A modular cis-regulatory system controls isoform-specific pitx expression in ascidian stomodaeum

Area of Science:

• Developmental Biology
• Genetics
• Evolutionary Biology

Background:

• Pituitary homeobox (pitx) genes are crucial for craniofacial and pituitary development in vertebrates.
• Conserved expression of pitx genes in the anterior neural boundary (ANB) and stomodaeum (oral ectoderm) is observed across chordates.
• Understanding pitx cis-regulatory mechanisms provides insights into the evolution of oral structures.

Purpose of the Study:

• To investigate the organization and cis-regulatory logic of pitx genes in the ascidian Ciona intestinalis during early oral development.
• To identify cis-regulatory elements responsible for isoform-specific expression of Ci-pitx in the ANB and stomodaeum.
• To explore the evolutionary conservation of pitx gene regulation in chordates.

Main Methods:

• Phylogenetic footprinting to identify conserved noncoding sequences (CNSs) in pitx loci of Ciona intestinalis and Ciona savignyi.
• Transient transgenesis in Ciona intestinalis to test the function of identified CNSs as cis-regulatory modules (CRMs).
• Confocal imaging to visualize and analyze spatiotemporal expression patterns driven by CRMs.

Main Results:

• Two distinct Ci-pitx mRNA variants were identified, exhibiting mutually exclusive embryonic expression domains.
• Ci-pitx shares similar exon usage and organization with vertebrate pitx2 genes, suggesting conserved transcriptional unit ancestry.
• Two CRMs were identified within conserved regions, driving complementary ANB/stomodaeal expression of Ci-pitx in specific patterns.

Conclusions:

• The study elucidates the cis-regulatory system governing Ci-pitx expression in the ascidian oral ectoderm.
• Identified CRMs provide a foundation for understanding gene regulatory networks (GRNs) controlling oral structure formation in chordates.
• Findings highlight conserved regulatory principles of pitx genes across diverse chordate species.