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Retinoic acid perturbs Otx gene expression in the ascidian pharynx
1Department of Zoology and Entomology, University of Queensland, Brisbane, Queensland 4072, Australia.
Abstract:
In vertebrate embryos, ectopic application of all-trans retinoic acid (RA) alters the expression of Otx genes in the developing midbrain. In conjunction with RA-induced misexpression of other regulatory genes this leads to a loss of anterior CNS. In the ascidian Herdmania curvata, RA primarily inhibits the development of the juvenile pharynx. An ascidian Otx gene, Hec-Otx, is expressed largely in this tissue, associated stomodeal structures and the anterior endostyle of the juvenile. Treatment with 10-6 M RA reduces Hec-Otx mRNA levels in the juvenile to about 12% of normal and is correlated closely with the loss of pharyngeal structures. During embryogenesis the expression of Hec-Otx becomes restricted to cell lineages fated to give rise to the anterior-most nervous system and the stomodeal component of the primordial pharynx. In hatched larvae Hec-Otx transcripts are detected only in the sensory (brain) vesicle. RA reduces Hec-Otx expression in the tailbud stomodeal pharynx primordium/anterior nervous system cell line but not in the larval sensory vesicle, suggesting that RA regulation of Hec-Otx expression is restricted to pharyngeal tissues throughout embryonic and postlarval development. RA does not affect expression of Hec-Pax2/5/8, which is normally expressed within the developing nervous system immediately posterior to Hec-Otx at the tailbud stage, lending support to the proposition that RA does not impact CNS axial patterning. These data combined with those from other chordates suggest that RA regulation of Otx expression in the anterior nerve cord and pharynx is a primitive chordate feature which has been maintained predominantly in pharyngeal tissues in the ascidian.
Insights
Retinoic acid (RA) affects Otx gene expression in developing embryos, impacting the central nervous system (CNS). In ascidians, RA inhibits pharynx development by reducing Hec-Otx mRNA, suggesting a conserved role in chordate anterior development.
Area of Science:
- Developmental biology
- Chordate evolution
- Gene regulation
Background:
- Retinoic acid (RA) is crucial for vertebrate embryonic development, influencing gene expression and tissue patterning.
- Otx genes are key regulators of anterior neural development in vertebrates.
- Ascidians, as invertebrate chordates, offer insights into conserved developmental mechanisms.
Purpose of the Study:
- To investigate the role of retinoic acid (RA) in regulating the expression of the Otx gene (Hec-Otx) in the ascidian Herdmania curvata.
- To understand the evolutionary conservation of RA-mediated Otx gene regulation in chordates.
- To determine the impact of RA on ascidian pharyngeal and nervous system development.
Main Methods:
- Treatment of Herdmania curvata embryos and larvae with all-trans retinoic acid (RA).
- Quantitative analysis of Hec-Otx mRNA levels using techniques like in situ hybridization.
- Examination of morphological changes in pharyngeal structures and the nervous system.
Main Results:
- RA treatment significantly reduced Hec-Otx mRNA levels in juvenile ascidians, correlating with pharyngeal structure loss.
- Hec-Otx expression in embryos was restricted to anterior nervous system and pharynx precursors.
- RA's effect on Hec-Otx was specific to pharyngeal tissues, not impacting the larval sensory vesicle or Hec-Pax2/5/8 expression.
Conclusions:
- RA regulation of Otx gene expression in the anterior nerve cord and pharynx is a primitive chordate feature.
- In ascidians, this regulation is predominantly maintained in pharyngeal tissues.
- RA plays a significant role in inhibiting ascidian pharynx development via Hec-Otx downregulation.