Cell Cycle Regulation
Most assays which measure cell cycle-regulated
transcription do so by monitoring either promoter activity or
mRNA accumulation on a population basis. For example, we
have clearly shown that cad (a Myc target gene) and dhfr (an E2F
target gene) mRNAs increase in abundance at the G1/S phase
boundary when mRNA is prepared from dishes of cultured cells and
that the cad and dhfr promoters display increased transcriptional
activity at the G1/S phase boundary when monitored using a
promoter-reporter assay (Miltenberger et al., 95; Slansky et al.,
93). Taken together, these measurements have suggested a
10-20 fold increase in promoter activity as cells progresss from
G0 to S phase. However, these studies do not reveal whether
a 10-20 fold increase is occuring in every cell on the dish or
whether the increase reflects an average value, with some cells
displaying a higher fold increase and some cells showing little
or no increase in transcriptional activity. Our recent
studies have suggested that for the cad (Boyd, MCB 99) and dhfr
(Wells et al., 2000) promoters, several different transcription
complexes have the potential to form, even in a synchronized cell
population. These results raise the possibilities that
either the different transcription complexes are functionally
redundant or that different cells in a clonal population are
responding differently to environmental stimuli. We are
currently using two different experimental approaches to
distinguish these possibilitiese. First, we are analyzing
mRNA accumulation on a single cell basis using in situ
hybridizations and second, we are separating functional from
nonfunctional transcription complexes (using cell sorting) and
identifying the specific transcription factors which compose each
type of complex.
Relevant publications:
Maser, R. S., Mirzoeva, O., Wells, J., Olivares, H., Williams,
B., Zinkel, R., Farnham, P. J., and Petrini, J. H. J. The MRE11 complex:
diverse roles in S phase progression. Mol. Cell. Biol., 21: 6006-6016,
2001. [Abstract] [pdf]
Wells, J., Boyd, K. E., Fry, C. J., Bartley, S. M., and
Farnham, P. J. Target gene specificity of E2F and pocket protein family
members in living cells. Mol. Cell Biol. 20: 5987-5807, 2000. [Abstract][pdf]
Lee, T.A. and Farnham, P. J. Exogenous E2F1 is growth
inhibitory before, during, and after neoplastic transformation. Oncogene.
19:2257-2268, 2000. [Abstract][pdf]
Lukas, E. R., Bartley, S. M., Graveel, C. R., Diaz, Z.
M., Dyson, N., Harlow, E., Yamasaki, L., and Farnham, P. J. Loss of E2F1
does not affect liver regeneration or hepatocarcinogenesis in C57BL/6J or
C3H/HeJ mice. Molecular Carcinogenesis: 25:295-303, 1999. [Abstract][pdf]
