Spindle pole body

The spindle pole body (SPB) is the microtubule organizing center in yeast cells, functionally equivalent to the centrosome. Unlike the centrosome the SPB does not contain centrioles. The SPB organises the microtubule cytoskeleton which plays many roles in the cell. It is important for organising the spindle and thus in cell division. SPB structure in Saccharomyces cerevisiae The molecular mass of a diploid SPB, including microtubules and microtubule associated proteins, is estimated to be 1–1.5 GDa whereas a core SPB is 0.3–0.5 GDa. The SPB is a cylindrical multilayer organelle. These layers are: an outer plaque (OP), which connects to the cytoplasmic microtubules (cMT); a first intermediate layer (IL1) and an electrondense second intermediate layer (IL2); an electrondense central plaque (CP), which is at the level of the nuclear envelope and is connected to it by hook-like structures, an ill-defined inner plaque (IP); and a layer of the inner plaque that contains capped nucl

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The Schizosaccharomyces pombe septation initiation network (SIN) is required for spore formation in meiosis

Elena Cano, Andrea Krapp, Viesturs Simanis

When nutrients are abundant, S. pombe cells grow as rods, dividing by fission after formation of a medially placed cell wall or division septum. Septum formation is triggered by a group of proteins, called the septation initiation network or SIN, that trigger contraction of the acto-myosin contractile ring at the end of mitosis. Ectopic activation of the SIN can uncouple septum formation from other cell-cycle events, whereas loss of SIN signalling gives rise to multinucleated cells due to the failure of cytokinesis. When starved, S. pombe cells of opposite mating types fuse to form a diploid zygote that undergoes meiosis and produces four spores. No septa or contractile rings are formed during meiosis. In this study, we have investigated the role of the SIN in meiosis. Our data show that, whereas the meiotic divisions appear normal, SIN mutants cannot form spores. Forespore membrane formation is initiated, but the nuclei are not encapsulated properly. The SIN proteins localise to the spindle pole body in meiosis. The protein kinases Sid1p and Cdc7p do not associate with the spindle pole body until meiosis II, when forespore membrane deposition begins. These data indicate a role for the SIN in regulating spore formation during meiosis.

2006

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Mitotic hyperphosphorylation of the fission yeast SIN scaffold protein cdc11p is regulated by the protein kinase cdc7p

Elena Cano, Andrea Krapp, Viesturs Simanis

The fission yeast septation initiation network (SIN) triggers the onset of septum formation and cytokinesis. SIN proteins signal from the spindle pole body (SPB), to which they bind in a cell cycle-dependent manner, via the scaffold proteins sid4p and cdc11p. cdc11p becomes hyperphosphorylated during anaphase, when the SIN is active. We have investigated the phosphorylation state of cdc11p during mitosis in various mutant backgrounds. We show that association of cdc11p with the spindle pole body is required for its phosphorylation and that ectopic activation of the SIN results in hyperphosphorylation of cdc11p. We demonstrate that mitotic hyperphosphorylation of cdc11p requires the activity of cdc7p and that its dephosphorylation at the end of mitosis requires PP2A-par1p. Furthermore, spindle checkpoint arrest prevents cdc11p hyperphosphorylation. Finally, we show that the septation inhibitor byr4p interacts preferentially with hypophosphorylated cdc11p. We conclude that cdc11p hyperphosphorylation correlates with activation of the SIN and that this may be mediated primarily by cdc7p in vivo.

2003

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Analysis of the S. pombe signalling scaffold protein Cdc11p reveals an essential role for the N-terminal domain in SIN signalling

Elena Cano, Andrea Krapp, Viesturs Simanis

The initiation of cytokinesis in the fission yeast Schizosaccharomyces pombe is signalled by the septation initiation network (SIN). Signalling originates from the spindle pole body (SPB), where SIN proteins are anchored by a scaffold composed of cdc11p and sid4p. Cdc11p links the other SIN proteins to sid4p and the SPB. Homologues of cdc11p have been identified in Saccharomyes cerevisiae (Nud1p) and human cells (Centriolin). We have defined functional domains of cdc11p by analysis of deletion mutants. We demonstrate that the C-terminal end of cdc11p is necessary for SPB localisation. We also show that the N-terminal domain is necessary and sufficient for signal transduction, since tethering of this domain to the SPB will substitute for cdc11p in SIN function.

2004

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Centrosome

thumb|right|upright=1.6|Schéma d'un centrosome. droite Animal Cell.svg Dans les cellules animales, le centrosome est le centre cellulaire organisateur des microtubules, COMT (MTOC en anglais pour «

Microtubule

Les microtubules (MT) sont des fibres constitutives du cytosquelette, au même titre que les microfilaments d'actine et que les filaments intermédiaires. Ils ont un diamètre d'environ 25 nm et une l

Fuseau mitotique

vignette|480x480px|Fuseau mitotique à la métaphase, on retrouve les 2 centrosomes, les divers types de microtubules et les différents moteurs protéiques.Le fuseau mitotique, ou appareil mitotique achr

BIO-464: Scientific project design in cell and developmental biology

Students are lead to understand selected concepts in cell and developmental biology, primarily through the analysis of scientific literature, and then to apply these concepts to the design and execution of a group project in the Gönczy or Oates laboratory.

BIO-205: Cellular and molecular biology I

The course covers the regulation of gene expression, which translates the information contained in the genome into function, by adjusting the levels and activities of mRNAs and proteins to the needs of specific cells, tissues and environments. A particular emphasis is given on experimental methods.