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Genetic evidence that the retinoid signal is transduced by heterodimeric RXR/RAR functional units during mouse
P Kastner1, M Mark, N Ghyselinck
1Institut de Géńetique et de Biologie Moléculaire et Cellulaire, CNRS-INSERM-ULP-Collège de France, Illkirch, France.
Abstract:
We describe here the analysis of congenital malformations in compound mutant fetuses bearing null alleles in one RXR (alpha, beta or gamma) and one RAR (alpha, beta or gamma) isotype gene. A marked synergy was observed between the effects of mutations in RXR alpha and RARs, as a large number of developmental defects previously found mainly in RAR single and compound mutants were recapitulated in specific RXR alpha/RAR compound mutants. Several malformations were seen only in one type of RXR alpha/RAR mutant combination, whereas others were seen in several types of RXR alpha/RAR double mutants. No synergy was observed between the effects of mutations of either RXR beta or RXR gamma mutations and those of any of the RAR mutations. These genetic data suggest that RXR/RAR heterodimers are the functional units transducing the retinoid signal for a large number of RA-dependent processes, and furthermore, that RXR alpha is the main RXR implicated in the developmental functions of RARs. The significance of these observations is discussed with respect to the problem of functional specificity and redundancy among retinoid receptors in vivo.
Insights
Genetic analysis revealed that RXR alpha, not RXR beta or gamma, synergizes with RARs to cause developmental defects. This highlights RXR alpha
Area of Science:
- Developmental biology
- Genetics
- Molecular biology
Background:
- Retinoids are crucial signaling molecules regulating gene expression.
- Retinoic acid receptors (RARs) and retinoid X receptors (RXRs) mediate retinoid signaling.
- Understanding the in vivo function of specific receptor interactions is essential for developmental studies.
Purpose of the Study:
- To investigate the functional synergy between different RXR and RAR receptor isotypes in embryonic development.
- To determine the specific roles of RXR alpha, beta, and gamma in conjunction with RARs during development.
Main Methods:
- Analysis of congenital malformations in compound mutant mouse fetuses.
- Generation of double mutant mice with null alleles in RXR and RAR genes.
- Comparative analysis of developmental defects across different RXR/RAR mutant combinations.
Main Results:
- Significant synergy between RXR alpha mutations and RAR mutations, leading to numerous developmental defects.
- Specific malformations were unique to certain RXR alpha/RAR compound mutant combinations.
- No observed synergy between RXR beta or RXR gamma mutations and any RAR mutations.
Conclusions:
- RXR/RAR heterodimers are the primary functional units for retinoid signaling in many developmental processes.
- RXR alpha plays a predominant role in mediating the developmental functions of RARs.
- These findings clarify the functional specificity and redundancy of retinoid receptors in vivo.