Chelicerata sDscam isoforms combine homophilic specificities to define unique cell recognition

Area of Science:

• Neuroscience
• Evolutionary Biology
• Molecular Biology

Background:

• Down syndrome cell adhesion molecule (Dscam1) and clustered protocadherins (cPcdh) establish neural circuits through homophilic specificity.
• Neuronal self-avoidance relies on strict homophilic recognition, but the role of shortened Dscam (sDscam) proteins in Chelicerata is less understood.

Purpose of the Study:

• Investigate the interaction mechanisms and specificity of Chelicerata sDscam proteins.
• Determine how sDscam isoforms contribute to neuronal identity and self-nonself discrimination.

Main Methods:

• Studied protein-protein interactions of sDscamα and sDscamβ isoforms.
• Analyzed the role of specific domains (Ig, fibronectin-type III) in cis and trans interactions.
• Assessed the impact of isoform combinations on cell-cell interactions.

Main Results:

• Chelicerata sDscamα and some sDscamβ exhibit strictly homophilic trans interactions via the first Ig domain.
• Different sDscam isoforms interact promiscuously in cis through fibronectin-type III domains.
• Cell-cell interactions depend on the combinatorial identity of all expressed sDscam isoforms, with single mismatches disrupting recognition.

Conclusions:

• sDscam cis and trans associations generate extensive combinatorial homophilic recognition specificities.
• sDscam combinatorial specificity provides unique neuronal identities for self-nonself discrimination in Chelicerata.
• Findings suggest convergent evolution of neuronal self-avoidance mechanisms between Chelicerata sDscams and vertebrate cPcdhs.