HMG-B transcription factors of unicellular opisthokonts and their relatedness to the Sox-Tcf/Lef-Mata proteins of Metazoa and fungi

[Display omitted] •The Sox-Tcf/Lef-Mata (STM) family of HMG-B transcription factors appeared in the common ancestor of Opisthokonta and Amoebozoa.•In the opisthokont clade of the STM family, the Sox protein arose in the common ancestor of Opisthokonta. The branches containing the Mata (holomycotan) and Tf7 + Tcf/Lef (holozoan) proteins arose after separation of the Sox protein lineage.•Due to recent reports of interaction of Sox proteins with β-cathenin there is a possibility that the interaction with β-cathenin is a basic property of SLM proteins.•Intranuclear part of the Wnt signaling pathway could have developed in the ancestor of Metazoa on the basis of a pre-existing protein interaction. A phylogenetic analysis of transcription factors of the Sox-Tcf/Lef-Mata (STM) family of the HMG-B superfamily was carried out in order to clarify the evolutionary roots of the Wnt signaling pathway in unicellular organisms. The data set for analysis included protein sequences of metazoans, fungi, unicellular opisthokonts, apusomonads and amoebozoans. The topology of the phylogenetic tree suggests that STM-related proteins arose in the common ancestor of Opisthokonta and Amoebozoa, two of amoebozoan STM proteins are sister-related to opisthokont ones and the three known lineages of STM transcription factors (STM family in narrow sence) are found in Opisthokonta only. Of these, the holozoan Sox protein branch is the result of either the first or second branching, that originated in the common ancestor of Opisthokonta. The lineage containing Tcf/Lef proteins (holozoan) and the lineage containing Mata proteins (holomycotan) are sister. They derived either at the time of the Holozoa and Holomycota divergence or originate from two paralogs of the common ancestor of Opisthokonta, which arose after the separation of the Sox lineage. Interaction with Armadillo-like proteins may be an original feature of the STM protein family and existed in the unicellular ancestors of multicellular animals; a connection is possible between the presence of Mata-related proteins in Aphelidium protococcorum and specific genome feature of this species.