[
Crit Rev Eukaryot Gene Expr,
2002]
Nuclear receptors (NRs) have key regulatory functions in a wide range of biological processes and are one of the most abundant classes of transcriptional regulators in metazoans. NRs are particularly numerous in nematodes, in which the NR gene family has undergone extensive expansion and diversification, providing an evolutionary structure function experiment that is yielding new perspectives on the mechanisms of NR function and on nematode biology. The genome sequence of the free-living nematode Caenorhabditis elegans reveals 270 predicted NR genes, more than fivefold more than observed for any other species to date, though existing data suggest that NR genes are similarly abundant in other nematodes. Most of the currently available information regarding the functions of nematode NRs comes from ongoing studies with C. elegans, and we review here what has been learned thus far in three key areas: the relationships of C. elegans NRs to those in other species; the biochemical consequences of nematode NR sequence diversity.
[
Trends Genet,
2001]
Large-scale sequencing efforts are providing new perspectives on similarities and differences among species. Sequences encoding nuclear receptor (NR) transcription factors furnish one striking example of this. The three complete or nearly complete metazoan genome sequences - those of the nematode Caenorhabditis elegans, the fruit fly (Drosophila melanogaster) and the human - reveal dramatically different numbers of predicted NR genes: 270 for the nematode, 21 for the fruit fly and similar to 50 for the human. Although some classes of NRs present in insects and mammals are also represented among the nematode genes, most of the C. elegans NR sequences are distinct from those known in other phyla. Questions regarding the evolution and function of NR genes in nematodes, framed by the abundance and diversity of these genes in the C. elegans genome, are the focus of this article.
[
Biochim Biophys Acta,
2015]
The development of complex multicellular organisms is dependent on regulatory decisions that are necessary for the establishment of specific differentiation and metabolic cellular states. Nuclear receptors (NRs) form a large family of transcription factors that play critical roles in the regulation of development and metabolism of Metazoa. Based on their DNA binding and ligand binding domains, NRs are divided into eight NR subfamilies from which representatives of six subfamilies are present in both deuterostomes and protostomes indicating their early evolutionary origin. In some nematode species, especially in Caenorhabditis, the family of NRs expanded to a large number of genes strikingly exceeding the number of NR genes in vertebrates or insects. Nematode NRs, including the multiplied Caenorhabditis genes, show clear relation to vertebrate and insect homologues belonging to six of the eight main NR subfamilies. This review summarizes advances in research of nematode NRs and their developmental functions. Nematode NRs can reveal evolutionarily conserved mechanisms that regulate specific developmental and metabolic processes as well as new regulatory adaptations. They represent the results of a large number of natural experiments with structural and functional potential of NRs for the evolution of the phylum. The conserved and divergent character of nematode NRs adds a new dimension to our understanding of the general biology of regulation by NRs. This article is part of a Special Issue entitled: Nuclear receptors in animal development.