GLUTAMINE-SYNTHETASE (GS) ACTIVITY AND SPATIAL AND TEMPORAL PATTERNS OF GS EXPRESSION IN THE DEVELOPING CHICK RETINA - RELATIONSHIP WITH SYNAPTOGENESIS IN THE OUTER PLEXIFORM LAYER
Fa. Prada et al., GLUTAMINE-SYNTHETASE (GS) ACTIVITY AND SPATIAL AND TEMPORAL PATTERNS OF GS EXPRESSION IN THE DEVELOPING CHICK RETINA - RELATIONSHIP WITH SYNAPTOGENESIS IN THE OUTER PLEXIFORM LAYER, Glia, 22(3), 1998, pp. 221-236
The profile of glutamine synthetase (GS) activity in the neural retina
of chicken embryos and adults was studied alongside the in vivo spati
o-temporal patterns of generation and morphogenesis of Muller cell and
of retinal synaptogenesis. The rise of GS activity during development
is not related to Muller cell differentiation but to synaptogenesis i
n the outer plexiform layer (opl). GS expression was investigated by i
mmunoreaction with GS-specific antiserum. Three spatial gradients of d
ecreasing labeling were observed between embryonic (E)15 and E18, from
central to peripheral retina, dorsal to ventral, and temporal to nasa
l, which are in spatio-temporal relationship with synaptogenesis in th
e opl. GS is localized in Muller cells and apparently also in a popula
tion of astrocyte-like glial cells, located in the ganglion cell layer
throughout the retina. Precocious induction by hydrocortisone, in ovo
, at E10, does not show the spatial pattern of GS immunoreactivity obs
erved in control retinas at the time of natural induction (E15). We al
so show that dissociated (noncultured) Muller cells of E18-20 retinas,
to which only photoreceptors or photoreceptors and neurons remain joi
ned, maintain an immunodetectable level of GS, while those in isolated
state lose GS immunoreactivity rapidly. Our results suggest that the
induction of GS expression might be mediated by Muller cell-neuron int
eractions at the opl and also perhaps at the outer nuclear layer (onl)
. An analysis of our results and those of previous authors suggests th
at the level of GS in differentiated Muller cells could be determined
by conjoint cell interactions at the onl, opl, and inner plexiform lay
er. (C) 1998 Wiley-Liss, Inc.