Conserved expression control and shared activity between cognate T‐box genes Tbx2 and Tbx3 in connection with Sonic hedgehog signaling during Xenopus eye development

Abstract

Tbx2 and Tbx3 are considered to be cognate genes within a Tbx2/3/4/5 subfamily of T-box genes and are expressed in closely overlapping areas in a variety of tissues, including the eye. Herein, we show that misexpression of Tbx2 and Tbx3 in Xenopus embryos gave rise to defective eye morphogenesis, which was reminiscent of the defect caused by attenuated Sonic hedgehog (Shh) signaling. Indeed, Tbx2/3 misexpression suppressed Gli1, Gli2, Ptc2 and Pax2, mediators or targets of Hedgehog (Hh) signals. From these data, Tbx2/3 may have a shared function in inhibiting Gli-dependent Shh signaling during eye development. Conversely, the expression of Tbx2/3 was severely affected by both Shh and a putative dominant negative form of Hh, as well as by both transactivator and transrepressor forms of Gli-fusion proteins, suggesting that the expression of Tbx2/3 may be regulated by a Gli-dependent Hh signal transduction pathway. Because the Shh signal has been considered to play crucial roles in the formation of the proximal-distal and dorsal-ventral axes in the eyes, these findings about the mutual regulatory mechanism between Tbx2/3 and Gli-dependent Hh signaling provide valuable insight into the cause of the localized expression of Tbx2/3 and their role during the formation of these axes. In addition, our findings also imply the conserved regulation and shared activity between the cognate genes of Tbx2 and Tbx3.

Xtbx6r, a novel T-box gene expressed in the paraxial mesoderm, has anterior neural-inducing activity

“…Xtbx6r-VP16 and Ztbx24 induce tail-like structures when overexpressed in the animal region. This phenomenon has also been observed in injection experiments involving Xbra (Tada-et al, 1997), Xtbx6 (Yabe, data not shown), or Xtbx2/3-VP16 (Takabatake et al, 2002), suggesting that this activity is common to transcriptional activator-type T-box genes. These results also indicate that Xtbx6r and Ztbx24 have quite opposite effects, suggesting that Xtbx6r is not an ortholog of Ztbx24.…”

“…Xtbx2 and Xtbx3/ET are first expressed in the anterior neural plate and become localized later in the dorsal retina of the tadpole (Li et al, 1997;Hayata et al, 1999). Overexpression of these genes in the eye field causes defects in the ventral retina (Takabatake et al, 2002). Eomesodermin is first expressed in the dorsal mesoderm, but also expressed later in the telencephalon of the tadpole and is suggested to be involved in neural differentiation (Ryan et al, 1996;.…”

MID1 and MID2 are required for Xenopus neural tube closure through the regulation of microtubule organization

“…The following primers were used: xMID1, 5Ј-GTTGTCTTCTCTGTTGAATAA-3Ј and 5Ј-TGTATAATGGT TCT -GTTTGAT-3Ј; xMID2, 5Ј-GTCATGAAGTTAAGAAAACTTGCTC-3Ј and 5Ј-ACCTTCAAGCAATTTCTTCTCTCTG-3Ј; NCAM, 5Ј-GCCT G -TAGAATTACAATGCTG-3Ј and 5Ј-AGCATCTTGGCT GCTGGCATT-3Ј; Sox2, 5Ј-GAGGATGGACACTTATGCCCAC-3Ј and 5Ј-GGACATGC -TGTAGGTAGGCGA-3Ј; Epidermal keratin I, 5Ј-CGGTTGAAGG -TAACCTGA-3Ј and 5Ј-CAACCTTCCCATCAACCA-3Ј; ODC, 5Ј-CAG -CTAGCTGTGGTGTGG-3Ј and 5Ј-CAACATGGAA ACTCACACC-3Ј. The following plasmids were used for probe synthesis: xMID1 and xMID2 (constructed for this study); Sox2 (XL039o24, XDB3); NCAM (Kintner and Melton, 1987); N-cadherin (XL289n05ex, XDB3); Epidermal keratin I (XL056e18, XDB3); Shh (Yakushiji et al, 2007); Ptc2 (Yakushiji et al, 2007); Gli1 (Takabatake et al, 2000); Gli3 (Takabatake et al, 2000); HNF3 (FoxA2a) (XL016l12, XDB3); Pintallavis (FoxA4a) (XL047n03, XDB3); N-tubulin (Takabatake et al, 2002); Shroom3 (Haigo et al, 2003); and Pax3 (XL014p10, XDB3).…”

Stem Cells and the Retina – Challenges for Regenerative Medicine

“…ET/Tbx3, a T-box protein involved in the block of Rx1 transcriptional activity, is expressed in eye and cement gland primordia (Zuber et al, 2003). Moreover, both Six3 and ET are involved in Sonic hedgehog (Shh) signaling activity during the formation of the two bilateral eye fields from the initially single one (Takabatake et al, 2002;Geng et al, 2008). Lhx2, a LIM-homeodomain protein, is recruited in EFTFs transcriptional complexes, but it is involved in later events such as optic cup and lens formation (Yun et al, 2009).…”