Gap genes are involved in segment determination during early development of the vinegar fly Drosophila melanogaster and other dipteran insects (flies, midges and mosquitoes). They are expressed in overlapping domains along the antero-posterior (A-P) axis of the blastoderm embryo. While gap domains cover the entire length of the A-P axis in Drosophila, there is a region in the blastoderm of the moth midge Clogmia albipunctata, which lacks canonical gap gene expression. Is a non-canonical gap gene functioning in this area? Here, we characterize tarsal-less (tal) in C. albipunctata. The homologue of tal in the flour beetle Tribolium castaneum (called milles-pattes, mlpt) is a bona fide gap gene. We find that Ca-tal is expressed in the region previously reported as lacking gap gene expression. Using RNA interference, we study the interaction of Ca-tal with gap genes. We show that Ca-tal is regulated by gap genes, but only has a very subtle effect on tailless (Ca-tll), while not affecting other gap genes at all. Moreover, cuticle phenotypes of Ca-tal depleted embryos do not show any gap phenotype. We conclude that Ca-tal is expressed and regulated like a gap gene, but does not function as a gap gene in C. albipunctata.

This work was funded by the MEC-EMBL agreement for the EMBL/CRG Research Unit in Systems Biology, SGR Grant 406 from the Catalan funding agency AGAUR, and by grant BFU2009-10184 and BFU2012-33775 from the Spanish Ministerio de Economia y Competitividad (MINECO). The Centre for Genomic Regulation (CRG) acknowledges support from MINECO, ‘Centro de Excelencia Severo Ochoa 2013–2017', SEV-2012-0208.