Abstract
The Sp family of transcription factors plays important functions during development and disease. An evolutionary conserved role for some Sp family members is the control of limb development. The family is characterized by the presence of three C2H2-type zinc fingers and an adjacent 10 aa region with an unknown function called the Buttonhead (BTD) box. The presence of this BTD-box in all Sp family members identified from arthropods to vertebrates, suggests that it plays an essential role during development. However, despite its conservation, the in vivo function of the BTD-box has never been studied. In this work, we have generated specific BTD-box deletion alleles for the Drosophila Sp family members Sp1 and buttonhead (btd) using gene editing tools and analyzed its role during development. Unexpectedly, btd and Sp1 mutant alleles that lack the BTD-box are viable and have almost normal appendages. However, in a sensitized background the requirement of this domain to fully regulate some of Sp1 and Btd target genes is revealed. Furthermore, we have also identified a novel Sp1 role promoting leg vs antenna identity through the repression of spineless (ss) expression in the leg, a function that also depends on the Sp1 BTD-box.
Highlights
The evolutionary conserved family of Sp transcription factors has been implicated in multiple developmental processes and diseases from C. elegans to humans (Zhao and Meng, 2005, Beishline and Azizkhan-Clifford, 2015)
We investigated the expression of Dll as a marker of the antennal segment and ventral thoracic primordia in btdΔBTD-box, Sp1ΔBTD-box homozygous embryos and in btdΔBTD-box, Sp1ΔBTD-box/Df(btd, Sp1) mutant embryos
To monitor danr expression we have identified a dedicated cis-regulatory modules (CRMs) that reproduces its expression in the antenna and, just as the endogenous dan/danr genes, it is not activated in the leg disc (See Material and Methods and Fig. S4) (Emerald et al, 2003; Suzanne et al, 2003)
Summary
The evolutionary conserved family of Sp transcription factors has been implicated in multiple developmental processes and diseases from C. elegans to humans (Zhao and Meng, 2005, Beishline and Azizkhan-Clifford, 2015). The common structural features of all Sp members are the presence at the C-terminal region of three C2H2-type zinc fingers and the Buttonhead (BTD) box (Schaeper et al, 2010; Suske et al, 2005; Presnell et al, 2015). First identified in the Drosophila gene buttonhead (btd) (Wimmer et al, 1993), the BTD-box is a 10 aa stretch (R-X0–4-C-X-[C/D/N]-P-[N/Y]-C) adjacent to the DNA binding domain whose function is unknown. The existence of the BTD-box in all Sp family members identified from arthropods to vertebrates suggested an important role during development compared to the more variable presence of other structural domains (Presnell et al, 2015; Schaeper et al, 2010). Despite its conservation, the in vivo requirements of the BTD-box have never been studied
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