In extended germ band stage embryos, pre-mRNA transcripts of Scr
can be found in both the labial segment and, less abundantly, in the anterior half of the prothoracic segment. In contrast, Scr
protein expression is limited to the labial segment.
is ectopically expressed in parasegment 3 and the anterior part of parasegment 4 in tsh Antp
double mutants. The same pattern is observed in embryos lacking tsh
, and Abd-B
is normally expressed in the labial segment and the dorsolateral part of the prothoracic segment after germband elongation. In a tsh
is ectopically expressed in the ventral ectoderm of the prothorax.
During embryogenesis, Scr
transcript is first detected at the start of gastrulation in a 3-4 cell wide band just posterior to the cephalic furrow. At the extended germ band stage, Scr
transcript is detected in both layers of the ectoderm of the labial segment, as well as in the anterior portion of the outer ectodermal layer and the mesoderm of the first thoracic segment. This pattern is still detected at the start of germ band contraction, but additional hybridization is detected throughout the outer ectodermal layer of the first th racic segment. After the start of head involution, Scr
transcript accumulates in a pattern similar to that of Scr
protein, with grains detected in a subset of the ventral nerve cord, wall of the anterior midgut, and continued epidermal labeling in labial and first thoracic segments.
In the cellular blastoderm, Scr
transcripts are located in a band 3-4 cells wide located adjacent to the band of Dfd
expression. The band of expression is present only in lateral and dorsal parts of the embryo. Lower levels of expression are observed in six additional bands spaced at double segment intervals posterior to the main band of expresssion. Using en
as a marker, the main band of Scr
expression was localized to parasegment 2. The more posterior expression is thought to correspond to the remaining even-numbered parasegments. In stages 9-10, Scr
transcripts accumulate in ectodermal cells of PS2 but not in the overlying mesoderm but do accumulate in mesoderm overlying PS3. By stage 11, the entire labial bud expresses Scr
. There is a gradient of Scr
expression across PS3 with the strongest expression in the area closest to PS2. Scr
expression is also seen in neural derivatives of PS3 and at a lower level in PS6-12. Scr
is expressed in the mesoderm of PS3 at stage 11 in both somatic and visceral components. Expression is seen at stage 12 in all myoblasts of T1 and in a portion of the mesoderm surrounding the anterior midgut. This pattern persists until hatching. Later some expression is seen in visceral mesoderm of the posterior midgut. In larvae, exrpession is observed in the labial, and dorsal and ventral prothoracic discs. In addition, some cells of the wing and second leg disc express Scr
. Their position suggests that they are adepithelial cells.
transcripts accumulate ventrally in the labial and prothoracic segments in germband extended embryos. Following germ band retraction, signal is detected in the nervous system, particularly in the suboesophageal and prothoracic ganglion, as well as in the pharynx.
transcripts accumulate on the anterior ventral side of the embryo at stage 5 in a region that corresponds to the labial and prothoracic segments on the fate map. After germ band retraction, the strongest expression is observed in the suboesophageal ganglion and the anterior part of the prothoracic ganglion. Weaker staining is observed over the entire nervous system and brain. Strong labelling is also seen in the region of the pharynx.