Homozygous neonates are smaller than their wildtype and heterozygous littermates. They develop normally until approximately 21 days of age, when they develop an acute and rapid, aging-like degenerative pathology resulting in death by postnatal day 24. Homozygous mutant mice exhibit subcutaneous fat loss, lordokyphosis (hunchbacked spine) with osteopenia (30% loss of bone mineral density), colitis, and severe lymphopenia due to increased lymphocyte apoptosis. At day 12, mice have reduced insulin-like growth factor I (IGF-1) levels in serum, and develop severe hypoglycemia. Mouse embryonic fibroblasts (MEFs) prepared from homozygous embryos exhibit reduced proliferation, defective base excision repair function, as indicated by increased sensitivity to alkylating agents and ionizing radiation, and increased chromosomal aberrations. The donating investigators report that no gene product (mRNA or protein) is detected by RT-PCR or immuoblot analysis of tissues, MEFs or embryonic stem cells from homozygotes. The targeting construct placed a lacZ expression cassette in frame into exon 1 of the mRNA coding sequence, and beta-galactosidase staining is detected in most adult and embryonic tissues. This mutant mouse strain may be useful in studies related to DNA damage repair, genomic stability, and aging.
