45
dissociated 7 or 8 day tectum. Similarly, no GC(+)
oligodendrocytes appeared in cultures of either unpurified
or purified cells (not shown). GC(+) cells appear by day 12
of development (see Chapter 3).
GS Expression In Vitro
The expression of glutamine synthetase was examined in
both aggregate and monolayer cultures to determine whether
or not purified and unpurified cultures were similar in
this respect. A quantitative assay revealed that both
purified and unpurified cells produced the same levels of
GS when allowed to reaggregate on poly(HEMA) (Fig.2-10).
Similarly, immunostaining for GS revealed the same staining
patterns in both purified and unpurified monolayer
cultures; GS was produced in glia under or near aggregates
of neurons (Fig.2-10). Thus, the production of GS in glia
in purified cultures parallels that of unpurified cultures
both quantitatively and with respect to position to
neurons.
DNA Synthesis In Vitro
The synthesis of new DNA was examined by combining
A2B5 immunostaining with 3H-thymidine autoradiography of
both newly plated cells and of monolayer cultures. Newly
plated cells were subjected to continuous labelling with
3H-thymidine for 24 hours, followed by immunostaining with
A2B5 and autoradiography. With both purified and unpurified
cells only a small number of nuclei were labelled (<5%;