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Targeted disruption of hoxc-4 causes esophageal defects and vertebral transformations
1Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, Utah, 84112, USA.
Abstract:
Mice carrying a nonfunctional allele of hoxc-4 have been generated by gene targeting. The phenotype of mice homozygous for this mutation is strikingly different from those reported in mice lacking the paralogous genes hoxa-4, hoxb-4, and hoxd-4. In contrast to the mutants of the paralogous family members, hoxc-4 homozygotes do not manifest abnormalities in the cervical vertebrae, but instead show vertebral defects that extend from the second thoracic vertebra (t2) to t11. Therefore, defects do not correspond to the anterior limit of expression of hoxc-4, but rather begin within the region of strong hoxc-4 expression in the prevertebral anlagen (i.e., pv7-14). While hoxc-4 mutant homozygotes that reach adulthood are fertile and appear outwardly normal, most die before weaning age. The high lethality appears to result from partial or complete blockage of the lumen of the esophagus over a large portion of its length, as well as disorganization of the esophageal musculature. Although the Drosophila homolog of hoxc-4, Deformed, is autoregulated, mutation of the hoxc-4 gene does not affect transcription of its paralogous family members. However, in hoxc-4 mutant embryos, transcription of both the hoxc-5 and hoxc-6 genes is altered. Employment of cissolidustrans analysis showed that the hoxc-4 mutation acts in cis to affect the pattern of hoxc-5 expression. Therefore, this mutation is likely to cause a reduction of hoxc-5 function as well as complete loss of hoxc-4 function.
Insights
Gene targeting of hoxc-4 in mice reveals distinct vertebral defects and high lethality due to esophageal abnormalities. This mutation also impacts hoxc-5 expression, suggesting a dual loss of function.
Area of Science:
- Developmental Biology
- Genetics
- Molecular Biology
Background:
- Hox genes are crucial for embryonic development, controlling body plan formation.
- Paralogous Hox genes often have overlapping functions, making individual gene roles complex to determine.
- Previous studies focused on hoxa-4, hoxb-4, and hoxd-4, leaving the specific role of hoxc-4 less understood.
Purpose of the Study:
- To investigate the in vivo function of the hoxc-4 gene using gene targeting in mice.
- To characterize the developmental abnormalities resulting from a loss-of-function mutation in hoxc-4.
- To explore the relationship between hoxc-4 and its paralogous genes, including potential cis-regulatory interactions.
Main Methods:
- Gene targeting in mice to create a nonfunctional hoxc-4 allele.
- Phenotypic analysis of homozygous hoxc-4 mutant mice, including skeletal and organ development.
- Assessment of gene expression patterns for hoxc-4 and its paralogs in mutant embryos.
- Cis-trans analysis to determine the regulatory effects of the hoxc-4 mutation.
Main Results:
- Homozygous hoxc-4 mutant mice exhibit severe vertebral defects from T2 to T11, unlike paralog mutants.
- High embryonic lethality is observed, primarily due to esophageal lumen blockage and muscular disorganization.
- The hoxc-4 mutation does not affect transcription of its paralogs but alters hoxc-5 and hoxc-6 expression.
- Cis-trans analysis confirms the hoxc-4 mutation acts in cis to affect hoxc-5 expression.
Conclusions:
- hoxc-4 plays a unique and essential role in murine vertebral development, distinct from its paralogs.
- Loss of hoxc-4 function leads to critical esophageal defects and embryonic lethality.
- The hoxc-4 mutation results in a combined loss of hoxc-4 function and a reduction in hoxc-5 function due to cis-regulation.