Sox transcription factors are intimately involved in the development of multicellular organisms and accordingly understanding the role Sox genes play in diverse species of metazoans will hopefully shed light on the evolution of multicellularity. Here we review our current knowledge of the Sox genes isolated and characterised in invertebrates, ranging from the very simplest organisms through to complex chordates. While Sox genes have been identified in many invertebrate species, comparatively little is known about their functions outside the well-studied models, Drosophila, sea urchin and nematode. Consequently, we centre this review around the Sox family in Drosophila, comparing this with what is known about orthologous genes in other invertebrate species. We highlight several conserved themes that emerge when looking at the roles Sox proteins appear to play during embryogenesis, including early functions in CNS development and widespread interactions with the Wnt signalling pathway. Comparing the expression of Sox genes in insect species, where genome organisation is conserved but expression is apparently not, highlights the need for more functional data on the roles that related Sox proteins play in organisms outside the well-characterised models.
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