Juan Santana and Samuel Trammell will present their research on January 17th 2013

Juan Santana’s Research abstract

Drosophila Myb represses retrotransposition and regulates DNA copy number

c-Myb is a proto-oncogene associated with leukemias and lymphomas in birds and mammals. Vertebrates have three representatives of the Myb gene family consisting of A-, B- and c-Myb, all of which encode DNA-binding factors that are important for the proper expression of large numbers of genes including those that regulate cell cycle progression and cell differentiation.  Drosophila melanogaster contains a single Myb gene (Dm-Myb), mutants of which die before reaching adulthood. Small interfering RNA (siRNA) knockdown of Dm-Myb in an embryonic Drosophila cell line was shown to prevent the proper expression of genes with prominent roles in coordinating cell division.  Along the same lines, Dm-Myb mutant flies display cell cycle defects such as aneuploidy, aberrant spindle formation, and abnormal numbers of centrosomes.  Dm-Myb protein is present in a complex which includes the nucleosome remodeling factor NURF. Through yeast two-hybrid experiments and genetic screens, we show that Dm-Myb is specifically interacting with the major subunit of NURF (NURF301) and that these proteins are co-regulating a large number of genes, including those involved in cell cycle control.  More surprising, we show that Dm-Myb and NURF301 are working in concert to repress transcription of repeat elements. Finally, we show that both proteins are required to repress DNA replication of a multitude of genomic regions in polytene tissue nuclei.  Collectively, these data have allowed us to identify two new roles for Dm-Myb in controlling large-scale genomic processes which, when compromised, lead to deleterious effects on genome function.

Samuel Trammell’s Research Abstract

Replicative life-span extension by calorie restriction in yeast is non-cell autonomous

Wild-type Saccharomyces cerevisiae are calorie restricted by lowering glucose from 2.0% (v/v) to 0.2% or 0.5%. Under calorie restriction (CR), replicative life-span is extended in a manner depending upon protein deacetylase Sir2p and biogenesis of the Sir2p substrate, NAD+. Given the role of NAD+ in glycolysis, many postulated reduction of glucose concentration alters the abundance of NAD+ metabolites and consequentially increases Sir2p activity. CR does not significantly alter NAD+ metabolite abundances. To further dissect the relationship of CR to  NAD+ and Sir2p, we measured the copy number of NAD+ biosynthetic, consuming, and requiring enzymes. Only Sir2p and Pnc1p, which would convert NAD+ to nicotinic acid (NA) as a final product, are increased in expression with CR. Given intracellular NA did not change, we hypothesized extracellular NA increased with CR and was responsible for increased replicative life-span (RLS). We will present data acquired through a novel bioassay that CR depends upon the extracellular environment, NA is sufficient to extend RLS, and extracellular NA does not increase with CR. We will reveal evidence of a molecule of a known molecular weight but unknown identity that increases extracellularly as a function of CR that is strain specific.

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Posted on January 8, 2013, in Student Seminar. Bookmark the permalink. Leave a comment.

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