Comparative expression of mouse and chicken shisa homologues during early development

During vertebrate embryogenesis, fibroblast growth factor (FGF) and Wnt signaling have been implicated in diverse cellular processes, including cell growth, differentiation, and tissue patterning. The recently identified Xenopus Shisa protein promotes head formation by inhibiting Wnt and FGF signaling through its interaction with the immature forms of Frizzled and FGF receptors in the endoplasmic reticulum, which prevents their posttranslational maturation. Here, we describe the mouse and chicken homologues of Xenopus Shisa. The mouse and chicken Shisa proteins share, respectively, 33.6% and 33.8% identity with the Xenopus homolog. In situ hybridization analysis shows that mouse shisa is expressed throughout embryonic development, predominantly in the anterior visceral endoderm, headfolds, somites, forebrain, optic vesicle, and limb buds. Cross-species comparison shows that the expression pattern of cshisa closely mirrors that of mshisa. Our observations indicate that the Shisa family genes are typically expressed in tissues known to require the modulation of Wnt and FGF signaling. Developmental Dynamics 235:2567-2573, 2006. (c) 2006 Wiley-Liss, Inc

Cell interactions, signals and transcriptional hierarchy governing placode progenitor induction

In vertebrates, cranial placodes contribute to all sense organs and sensory ganglia and arsise from a common pool of Six1/Eya2+ progenitors. Here we dissect the events that specify ectodermal cells as placode progenitors using newly identified genes upstream of the Six/Eya complex. We show that two different tissues, the lateral head mesoderm and the prechordal mesendoderm, gradually induce placode progenitors: cells pass through successive transcriptional states, each identified by distinct factors and controlled by different signals. Both tissues initiate a common transcriptional state, but over time impart regional character and the acquisition of anterior identity depends on Shh signalling. Using a network inference approach we predict the regulatory relationships among newly identified transcription factors and verify predicted links using knock-down experiments. Based on this analysis we propose a new model for placode progenitor induction, in which the initial induction of a generic transcriptional state precedes regional divergence