Gs. Boyan et Jld. Williams, EMBRYONIC-DEVELOPMENT OF THE PARS INTERCEREBRALIS CENTRAL COMPLEX OF THE GRASSHOPPER, Development, genes and evolution, 207(5), 1997, pp. 317-329
We have studied the embryonic development of the pars intercerebralis/
central complex in the brain of the grasshopper using immunocytochemic
al arid histochemical techniques. Expression of the cell-surface antig
en lachesin reveals that the neuroblasts of the pars intercerebralis f
irst differentiate from the neuroectoderm at around 26% of embryogenes
is. Differentiation of medial and lateral neuroblasts occurs first. By
the 28% stage a more or less uniform sheet of 20 neuroblasts has form
ed. As a result of both cell proliferation and cell translocation, the
pars intercerebralis proliferative cluster in each hemisphere expands
so that at 30% the most medial neuroblasts lie apposed at the midline
. We followed the further development of the pars intercerebralis of e
ach brain hemisphere using bromo-deoxy-uridine incorporation and osmiu
m-ethyl-gallate staining. Within the pars intercerebralis itself, the
neuroblasts redistribute into discrete subsets. The neuroblasts of eac
h subset generate clusters of progeny which extend in a stereotypic, s
ubset-specific direction in the brain. We have used this feature, to i
dentify one subset of four neuroblasts as being the likely progenitor
cells for four clusters of embryonic neurons (W, X, Y, Z) which develo
p at around 55% of embryo-genesis. We show that these progeny project
axons via four discrete fascicles (w, x, y, z) into the embryonic cent
ral complex. At the single cell level, Golgi impregnation reveals that
the axons from these neighbouring cell clusters remain discrete, and
those from the same cluster tightly fasciculated, as they project into
the central complex, consistent with a modular organization for this
brain region.