The C. elegans labial/Hox1 type gene
ceh-13 , in contrast to some other members of the C. elegans Hox cluster, is required for viability, in particular for proper organization of anterior structures during embryogenesis 1 . Since spaciotemporal
ceh-13 expression appears to be controlled at the level of transcription 1,2 we have undertaken a deletional and mutational promoter analysis 3 . In order to complement these earlier studies we have cloned and preliminarily sequenced the
ceh-13 ortholog from C. remanei (
Cr-ceh-13 ) and compared its sequence with
Ce-ceh-13 and with
ceh-13 from C. briggsae (
Cb-ceh-13 ) that has recently been sequenced by the C. briggsae sequencing consortium. The intron exon structure of
ceh-13 is conserved in all three species. At the amino acid level the overall identities / similarities are 77% / 80% for
Ce-ceh-13 and
Cb-ceh-13 , 81% / 87% for
Ce-ceh-13 and
Cr-ceh-13 and 83% / 86% for
Cb-ceh-13 and
Cr-ceh-13 (Fig. 1). Not surprisingly the homeodomain is 100% conserved between the three species. A Ce -
ceh-13:: gfp reporter construct (pMF1 2 ) that reflects
ceh-13 expression very well at all developmental stages tested, appears to be correctly controlled also in C. briggsae . Therefore we expected to find conserved elements also in non-coding regions. Indeed, in a preliminary analysis we found short conserved stretches that might be regulatory elements. Interestingly, the three most obvious ones are located in regions that had previously been shown to be important for the control of Ce -
ceh-13 expression. A first element with 26 bp that are identical in all three species is located in a region of 400bp that is sufficient to confer
ceh-13 like expression to GFP in, among other places, the male tail. A second element with 15 bp out of 16 bp that are identical in all three species lies within a fragment of 740bp that is sufficient to drive correct early embryonic
ceh-13 expression 3 . Finally there is a stretch of 15 identical bp that resides within intron 1. From earlier studies we suspect that intron 1 is required to prevent
ceh-13 expression in adult body wall muscles 4 . We are currently performing mutational analyses to test the significance of these findings. Fig. 1: Comparison of the predicted CEH-13 amino acid sequences from the three Caenorhabditis species. The 100% conserved homeodomain is underlined; amino acids that are identical in all three species are in bold . 1) Brunschwig et al. (1999) Development 126:1537-1546 2) Wittmann et al. (1997) Development 124:4193-41200 3) Streit et al. submitted 4) Reto Kohler (1999) Ph.D. thesis, University of Fribourg.