cells (NSCs) and progenitor cells, but it cannot discriminate
between these two populations. Given two assays
have purported to overcome this shortfall, we performed
a comparative analysis of the distribution and frequency
of NSCs and progenitor cells detected in 400 m coronal
segments along the ventricular neuraxis of the adult
mouse brain using the neurosphere assay, the neural
colony forming cell assay (N-CFCA), and label-retaining
cell (LRC) approach. We observed a large variation in the
number of progenitor/stem cells detected in serial sections
along the neuraxis, with the number of neurosphereforming
cells detected in individual 400 m sections varying
from a minimum of eight to a maximum of 891
depending upon the rostral-caudal coordinate assayed.
Moreover, the greatest variability occurred in the rostral
portion of the lateral ventricles, thereby explaining the
large variation in neurosphere frequency previously reported.
Whereas the overall number of neurospheres
(3730 276) or colonies (4275 124) we detected along
the neuraxis did not differ significantly, LRC numbers
were significantly reduced (1186 188, 7 month chase) in
comparison to both total colonies and neurospheres.
Moreover, approximately two orders of magnitude fewer
NSC-derived colonies (50 10) were detected using the
N-CFCA as compared to LRCs. Given only 5% of the
LRCs are cycling (BrdU/Ki-67) or competent to divide
(BrdU/Mcm-2), and proliferate upon transfer to culture,
it is unclear whether this technique selectively detects
endogenous NSCs. Overall, caution should be taken
with the interpretation and employment of all these techniques
