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Alternative olfactory neuron fates are specified by the LIM homeobox gene lim-4.

ABSTRACT: The Caenorhabditis elegans AWA, AWB, and AWC olfactory neurons are each required for the recognition of a specific subset of volatile odorants. lim-4 mutants express an AWC reporter gene inappropriately in the AWB olfactory neurons and fail to express an AWB reporter gene. The AWB cells are morphologically transformed toward an AWC fate in lim-4 mutants, adopting cilia and axon morphologies characteristic of AWC. AWB function is also transformed in these mutants: Rather than mediating the repulsive behavioral responses appropriate for AWB, the AWB neurons mediate attractive responses, like AWC. LIM-4 is a predicted LIM homeobox gene that is expressed in AWB and a few other head neurons. Ectopic expression of LIM-4 in the AWC neuron pair is sufficient to force those cells to adopt an AWB fate. The AWA nuclear hormone receptor ODR-7 described previously also represses AWC genes, as well as inducing AWA genes. We propose that the LIM-4 and ODR-7 transcription factors function to diversify C. elegans olfactory neuron identities, driving them from an AWC-like state into alternative fates.

SUBMITTER: Sagasti A

PROVIDER: S-EPMC316880 | biostudies-literature | 1999 Jul

REPOSITORIES: biostudies-literature

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Alternative olfactory neuron fates are specified by the LIM homeobox gene lim-4.

Sagasti A A Hobert O O Troemel E R ER Ruvkun G G Bargmann C I CI

Genes & development 19990701 14

The Caenorhabditis elegans AWA, AWB, and AWC olfactory neurons are each required for the recognition of a specific subset of volatile odorants. lim-4 mutants express an AWC reporter gene inappropriately in the AWB olfactory neurons and fail to express an AWB reporter gene. The AWB cells are morphologically transformed toward an AWC fate in lim-4 mutants, adopting cilia and axon morphologies characteristic of AWC. AWB function is also transformed in these mutants: Rather than mediating the repuls ...[more]

PMID: 10421632

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Project description:BackgroundLIM homeobox (Lhx) transcription factors are unique to the animal lineage and have patterning roles during embryonic development in flies, nematodes and vertebrates, with a conserved role in specifying neuronal identity. Though genes of this family have been reported in a sponge and a cnidarian, the expression patterns and functions of the Lhx family during development in non-bilaterian phyla are not known.ResultsWe identified Lhx genes in two cnidarians and a placozoan and report the expression of Lhx genes during embryonic development in Nematostella and the demosponge Amphimedon. Members of the six major LIM homeobox subfamilies are represented in the genomes of the starlet sea anemone, Nematostella vectensis, and the placozoan Trichoplax adhaerens. The hydrozoan cnidarian, Hydra magnipapillata, has retained four of the six Lhx subfamilies, but apparently lost two others. Only three subfamilies are represented in the haplosclerid demosponge Amphimedon queenslandica. A tandem cluster of three Lhx genes of different subfamilies and a gene containing two LIM domains in the genome of T. adhaerens (an animal without any neurons) indicates that Lhx subfamilies were generated by tandem duplication. This tandem cluster in Trichoplax is likely a remnant of the original chromosomal context in which Lhx subfamilies first appeared. Three of the six Trichoplax Lhx genes are expressed in animals in laboratory culture, as are all Lhx genes in Hydra. Expression patterns of Nematostella Lhx genes correlate with neural territories in larval and juvenile polyp stages. In the aneural demosponge, A. queenslandica, the three Lhx genes are expressed widely during development, including in cells that are associated with the larval photosensory ring.ConclusionsThe Lhx family expanded and diversified early in animal evolution, with all six subfamilies already diverged prior to the cnidarian-placozoan-bilaterian last common ancestor. In Nematostella, Lhx gene expression is correlated with neural territories in larval and juvenile polyp stages. This pattern is consistent with a possible role in patterning the Nematostella nervous system. We propose a scenario in which Lhx genes play a homologous role in neural patterning across eumetazoans.

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Alternative olfactory neuron fates are specified by the LIM homeobox gene lim-4.

Publications

Alternative olfactory neuron fates are specified by the LIM homeobox gene lim-4.

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