Talk abstracts
Talk on Saturday 09:30-09:45am submitted by Isa Ozdemir
CHD7 regulates replication-dependent histone expression via altered 3 end mRNA processing
sa zdemir (Department of Biological Sciences, University of Pittsburgh), Santana Lardo (Department of Biological Sciences, University of Pittsburgh), Sarah Hainer (Department of Biological Sciences, University of Pittsburgh)
Abstract:
Replication-dependent (canonical) histone mRNAs are uniquely regulated among mammalian transcripts. Their expression is restricted almost exclusively to S-phase, and unlike nearly all other protein-coding genes, they are not polyadenylated. Instead, their transcription is terminated just downstream of a conserved 3 stem-loop structure, via cleavage directed by the U7 snRNP. The resulting stem-loop is bound by SLBP, which is required not only for correct 3-end formation but for every downstream step in the histone mRNA life cycle.
Here, by acutely depleting the ATP-dependent nucleosome remodeler CHD7 in mouse embryonic stem cells, we find that its loss causes 3 read-through transcription past the stem-loop terminator at histone loci, indicative of a defect in 3-end processing. This defect occurred without changes in core histone biogenesis factor expression, including SLBP and U7 snRNP components, arguing against an indirect effect from loss of the processing machinery. CUT&RUN revealed that CHD7 does not localize to histone loci, ruling out a direct, local chromatin-remodeling mechanism. This defect was also absent in ATPase-dead CHD7 mutants, further indicating that CHD7 governs histone mRNA 3-end processing independent of its catalytic nucleosome-remodeling function.
Consistent with impaired 3-end processing, histone transcript and protein levels were persistently and selectively increased following 8- and 24-hour CHD7 depletion. This increase occurred without detectable alterations in cell cycle distribution, challenging a simple expansion of the S-phase population as the explanation. Together, these results reveal a termination-coupled 3-end processing defect that co-occurs with persistent histone mRNA and protein accumulation upon CHD7 loss, suggesting a new, non-catalytic role for this nucleosome remodeler in replication-coupled RNA processing fidelity, with implications for histone supply during rapid proliferation and cell differentiation.
Keywords: histone transcript 3 end processing, CHD7