|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 6. Morphologically and molecularly distinct cell monolayer coats, first, trunk
then tail somites. Embryos at stage 22(A), stage 28 (B,C) and stage 35 (D-F)
were plastic embedded, transversally sectioned and stained with violet
fuchsin. NT, neural tube; Not, notochord; Epi, epidermal bilayer. Yolk
droplets appear yellow. A distinct superficial layer of cells covers trunk
somites prior to superficial slow fibre differentiation (A,B,D, arrows) and
anterior tail somites after slow fibre formation is initiated (E, arrows,
compare with Fig. 1D). Insets
show superficial layer (arrows) in middle of somite (D) and at dorsomedial lip
(E) at stage 35. Note the transient lack of this layer in the nascent
posterior somites present at stage 28 (C) and stage 35 (F), when single cells
can be observed elongated across the somite (arrowheads). (G,H) Electron
micrographs show a distinct dermomyotome (arrows) in somite 8 (G) but only
spindly cells in somite 18 (H) above a layer of well-differentiated muscle
with basal myofibrils (arrowheads). Pax3 mRNA was detected by
whole-mount in situ hybridisation of stage 29-38 embryos (I-K, upper panels)
and En1 mRNA marked a subset of medial cells in the superficial
somite level with the notochord (L, arrowheads). Serial transverse 100 µm
vibratome sections revealed that signal is superficial within the somite (I-K,
lower panels, arrowheads) and non-overlapping with 12/101, a marker of
differentiated muscle. Dorsal and ventral groups of cells in the tailbud
express highly (K, inset, arrows). Expression persists in a complex pattern in
all somites, but is consistently stronger in trunk somites anterior to about
somite 12 at stage 29 (G) and stage 33/34 (H). Subsequently, Pax3
increases in tail somites (I).
|
