5-Bromo-2'-deoxyuridne (BrdU) and H-3-thymidine label mitotically active ce
lls, but they do not adequately mark the progeny of dividing cells for long
term study. An alternative method is to label cells using the replication-
defective CXL retroviral vector, which carries the lacZ gene encoding beta-
galactosidase; however. the ability of the CXL retroviral vector to pulse-l
abel mitotically active cells selectively is not known. Cultures of prolife
rating muscle cells were simultaneously incubated with the CXL retrovirus a
nd BrdU (10 mu M) for 2 hr. After removing the retrovirus containing medium
. the cells were maintained for an additional 24 hr in vitro before they we
re stained to detect beta-galactosidase and BrdU simultaneously. More than
95% of beta-galactosidase positive cells were also BrdU positive suggesting
that the majority of beta-galactosidase positive cells were in the S-phase
of the cell cycle at the time of CXL retroviral administration. Therefore,
the CXL retroviral vector is an appropriate pulse marker for dividing cell
s, and it is useful when it is desirable to know the fate of the progeny of
a particular cell following a mitotic event.