TARGETED DISRUPTION OF THE MURINE INT-1 PROTOONCOGENE RESULTING IN SEVERE ABNORMALITIES IN MIDBRAIN AND CEREBELLAR DEVELOPMENT

THE int-1 proto-oncogene was first identified as a gene activated in virally induced mouse mammary tumours1,2. Expression studies, however, suggest that the normal function of this gene may be in spermatogenesis and in the development of the central nervous system3-5. Genes sharing sequence similarity with int-1 have been found throughout the animal kingdom. For example, int-1 has 54% amino-acid identity to the Drosophila segment polarity gene wingless (wg)6. Both the int-1 and wg gene products seem to be secreted proteins, presumably involved in cell-cell signalling7-11. We have now explored the function of int-1 in the mouse by disrupting one of the two int-1 alleles in mouse embryo-derived stem cells using positive-negative selection12. This cell line was used to generate a chimaeric mouse that transmitted the mutant allele to its progeny13-16. Mice heterozygous for the int-1 null mutation are normal and fertile, whereas mice homozygous for the mutation may exhibit a range of phenotypes from death before birth to survival with severe ataxia. The latter pathology in mice and humans is often associated with defects in the cerebellum. Examination of int-l-/int-l- mice at several stages of embryo-genesis revealed severe abnormalities in the development of the mesencephalon and metencephalon indicating a prominent role for the int-1 protein is in the induction of the mesencephalon and cerebellum. © 1990 Nature Publishing Group.