Expression, function and regulation of Brachyenteron in the short germband insect Tribolium castaneum

Abstract

T-domain transcription factors are involved in many different processes during embryogenesis, such as mesoderm, heart or gut development in vertebrates and in invertebrates. In insects, the following five types of T-box genes are known: brachyenteron (byn), optomotor-blind (omb), optomotor-blind-related-gene-1 (org-1), dorsocross (doc) and H15. As all these classes are present in the genome of the fruit fly Drosophila melanogaster and the flour beetle Tribolium, the multiplicity of the five types of genes varies from dipterans to the beetle. In higher dipterans, a small cluster of three doc genes (doc1-doc3) exists, while the Tribolium genome contains a single Tc-doc gene only. Two H15 genes, Tc-H15a and Tc-H15b, are present in the Tribolium genome compared to a single H15 gene in Drosophila. We have analysed the expression and function of the Tribolium brachyenteron ortholog (Tc-byn). During embryogenesis, Tc-byn is exclusively expressed in the growth zone of the extending germband and later becomes confined to the distal proctodeum and the hindgut, a situation that parallels the expression pattern of byn in Drosophila. Tc-byn-RNAi treated embryos phenocopy Drosophila byn mutants and form no hindgut. In addition, we have characterised a regulatory element upstream of the Tc-byn transcription start site that confers specific gene expression in the developing hindgut of the Drosophila embryo. Our results demonstrate a highly conserved role for Brachyury-type transcriptional regulators in posterior gut development of insects at the level of expression, function and regulation.

A context-dependent combination of Wnt receptors controls axis elongation and leg development in a short germ insect

“…7C) but subsequently die, probably due to a non-functional hindgut and stunted mouth appendages. A similar gut phenotype has been observed in brachyenteron RNAi experiments (Berns et al, 2008) indicating that Tc-byn and Tc-Fz4 might function within the same pathway. Indeed, byn has been shown to be a target of the Wnt signalling cascade in vertebrates (Arnold et al, 2000;Yamaguchi et al, 1999).…”

Autoregulatory and repressive inputs localize Hydra Wnt3 to the head organizer

“…It is not known yet whether the same genetic cascades act in maintaining Wnt expression. In zebrafish, a Brachyury/Wnt loop acts in Wnt3a and Wnt8 expression in the posterior growth zone (25), which is not present in insects (26,27). A positive feedback regulation by Wnt/β-catenin signaling has been also shown for the sea urchin Wnt8 (28,29), in which it is required for the maintenance of the vegetal Wnt signaling center during gastrulation.…”

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…After hindgut invagination, byn is expressed throughout most of the hindgut primordium. In all three species, loss of byn function leads to substantial reduction or loss of the hindgut as a result of apoptosis (Singer et al 1996 ;Shinmyo et al 2006 ;Berns et al 2008 ). Genes that are regulated either directly or indirectly by byn include caudal , which encodes a homeodomain transcription factor, and wingless ( wg / Wnt1 ), decapentaplegic ( dpp ), and hedgehog ( hh ), which encode secreted signaling ligands in the Wnt, BMP, and Hedgehog pathways, respectively (Takashima and Murakami 2001 ).…”