A protocadherin mediates oral placode morphogenesis in the tunicate Ciona

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Cell Biology

Background:

• Placodes are ectodermal thickenings in chordate embryos forming sensory organs.
• While often considered vertebrate-specific, homologous placodes may exist in non-vertebrate chordates.
• The oral siphon placode (OSP) in Ciona robusta, derived from a cranial-like placode, forms the adult mouth.

Purpose of the Study:

• To investigate the molecular mechanisms regulating the morphogenesis and physical separation of the OSP.
• To determine the role of cell-cell interactions in OSP development.
• To identify key molecules and genetic factors involved in OSP formation.

Main Methods:

• Utilized CRISPR/Cas9 gene editing to disrupt Pcdhe.e expression in Ciona robusta.
• Performed overexpression experiments of Pcdhe.e in anterior surface ectoderm.
• Analyzed the effects of genetic manipulations on OSP morphology and tissue separation.
• Investigated the dependence of Pcdhe.e expression on transcription factors Six1/2 and Pitx.

Main Results:

• Protocadherin.e (Pcdhe.e) is specifically expressed in the OSP.
• Disruption of Pcdhe.e leads to the failure of OSP physical separation from adjacent ectoderm.
• Overexpression of Pcdhe.e also causes loss of OSP distinctness.
• Pcdhe.e functions via homophilic adhesion.
• Pcdhe.e expression is regulated by oral placode-specific transcription factors like Six1/2 and Pitx.

Conclusions:

• Protocadherin-mediated cell-cell interactions are essential for proper OSP morphogenesis in Ciona robusta.
• OSP formation requires precise regulation of homotypic cell-cell adhesion.
• These findings suggest conserved mechanisms for placode formation across chordates.