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Fig. 2. sal is required in R3 for the establishment of correct chirality.
(A) Tangential sections of adult eyes containing sal null mutant
clones [in all experiments we used a small chromosomal deficiency –
Df(2L)32FP5 – covering only salm and salr
(Barrio et al., 1999)].
sal mutant (sal–) cells are shown by the
absence of the pigment (w) marker (dark dots at the base of each
rhabdomere and in pigment cells). In schematic drawings, black arrows
represent dorsal and red arrows ventral orientation. Green arrows represent
ommatidia where it is possible to identify R1/R6 and R7, but not R3 or R4.
Black circles represent ommatidia where it is impossible to score orientation,
because R7 or R8 are transformed into outer PRs, or they contain extra
photoreceptors. Top panel: note that in the ommatidium with (wrong) ventral
chirality, only the presumptive R3 precursor is sal–
and has acquired an R4 fate. (B) Statistical analysis of mosaic ommatidia that
always present correct chirality. sal– cells are
represented as white circles and non-mutant cells as black circles. The number
of ommatidia is indicated below each configuration. The inset at the top right
corner represents the common feature of these configurations, which is that R3
always has the sal+ genotype. The numbers inside the
circles represent the identity of each PR. (C) Statistical analysis of mosaic
ommatidia exhibiting chirality inversions. The common feature of these
configurations is that the cell in the R4 position always has the
sal– genotype. This R4 mutant cell corresponds to a
R3 precursor that made the wrong chiral choice.
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