PBX-dependent and independent Hox programs establish and maintain motor neuron terminal Identity

Area of Science:

• Developmental Biology
• Neuroscience
• Genetics

Background:

• Motor neuron (MN) diversity is crucial for complex animal movements.
• Molecular mechanisms specifying MN subtypes, particularly along the anterior-posterior (A-P) axis, are not fully understood.
• Hox genes and their cofactors are key regulators of positional identity in development.

Purpose of the Study:

• To investigate the roles of Hox genes and PBX cofactors in specifying cholinergic MN subtype identity in the C. elegans ventral nerve cord (VNC).
• To elucidate how these factors interact with terminal selectors to generate neuronal diversity.

Main Methods:

• Genetic analysis in C. elegans.
• Investigation of Hox gene expression patterns and functions.
• Analysis of PBX cofactor (ceh-20) interactions with Hox genes and terminal selectors (unc-3).

Main Results:

• Anterior Hox genes (ceh-13, lin-39) collaborate with ceh-20 and unc-3 to activate anterior MN identity genes.
• Posterior Hox gene mab-5 represses posterior MN identity by antagonizing unc-3 in a ceh-20-dependent manner, required for both development and maintenance.
• Posterior Hox gene egl-5 acts with unc-3 to activate lumbar MN identity independently of ceh-20.
• ceh-20 is essential for Hox gene expression in VNC MNs, suggesting PBX activity is required for Hox autoregulation.

Conclusions:

• Hox genes and PBX cofactors play critical, context-dependent roles in establishing and maintaining MN subtype identity along the A-P axis.
• Combinatorial interactions between Hox factors and terminal selectors (like unc-3) generate neuronal subtype diversity.
• Findings reveal both PBX-dependent and independent functions of Hox genes in neuronal specification.