5 DISRUPTION OF THE HIGH MOBILITY GROUP AT-HOOK 2 (HMGA2) GENE IN SWINE REDUCES POSTNATAL GROWTH

Abstract

The high mobility group AT-hook 2 (HMGA2) protein has been shown to be a crucial gene for cell growth, proliferation, and apoptosis; HMGA2 is also a strong biological candidate for growth, because mutations in this gene alter body size in mice and humans. Compared with wild-type controls, adult mice lacking HMGA2 are 60% smaller, and adult heterozygous mutants are 20% smaller. In humans, HMGA2 has been associated with adult and childhood height without any other deleterious effect. Additionally, a microdeletion in the HMGA2 gene in a human patient resulted in short stature, with no dysmorphologies and normal puberty. In order to determine the effect of HMGA2 on fetal and adult growth in pigs, a transgenic pig line deficient in HMGA2 expression was generated by gene targeting in fetal fibroblasts (FF). Using a targeting vector carrying a reporter gene, and homology arms specific to HMGA2, heterozygous mutant cell lines were generated. The cell lines were then used to generate 6 heterozygous females by somatic cell nuclear transfer (SCNT). Bodyweights and lengths from snout to base of tail were measured every 2 weeks for a year for mutant (n = 6) and wild-type farm gilts (n = 6). Data were analysed by one-way ANOVA. As in mice, disruption of one allele of the HMGA2 gene resulted in 25% reduction in weight (P < 0.0001) and 14% reduction in length (P < 0.0001). Early in postnatal growth (2 months), weights of mutants were not different than wild-type. However, mutants were 20 to 35% lighter (P < 0.05) during mid stages (6 months) and 25 to 30% (P < 0.0001) in late stages (3 months). The same insertional mutation generated 8 heterozygous male clones by SCNT. In addition, 7 nontransgenic males from the same FF line were generated as SCNT controls. Bodyweights and lengths were measured every 2 weeks for 30 weeks for HMGA2 heterozygous mutants (n = 8), control SCNT (n = 7) and wild-type farm boars (n = 5). The weight curve of boars showed similar pattern as for mutant gilts. At 30-week postnatal stage, mutants were 17% (P < 0.05) and 16% (P < 0.05) lighter in weight compared with littermate and wild-type animals, respectively. We are presently developing homozygous HMGA2 mutant lines. Currently, 3 of 6 heterozygous gilts have been bred with heterozygous boars, with 1 confirmed pregnancy. The expectation is that the homozygous animals will, like mice, be 60% smaller than the wild-type animals. The approach described here will result not only in a valuable large-animal model of dwarfism, but also in a tool to reduce the size of existing transgenic and nontransgenic swine lines. This, in turn, will increase the receptivity of valuable transgenic lines by the biomedical community. Funding for this work was provided by NIH grant R21-OD010553 to JP.