Functional retinoid receptors in budding ascidians.

Area of Science:

• Molecular Biology
• Developmental Biology
• Genetics

Background:

• Retinoid X receptors (RXRs) are crucial nuclear receptors involved in gene regulation.
• Retinoic acid (RA) signaling pathways play significant roles in embryonic development and morphogenesis.
• Understanding the function of RXR and RAR homologs in invertebrate development provides insights into conserved signaling mechanisms.

Purpose of the Study:

• To clone and characterize a homolog of retinoid X receptors (RXR) from the ascidian Polyandrocarpa misakiensis (PmRXR).
• To investigate the interaction between PmRXR and a previously identified P. misakiensis retinoic acid receptor (PmRAR).
• To determine the functional role of the PmRXR/PmRAR complex in retinoic acid-mediated gene activation during ascidian development.

Main Methods:

• Cloning of PmRXR cDNA from Polyandrocarpa misakiensis.
• Gel-shift assays to assess DNA-binding complex formation between PmRXR and PmRAR.
• Transfection assays using a reporter gene (lacZ) driven by a retinoic acid response element (RARE).
• Construction of chimeric effector genes involving PmRXR and PmRAR cDNA fragments.

Main Results:

• PmRXR formed a complex with PmRAR that binds to vertebrate-type RAREs.
• Retinoic acid (RA) treatment activated a reporter gene in notochord cells when embryos were transfected with PmRXR, PmRAR, and a RARE-lacZ construct.
• PmRXR mRNA was detected in glomerulocytes, a cell type also expressing PmRAR mRNA in the developing ascidian bud.

Conclusions:

• The PmRXR/PmRAR complex functions as an RA-dependent transcriptional activator in ascidian development.
• This complex likely mediates RA signaling in glomerulocytes, potentially regulating genes involved in bud morphogenesis.
• The findings suggest a conserved role for RXR/RAR heterodimers in RA signaling across different animal groups.