Transgenic mice expressing a mutant human GH gene causing type 2 IGHD

Abstract

Several mutations were identified in the intron 3 of human growth hormone gene 1 (hGH-1) in patients with isolated GH deficiency (IGHD) type 2 characterized by an autosomal dominant trait. The mutations result in exon 3 skipping, and generation of 17 Kd mutant GH. To elucidate how the mutation causes dominant trait, transgenic mice expressing a mutant hGH gene (the first guanine to adenine transversion in intron 3: GH-1; IVS3+1: G-A) were produced in C57BL/6 strain. Genotypes of mice were identified by PCR-amplified products of tail snip DNAs. Delivery of the mutant hGH transgene into 76 fertilized eggs resulted in production of two male heterozygous transgenic mice (hGH(sup +/-), the zero filial generation, F0). Since the mating of the transgenic mice with the same strain was unsuccessful, they were outcrossed with CD-1 (ICR) strain. Only one mouse gave birth, producing 4 male and 7 female (F1) harboring the mutant hGH gene in one allele (hGH(sup +1/-)). F1 mice were mated again with the wild type ICR strain, generating 82 hGH(sup +/-) mice (F2:51 males and 31 females). To study whether somatotrophs in F2 mice express the mutant hGH gene, RNA extracted from the pituitary was subjected to RT-PCR. It was demonstrated that the F2, hGH(sup +/-) mice express the mutant hGH gene, lacking exon 3. Thus, these heterozygous mice were sib-mated to generate homozygous mice (F3). The mating resulted in 27 percent hGH(sup -/-), 64 percent hGH(sup +/-) and 9 percent hGH(sup +/+) mice, indicating that the transgene was carried stably to the descendants and did not interfere with the reproduction. These mice will be a valuable model to study how type 2 IGHD develops during the course of development.