Page 46 - The Hormel Institute 2024 Annual Report

46 | THE HORMEL INSTITUTE
// UNIVERSITY OF MINNESOTA
UNDERSTANDING NUCLEOSOME ASSEMBLY PATHWAY REGU􏰀TION
Mutations in chromatin regulators, which lead
to genome instability, are frequently associated with human cancers. Furthermore, altered ex- pressions of proteins known as histone chaper- ones have been linked to breast, gastrointestinal, laryngeal, and prostate cancers. Understand-
ing how nucleosome assembly pathways are regulated provide new opportunities to under- stand human cancer caused by the alteration in epigenetic states.
DNA replication is crucial for maintaining stable gene expression. During replication, the process during which DNA is copied in cells, parental H3-H4 histones are recycled onto newly synthe- sized DNA strands, ensuring the preservation
of histone posttranslational modifications. This recycling process involves two distinct path- ways: leading strand deposition, mediated by DNA polymerase epsilon subunits Dpb3/Dpb4, and lagging strand deposition, facilitated by the MCM helicase subunit Mcm2.
DEFECTIVE TRANSFER OF PARENTAL HISTONE DECREASES FREQUENCY OF HOMOLOGOUS RECOMBINATION
Our research in budding yeast has demonstrat- ed that disruptions in these two pathways affect parental H3-H4 histone transfer, leading to com- pensatory mechanisms where the remaining pathway predominates.
DNA POLYMERASE DELTA GOVERNS PARENTAL HISTONE TRANSFER TO DNA REPLICATION 􏰀GGING STRAND
Despite the known roles of Dpb3/Dpb4 and Mcm2 in leading and lagging strand histone deposition, respectively, the mechanism by which Mcm2 facilitates the transfer of parental histones to the lagging strand, while moving along the leading strand, remains unclear.
Our recent findings reveal that Pol32, a nones- sential subunit of the major lagging-strand DNA polymerase delta, plays a critical role in histone transfer. Deletion of Pol32 results in a predomi- nant transfer of parental histone H3–H4 to the leading strand during replication.
Biochemical analyses show that Pol32 can bind histone H3–H4 both in vivo and in vitro, and this interaction is disrupted by mutations in the his- tone H3–H4 binding domain within Mcm2. This discovery positions Pol32 as a crucial histone chaperone downstream of Mcm2, mediating the transfer of parental histones to the lagging strand during DNA replication.
Together, our findings underscore the importance of proper parental histone transfer in maintaining chromatin integrity and ensuring faithful inheri- tance of genetic and epigenetic information, with DNA polymerase delta subunit Pol32 identified as a key mediator in this process.