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Sansam, Christopher Whitman Center Scientist, Whitman Center

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The human body is composed of billions of cells, yet every one of us begins as just a single cell. This means that countless cell divisions occur during a human lifetime. Each cell carries the full set of genes from mom and dad, so every time a cell divides, the genome must be accurately and completely duplicated. We call the process of duplicating genes during cell division "DNA replication." When considering how many cell divisions occur in each of us and how complicated the process of DNA replication must be, it is not surprising that mistakes during DNA replication cause birth defects and cancer. Despite its fundamental importance for all life, we still know little about how DNA replication is controlled in humans. The Sansam laboratory is identifying the genes, molecules, and mechanisms that are needed to replicate our DNA. We expect that such knowledge will provide a clearer understanding of how a wide range of human diseases occur and ultimately will lead to the development of better treatments for diseases such as cancer. Lucky for us, DNA replication is so important that even very simple organisms share most of the genes and mechanisms involved with humans. In fact, scientists continue to shed light on how human DNA replication occurs by studying single-cell organisms such as yeast. Of course our genomes are more complicated than yeast, and not surprisingly, humans and other vertebrates have a more elaborate mechanisms for regulating DNA replication. The Sansam laboratory uses two experimental systems to shed light on the process of DNA replication in humans and vertebrate animals. First, to directly study how DNA replication is generally replicated in people, we use human cells dividing in culture. Second, to understand how DNA replication is regulated during the multitude of cell divisions that occur in the developing embryo, we use a simple vertebrate animal called the zebrafish. The zebrafish is the preeminent "model" organism for studying vertebrate embryonic development because it has a complex genome like humans, shares most genes with people, and is highly accessible for observation and manipulation. Using human cell culture and zebrafish, we can understand the genes and fundamental principles of DNA replication both at the single cell level as well as in the context of a real embryo.

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