|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 4. Development of internal tendons and late steps of appendicular myogenesis.
Tendons are visualised in the leg discs of (A) 1151-Gal4/UAS-GFP and (B)
Stripe-Gal4/UAS-GFP pupae at 8 hours APF. Tendon precursors are annotated as
in Fig. 2. Two tendon
precursors, a and b, are located within the femur, two, g and c, are located
in the tibia, and two others, e and f, in the proximal part of the leg. At
this stage we are unable to define precisely the identity of proximal tendon
precursors annotated e and f. (A) In addition to tendon precursors,
1151-Gal4/UAS-GFP also marks myoblasts, showing that they are deployed in all
leg segments. A few individual 1151-GFP-positive cells, corresponding most
probably to myoblasts, are detected at 8 hours APF in the tarsus. These cells
do not express twi (see Fig. 7) and are no longer detected in later
stages of development (see D). (C-E) General views and (F-H) enlarged views of
dissected femur, tibia and tarsus from 1151-Gal4/UAS-GFP pupae at three
different times during metamorphosis. In enlarged views asterisks mark the
tendons. (C) General organisation of tendons and myoblasts at 20 hours APF.
(F) Enlarged view of the region indicated in C, showing a proximal part of the
femur a and b tendons. Myoblasts (arrows) lie tightly around the tendons. Note
that only very rare myoblasts (arrowheads in F) appear not to be associated
with tendons. (D) At 25 hours APF, the number of non-associated myoblasts
increases (arrowheads). (G) Enlarged area corresponding to that shown in D.
The arrangement of myoblasts associated with tendons has changed so that they
form syncytial muscle fibre precursors composed of 5 to 10 nuclei (arrows).
(E) At 35 hours APF, the precursors of the muscle fibres elongate. Myoblasts
not associated with tendons are no longer detected. (H) Enlarged view of the
region indicated in E, showing an increased number of myoblast nuclei in the
muscle fibres (arrows). (I,J) Proximal part of the ventral tibia dissected
from the Stripe-Gal4/UAS-GFP pupae, showing differentiation of the epithelial
muscle attachment sites, the apodemes (arrows). Asterisks indicate the ventral
internal tibia tendon, previously annotated c. Muscle fibres are visualised by
their autofluorescence. (I) At 40 hours APF, Stripe-GFP expression appears in
the nuclei of some epithelial cells (arrows). At this time, muscle fibres seem
not to be attached to the epithelium. (J) At 55 hours APF, the Stripe-GFP
cells are easy to detect. They have delaminated from the leg epithelium to
form muscle attachment sites called apodemes (arrows). Muscle fibres attach to
the apodemes. Note that a morphologically distinct area forms at the junction
between the muscle fibres and the internal tendon (arrowhead). (G,H) Ventral
tibia regions from MHC-tauGFP pupae, showing Myosin Heavy Chain (MHC-tauGFP)
expression in differentiating myotubes. (G) At 40 hours APF, low levels
MHC-tauGFP expression can be detected in appendicular tibia fibres. (H) About
10 hours later, MHC-tauGFP levels increase.
|
