A regulatory cascade of three transcription factors in a single specific neuron, DVC, in Caenorhabditis elegans

Abstract

Homeobox proteins are critical regulators of developmental gene transcription and cell specification. Many insights into transcriptional regulation have been gained from studies in the nematode Caenorhabditis elegans. We investigated the expression and regulation of the C. elegans homeobox gene ceh-63, which encodes a single-homeodomain transcription factor of 152 amino acids. ceh-63 is expressed in the interneuron DVC in both sexes, from late embryogenesis through adulthood, and two pairs of uterine cells in reproductive hermaphrodites only. A reporter gene fusion, encoding GFP fused to the full-length CEH-63, also drove weak inconsistent expression in additional unidentified cells in the head and tail. A potential ceh-63 null mutant had no obvious abnormalities, except for a possible increase in subtle defects of the DVC axon projection. No behavioural responses were observed upon either laser ablation of DVC or activation of DVC through light stimulation of channelrhodopsin-2 specifically expressed in this neuron. The function of DVC therefore remains enigmatic. A transcriptional regulatory cascade operating in DVC was defined from the LIM-homeodomain protein CEH-14 through CEH-63 to the helix–turn–helix transcription factor MBR-1. Both CEH-14 and CEH-63 individually bound the mbr-1 promoter in a yeast one-hybrid assay. A model is proposed suggesting that CEH-14 activates ceh-63 and then along with CEH-63 co-ordinately activates mbr-1.

Optogenetic manipulation of neural activity in C. elegans: From synapse to circuits and behaviour

“…Further studies include the functional analysis of the homeodomain transcription factor CEH‐63 that is strongly expressed in the proprioceptive DVC neuron of which the cell body is located in the dorsal–rectal ganglion of the tail. However, laser ablation of DVC or photostimulation of this neuron did not reveal any obvious behavioural changes (Feng et al, 2012).…”

“…Cells Manipulated References Forward and Reverse Locomotory circuit AVA, AVD, AVE, PVC, AVB AIB, RIM (Stirman et al, 2011;Husson et al, 2012a;Husson et al, 2012b;Schmitt et al, 2012) Motor Circuit, Wave propagation Cholinergic motor neurons, muscles Zhang et al, 2007;Leifer et al, 2011;Stirman et al, 2011;Husson et al, 2012b;Singaram et al, 2011;Wen et al, 2012) Mechanosensation (gentle touch) ALM, AVM, PVM, PLM Leifer et al, 2011;Stirman et al, 2011;Timbers et al, 2013;Husson et al, 2012a;Husson et al, 2012b) Mechanosensation (harsh touch) PVD, FLP, PHA,PHB, BDU, SDQR, AQR (Li et al, 2011;Husson et al, 2012a) Polymodal nociception ASH (Guo et al, 2009;Ezcurra et al, 2011;Faumont et al, 2011;Lindsay et al, 2011;Husson et al, 2012b) Oxygen sensation AQR, PQR, URX (Milward et al, 2011; (Feng et al, 2012;Wen et al, 2012) Chemosensation AWC, AIY (Kocabas et al, 2012) Table 1: Circuits, systems and neurons that have been interrogated using optogenetic techniques. (Pirri et al, 2009).…”

The LIM homeobox gene ceh-14 is required for phasmid function and neurite outgrowth

“…This observation indicates that this is not a permanent developmental defect, but function can be restored even in late stages. A late or subtle role for ceh-14 also exists in the DVC neuron, where ceh-14 and ceh-63 together regulate the transcription factor MBR-1, though no phenotypes have been observed so far (Feng et al, 2012).…”

Cross-referencing online activity with the connectome to identify a neglected but well-connected neuron

“…To investigate the role of DVC we used optogenetics for controlled activation, as previous reports suggested its ablation had no obvious behavioral consequence [5,6]. Using the ceh-63 promoter for targeted expression of the blue-light gated cation channel, Channelrhodospin-2 (ChR2), Feng et al [5] could not attribute any response to photocurrents in DVC; however, their transgenic background had a locomotion deficit caused by the dominant rol-6 allele used as a co-injection marker.…”

“…Using the ceh-63 promoter for targeted expression of the blue-light gated cation channel, Channelrhodospin-2 (ChR2), Feng et al [5] could not attribute any response to photocurrents in DVC; however, their transgenic background had a locomotion deficit caused by the dominant rol-6 allele used as a co-injection marker. We repeated the experiment using the same ChR2 expression vector with a fluorescent co-injection marker (myo-2p::mCherry) and computer vision software [7] for quantitative behavioral analysis.…”