Correlated responses to selection for large body size in oMt1a-oGH transgenic mice: organ traits

The objective of the present study was to compare correlated responses in l iver, spleen, kidney, heart and testis absolute weights and as a percentage of 8-week body weight following selection for large 8-week body weight in twice-replicated nontransgenic and transgene-carrier lines of mice from two genetic backgrounds. The transgene was an ovine metallothionein 1a-ovine g rowth hormone (oMt1a-oGH) construct, which was activated by adding 25 mM Zn SO4 to the drinking water. Lines NM and NC were nontransgenic lines derived from a high-growth and randomly selected background, respectively. Lines T M and TC were transgene-carrier lines formed from the respective genetic ba ckgrounds. Line CC was a nontransgenic control from the randomly selected b ackground. At weaning, male mice from each line were assigned to either zin c supplemented or control drinking water. Toe-clips were assayed by PCR for the presence or absence of the transgene. Correlated responses of absolute weights of all organs in nontransgenic lines indicated moderately high gen etic correlations of organ weights with body weight, but on a percentage of body weight basis, the correlated responses were much lower. The correlate d responses in visceral organ weights were lower in the presence of the ina ctivated oMt1a-oGH transgene than in its absence. The presence of the activ ated oMt1a-oGH combined with the effects of selection for growth increase h ad a greater impact on increasing the size of the splanchnic organs than di d selection for large body weight in the absence of the transgene.