Improved Pituitary Specificity of Cre Recombinase Transgenic Mice by Recombineering of a Mouse αGSU Bacterial Artificial Chromosome

MARÍA INÉS PÉREZ MILLÁN; CAMPER SA; DAVIS SW

Boston, MA

Congreso; The Endocrine Society´s Annual Meeting; 2011

The Cre-loxP system is a powerful tool to study the effects of gene deletion, especially when tissue-specific and/or cell-specific deletion of a gene is required. In order to study the pituitary-specific effects of gene deletion, we generated transgenic mice that express the cre recombinase under the transcriptional control of the mouse glycoprotein hormone α-subunit (αGSU or Cga) gene. The αGSU protein is expressed in adult pituitary gonadotropes and thyrotropes and heterodimerizes with separate β-subunits of the glycoprotein hormones, LH, FSH and TSH, to give the biologically active heterodimeric hormones. αGSU is also expressed in the pituitary primordium, Rathke´s pouch, extra-ocular mesenchyme, and olfactory epithelium. A sequence of 4.6 kb of the mouse αGSU gene promoter and enhancer targets the gonadotropes and thyrotropes, as well as the other hormone-producing cells of the adult anterior pituitary gland (1). These sequences are sufficient to confer developmentally regulated and hormone-responsive gene expression in the pituitary gland and have been used successfully to create pituitary-specific deletions of several genes (2, 3, 4). Ectopic cre activity is observed in the skeletal and cardiac muscle of the 4.6 kb αGSU transgenic mice, however, limiting the usefulness of this transgene for some purposes. To generate αGSU-cre mice that more accurately recapitulate endogenous αGSU gene expression, we used homologous recombination in E. coli to introduce cre coding sequences into a 228 kb bacterial artificial chromosome containing the mouse αGSU gene. To determine the specificity and ability of these new αGSU-cre transgenic mice to induce loxP mediated recombination we bred them with genetically engineered reporter mice that express the lacZ gene (R26R) only after cre-mediated recombination occurs. αGSU-cre;R26R double transgenic mice exhibited robust lacZ expression in the thyrotropes and gonadotropes, where αGSU is expressed. Little or no expression was observed in other tissues where the previous αGSU-cre showed ectopic expression, including the skeletal and cardiac muscle, brain, kidney, lungs, testis, ovaries, tail and liver. Therefore, we have generated a valuable transgenic mouse strain to induce specific mutations of floxed genes, for examining gene function in the pituitary gland.