The Evolutionarily Conserved LIM Homeodomain Protein LIM-4/LHX6 Specifies the Terminal Identity of a Cholinergic and Peptidergic C. elegans Sensory/Inter/Motor Neuron-Type.

Jinmahn Kim,Myoung Ok Kim,Yang Hoon Huh,Kyeongjin Kang,Kyuhyung Kim,Zae Young Ryoo,Won Bae Jeon,Seong-Kyoon Choi,Hee-Seok Kweon,Chris Li,Jihye Yeon,Zi Fang,Seo Jin Park

doi:10.1371/journal.pgen.1005480

Abstract

The expression of specific transcription factors determines the differentiated features of postmitotic neurons. However, the mechanism by which specific molecules determine neuronal cell fate and the extent to which the functions of transcription factors are conserved in evolution are not fully understood. In C. elegans, the cholinergic and peptidergic SMB sensory/inter/motor neurons innervate muscle quadrants in the head and control the amplitude of sinusoidal movement. Here we show that the LIM homeobox protein LIM-4 determines neuronal characteristics of the SMB neurons. In lim-4 mutant animals, expression of terminal differentiation genes, such as the cholinergic gene battery and the flp-12 neuropeptide gene, is completely abolished and thus the function of the SMB neurons is compromised. LIM-4 activity promotes SMB identity by directly regulating the expression of the SMB marker genes via a distinct cis-regulatory motif. Two human LIM-4 orthologs, LHX6 and LHX8, functionally substitute for LIM-4 in C. elegans. Furthermore, C. elegans LIM-4 or human LHX6 can induce cholinergic and peptidergic characteristics in the human neuronal cell lines. Our results indicate that the evolutionarily conserved LIM-4/LHX6 homeodomain proteins function in generation of precise neuronal subtypes.

Highlights

The proper generation and maintenance of cells in the nervous system is essential for multi-cellular organisms
We show that the lim-4 LIM homeodomain transcription factor is necessary and sufficient to promote and maintain the specific cholinergic and peptidergic properties and functions via binding to unique DNA sequences
We demonstrate that C. elegans lim-4 and human LHX6 show striking functional similarity; C. elegans LIM-4 or human LHX6 can induce cholinergic and peptidergic characteristics in human neuronal cell lines

Summary

Introduction

The proper generation and maintenance of cells in the nervous system is essential for multi-cellular organisms. Several genes that function in terminal differentiation and specification of cholinergic neuronal fate have been identified, including the Olf/EBF transcription factor unc-3 for the A-, B-, and AS-type ventral nerve cord and SAB motor neurons, LIM homeobox transcription factor ttx-3 (ortholog of mammalian Lhx2/9) for the AIY and AIA interneurons, Paired-like homeobox gene ceh-10 for the AIY interneurons, and POU homeobox gene unc-86 for the IL2 sensory neurons, URA motor neurons and URB interneurons [6, 7, 8, 9, 10] These transcription factors act as terminal selectors to directly or indirectly regulate expression of most terminal differentiation genes, such as the cholinergic gene battery but not that of pan-neuronal genes, and broadly affect terminal differentiation of each cholinergic neuron types [2]. The terminal selector transcription factors that are required for terminal differentiation of half of the cholinergic neurons have been identified, mechanisms and genes that differentiate other morphologically and functionally different cholinergic neuron types remain to be elucidated

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