87
Development of A2B5+1 Cells In Vitro
Although up to this point the phenomenon of appearance
of A2B5(+) cells in purified cultures of day 12 and 13
cells appeared similar to recruitment in purified day 7 and
8 cells, the appearance of A2B5(+) cells in long-term
monolayers differed markedly. A2B5(+) cells that appeared
in purified cultures for the most part did not have a
neuronal morphology. They exhibited a flattened glial
morphology (Fig.3-4) after about a week in culture and
rested atop the A2B5(-) flat cells and were then round
after several more days or when the cultures had become
confluent. The appearance of these A2B5(+) cells with
nonneuronal morhpology in purified cultures was not
prevented by adding back the cells that were removed by the
microspheres (data not shown). A2B5(+) cells with
nonneuronal morphology also appeared in cultures made from
dissociated cells that were kept in methylcellulose for a
day (Fig.3-4). This was in contrast to the appearance of
A2B5(+) cells in unpurified monolayer cultures. These cells
exhibited a purely neuronal morphology in vitro and not the
nonneuronal morphologies observed in the purified cultures.
Nonneuronal A2B5(+) cells were also absent from cultures
made from cells recovered from the microspheres and this
fraction appeared to contain the largest and most numerous
aggregates of neurons (data not shown). Some A2B5(+) cells
with neuronal morphology were observed in purified