A common theme for LIM homeobox gene function across phylogeny?

Abstract

The identification of the molecular components of the developmental neurogenic programs in different organisms has revealed an astounding degree of conservation across phylogeny, suggesting that the basic mechanisms of neural development have also been conserved in evolution. One class of conserved neural regulatory genes, the LIM homeobox genes, encode transcription factors with two Zn-finger-like LIM domains and a DNA-binding homeodomain (1). Vertebrate members of this class have been implicated in neurogenesis by correlative expression evidence; e.g., the combinatorial expression of LIM homeobox genes in the vertebrate spinal cord suggested a “LIM-code” for specific motorneuronal targeting choices (2). Genetic analysis in Drosophila also demonstrated their essential role in axon pathfinding and the determination of neurotransmitter identity (3, 4). The genome of the nematode Caenorhabditis elegans is almost completely sequenced, thus allowing the analysis of complete gene families in a metazoan organism. C. elegans contains seven LIM homeobox genes. Almost all C. elegans LIM homeobox genes fall into subclasses that are defined by the presence of similar genes from arthropods and vertebrates, suggesting a common origin for different subclasses of LIM homeobox genes (Fig. 1; C. elegans proteins are underlined).