Sall genes regulate region-specific morphogenesis in the mouse limb by modulating Hox activities

Abstract

The genetic mechanisms that regulate the complex morphogenesis of generating cartilage elements in correct positions with precise shapes during organogenesis, fundamental issues in developmental biology, are still not well understood. By focusing on the developing mouse limb, we confirm the importance of transcription factors encoded by the Sall gene family in proper limb morphogenesis, and further show that they have overlapping activities in regulating regional morphogenesis in the autopod. Sall1/Sall3 double null mutants exhibit a loss of digit1 as well as a loss or fusion of digit2 and digit3, metacarpals and carpals in the autopod. We show that Sall activity affects different pathways, including the Shh signaling pathway, as well as the Hox network. Shh signaling in the mesenchyme is partially impaired in the Sall mutant limbs. Additionally, our data suggest an antagonism between Sall1-Sall3 and Hoxa13-Hoxd13. We demonstrate that expression of Epha3 and Epha4 is downregulated in the Sall1/Sall3 double null mutants, and, conversely, is upregulated in Hoxa13 and Hoxd13 mutants. Moreover, the expression of Sall1 and Sall3 is upregulated in Hoxa13 and Hoxd13 mutants. Furthermore, by using DNA-binding assays, we show that Sall and Hox compete for a target sequence in the Epha4 upstream region. In conjunction with the Shh pathway, the antagonistic interaction between Hoxa13-Hoxd13 and Sall1-Sall3 in the developing limb may contribute to the fine-tuning of local Hox activity that leads to proper morphogenesis of each cartilage element of the vertebrate autopod.

Dedifferentiation and the role of sall4 in reprogramming and patterning during amphibian limb regeneration

“…SALL4 can heterodimerize with other family members such as SALL1 (Sakaki-Yumoto et al, 2006) and Sall1, Sall2, and Sall3 have essential redundant functions during murine neurulation (Bohm et al, 2008). Sall1 and Sall3 are involved in Shh linked A/P patterning of developing mouse limbs (Kawakami et al, 2009) and human Sall1 mutations produce TownesBrocks Syndrome, most likely caused by the dominant-negative effect of truncated SALL1, which includes among its defects thumb abnormalities (Kohlhase et al, 1998;de Celis and Barrio, 2009). Functional gene knockout studies of mouse autopod development showed that Sall1 and Sall3 are partially redundant.…”

Sall4-Gli3 system in early limb progenitors is essential for the development of limb skeletal elements

“…They play diverse roles in embryonic development, including the development of limbs (12,13). Among four Sall genes in mammals, Sall4 is a key regulator of stemness in stem cells and progenitor cells, such as embryonic stem cells, induced pluripotent stem cells, spermatogenial progenitor cells and cancer cells (14)(15)(16)(17)(18)(19).…”

Spatiotemporal changes in cell adhesiveness during vertebrate limb morphogenesis

“…Hoxa13-misexpressed cells are sorted out from Hoxa13-negative cells (Yokouchi et al, 1995). In addition, Hox13 paralogue genes coordinately regulate the expression of the cell surface receptor, EphA, during limb development (Stadler et al, 2001;Cobb and Duboule, 2005;Salsi and Zappavigna, 2006;Kawakami et al, 2009). Interactions of Eph receptors with their ephrin ligands lead to cellular recognition and subsequent cell repulsion.…”

“…In addition to EphA4, other EphA receptors, such as EphA3 and EphA7, are also expressed in the distal region of mouse limb bud (Stadler et al, 2001;Cobb and Duboule, 2005;Kawakami et al, 2009). EphA7 is expressed in the distal region of the limb bud, and restricted to presumptive digits.…”