr3-reduced (Mctr), were coupled with four knockdown strategies separately including: ds-sh RNA targeting the 5′ end (N1) or 3′ end (N2) of channel catfish nanos, full-length cDNA sequence of channel catfish nanos for overexpression (cDNA), and ds-sh RNA-targeting channel catfish dead end (DND). Each construct had an untreated group and treated group with copper sulfate as the repressor compound. Spawning rates of full-sibling P1 fish exposed or not exposed to the constructs as treated and untreated embryos were 85 and 54%, respectively, indicating potential sterilization of fish and repression of the constructs. In F1 fish, mRNA expressions of PGC marker genes for most constructs were downregulated in the untreated group and the knockdown was repressed in the treated group. Gonad development in transgenic, untreated F1 channel catfish was reduced compared to non-transgenic fish for MctrN2, MN1, MN2, and MDND. For 3-year-old adults, gonad size in the transgenic untreated group was 93.4% smaller than the non-transgenic group for females and 92.3% for males. However, mean body weight of transgenic females (781.8 g) and males (883.8 g) was smaller than of non-transgenic counterparts (984.2 and 1254.3 g) at 3 years of age, a 25.8 and 41.9% difference for females and males, respectively. The results indicate that repressible transgenic sterilization is feasible for reproductive control of fish, but negative pleiotropic effects can result.