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Temporally-regulated retinoic acid depletion produces specific neural crest, ocular and nervous system defects
E D Dickman1, C Thaller, S M Smith
1Department of Nutritional Sciences, University of Wisconsin-Madison, 53706, USA.
Abstract:
Both retinoid receptor null mutants and classic nutritional deficiency studies have demonstrated that retinoids are essential for the normal development of diverse embryonic structures (e.g. eye, heart, nervous system, urogenital tract). Detailed analysis of retinoid-modulated events is hampered by several limitations of these models, including that deficiency or null mutation is present throughout gestation, making it difficult to isolate primary effects, and preventing analysis beyond embryolethality. We developed a mammalian model in which retinoid-dependent events are documented during distinct targeted windows of embryogenesis. This was accomplished through the production of vitamin A-depleted (VAD) female rats maintained on sufficient oral retinoic acid (RA) for growth and fertility. After mating to normal males, these RA-sufficient/VAD females were given oral RA doses which allowed for gestation in an RA-sufficient state; embryogenesis proceeded normally until retinoids were withdrawn dietarily to produce a sudden, acute retinoid deficiency during a selected gestational window. In this trial, final RA doses were administered on E11.5, vehicle at E12.5, and embryos analyzed on E13.5; during this 48 hour window, the last RA dose was metabolized and embryos progressed in a retinoid-deficient state. RA-sufficient embryos were normal. Retinoid-depleted embryos exhibited specific malformations of the face, neural crest, eyes, heart, and nervous system. Some defects were phenocopies of those seen in null mutant mice for RXR alpha(-/-), RXR alpha(-/-)/RAR alpha(-/-), and RAR alpha(-/-)/RAR gamma(-/-), confirming that RA transactivation of its nuclear receptors is essential for normal embryogenesis. Other defects were unique to this deficiency model, showing that complete ligand 'knock-out' is required to see those retinoid-dependent events previously concealed by receptor functional redundancy, and reinforcing that retinoid receptors have separate yet overlapping contributions in the embryo. This model allows for precise targeting of retinoid form and deficiency to specific developmental windows, and will facilitate studies of distinct temporal events.
Insights
Retinoids are crucial for embryonic development. A new rat model allows precise timing of retinoid deficiency, revealing specific malformations and enhancing understanding of retinoid receptor roles in embryogenesis.
Area of Science:
- Developmental Biology
- Molecular Biology
- Teratology
Background:
- Retinoids, vitamin A derivatives, are essential for embryonic development, influencing structures like the eye, heart, and nervous system.
- Previous models (null mutants, nutritional deficiencies) have limitations, including effects throughout gestation and early lethality, hindering precise analysis.
- Understanding the temporal roles of retinoids and their receptors is critical for developmental processes.
Purpose of the Study:
- To develop a novel mammalian model for precise temporal analysis of retinoid-dependent embryogenesis.
- To investigate the specific embryonic defects caused by acute, windowed retinoid deficiency.
- To elucidate the roles of retinoid receptors in distinct developmental stages.
Main Methods:
- Created vitamin A-depleted (VAD) female rats, maintained on retinoic acid (RA) for fertility.
- Administered controlled RA doses during gestation, followed by dietary withdrawal to induce acute deficiency in a specific gestational window (E11.5-E13.5).
- Analyzed embryos for malformations and compared defects to known receptor null mutants.
Main Results:
- Acute retinoid deficiency during a specific window caused specific malformations in the face, neural crest, eyes, heart, and nervous system.
- Observed defects phenocopied some known receptor null mutant phenotypes (RXR alpha, RAR alpha/gamma).
- Identified unique defects, suggesting complete ligand withdrawal reveals previously masked retinoid-dependent events and receptor functions.
Conclusions:
- The developed VAD rat model enables precise temporal targeting of retinoid deficiency during embryogenesis.
- This model facilitates the study of distinct temporal events in retinoid signaling and receptor contributions.
- The findings highlight the essential, stage-specific roles of retinoids and their receptors in normal embryonic development.