Human Molecular Genetics Advance Access published online on April 8, 2009
Human Molecular Genetics, doi:10.1093/hmg/ddp176
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A hypomorphic allele of Tsc2 highlights the role of TSC1/TSC2 in signaling to AKT and models mild human TSC2 alleles
Translational Medicine Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115
* Corresponding author: David J. Kwiatkowski, One Blackfan Circle, 6-216, Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital, Phone: 617-355-9005, Fax: 617-355-9016, Email: dk{at}rics.bwh.harvard.edu
Received December 29, 2008; Revised March 16, 2009; Accepted April 6, 2009
Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome in which hamartomas develop in multiple organ systems. Knockout and conditional alleles of Tsc1 and Tsc2 have been previously reported. Here we describe the generation of a novel hypomorphic allele of Tsc2 (del3), in which exon 3, encoding 37 amino acids near the N-terminus of tuberin, is deleted. Embryos homozygous for the del3 allele survive until E13.5, two days longer than Tsc2 null embryos. Embryos die from underdevelopment of the liver, deficient hematopoiesis, aberrant vascular development, and hemorrhage. Mice that are heterozygous for the del3 allele have a markedly reduced kidney tumor burden in comparison to conventional Tsc2+/- mice. Murine embryo fibroblast (MEF) cultures that are homozygous for the del3 allele express mutant tuberin at low levels, and show enhanced activation of mTORC1, similar to Tsc2 null MEFs. Furthermore, the mutant cells show prominent reduction in the activation of AKT. Similar findings were made in the analysis of homozygous del3 embryo lysates. Tsc2-del3 demonstrates GAP activity comparable to that of wild type Tsc2 in a functional assay. These findings indicate that the del3 allele is a hypomorphic allele of Tsc2 with partial function due to reduced expression, and highlight the consistency of AKT downregulation when Tsc1/Tsc2 function is reduced. Tsc2-del3 mice also serve as a model for hypomorphic TSC2 missense mutations reported in TSC patients.