Zheng C, Lee HMT, Pham K. Nervous system-wide analysis of Hox regulation of terminal neuronal fate specification in Caenorhabditis elegans.
PLoS Genet 2022;
18:e1010092. [PMID:
35226663 PMCID:
PMC8912897 DOI:
10.1371/journal.pgen.1010092]
[Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 03/10/2022] [Accepted: 02/12/2022] [Indexed: 12/01/2022] Open
Abstract
Hox genes encode evolutionarily conserved transcription factors that specify regional identities along the anterior-posterior (A-P) axis. Although some Hox genes are known to regulate the differentiation of certain neurons, to what extent Hox genes are involved in the terminal specification of the entire nervous system is unclear. Here, we systematically mapped the expression of all six Hox genes in C. elegans nervous system and found Hox expression in 97 (32%) of the 302 neurons in adult hermaphrodites. Our results are generally consistent with previous high-throughput expression mapping and single-cell transcriptomic studies. Detailed analysis of the fate markers for these neurons revealed that Hox genes regulate the differentiation of 29 (25%) of the 118 classes of C. elegans neurons. Hox genes not only regulate the specification of terminal neuronal fates through multiple mechanisms but also control subtype diversification along the A-P axis. The widespread involvement of Hox genes in neuronal differentiation indicates their roles in establishing complex nervous systems.
The nervous system contains an extraordinary array of neuron types. How this neuronal diversity arises during development and what genes regulate the differentiation of each neuron type are among the major questions of neurobiology. Hox genes are a set of transcription factors highly conserved in the animal kingdom and are involved in setting up the body plan in the embryos. Hox genes are known to regulate the differentiation of some neurons, but their contribution to the overall development of a nervous system is unclear. In this study, we analyzed the activity of the Hox genes in the differentiation of the 302 neurons of the C. elegans nervous system in its entirety. We found that the six Hox genes are expressed in 32% of all neurons and five Hox genes regulate the differentiation of 25% of all neuron types through multiple mechanisms and act at various stages of cellular development. Thus, our results suggest that a small number of Hox genes could control the development of a significant portion of the nervous system. Given the conserved functions of Hox genes across species, we suspect that the increasing number of Hox genes may have allowed increased complexity in the nervous system in animal evolution.
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