Fig. 3. The role of TSH in disco mRNA distribution. (A) disco
mRNA accumulation in a wild-type embryo as the germband begins to retract.
Segment abbreviations are as in Fig.
1. Note the spots of expression in the thorax and abdomen,
indicated by white arrows. In the thorax, these demark the Keilin's Organ
precursors. (B) In homozygous tsh8 embryos, gnathal
expression of disco is normal, but the trunk distribution is altered.
There is a wider distribution in the ventral and ventral-lateral region of
trunk segments, particularly notable in the thoracic segments. Note that the
spots marking the Keilin's Organs are missing. (C) Ectopic activation of
disco caused by Gal4-driven DFD. Interestingly, the distribution of
disco mRNA is quite similar to that in B, above, except that the
spots marking the Keilin's Organ precursors are still present in C. (D-F)
Ectopic expression of tsh represses the normal accumulation of
disco mRNA in the gnathal segments. (D) Wild-type late stage 12
embryo. disco mRNA distribution is fairly uniform in the gnathal
segments except where the maxillary and labial sense organs will form and in
the salivary primordia (ventral labial). (E) In arm
tsh
embryos (stage 12), as the germband retracts, disco mRNA diminishes
in the epidermis of the gnathal lobes. However, staining increases in the
central region of the mandibular, maxillary and labial lobes. Later (stage 13)
(F), the labial lobe has taken on the appearance of a first thoracic segment,
and disco is strongly expressed in the sensory precursor, which has
been transformed toward a Keilin's Organ. No difference was noted in the trunk
disco expression.