An arthropod cis-regulatory element functioning in sensory organ precursor development dates back to the Cambrian.
BACKGROUND
An increasing number of publications demonstrate conservation of function of cis-regulatory elements without sequence similarity. In invertebrates such functional conservation has only been shown for closely related species. Here we demonstrate the existence of an ancient arthropod regulatory element that functions during the selection of neural precursors. The activity of genes of the achaete-scute (ac-sc) family endows cells with neural potential. An essential, conserved characteristic of proneural genes is their ability to restrict their own activity to single or a small number of progenitor cells from their initially broad domains of expression. This is achieved through a process called lateral inhibition. A regulatory element, the sensory organ precursor enhancer (SOPE), is required for this process. First identified in Drosophila, the SOPE contains discrete binding sites for four regulatory factors. The SOPE of the Drosophila asense gene is situated in the 5' UTR.


RESULTS
Through a manual comparison of consensus binding site sequences we have been able to identify a SOPE in UTR sequences of asense-like genes in species belonging to all four arthropod groups (Crustacea, Myriapoda, Chelicerata and Insecta). The SOPEs of the spider Cupiennius salei and the insect Tribolium castaneum are shown to be functional in transgenic Drosophila. This would place the origin of this regulatory sequence as far back as the last common ancestor of the Arthropoda, that is, in the Cambrian, 550 million years ago.


CONCLUSIONS
The SOPE is not detectable by inter-specific sequence comparison, raising the possibility that other ancient regulatory modules in invertebrates might have escaped detection.
Ayyar
Savita
S
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
Negre
Barbara
B
Simpson
Pat
P
Stollewerk
Angelika
A
D058145:Achaete-Scute Complex Genome Region / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001181:Arthropods / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D001665:Binding Sites / Q000235:genetics; D005075:Biological Evolution; D017124:Conserved Sequence / Q000235:genetics; D020440:Gene Duplication / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D009420:Nervous System / Q000254:growth & development* / Q000378:metabolism; D054258:Neural Plate / Q000378:metabolism; D010802:Phylogeny; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D016415:Sequence Alignment; D013045:Species Specificity
D051792:Basic Helix-Loop-Helix Proteins