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Fig. 1. Schematic representation of the development of the indirect flight muscles
(IFMs) and the abdominal muscles. The IFMs are anatomically and functionally
subdivided into two distinct groups: the dorsal longitudinal muscles (DLMs)
and the dorsoventral muscles (DVMs). (A) The precursor myoblasts (yellow) for
the IFMs are attached to the wing disc during the larval life. At the onset of
metamorphosis larval muscles begin to histolyse, with the exception of three
oblique muscles. (B) By 12 hours APF, histolysis is complete and the three
larval templates are clearly visible. By this stage, myoblasts migrate into
the muscle-forming regions. (C) The larval templates start splitting by 13
hours APF and the process is complete by 16-17 hours APF. At the same time,
the DVMs form by the de novo fusion of myoblasts. (D) By 24 hours APF, the
DLMs and the DVMs are complete. Muscle formation in the abdomen occurs later
than in the thorax. The abdominal muscles develop from an adult myoblast pool
(yellow) associated with the segmental and intersegmental nerves (A). (A-D)
During early pupal stages (from 0-24 hours APF), myoblasts proliferate and
migrate out along the nerves. (E) Fusion of these myoblasts begins by 28-30
hours APF. (F) The arrangement of the DLMs, the DVMs (I, II and III) and the
dorsal muscles of the first abdominal segment in an adult fly: by 50 hours
APF, the pattern of the adult muscles is largely complete.
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