hh RNA can be detected in ganglion mother cells at 72 hours after larval hatching (ALH), but not at 48 hours ALH.
hh is expressed strongly in the anterior escort cells, and weakly in the posterior escort cells
At early stage 11,
hh expression extends from the posterior optic lobe into the anterior optic lobe. It becomes restricted to the posterior optic lobe at mid stage 11 and later localizes to Bolwig organ precursor cells in the ventral posterior optic lobe.
hh is expressed in cells immediately anterior to the tracheal pits.
hh transcripts are expressed in embryos, larvae, pupae and adults with peaks of expression in 6-12hr embryos and early pupae. Transcripts are first detected in embryonic stage 5 in a few stripes at the anterior and posterior ends of the embryo. The number of stripes gradually increases to 17. The terminal stripes are 2-3 cells wide and the internal stripes are 1 cell wide. Expression is stronger in every second stripe and is stronger laterally than in dorsal and ventral regions. The expression in stripes reaches a maximum at stages 8-11. By the end of germband retraction, the stripes are situated in the posterior compartments of the lateral ectoderm.
Peaks of
hh expression are observedin 2-10hr embryos and in pupae. In embryos,
hh transcripts are firstexpressed in a discrete pattern in the maxillary segment followed by apattern of 14 parasegmental stripes. At germ band extension, a 15th stripeis seen.
hh expression in the metameric portion of the embryo closelyresembles
en expression. Expression is also described in a variety ofsites in the nonmetameric portion of the embryo including the intercalaryand antennal segments, the procephalon, the gnathal segments, and portionsof the hindgut. Expression in imaginal discs is described for theassociated
Ecol\lacZ insertion.
hh expression is pair-rule dependent. In
ftz mutants, expression in the even-numbered parasegments is missing.
wg mutations caused diminished expression and
ptc mutants causeexpression in an ectopic stripe in each segment.
nkd mutations causebroadening of the stripes.
hh transcripts are first detected at the cellular blastoderm stage in 17 segmental stripes. 14 of the stripes are one cell wide and extend from 10-70% egg length. There are two 3-cell-wide stripes at 5% and 75% egg length and a dorsal anterior spot at 97% egg length. The stripes appear asynchronously. Even parasegmentally-numbered stripes precede odd-numbered stripes and anterior stripes precede more posterior stripes. The stripes are activated around the entire circumference of the embryo but disappear from the amnioserosa and mesoderm after gastrulation. At stage 11, the stripes are located just posterior to the parasegmental furrow and are spaced one cell anterior to the tracheal pit in each segment. Stripes persist after germ band retraction and are located in the posteriormost portion of the lateral ectoderm of each segment.
hh transcripts are also expressed in the fore- and hindguts following gastrulation and germ band extension as well as in the cephalic region of the embryo. Up to stage 10, the intensity of staining is heavier in the nucleus than in the cytoplasm. After stage 10, RNA staining is predominantly cytoplasmic.
At the cellular blastoderm stage,
hh transcripts are located predominantly in a single stripe at 75% egg length with additional transcripts at the anterior tip and along the ventral side. At gastrulation,
hh is expressed in 14 single-cell-wide stripes between 30% and 65% egg length. The stripes are coincident with
en expression and occur in the cells of the posterior compartments. They appear in a characteristic order, even-numbered ones before odd-numbered ones and anterior ones before posterior ones.
hh is also expressed in a block of cells at the anterior end and in wide stripes at 10% and 75% egg length.
hh transcripts are expressed later in the foregut, pharynx, esophagus, hindgut, and salivary glands.
hh transcripts are exressed in imaginal discs where they are localized to the posterior compartments. The differences between
hh and
en expression are noted.
