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Presenting Author(s) Dayana Krawchuk
Abstract Title Hand2 and Twist1 Interact Antagonistically in the Vertebrate Limb.
Full author List Ed Laufer 1, Beth Firulli 2, Dayana Krawchuk 1 , Victoria Centonze 3, David Virshup 4, Simon Conway 2, Peter Cserjesi 5, and Anthony Firulli 2
Text of abstract

Interactions among basic helix-loop-helix (bHLH) transcription factors in vertebrate limb development are poorly defined. Twist1 and Hand2, members of the Twist bHLH family, have dynamic, overlapping expression patterns in the limb. Loss-of-function Twist1 mutations in mice or in humans with Saethre-Chotzen syndrome (SCS), cause craniosynostosis and limb defects that include mirror image digit duplications, interdigital webbing, and shortened digits. We find that Hand2 overexpression phenocopies multiple Twist1 loss of function limb phenotypes, including digit duplications and shortened digits, consistent with Twist1 and Hand2 interacting antagonistically. To test this, we overexpressed Twist1 in combination with Hand2 in the developing chick limb and found a significant decrease in the severity of digit duplications when compared with overexpression of Hand2 alone. Conversely, while 35% of Twist1 heterozygous null mice have hindlimb digit duplications, no Twist1+/- Hand2+/- animals exhibit this phenotype. Twist1 and Hand2 thus genetically interact in a dose-dependent manner. We also find that a PKA/PKC phosphorylation and PP2A:B56delta dephosphorylation circuit can modify conserved residues in Twist1 and Hand2, and phosphomimic mutant data suggest the phosphorylation state of these residues alters dimerization partner choice. Furthermore multiple SCS mutations affect phosphorylation of these critical residues. These data thus support a novel mechanism whereby both phosphorylation and relative expression levels of Twist1 and Hand2 regulate dimerization partner choice, that when disrupted leads to developmental defects.

Which session is your work most relevant to: Limb patterning