CHAPTER III
SEPARATION OF DAY 12-13 CELLS
Introduction
The previous chapter described an immunomagnetic
separation method to separate cells from early (day 7-8)
embryonic chick optic tectum. This method resulted in
extremely pure populations of cells that were negative for
the cell surface marker A2B5 (Eisenbarth et al., 1979). It
was found, however, that the A2B5 antigen was modulated on
the surfaces of about half of the purified cells in direct
response to the depletion of A2B5(+) cells. Neurons were
also apparently recruited in these cultures. Thus, day 7
and 8 optic tectum cells showed a remarkable ability to
maintain the correct number of A2B5(+) cells and neurons.
It was not clear, though, from what population of cells the
recruitment was occuring. This was largely due to the fact
that no glial differentiation markers which occur later in
development were present at days 7 and 8 to identify
definitive glia.
During development of the chick optic tectum, commonly
recognized glial differentiation markers do not appear
until relatively late in development (Linser and Perkins,
1987a). Glutamine synthetase (GS) is detectable by
immunohistochemistry in some astrocytes at day 9 and is
69