Expression of Shisa2, a modulator of both Wnt and Fgf signaling, in the chick embryo.

Shisa proteins are a recently-identified family of modulators of both FGF and Wnt signaling that block both maturation and transport to the cell surface of their respective receptors. The latter are retained within the endoplasmic reticulum, thereby inhibiting or reducing cellular responses to the ligands. We describe expression of a Shisa2 orthologue in an amniote: the chick embryo. We show that Shisa2 transcripts are expressed in a dynamic manner along the anteroposterior axis, in a manner consistent with a role in head development as demonstrated for Xenopus Shisa, being ubiquitously expressed in anterior tissues. However, expression is progressively restricted anteriorly within the developing neural tube and adjacent mesenchyme and ectoderm, eventually becoming restricted to the telencephalic lobes. Similarly, from being ubiquitous within the optic cups, transcripts become restricted to the prospective ciliary margin. A similar process is evident in the somites, where expression is initially ubiquitous but remains at high levels first in dermamyotome and subsequently is only detected in myotome. During the initial stages of organogenesis, Shisa2 transcripts are detected in cardiac and lung bud mesenchyme and in nephric ducts and tubules. Within the pharyngeal region, expression is observed in pharyngeal pouches from their first appearance and later in mesenchyme of all pharyngeal arches, as well as in cranial ganglia. Transcripts are also detected in the dorsal mesenchyme of the limb bud.