Genetic variants of the tuberous sclerosis 2 tumour suppressor gene in mouse t haplotypes

The murine t complex on chromosome 17 contains a number of homozygous letha l and semi-lethal mutations that disrupt development of the mouse embryo. W e recently characterized an embryonic lethality in the rat that results fro m a germ-line mutation in the tuberous sclerosis 2 (Tsc-2) tumour suppresso r gene (the Eker mutation). Remarkably, mouse embryos homozygous for t(w8) mutation display cranial defects reminiscent of those observed in rat embry os homozygous for the Eker mutation. To determine whether the Tsc-2 gene, w hich is in the t complex, is mutated in t(w8) or other t haplotypes, we cha racterized this gene in a series of t haplotype mice. Four Tsc-2 polymorphi sms were identified: three in the coding region and one intronic that appea red to be common to all t haplotypes analysed. No evidence was found to arg ue that the Tsc-2 gene is altered in t(w8) haplotype mice. However, in the t(w5) haplotype we found a G to T mutation in Tsc-2 that was present only i n this t haplotype. In contrast to other polymorphisms within the Tsc-2 cod ing region which did not result in amino acid changes in Tsc-2 gene product tuberin, this mutation substituted a phenylalanine for a conserved cystein e in t(w5) tuberin. Within the t complex, the Tsc-2 gene and the putative t (w5) locus appeared to map to different positions, complicating identificat ion of Tsc-2 as a candidate for the t(w5) locus and suggesting that the G t o T mutation in the Tsc-2 gene may have arisen independently of the t(w5) f unctional mutation.