Conservation and Diversification of Msx Protein in Metazoan Evolution

Abstract

Msx (/msh) family genes encode homeodomain (HD) proteins that control ontogeny in many animal species. We compared the structures of Msx genes from a wide range of Metazoa (Porifera, Cnidaria, Nematoda, Arthropoda, Tardigrada, Platyhelminthes, Mollusca, Brachiopoda, Annelida, Echiura, Echinodermata, Hemichordata, and Chordata) to gain an understanding of the role of these genes in phylogeny. Exon-intron boundary analysis suggested that the position of the intron located N-terminally to the HDs was widely conserved in all the genes examined, including those of cnidarians. Amino acid (aa) sequence comparison revealed 3 new evolutionarily conserved domains, as well as very strong conservation of the HDs. Two of the three domains were associated with Groucho-like protein binding in both a vertebrate and a cnidarian Msx homolog, suggesting that the interaction between Groucho-like proteins and Msx proteins was established in eumetazoan ancestors. Pairwise comparison among the collected HDs and their C-flanking aa sequences revealed that the degree of sequence conservation varied depending on the animal taxa from which the sequences were derived. Highly conserved Msx genes were identified in the Vertebrata, Cephalochordata, Hemichordata, Echinodermata, Mollusca, Brachiopoda, and Anthozoa. The wide distribution of the conserved sequences in the animal phylogenetic tree suggested that metazoan ancestors had already acquired a set of conserved domains of the current Msx family genes. Interestingly, although strongly conserved sequences were recovered from the Vertebrata, Cephalochordata, and Anthozoa, the sequences from the Urochordata and Hydrozoa showed weak conservation. Because the Vertebrata-Cephalochordata-Urochordata and Anthozoa-Hydrozoa represent sister groups in the Chordata and Cnidaria, respectively, Msx sequence diversification may have occurred differentially in the course of evolution. We speculate that selective loss of the conserved domains in Msx family proteins contributed to the diversification of animal body organization.

Msx1 and Msx2 act as essential activators of Atoh1 expression in the murine spinal cord

“…Later on, Msx1 and Msx2 expression domains become progressively restricted to the RP, whereas Msx3 expression persists in the dorsal part of the spinal cord excluding the RP (Hill et al, 1989;Robert et al, 1989;Shimeld et al, 1996). HD sequences and Engrailed homology 1 motif (Eh1) domains in their N-terminus are highly conserved between Msx1, Msx2 and Msx3 and between species (Takahashi et al, 2008). Consistent with the presence of an Eh1 repressor domain, Msx1 and Msx2 are described as transcriptional repressors.…”

“…Since amino acids F and S of the Msx Eh1 motif are required for its interaction with Groucho/TLE family members (Takahashi et al, 2008;Rave-Harel et al, 2005;Goldstein et al, 2005), they were replaced by G and A in Msx1 (Msx1*) and Msx2 (Msx2*) to abolish their repressive activity (Fig. 5Dc).…”

“…Msx1 and Msx2 act as transcriptional repressors in various contexts, either by directly interfering with the transcriptional machinery (Shetty et al, 1999;Hovde et al, 2001) or via a repressor complex containing Groucho factors (Takahashi et al, 2008;Rave-Harel et al, 2005). Activation of transcription by Msx1 and Msx2 is much less documented: Msx1 and Msx2 proteins have been shown to activate the Hspa1b promoter by interacting with heat shock factors Hsf1 and Hsf2 in a DNA binding-independent manner (Zhuang et al, 2009).…”

Expression pattern of annelid Zic in embryonic development of the oligochaete Tubifex tubifex

“…The Emx sequence was deposited in the DDBJ database with accession number AB439506. Tubifex Zic (Ttu-Zic, AB231870) and Tubifex Msx (Ttu-Msx, AB302957) cDNAs were previously described (Aruga et al 2006;Takahashi et al 2008). …”

“…To learn whether the aforementioned spatiotemporal expression pattern of Ttu-Zic is widespread among genes expressed in the mesodermal cell lineage (i.e., in the germ band), we examined the expression pattern of another developmental tool-kit gene, Ttu-Msx (Takahashi et al 2008), which was shown to be expressed in the mesodermal lineage in a preliminary observation. Expression of Ttu-Msx begins at late stage 14, and hybridization signals are detected as transverse, regularly repeating stripes in the anterior region of the mesodermal germ band (Fig.…”