Protein can be detected in myoblasts in the presumptive and larval wing disc.
transcript are first detectable during nuclear cycle 12 as a diffuse band half the width of the presumptive mesoderm. Although the expression patterns of sna
transcript and protein are similar early in embryogenesis, there are some subtle differences. At mid-cellularization, the sna
transcript and protein expression boundaries sharply delimit the presumptive mesoderm. At the same time, twi
transcript and protein is expressed in a gradient which overlaps and extends past the sna
expression zone into the presumptive ectoderm. The twi
transcript and protein expression pattern gets sharper later, during gastrulation. twi
protein is expressed in the mesoderm throughout germ band extension, whereas the sna
protein product disappears from the mesoderm partway through germ band extension, and appears in neurectodermal cells which might be neuroblasts.
During stage 5 of embryogenesis, the twi
protein is expressed ventrally, extending past the anterior and posterior poles. During stage 6, twi
protein is seen in the presumptive mesodermal cells of the invaginating ventral furrow, in endodermal cells in the anterior and posterior regions of the embryo, and in the ectodermal cells of the anterior midgut primordium. The mesodermal cells forming the ventral furrow, as well as the four adjoining mesectodermal cells express twi
protein at stage 7. At stage 7, twi
protein is no longer detected in the cells which will form the posterior midgut rudiment, although labeling is still seen in the anterior midgut rudiment. twi
protein becomes restricted to the mesoderm starting at stage 9. In stage 11 embryos, only a few mesodermal cells in each segment express twi
protein. At stage 12, a subset of the cells of the somatopleura and the splanchnopleura (mesodermally derived cells which will give rise to the somatic and visceral musculature, respectively) are labeled by anti-twi
antibody, and by stage 14, only the splanchnopleura labeling is visible.