Amon Lab

Angelika Amon

Michelle Attner

Sexual reproduction depends on meiosis, the process by which haploid gametes are generated from a diploid progenitor cell. To achieve this goal, two rounds two rounds of chromosome segregation follow one round of DNA replication, unlike in the mitotic cell cycle.

Oscillations in cyclin-dependent kinase (CDK) activity drive the mitotic cell cycle, and CDK activity is strictly controlled in all eukaryotes. In mitosis, Clb-CDK activity is high, and at exit from mitosis Clbs are inactivated. The protein phosphatase Cdc14 is responsible for triggering CDK inactivation through dephosphorylation of its targets. During most of the cell cycle, Cdc14 is sequestered in the nucleolus. Two pathways in budding yeast control Cdc14 release from the nucleolus: the Cdc-fourteen early anaphase release (FEAR) network, and the mitotic exit network (MEN). The FEAR network is a non-essential pathway that promotes a transient release of Cdc14 during early anaphase, whereas the MEN is an essential pathway required for promoting Cdc14 release and maintaining Cdc14 in its released state during anaphase.

In meiosis, however, the FEAR network is essential. Cells lacking SPO12 or SLK19, two FEAR components, fail to disassemble anaphase I spindles, and meiosis II events occur on a meiosis I spindle. I am characterizing the MEN in meiosis, in order to elucidate how the activity or inactivity of this pathway contributes to proper progression through meiosis.

John Barney

Luke Berchowitz

Meiotic cell division is a hallmark of sexually reproducing species and Clb-CDK is a key regulator of this critical process. My research is aimed at elucidating the mechanisms by which the cell regulates translation in order to execute meiosis. In budding yeast, the Clb cyclins associated with the CDK Cdc28 govern progression through the meiotic cycle. Clb3-CDK is present during mitosis and meiosis II, but is not present during meiosis I. Regulation of CLB3 is unusual in that the CLB3 RNA, but not the protein, is stably expressed throughout meiosis I. The CLB3 5´UTR is essential for translational inhibition. My research is aimed at determining the mechanism by which cis and trans factors inhibit translation of CLB3 during meiosis I. To characterize the CLB3 5´UTR (cis factors), I am employing a mutagenesis strategy to identify the bases within the UTR necessary for translational inhibition. To identify trans factors necessary for Clb3-CDK regulation, I am employing a purification strategy, followed by CLIP to recapitulate the interaction in vivo. In parallel, I am conducting a forward screen designed to identify trans factors that when mutated relieve CLB3 5´UTR-mediated translational inhibition. I am also characterizing trans factors derived from the above approaches that modulate CLB3 translation.

Heidi Blank

Aneuploidy, or having an abnormal number of chromosomes that is not an exact multiple of the haploid number, is a condition associated with decreased proliferation in all organisms in which it has been studied. Yet a strong correlation exists between aneuploidy and cancer, a disease of enhanced proliferative capacity. In order to study this paradox of aneuploidy, the lab has previously constructed 13 haploid yeast strains, referred to as disomes, each containing one additional copy of the extra chromosome.

Disomic strains all display one or more forms of genomic instability, this being a possible mechanism whereby aneuploidy could lead to a faster evolution of tumor causing mutations. My current work focuses on determining the basis of the genomic instability, including assaying the disomes for defects in DNA replication and repair and also for problems with kinetochore-microtubule attachments.

Megan Bonney

Jenny Cimino

Stacie Dodgson

Jill Falk

Checkpoints are surveillance mechanisms that couple cell cycle events such that one event is contingent on the occurrence of another. During mitosis, the spindle position checkpoint ensures that the mitotic spindle elongates along the mother-bud axis before mitotic exit, so that both mother and daughter cell receive one full DNA complement. One component of this checkpoint, the kinase Kin4, functions as a negative regulator of mitotic exit by blocking Cdc5 phosphorylation of Bfa1. I am interested in how Kin4 itself is regulated as well as how mitotic exit, in general, is controlled in budding yeast.

Alexi Goranov

Cells coordinate growth (increase in size) and proliferation (increase in number, cell division) to best explore and survive in their environment, and loss of this coordination can lead to cell death or various disease states. However, how cells coordinate growth and proliferation is not well understood. I am interested in addressing the issue of whether proliferation regulates growth in the budding yeast Saccharomyces cerevisiae. We have shown that cells growth varies at different cell-cycle stages and in particular that polarization of actin decreases the capacity of cells to grow. How actin polarization downregulates protein synthesis is the subject of my current work.

Kristin Knouse

Laurens Lambert

Gabriel Neurohr

Ana Oromendia

Aneuploidy is a consequence of faulty chromosomal segregation during cell division in which an unequal number of chromosomes goes to each progeny resulting in n+1 in haploid organisms and 2n+1 in diploid cells and rarely 2n-1. We see aneuploidy as a systemic, chronic condition to which cells must adapt and compensate for if they are going to proliferate. To study the underlying biology and coping mechanisms we have generated 13 of the 16 possible disomic strains (n+1) in Saccharomyces cerevisiae, and after extensive initial characterization, we know that the additional chromosomes are active and that the resulting imbalances in intracellular protein composition interfere with cellular physiology. My main interest is in characterizing consequences of aneuploidy on cell physiology. Given that most (if not all) the disomes are temperature sensitive; we hypothesize that aneuploidy causes stress on the protein folding machinery and I am investigating how the cells cope with this stress by looking at the heat shock and unfolded protein response in the disomes.

Sarah Pfau

Aneuploidy, or having an incorrect number of chromosomes, is extremely detrimental when present in an entire organism. In humans, only three autosomal aneuploidies survive to birth, and individuals harboring such aneuploidies—notably individuals with trisomy 21, or Down’s Syndrome—exhibit many developmental abnormalities. Yet, cellular aneuploidy is frequently observed in cancer cells and is thought to play a causal role in tumorigenesis. Previous studies in our lab of cellular systems in both yeast and mice revealed that aneuploid cells exhibit a common stress response in vitro. I am working to characterize the effects of cellular aneuploidy in an in vivo context by generating transplantation chimeras with hematopoietic stem cells (HSCs) derived from trisomic embryos. By monitoring these transplantations over time, these assays will permit long term in vivo analysis of trisomic cells and will reveal phenotypes that manifest when aneuploid cells are present over long periods in an adult organism.

Arzu Sandikci

Stefano Santaguida

Jason Sheltzer

Aneuploidy decreases cellular proliferation in all normal cells analyzed to date. Yet, aneuploidy is also a hallmark of cancer, a disease of unlimited cell proliferation. It is therefore believed that aneuploidy can have growth-advantageous properties, though what exactly these are remains controversial. One hypothesis that has been proposed to explain the apparently contradictory effects of aneuploidy on cell proliferation suggests that aneuploidy increases genomic instability, thereby accelerating the development of potentially growth-promoting genetic alterations. I am exploring this possibility in aneuploid yeast and mammalian cells. I am currently measuring various determinants of genomic stability, including the rates of mutation, chromosome loss, and mitotic recombination, in order to determine whether aneuploidy affects these processes. These results will shed light on the consequences of aneuploidy, a condition present in greater than 90% of human tumors.

Yun-Chi Tang

Aneuploidy, the case that cells harbor abnormal chromosome numbers, is the leading cause of miscarriages and mental retardation in humans and a hallmark of cancer. However, whether aneuploidy is a cause or a consequence of cancer remains an unsolved question. I will examine the effects of aneuploidy in primary mouse cells by generating a series of cell lines that carry an additional extra copy of mouse chromosome. Preliminary data from our earlier studies in four trisomic mouse embryonic fibroblast (MEF) lines have suggested a general proliferative disadvantage conferred by aneuploidy. I will extend these analyses by examining more trisomies as well as characterize the effects of trisomy on cell proliferation and metabolism. In addition, as aneuploid cells are refractory to proliferation, cancer cells must develop mechanisms to overcome the proliferative and immortalizing disadvantages caused by aneuploidy. By applying a chemical screening, my aim is to identify genes and pathways that involve in the suppression of the proliferative disadvantage of aneuploid cells.

Becky Thorburn

Errors in chromosome segregation during cell division create cells with an abnormal number or chromosomes, a condition known as aneuploidy. Our lab has generated 13 of the 16 possible aneuploid yeast strains containing one extra chromosome (N+1), which we refer to as disomic cells. Most disomic cells show a decrease in proliferative capacity and an increase in cell size due to a G1 delay. I am focusing on the effects aneuploidy has on the cell cycle, in particular the G1 delay and commitment to cell cycle entry.

Elcin Unal

Meiosis is a specialized cell division that produces gametes for sexual reproduction. Errors during meiosis lead to aneuploidy, which causes miscarriages and mental retardation in humans. There is a striking correlation between age and high incidence of chromosome missegregation in meiosis. In addition, aging decreases gamete production and increases mutation rate in the germ line. However, a coherent picture of how aging influences the meiotic cell division is missing and the molecular nature of the age-induced meiotic dysfunctions remains unknown. Despite the fact that the germ line is vulnerable to aging, germ cells are essentially immortal, suggesting that special mechanisms exist in germ cells to reverse the age-induced damage. Using budding yeast as a model system, I would like to analyze the effects of aging on meiosis as well as to test the rejuvenatory potential of the meiotic program on replicative lifespan.

Folkert van Werven

Meiosis is a specialized cell division by which gamates (eggs and sperm) are produced. During meiosis the genetic content is halved through two consecutive chromosome segregation phases, and allows organism to create new genetic combinations. It has been known for decades that age affects the fidelity of gamete production in humans. Particularly, non-disjunctions, the failure of chromosome pairs to separate properly during cell divisions, increase with age in human females. The first aim is to determine how age effects the gene expression of IME1, a key regulator of meiotic entry in budding yeast. In order to characterize IME1 expression, we intend to do systematic analysis of transcription regulation at the IME1 promoter. The second aim is to answer the question why chromosome mis-segregation is increased during meiosis and what are the molecular mechanisms that cause this. It is our hope that our studies in Saccharomyces cerevisiae will shed light on how age affects meiotic entry and chromosome segregation in all organisms.

Hilla Weidberg