Current Amon Lab Members
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Angelika Amon
PI
Michelle Attner
Graduate Student
May 2007-
Monica Boselli
Graduate Student
November 2000-
Gloria Brar
Graduate Student
May 2003 -
Meiosis differs from mitosis in one major respect: following DNA replication, meiotic cells undergo two chromosome segregation phases rather than the single equational division seen in mitosis. The first meiotic division is called a reductional division and requires homologs to segregate apart. In order for this to occur properly, homologs must find each other in the nucleus and align in a process called pairing. I am interested in understanding how pairing is achieved. To address this problem, I am trying to characterize the roles that events such as DNA replication and double-strand break (DSB) formation play in initiating pairing.
Another meiotic adaptation made to deal with two divisions is the stepwise loss of sister chromatid cohesion. In mitosis, the cohesion complex is removed from all along the chromosomes in the transition from metaphase to anaphase. In meiosis, only cohesion distal to crossovers is removed at MI; the remaining centromere-proximal cohesion is then removed at MII, allowing faithful segregation of sister chromatids. This differential regulation of meiotic cohesion is not well understood, but is thought to depend on Rec8, the meiosis-specific component of the cohesion complex. I am investigating the role that phosphorylation plays in Rec8 regulation through mass spec mapping of in vivo phosphorylation sites.
Ilano Brito
Graduate Student
May 2005 -
During meiosis, the monopolin complex promotes the cosegregation of sister chromatids to opposite ends of the spindle pole. The monopolin complex is made up of a meiosis-specific protein, MAM1, and two proteins, LRS4 and CSM1, which are also present during mitosis where they remain sequestered in the nucleolus. We recently noticed that these two proteins are released from the nucleolus during anaphase and are regulated in a similar manner to CDC14. While cosegregation does not happen during mitosis, it suggests that they may have a separate mitotic function. We are now exploring the specific roles of these proteins and the significance of their nuclear release during anaphase.
Thomas Carlile
Graduate Student
May 2004 -
During the meiotic cell cycle two rounds of chromosome segregation follow a single round of DNA replication. This necessitates modification of both chromosome segregation machinery and cell cycle controls. How the cell modifies these controls to carry out two sequential chromosome segregation phases is a key question in understanding meiosis. Previous work in the lab has shown that in S. cerevisiae the FEAR network plays a critical role in coordinating the two meiotic divisions. The FEAR network mutants, spo12 and slk19, fail to disassemble the anaphase I spindle, and carry out both meiotic chromosome segregation phases on the meiosis I spindle. There is also evidence to suggest that CDK regulation plays an important role in establishing the pattern of meiotic divisions. Expression of a non-degradable cyclin during meiosis produces a phenotype similar to that of FEAR mutants. Work in Xenopus oocyte extracts shows that a modest amount of CDK activity remains between the meiotic divisions, and that this activity is important for preventing DNA rereplication between the two divisions. My research focuses on characterizing CDK activity and its regulation in meiosis. I am characterizing the roles of the FEAR network and MEN in meiosis, as these networks are important for CDK downregulation during exit from mitosis. Additionally, I am studying the meiotic roles of known CDK regulators such as the APC (Anaphase Promoting Complex) and the CDK inhibitor Sic1.
Leon Chan
Graduate Student
May 2005 -
Jenny Cimino
Administrative Assistant
March 2004 - Forever
Ly-sha Ee
Technician
July 2003 -
Alexi Goranov
Post Doc
September 2006 -
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. One aspect of the coordination between growth and cellular proliferation, which is conserved from bacteria to humans, is that growth stimulates proliferation. On the other hand, the effects of proliferation on the ability of cells to grow are less clear. I am interested in addressing the issue of whether proliferation regulates growth in the budding yeast Saccharomyces cerevisiae. I am investigating how arresting the cell cycle of S. cerevisiae at different stages affects the ability of the cells to grow.
Sheryl Krevsky Elkin
Post Doc
June 2005 -
The budding yeast protein Spo13 has been identified as a key regulator of meiotic events. It is required for centromeric cohesin protection and sister kinetochore coorientation, which are both necessary for the proper resolution of the first meiotic division. However, Spo13 appears to be degraded at the metaphase I/anaphase I transition, and overexpression of Spo13 in mitotic cells causes the cells to arrest in metaphase. Evidence suggests that Spo13 must be eliminated in order for meiosis II to proceed. My project seeks to elucidate the molecular mechanism of Spo13 regulation. We hypothesize that Spo13 is degraded in a ubiquitin- and proteosome-dependent manner, and I plan to perform experiments to test this hypothesis, as well as to identify the E3 ubiquitin ligase responsible for Spo13 targeting. Additionally, we will use rational and deletional mutagenesis to determine cis-acting elements that are required for Spo13 degradation. Upon isolating a non-degradable Spo13, we will analyze the effects of persistent Spo13 on the meiotic cell cycle. Finally, we will examine the regulation of other meiosis-specific proteins to determine whether there is a common program for the elimination of meiotic determinants. These experiments will help us to better understand the molecular events of meiotic chromosome segregation.
Christian Gonzalez
Graduate Student
May 2006 -
Karen Hunter
Technician
June 2006 - June 2007
Ashwini Jambhekar
Post Doc
March 2006 -
I am studying the signals regulating the switch from clonal reproduction to meiosis in yeast. Specifically, I am studying how respiration helps to govern this transition. It has long been known that respiration is required for cells to enter meiosis, but the molecular mechanisms by which this regulation is achieved remain elusive. My goals are to determine how the respiration signal is sensed and transduced to the nucleus in order to promote the appropriate pathway of cellular development.
Brendan Kiburz
Graduate Student
May 2003 - August 2007
The cohesin protein complex, containing meiosis-specific subunit Rec8, plays an important role in ensuring proper chromosome segregation in meiosis. Cohesin complexes are assembled concomitantly with DNA replication. At the metaphase I/anaphase I transition, cohesin is lost along chromosome arm regions but remains at centromeres until anaphase II. This persistent cohesin must be cleaved in meiosis II at the metaphase II/anaphase II transition. Both SGO1 and the meiosis-specific gene SPO13 are required for the maintenance of centromeric cohesion. We are interested in the characterization of centromeric cohesion in meiosis and the regulation of stepwise loss of cohesion. Using chromatin immunoprecipitation (ChIP) of an HA-tagged version of Rec8 and alleles engineered to enrich for distinct populations of meiotic cells, we can identify precisely the chromosomal regions protected from Rec8 cleavage in meiosis I. This method has led to the identification of pericentric regions distal to the ~120 bp S. cerevisiae point centromere where cohesin persists into the second division. Interestingly, these pericentric sites are also populated by the putative Rec8 protector Sgo1. We are pursuing the characterization of these pericentric protected cohesin sites and continuing to explore the roles of SGO1 and SPO13 in their protection.
Matt Miller
Graduate Student
May 2007-
Fernando Monje-Casas
Post Doc
November 2003 -
During exit from mitosis changes in the subcellular localization of MEN (Mitotic Exit Network) components is thought to be important for the accurate regulation of this cell cycle transition. In this way, Lte1 localizes to the bud cortex concomitant with bud formation, while Tem1 and Bfa1/Bub2 form a complex (the Tem1 complex) that localizes to the spindle pole body (SPB) that is destined to enter the bud during anaphase. The asymmetric association of these proteins with SPBs is conserved from budding to fission yeast. As the daughter SPB passes through the bud neck, Bfa1 is thought to be inactivated by Cdc5 and Cdc14, while Tem1 becomes activated by Lte1. Tem1 then recruits the Cdc15 and Dbf2 kinases to the SPB, triggering the exit from mitosis. How Bfa1, Bub2 and Tem1 localize to SPBs is only partly understood. Nud1 is required for Bfa1 and Bub2 association with SPBs. Furthermore, Tem1 localization to SPBs requires both BUB2 and BFA1 while Bfa1 and Bub2 localization at SPBs is interdependent but does not depend on Tem1. However, it is not known how the asymmetric localization of these proteins is accomplished. I am trying to determine the mechanisms whereby Tem1, Bub2 and Bfa1 asymmetry is established and investigate the consequences of disrupting this asymmetry on cell cycle progression.
Vineet Prabhu
Graduate Student
May 2005 -
An important aspect of meiosis is that in the first division, sister chromatids must attach to the same spindle pole body (co-orient) but then attach to opposite spindle pole bodies (bi-orient) in the second division. I am studying the role and regulation of Ipl1/Aurora Kinase in mediating kinetochore attachments in meiosis.
Rami Rahal
Graduate Student
May 2003 -
Two networks, the Cdc Fourteen Early Anaphase Release (FEAR) network and the Mitotic Exit Network (MEN), coordinately act during anaphase to release Cdc14 from the nucleolus. The FEAR network-dependent release of Cdc14 during early anaphase has many, as yet unidentified, functions, two of which include regulation of spindle midzone assembly and the segregation of late-replicating sequences. While, the FEAR network is not essential for cell viability, up to 20% of cells die during anaphase in its absence. I am interested in determining how the cell employs the FEAR pathway to orchestrate late steps in mitosis and how it coordinates a myriad of discrete events, such as chromosome segregation, nuclear division, and cytokinesis.
Other questions of interest include:
1. What are the two branches of the FEAR network monitoring during the cell cycle?
2. What is the significance of having two parallel branches?
3. How is signaling through the FEAR network initiated and how is it terminated?
4. How does the cell modulate FEAR network activity?
5. Are there other genes involved in the FEAR network?
Jeremy Rock
Graduate Student
May 2007-
Brett Tomson
Graduate Student
May 2004 -
I am fourth year graduate student studying why repetitive regions of the S. cerevisiae genome, such as the rDNA array and telomeres, require the activity of the phosphatase Cdc14 for proper chromosome segregation. Interestingly, it is the FEAR network-mediated release of Cdc14 that allows for the proper separation of sister chromatids at repetitive regions. The mechanism whereby Cdc14 promotes the segregation of the rDNA and telomeres is also partly understood as recruitment of condensin and is being characterized by my fellow lab member, Damien. Additionally, it is unclear why repetitive telomeric and rDNA regions even require Cdc14 s assistance for their segregation.
I am using genetic tools to study the question of why the rDNA array in S. cerevisiae requires FEAR network and Cdc14-dependent recruitment of condensin in order to segregate during anaphase. In order to do this I am setting up a genetic screen to identify genes required specifically for rDNA segregation as well as analyzing the contribution of silencing and recombination on rDNA segregation.
Eduardo Torres
Post Doc
October 2004 -
