Abstract
Growth hormone (GH) transgenic fish often exhibit remarkable transformations in growth rate and other phenotypes relative to wild-type. The 5750A transgenic coho salmon strain exhibits strong sexually dimorphic growth, with females possessing growth stimulation at a level typical of that seen for both sexes in other strains harbouring the same gene construct (e.g. M77), while males display a modest level of growth stimulation. GH mRNA levels were significantly higher in females than in males of the 5750A strain but equivalent in the M77 strain, indicating sex and transgene insertion locus altered transgene expression. We found that acute estradiol treatments did not influence GH expression in either strain (5750A and M77) or the transgene promoter (metallothionein-B), suggesting that estradiol level was not a significant factor influencing transgene activity. The feminization of XX and XY fish of the 5750A and M77 strains generated all-female groups and resulted in equalized growth of the two genetic sexes, suggesting that the presence of the Y chromosome was not directly capable of influencing the GH transgene–mediated growth in a physiological female conditions. These data suggest that the difference in growth rate seen between the sexes in the 5750A strain arises from non-estradiol-mediated sex influences on gene regulation at the transgene locus. This study shows how genetic factors and transgene insertion sites can influence transgene expression with significant consequent effects on phenotype.
Highlights
The successful development of transgenic strains for commercial use requires multiple generations to achieve and requires careful assessment of phenotype to ensure compatibility withThe majority of fast-growing transgenic salmon have been generated by non-homologous insertion of a heterospecific Growth hormone (GH) gene driven by a constitutively active promoter (Devlin et al 1994; Du et al 1992; Devlin et al 2004)
We examine whether the difference in growth stimulation seen between sexes and strains is due to the presence/absence of the Y chromosome or the reproductive physiology status of the animal, and assess whether GH and IGF-1 gene expression are differentially regulated between the sexes in the two strains and are correlated with the degree of growth stimulation
Preliminary observations of the 5750A strain suggested that males did not grow at the same fast rate seen for females of the same strain and for both sexes of other strains. To accurately assess these observations, a growth trial was conducted in which the 5750A strain was grown alongside the M77 strain of GH transgenic coho salmon which had shown no noticeable difference in the growth of males and females over previous generations
Summary
The successful development of transgenic strains for commercial use requires multiple generations to achieve and requires careful assessment of phenotype to ensure compatibility withThe majority of fast-growing transgenic salmon have been generated by non-homologous insertion of a heterospecific GH gene driven by a constitutively active promoter (Devlin et al 1994; Du et al 1992; Devlin et al 2004). In GH transgenic fish, the magnitude of growth response elicited by GH overexpression can be influenced by genetic factors such as promoter strength, location of insertion, transgene copy. Genomewide association studies (GWAS) have found that loci influencing growth and gene expression levels are highly distinct between GH transgenic and wild-type salmon (Kodama et al 2018b; Mcclelland et al 2020). For example the effect of a transgene on growth was very different between fish grown in tank vs stream environments (Sundström et al 2007). Together, these data show that the effect of a transgene is context specific, being influenced by both environmental background and genetic background
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
