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
.
Evolution of early development in dipterans: Reverse-engineering the gap gene network in the moth midge Clogmia albipunctata (Psychodidae)