The specification and development of organs depend on the localized expression of specific classes of transcription factors. One such class is that of the family of tsh-related Zn-finger (tshz) transcription factors. The Drosophila teashirt (tsh) gene (Fasano et al.,1991), the founding member of the family, has been shown to play critical roles during the development of the fly embryo and adult: tsh is required to pattern the midgut (Mathies et al.,1994) and to specify the identity of the trunk ectoderm in the embryo (Roder et al.,1992). tsh is also required for the establishment of the proximodistal axis of adult appendages, such as wings and legs (Abu-Shaar and Mann,1998; Erkner et al.,1999; Azpiazu and Morata,2000; Casares and Mann,2000; Wu and Cohen,2000,2002) and the specification of the eye (Pan and Rubin,1998; Singh et al.,2004; Bessa and Casares,2005). More recently, it has been shown that the tsh paralogue, tiptop (tio), albeit dispensable for Drosophila development, is functionally equivalent to tsh and can partially compensate its loss in tsh mutants (Laugier et al.,2005; Bessa et al.,2009; Datta et al.,2009). tshz genes have been also identified in vertebrates. At least, three tshz have been reported in mouse, chicken, and Xenopus (tshz1-3; Caubit et al.,2000; Long et al.,2001; Manfroid et al.,2004,2006; Koebernick et al.,2006; Onai et al.,2007) and one in zebrafish (tshz1; Wang et al.,2007). Molecularly, invertebrate and vertebrate tshz genes show similarity in their three first and widely spaced Zn-finger domains. Vertebrate tshz's show additional Zn-fingers and a vertebrate-specific homeodomain (Koebernick et al.,2006; Onai et al.,2007). Despite these molecular differences, the three murine tshz genes can function as the endogenous tsh when expressed in Drosophila (Manfroid et al.,2004). These various studies show that vertebrate tshz genes are expressed also with dynamic and complex patterns in many developing organs, including the central nervous system, mesodermal derivatives (somites, pronephros), limbs, and branchial arches. However, the functional characterization of this gene family in vertebrates is still fragmentary. During early Xenopus development, tshz3 is required for dorso–ventral axis formation (Onai et al.,2007), while tshz3 knock-out mice show ureteral defects (Caubit et al.,2008).
In this study, we have further investigated the evolution of the tshz gene family and made use of the zebrafish to explore the developmental expression of two of its members, zebrafish tshz2 and tshz3b.