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Targeted disruption of the murine int-1 proto-oncogene resulting in severe abnormalities in midbrain and cerebellar
1Howard Hughes Medical Institute, Department of Biology and Human Genetics, Salt Lake City, Utah 84112.
Abstract:
The int-1 proto-oncogene was first identified as a gene activated in virally induced mouse mammary tumours. Expression studies, however, suggest that the normal function of this gene may be in spermatogenesis and in the development of the central nervous system. 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). Both the int-1 and wg gene products seem to be secreted proteins, presumably involved in cell-cell signalling. 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 selection. This cell line was used to generate a chimaeric mouse that transmitted the mutant allele to its progeny. 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-1-/int-1- mice at several stages of embryogenesis 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.
Insights
The int-1 proto-oncogene is crucial for central nervous system development, particularly the midbrain and cerebellum. Its disruption leads to severe developmental abnormalities and ataxia in mice.
Area of Science:
- Developmental Biology
- Neuroscience
- Genetics
Background:
- The int-1 proto-oncogene, implicated in mammary tumors, shows expression patterns suggesting roles in spermatogenesis and central nervous system (CNS) development.
- int-1 shares sequence similarity with the Drosophila segment polarity gene wingless (wg), and both gene products are likely secreted signaling molecules.
Purpose of the Study:
- To investigate the function of the int-1 gene in mouse development by creating and analyzing a null mutation.
- To determine the specific roles of int-1 during embryogenesis, particularly in CNS formation.
Main Methods:
- Gene targeting was employed to disrupt one int-1 allele in mouse embryonic stem cells.
- Positive-negative selection was used for allele disruption.
- Chimeric mice were generated from modified stem cells to study the effects of the int-1 null mutation in vivo.
Main Results:
- Mice heterozygous for the int-1 null mutation (int-1+/-) were normal and fertile.
- Homozygous int-1 null mutant mice (int-1-/-) displayed a spectrum of phenotypes, including embryonic lethality and severe ataxia in survivors.
- Embryonic examination revealed significant abnormalities in the development of the midbrain (mesencephalon) and hindbrain (metencephalon) in int-1-/- embryos.
Conclusions:
- The int-1 gene plays a critical role in the proper development of the midbrain and cerebellum.
- int-1 is essential for the induction and patterning of key brain structures during mouse embryogenesis.
