Expression profiles of the Gα subunits during Xenopus tropicalis embryonic development.

Heterotrimeric G protein signaling plays major roles during different cellular events. However, there is a limited understanding of the molecular mechanisms underlying G protein control during embryogenesis. G proteins are highly conserved and can be grouped into four subfamilies according to sequence homology and function. To further studies on G protein function during embryogenesis, the present analysis identified four Gα subunits representative of the different subfamilies and determined their spatiotemporal expression patterns during Xenopus tropicalis embryogenesis. Each of the Gα subunit transcripts was maternally and zygotically expressed, and, as development progressed, dynamic expression patterns were observed. In the early developmental stages, the Gα subunits were expressed in the animal hemisphere and dorsal marginal zone. While expression was observed at the somite boundaries, in vascular structures, in the eye, and in the otic vesicle during the later stages, expression was mainly found in neural tissues, such as the neural tube and, especially, in the cephalic vesicles, neural crest region, and neural crest-derived structures. Together, these results support the pleiotropism and complexity of G protein subfamily functions in different cellular events. The present study constitutes the most comprehensive description to date of the spatiotemporal expression patterns of Gα subunits during vertebrate development.

The transcription factor chicken Scratch2 is expressed in a subset of early postmitotic neural progenitors.

Scratch proteins are members of the Snail superfamily which have been shown to regulate invertebrate neural development. However, in vertebrates, little is known about the function of Scratch or its relationship to other neural transcription factors. We report the cloning of chicken Scratch2 (cScrt2) and describe its expression pattern in the chick embryo from HH15 through HH29. cScrt2 was detected in cranial ganglia, the nasal placode and neural tube. At all stages examined, cScrt2 expression is only detected within a subregion of the intermediate zone of the neural tube. cScrt2 is also expressed in the developing dorsal root ganglia from HH22-23 onwards and becomes limited to its dorsal medial domain at HH29. phospho-Histone H3 and BrdU-labeling revealed that the cScrt2 expression domain is located immediately external to the proliferative region. In contrast, cScrt2 domain overlapped almost completely with that of the postmitotic neural transcription factor NeuroM/Ath3/NEUROD4. Together, these data define cScrt2-positive cells as a subset of immediately postmitotic neural progenitors. Previous data has shown that Scrt2 is a repressor of E-box-driven transcription whereas NeuroM is an E-box-transactivator. In light of these data, the co-localization detected here suggests that Scrt2 and NeuroM may have opposing roles during definition of neural subtypes.