Submitted on June 29, 2007
Accepted on January 2, 2008
Transcription of 125kb-long laminin-
1 chain gene in rat mesangial cells:
Constitutive and inducible RNA polymerase II recruitment and chromatin states
Joel D. Nelson1, Steve Flanagin2, Yasunobu Kawata3, Oleg Denisenko3, and Karol Bomsztyk4*
1 Seattle, Washington, United States; Molecular Cellular Biology, University of Washington, Seattle, Washington, United States
2 Seattle, Washington, United States; Medicine, University of Washington, Seattle, Washington, United States
3 Medicine, University of Washington, Seattle, Washington, United States
4 Medicine, University of Washington, Seattle, Washington, United States; Molecular Cellular Biology, University of Washington, Seattle, Washington, United States
* To whom correspondence should be addressed. E-mail: karolb{at}u.washington.edu.
The laminin 
1 chain, a critical component of the extracellular matrix, is encoded by the 125kb-long Lamc1 locus. We profiled RNA polymerase II (Pol II) and histone modifications along the Lamc1 locus to explore transcription of this gene in its native chromatin environment. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) increased Lamc1 mRNA in rat mesangial cells (RMC). This increase was matched by an increase in Pol II density along the entire length of the Lamc1 locus. In contrast, in the hepatocarcinoma cell line (HTC-IR) an increase in Pol II density was restricted to the promoter and was not followed by mRNA induction. The pattern of histone H3 methylation was similar for both cell types but an increase in H3 lysine 9 acetylation observed at the 5’ end was weaker in HTC-IR cells than in RMC. All of the histone modifications showed spatial patterns where levels differed greatly between the 5’ and 3’ ends of Lamc1. Conversely, at the short, highly induced egr-1 gene the differences in chromatin marks between the 5’ and 3’ ends were much smaller. The results of this study suggest that i) Lamc1 transcription can be controlled after transcription initiation, to our knowledge, the first time this has been shown in an extracellular matrix gene, and ii) the length of a gene is a factor that can affect the chromatin environment for Pol II elongation.
