Glial Precursor (GP)
LINEAGE: Unlike other neuroblasts, the glial precursor (sometimes
known as the glioblast) does not divide to make GMC's or neurons. The GP divides
roughly symmetrically during stage 11 to produce two cells which eventually divide
to generate six longitudinal glia. These cells migrate from their birthplace
laterally to prefigure the position of the longitudinal axon connectives. At
stage 16, the longitudinal glia are positioned on the dorsal side of the nerve cord, dorsal
to the longitudinal axon tracts. These cells have been proposed to function as
a substrate for longitudinal axon guidance. (
Jacobs and Goodman, 1989,
Jacobs et al., 1989).
GENE EXPRESSION: At formation at stage 10, the GP expresses
fushi-tarazu (
Doe et al., 1988), mirror-lacZ (Broadus et al., 1995), and repo/RK2
(Xiong et al., 1994;
Campbell et al.,
1994;
Halter et al., 1995). The expression of mirror-lacZ and repo/RK2
is maintained in the longitudinal glia at stage 16. ftz is not maintained,
though a few ftz-lacZ lines do maintain expression in these cells. prospero found
in the nuclei of the longitudinal glia. (Those are the green cells in the splash
picture of the lab home page). orthodentical (otd) protein was thought to be expressed
in the longitudinal glia, however this expression was found to be a
cross-reactivity of that particular antibody to the repo/RK2 protein (E.P. Spana, unpublished).. There are a variety of enhancer trap lines that express in the
longitudinal glia including: r56, KZ663, 566-Gal4, etc.
GENE FUNCTION: repo/RK2 mutants generate less longitudinal
glia cells. They have less pros positive cells per segment (usually 1 or 2 instead of 6), and have
faciculation defects in the longitudinal tracts (
Campbell et al., 1994). The longitudinal glia do not
differentiate and enwrap the axons in pros mutants
(Jacobs et al., 1993).
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