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Conserved transcription factors termed “terminal selectors” regulate neuronal sub-type specification and differentiation through combinatorial transcriptional regulation of terminal differentiation genes. The unique combinations of terminal differentiation gene products in turn contribute to the functional identities of each neuron. One well-characterized terminal selector is COE (Collier/Olf/Ebf), which has been shown to activate cholinergic gene batteries in C. elegans motor neurons. However, its functions in other metazoans, particularly chordates, is less clear. Here we show that the sole COE ortholog in the non-vertebrate chordate Ciona robusta , Ebf, controls the expression of the cholinergic locus VAChT/ChAT in a single dorsal interneuron of the larval Motor Ganglion, which is presumed to be homologous to the vertebrate spinal cord. We propose that, while the function of Ebf as a regulator of cholinergic neuron identity conserved across bilaterians, its exact role may have diverged in different cholinergic neuron subtypes (e.g., interneurons vs. motor neurons) in chordate-specific motor circuits.
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A cis ‐regulatory change underlying the motor neuron‐specific loss of Ebf expression in immotile tunicate larvae
Abstract Many species in the tunicate family Molgulidae have independently lost their swimming larval form and instead develop as tailless, immotile larvae. These larvae do not develop structures that are essential for swimming such as the notochord, otolith, and tail muscles. However, little is known about neural development in these nonswimming larvae. Here, we studied the patterning of the Motor Ganglion (MG) ofMolgula occulta, a nonswimming species. We found that spatial patterns of MG neuron regulators in this species are conserved, compared with species with swimming larvae, suggesting that the gene networks regulating their expression are intact despite the loss of swimming. However, expression of the key motor neuron regulatory geneEbf (Collier/Olf/EBF)was reduced in the developing MG ofM. occultawhen compared with molgulid species with swimming larvae. This was corroborated by measuring allele‐specific expression ofEbfin hybrid embryos from crosses ofM. occultawith the swimming speciesM. oculata. Heterologous reporter construct assays in the model tunicate speciesCiona robustarevealed a specificcis‐regulatory sequence change that reduces expression ofEbfin the MG, but not in other cells. Taken together, these data suggest that MG neurons are still specified inM. occultalarvae, but their differentiation might be impaired due to reduction ofEbfexpression levels.
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- Award ID(s):
- 1940743
- PAR ID:
- 10265542
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Evolution & Development
- Volume:
- 23
- Issue:
- 2
- ISSN:
- 1520-541X
- Page Range / eLocation ID:
- p. 72-85
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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