Timeline of Developmental Defects Generated upon Genetic Inhibition of the Retinoic Acid Receptor Signaling Pathway

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• The retinoic acid receptor (RAR) signaling pathway is vital for organ and system morphogenesis.
• Understanding the precise temporal requirements of RAR function is essential for developmental studies.

Purpose of the Study:

• To precisely determine the critical time windows for retinoic acid receptor (RAR) functions during embryonic development.
• To elucidate the specific morphogenetic events dependent on RAR signaling.

Main Methods:

• Temporally controlled genetic ablation procedures were employed.
• Phenotypic analysis of mutant embryos lacking RARs or ATRA-synthesizing enzymes.

Main Results:

• RAR functions are critical between embryonic days E8.5-E9.5 for axial rotation, sinus venosus appearance, vascular modeling, and formation of forelimb buds, lung buds, dorsal pancreas, lens, and otocyst.
• Between E9.5-E10.5, RARs are essential for trachea formation, lung branching, great artery patterning, optic fissure closure, inner ear, and facial process development.
• Cardiac looping is identified as the earliest morphogenetic event requiring functional all-trans retinoic acid (ATRA)-activated RAR signaling.

Conclusions:

• Specific temporal windows of RAR signaling are critical for distinct developmental processes.
• The study provides a detailed map of RAR-dependent morphogenesis during embryogenesis.
• ATRA-activated RAR signaling is fundamental for early cardiovascular development, initiating at cardiac looping.