Glutamine synthetase induction in chick embryo retina monolayers

Effects of alkaline phosphatase inhibitors on chick neural retinal cell differentiation in vitro: ultracytochemical studies

In the matured chick retina, alkaline phosphatase (ALPase) activity is specifically localized in the outer plexiform layer and in horizontal and Müller cells. In the developing chick retina, ALPase activity is first recognized in growing neurites from horizontal cells during the 13th day of incubation, when synaptogenesis begins in the outer plexiform layer. Intraocular administration of ALPase inhibitors to developing chick embryos resulted in developmental disturbances in differentiation of the outer plexiform layer and also of photoreceptor cells. We have now extended these studies to an in vitro system. ALPase activity was studied by ultracytochemistry in cultured retinal cells from chick embryos, and the effects of specific ALPase inhibitor on retinal development were also analyzed. Two cell types showed intense ALPase activity: 1) flat glial cell, which formed a multi-layered epithelial sheet and 2) neuronal cell found within cell aggregates. Some cellular processes forming a neuropil-like structure within these aggregates also showed ALPase activity. When the ALPase inhibitor bromotetramisole was present in the culture medium, there was delay in aggregate formation and the development of neuritic processes was also affected. Moreover, this treatment also caused a considerable reduction in the number of photoreceptor cells present in the culture. The present results indicate that ALPase activity plays a significant role in retinal cell differentiation.

Hormonal induction of glutamine synthetase in cultures of embryonic retina cells: requirement for neuron-glia contact interactions

Cortisol induces glutamine synthetase (GS) in gliocytes of chick embryo neural retina. Using adherent cultures of retina cells we have demonstrated that responsiveness of the gliocytes to GS induction by the hormone requires contact with neurons. GS is not inducible in high-density cultures depleted of neurons and consisting only of gliocytes. In neuron-containing cultures, induced GS was detected immunohistochemically only in those gliocytes that were closely juxtaposed with clusters of neurons. Unlike the induction of GS, the expression of carbonic anhydrase-C (which does not require cortisol) persisted in these glia cells also in the absence of neurons. The nature and role of glia-neuron interactions in the hormonal induction of GS are briefly discussed.

Effect of dissociative methods on cortisol binding and glutamyltransferase inducibility in chick embryo retina

The ability of the isolated embryonic chick retina (12 days) to bind a steroid (cortisol) decreases when the tissue is dissociated; the extent of this decrease depends upon the method of dissociation. Trypsin and mechanical dissociation decreased cortisol binding slightly; papain dissociation essentially eliminated it. Cortisol binding decreased with time in culture in both whole retina and monolayer cultures; this decrease may reflect, in part, a similar development decrease in ovo. Inducibility of glutamine synthetase in whole retinas and retinal monolayers prepared with either trypsin or papain also decreased with time in culture. For whole and trypsin-dissociated retinas, the drop in inducibility correlates with the drop in cortisol-binding capacity. This was not the case for monolayer cultures prepared by papain dissociation.