Biomedical Summer Undergraduate Research Experience Program (B-SURE)
The University of Texas Health Science Center at San Antonio (UTHSCSA)

YEW, P. Renee (Molecular Medicine):  Cell division is one of the most basic processes of living organisms, yet the mechanisms that regulate many steps of this complicated process remain unclear.  The research in our laboratory is focused on understanding the processes which regulate the onset and progression of DNA replication or S phase in vertebrates.  This point in the cell cycle is a major checkpoint of cell division where cells must correctly initiate the replication of the genome following mitosis while ensuring that replication occurs correctly, only once per cell cycle.  Premature entry into S phase, incomplete replication, or re-initiation of replication can result in genomic instability and the development of cancer.  For our studies, we mainly use two model systems including the eggs of the frog, Xenopus laevis, to study DNA replication during the simple embryonic cell cycle, and mammalian cells, to study DNA replication during the somatic cell cycle.

        Two of our studies focus on understanding how proteolysis by the ubiquitin pathway regulates the temporal events of DNA replication initiation.  We are purifying a protein complex associated with the ubiquitin-conjugating enzyme, CDC34, which is required for the initiation of DNA replication in Xenopus.  Once identified, we will study how this complex mediates the temporally regulated ubiquitination of key substrates to trigger the onset of S phase.  We are also studying the function and regulation of p27Xic1 (Xic1), a Cip/Kip-type cyclin-dependent kinase inhibitor in Xenopus.   Our studies have demonstrated that Xic1 is targeted for ubiquitination and proteolysis during DNA polymerase switching when recruited to a site of initiation by Proliferating Cell Nuclear Antigen.  Our current studies focus on identifying the steps of replication initiation that are blocked at the origin in the presence of non-degraded Xic1 and the regulation of Xic1 ubiquitination at a replication initiation site.  Another project examines the role of the Retinoblastoma (Rb) protein in directly regulating the onset of DNA replication at a site of initiation.  We use the Xenopus extract system to study how Rb may directly inhibit pre-replication complex proteins bound to an origin to prevent origin firing.  The long-term goal of our studies is to understand the temporal events that regulate the start of DNA replication in a vertebrate.  Our laboratory has trained three Molecular Medicine Summer Undergraduate Research Fellows (SURF) students and one non-SURF student during the past four summers.  We have demonstrated our commitment to undergraduate students by mentoring each student at the intellectual and technical level to complete his or her own independent research project.   Thus far, the effort of these students has resulted in two acknowledgements and one co-authorship on three publications.

P. Renee Yew's Research Web Page.


In situ hybridization in Xenopus