Early evolution of the T-box transcription factor family

Abstract

Developmental transcription factors are key players in animal multicellularity, being members of the T-box family that are among the most important. Until recently, T-box transcription factors were thought to be exclusively present in metazoans. Here, we report the presence of T-box genes in several nonmetazoan lineages, including ichthyosporeans, filastereans, and fungi. Our data confirm that Brachyury is the most ancient member of the T-box family and establish that the T-box family diversified at the onset of Metazoa. Moreover, we demonstrate functional conservation of a homolog of Brachyury of the protist Capsaspora owczarzaki in Xenopus laevis. By comparing the molecular phenotype of C. owczarzaki Brachyury with that of homologs of early branching metazoans, we define a clear difference between unicellular holozoan and metazoan Brachyury homologs, suggesting that the specificity of Brachyury emerged at the origin of Metazoa. Experimental determination of the binding preferences of the C. owczarzaki Brachyury results in a similar motif to that of metazoan Brachyury and other T-box classes. This finding suggests that functional specificity between different T-box classes is likely achieved by interaction with alternative cofactors, as opposed to differences in binding specificity.origin multicellularity | premetazoan evolution | subfunctionalization | Porifera | Holozoa T ranscriptional regulation is a central aspect of animal development. Thus, deciphering the early evolution of metazoan transcription factors is vital for achieving a better understanding of the origin of animals. The T-box family of genes is among the most important developmental transcription factors present in Metazoa. This family is characterized by an evolutionary conserved DNA-binding domain of 180-200 amino acids, known as the T-box domain (1-3). Brachyury is the founding and best-characterized member of the T-box family, with well-established roles in blastopore specification, mesoderm differentiation and, in chordates, notochord formation (4-6). It has been hypothesized that the ancestral role of Brachyury was primarily that of blastopore determination and gastrulation (5, 7).Other T-box classes include Tbx4/5, Tbx6, Tbx2/3, Eomes, and Tbx1/15/20. With only a few exceptions (8), all classes of T-box genes are widespread among bilaterian animals, with a handful being identified and studied in nonbilaterian metazoans, such as cnidarians (5, 9), ctenophores (7, 10), and sponges (11-14). T-box genes were initially thought to be specific to metazoans (13, 15), but two recent studies revealed the presence of T-box genes in nonmetazoan lineages (14, 16), including the unicellular filose amoeba Capsaspora owczarzaki, a close relative of animals, and the chytrid fungus Spizellomyces punctatus. T-box genes were not identified in any other sequenced eukaryote, suggesting that T-box genes were secondarily lost in choanoflagellates (both in unicellular and colonial species) and most fungi. Interestingly, one of the T-box genes identified in C. ow...

Developmental gene expression provides clues to relationships between sponge and eumetazoan body plans

“…However, we have recovered 21 Wnt genes, multiple downstream components of the Wnt pathway, 22 Tgfb ligands, 6 Smad genes, two each of Vasa and Pl10 genes, and single Nanos, Gata, Gli and Hedgling genes. Sycon Tbox genes, including two Brachyurys, have been reported 41 .…”

“…Several other Tbox family genes, including the Eomes class, are also involved in formation of the endomesoderm 53 . We have recently reported the presence and eumetazoan-like properties of two Brachyury homologues, and the presence of Eomes and basal class Tboxes in Sycon 41 . Here we report expression of these genes.…”

The T-box gene family: emerging roles in development, stem cells and cancer

“…It has long been known that the T-box gene family is ancient in origin and present in all metazoans (Bollag et al, 1994), but the increasing availability of sequenced genomes from diverse animal taxa has pushed back the origins of the family to unicellular organisms and fungi, in which one or two T-box genes, including T, have been identified (Degnan et al, 2009;Sebe-Pedros et al, 2013) (Fig. 3).…”

EphA4-dependent Brachyury expression is required for dorsal mesoderm involution in the Xenopus gastrula

“…The Brachyury gene is common to metazoans, and its early expression occurs typically at the blastopore or related structures (Technau, 2001;Marcellini, 2006;Sebe-Pedros et al, 2013), suggesting a role in gastrulation. For example, in sea urchins, Brachyury is expressed at the outer rim of the blastopore (Hibino et al, 2004), and its inhibition leads to defects consistent with a role in involution (Gross and McClay, 2001).…”