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Fig. 5. Requirement for Lz and Notch, but not EGFR, in primary pigment-cell
specification. (A-F) Pupal discs stained for Bar (red). (A)
Wild-type mid-pupal eye disc showed Bar expression in two primary pigment
cells per cluster. (B) hsp70-Gal4-UAS-EGFRDN pupal eye
disc subjected to heat shock at 29°C at the mid-pupal stage showed no
defects in Bar expression or primary pigment-cell specification. (C)
hsp70-Gal4, UAS-NDN pupal eye discs subjected to heat
shock at 29°C at the mid-pupal stage showed a loss of Bar expression. (D)
Primary pigment-cell specification in lzts114 at a
permissive (25°C) temperature showed a wild-type pattern of primary
pigment-cell specification. (E,F) Dosage-sensitive interaction between
Notch and lz during primary pigment-cell fate specification.
(E) lzts114/Y, Delta/+ (Dl/+)
combination incubated at 25°C showed dosage-sensitive interactions causing
a loss of Bar-expressing primary pigment cells. (F)
lzts114, EGFRnull/+ pupal eye disc
from flies incubated at 25°C showed no disruption in the specification of
primary pigment-cell fate. (G) Signal integration during primary
pigment-cell specification. In the larval cone cells, a low level of EGFR
activation is required for the establishment of their fate but is insufficient
to promote transcriptional activation of Delta. Once cone-cell fate is
established, EGFR activation continued to rise and, in the pupal stages,
caused the transcription of Delta. Activation of the Notch pathway in the
adjacent undifferentiated cells in combination with Lz promoted the
specification of primary pigment-cell fate. This process did not require input
from the EGFR pathway. (H) Summary of cellautonomous combinations of
Notch and EGFR inputs in the specification of neuronal (R1, R6 and R7) and
non-neuronal cell types from undifferentiated cells behind the furrow. The
fate specification of these cells also requires a transcriptional input from
Lz.
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