Apparent role of Tribolium orthodenticle in anteroposterior blastoderm patterning largely reflects novel functions in dorsoventral axis formation and cell survival.
In the short-germ beetle Tribolium castaneum, the head gap gene orthodenticle (Tc-otd) has been proposed to functionally substitute for bicoid, the anterior morphogen unique to higher dipterans. In this study we reanalyzed the function of Tc-otd. We obtained a similar range of cuticle phenotypes as in previously described RNAi experiments; however, we noticed unexpected effects on blastodermal cell fates. First, we found that Tc-otd is essential for dorsoventral patterning. RNAi depletion results in lateralized embryos, a fate map change that by itself can explain the observed loss of the anterior head, which is a ventral anlage in Tribolium. We find that this effect is due to diminished expression of short gastrulation (sog), a gene essential for establishment of the Decapentaplegic (Dpp) gradient in this species. Second, we found that gnathal segment primordia in Tc-otd RNAi embryos are shifted anteriorly but otherwise appear patterned normally. This anteroposterior (AP) fate map shift might largely be due to diminished zen-1 expression and is not responsible for the severe segmentation defects observed in some Tc-otd RNAi embryos. As neither Tc-sog nor Tc-zen-1 probably requires Otd gradient-mediated positional information, we posit that the blastoderm function of Tc-Otd depends on its initial homogeneous maternal expression and that this maternal factor does not provide significant positional information for Tribolium blastoderm embryos.
Kotkamp
Kay
K
Department of Biology, Developmental Biology Unit, Erlangen University, 90158 Erlangen, Germany. mschoppm@biologie.uni-erlangen.de
Klingler
Martin
M
Schoppmeier
Michael
M
D000818:Animals; D019521:Body Patterning / Q000235:genetics / Q000502:physiology; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D017344:Genes, Insect; D010641:Phenotype; D034622:RNA Interference; D014231:Tribolium / Q000166:cytology / Q000196:embryology* / Q000235:genetics*