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Fig. 7. Effects of dominant-negative Rac1 expression in adult myoblasts. (A) Fibres
of wild-type lateral muscles expressing myosin (brown) at 31 hours APF
(29°C). Each fibre has a brightly stained duf-lacZ nucleus (black
arrow). In some fibres, this nucleus is not present within the field of view.
Other nuclei in the fibres express duf-lacZ at lower levels and are
seen in a few fibres (black arrowheads). (B)
1151Gal4/UAS-Rac1N17-misexpression pupa of the same stage
showing the absence of syncitial fibres. The putative founder cells (one of
them indicated by the black arrow) are correctly specified and express
duf-lacZ and myosin. Unfused myoblasts also express myosin and, in
some cases, can be seen clustered around duflacZ-expressing founders
(arrowhead). (C-E) Two lateral founders, of the same stage as shown in in B,
at a higher magnification. The founder cells extending processes in an
orientation similar to that of the wild-type lateral fibres. The nucleus of
each cell expressing duflacZ is indicated by a black arrow. (C)
Extended processes of one of the founder cells are in focus (indicated by
white arrows). (D) Same preparation as in C, shown at a different plane of
focus. Black asterisks mark some of the unfused myoblasts surrounding the
founder cell. (E) Processes of the second founder cell are in focus in this
image (white arrows). Unfused myoblasts are again seen clustered around this
founder. (F-I) X-Gal and anti-MHC-stained lateral muscle fibres at 42 hours
APF (in 29°C) in wild-type (F,G,H) and
1151Gal4/UAS-Rac1N17-misexpression (I) pupae. (F) Lateral
muscles showing one duf-lacZ-expressing nucleus in each fibre. This
nucleus corresponds to the high duf-lacZ-expressing founder nucleus
observed in the fluorescent images in Fig.
3G and H. X-Gal staining cannot detect the low
ß-galactosidase activity in the remaining nuclei of the syncitium. These
nuclei can be detected at a higher magnification as shown in G and H. (G,H)
Magnified views of the region outlined by the box in F, at different planes of
focus showing the presence of multiple nuclei in each fibre. Each white
asterisk is placed below a nucleus in the plane of focus. (I) In the absence
of normal fusion, thin mononucleate lateral fibres span the region. (J,K)
Fluorescent preparations at 36 hours APF (at 29°C). (J) Wild-type DVM II
expressing myosin (red) and duf-lacZ (green). White arrows indicate
the nucleus in each syncitium that expresses high levels of duf-lacZ.
(K) Developing fibres of DVM II in a pupa with Rac1N17 misexpression in adult
myoblasts. The DV muscle fibres are reduced in size but the pattern of one
high duf-lacZ-expressing nucleus per fibre remains unaffected. (L)
Wild-type pattern of DLMs, and DVMs I, II and III, in one hemisegment of an
adult CS fly (grown at 29°C). Black asterisks indicate the DVM II fibres.
(M) Muscles in one thoracic hemisegment of a fly after Rac1N17 misexpression
in adult myoblasts. In focus are the two fibres of DVM II (black arrows).
Fibre size is severely reduced but fibre number remains unchanged. In A-I,
anterior is to the right, dorsal midline to the bottom; in J-K, anterior is to
the top, dorsal to the right; in L-M, anterior is to the left, dorsal to the
top. Scale bars: in A, 4 µm for A,B,F,I; in C, 4 µm for C,D,E; in G, 4
µm for G,H; in J, 20 µm for J,K; in L, 40 µm for L,M.
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