5
expression of specific glial gene products (Fisher, 1984;
Linser and Moscona, 1979). Glutamine synthetase (GS), for
example, is produced in glia in culture when the glia are
in contact with neurons (Linser and Moscona, 1983; Linser
and Perkins, 1987a; Wu et al., 1988). Obviously, to study a
phenomenon such as this it would be of great advantage to
be able to purify the immature glia so that neurons could
be added back to elicit GS production. Such an ability
could also in itself reveal other phenomena that involve
cell interactions.
A major obstacle to studying interactions that take
place during early development, such as those that lead to
GS production, is that they occur when only few if any
cells are identifiable by commonly recognized
differentiation markers. Also early in development, most
cells do not differ enough from each other physically to
make use of such cell purification techniques as buoyant
density centrifugation (Campbell et al., 1977; Sheffield et
al., 1980). Methods that do not need overt physical
differences for separation are those that utilize
monoclonal antibodies that discriminate between the
surfaces of different types of cells (immunoselection).
Complement-mediated cell lysis has been used successfully
with embryonic neural tissues (Politi and Adler, 1987;
Nagata et al., 1986), but this method does not allow
recovery of both cell types, and not all antibodies fix