Control of Gene Expression During the Cell Cycle 
and Development of the Mammalian Cerebellum 
Nathaniel Heintz, Ph.D. — Investigator 
Dr. Heintz is also Professor at the Rockefeller University. He received his Ph.D. degree at the State 
University of New York at Albany, where he studied the genetics and biochemistry of bacteriophage SPOl 
gene expression. During postdoctoral studies with Robert Roeder at Washington University, St. Louis, 
he initiated his work on histone gene expression during the cell cycle. Continuation of these studies 
and examination of the developing mammalian cerebellum are his current research interests. 
OUR studies are focused on the identification 
of molecular mechanisms controlling gene 
expression during the cell cycle and in the devel- 
oping cerebellum. The elucidation of these mech- 
anisms should provide fundamental insights into 
the biological transitions that underlie the con- 
trol of cell division and the development of the 
mammalian central nervous system. 
Control of Gene Expression During 
the Cell Cycle 
Transcription of histone genes during the S 
phase of the eukaryotic cell cycle is achieved 
through the agency of subtype-specific consensus 
elements within histone gene promoters and 
their cognate distinct transcription factors. Co- 
ordinate transcription of this gene family is ac- 
complished through biochemically distinct tran- 
scription factors; this suggests pleiotropic 
regulatory mechanisms that control the activities 
of these factors during the cell cycle. We wish to 
identify these mechanisms at the molecular level 
and elucidate their importance for cell-cycle pro- 
gression. Identification of such mechanisms may 
provide highly specific targets for intervention in 
cell growth. 
Recently we have examined the post-transla- 
tional modifications to the transcription factor 
Octl, which participates in histone H2b expres- 
sion during the cell cycle. Both monoclonal and 
polyclonal antisera have been used to analyze 
changes in phosphorylation of Octl as cells pro- 
ceed to division. We have discovered that multi- 
ple forms of Octl exist in the cell, and their dis- 
tribution is dramatically regulated during the cell 
cycle. 
Further analysis of Octl phosphorylation has 
established that late in the cell cycle this tran- 
scription factor appears to be a substrate for both 
CDC2 kinase and protein kinase A (PKA). Phos- 
phorylation of Octl by PKA occurs within its 
DNA-binding domain and results in loss of DNA 
binding in vitro. This correlates with a signifi- 
cant decrease in Octl DNA binding during mito- 
sis in vivo. These results indicate that modifica- 
tion of Octl during the cell cycle results in 
modulation of its function. Inactivation of Octl 
by phosphorylation during mitosis also provides 
a possible explanation of the long-standing ob- 
servation that transcription is generally sup- 
pressed during this time in the cell cycle. Our 
present efforts are to extend this analysis to the 
histone HI transcription factor H1TF2, to deter- 
mine whether its control during the cell cycle 
may occur through the same molecular mecha- 
nisms. Demonstration that the timing and nature 
of the post-translational modifications on Octl 
and H1TF2 are similar in vivo would prove the 
existence of the proposed pleiotropic molecular 
mechanism for regulation of transcription during 
the S phase. 
A question that has arisen from these studies is 
whether S-phase-specific transcription and DNA 
replication are mechanistically coupled. To ad- 
dress this issue we have focused on two specific 
questions: Are the regulatory proteins for S-phase 
histone gene transcription directly involved in 
DNA synthesis? Might proteins that regulate DNA 
synthesis at specific chromosomal origins of repli- 
cation be activated by the same mechanisms that 
modulate those transcription factors? 
In collaboration with Nicholas Heintz (Univer- 
sity of Vermont) and Lisa Dailey (Rockefeller Uni- 
versity) we have identified a cellular protein 
complex with several properties expected of rep- 
lication-initiation factors. We have recently pre- 
pared antibodies and obtained primary amino 
acid sequences from one of these proteins 
(RIP60) and are using these tools to determine 
whether this factor participates in cellular DNA 
synthesis. Analysis of this factor during the cell 
cycle may help answer the two questions posed 
above. 
Development of the Mammalian Cerebellum 
The mammalian cerebellum is a complex and 
highly stereotyped structure in which major pat- 
tern formation and functional organization occur 
postnatally. The precise description of the cellu- 
lar events occurring during cerebellar develop- 
ment, and the existence of many mutant mouse 
strains in which normal development of the cere- 
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