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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The septins are a conserved family of proteins that are involved in cytokinesis and other aspects of cell-surface organization. In Drosophila melanogaster, null mutations in the pnut septin gene are recessive lethal, but homozygous pnut mutants complete embryogenesis and survive until the pupal stage. Because the completion of cellularization and other aspects of early development seemed likely to be due to maternally contributed Pnut product, we attempted to generate embryos lacking the maternal contribution in order to explore the roles of Pnut in these processes. We used two methods, the production of germline clones homozygous for a pnut mutation and the rescue of pnut homozygous mutant flies by a pnut(+) transgene under control of the hsp70 promoter. Remarkably, the pnut germline-clone females produced eggs, indicating that stem-cell and cystoblast divisions in the female germline do not require Pnut. Moreover, the Pnut-deficient embryos obtained by either method completed early syncytial development and began cellularization of the embryo normally. However, during the later stages of cellularization, the organization of the actin cytoskeleton at the leading edge of the invaginating furrows became progressively more abnormal, and the embryos displayed widespread defects in cell and embryo morphology beginning at gastrulation. Examination of two other septins showed that Sep1 was not detectable at the cellularization front in the Pnut-deficient embryos, whereas Sep2 was still present in normal levels. Thus, it is possible that Sep2 (perhaps in conjunction with other septins such as Sep4 and Sep5) fulfills an essential septin role during the organization and initial ingression of the cellularization furrow even in the absence of Pnut and Sep1. Together, the results suggest that some cell-division events in Drosophila do not require septin function, that there is functional differentiation among the Drosophila septins, or both.
Mol Biol Cell 2000 Sep
PMID:Evidence for functional differentiation among Drosophila septins in cytokinesis and cellularization. 1098 5

The Saccharomyces cerevisiae Cdc42p GTPase interacts with multiple regulators and downstream effectors through an approximately 25-amino-acid effector domain. Four effector domain mutations, Y32K, F37A, D38E, and Y40C, were introduced into Cdc42p and characterized for their effects on these interactions. Each mutant protein showed differential interactions with a number of downstream effectors and regulators and various levels of functionality. Specifically, Cdc42(D38E)p showed reduced interactions with the Cla4p p21-activated protein kinase and the Bem3p GTPase-activating protein and cdc42(D38E) was the only mutant allele able to complement the Deltacdc42 null mutant. However, the mutant protein was only partially functional, as indicated by a temperature-dependent multibudded phenotype seen in conjunction with defects in both septin ring localization and activation of the Swe1p-dependent morphogenetic checkpoint. Further analysis of this mutant suggested that the multiple buds emerged consecutively with a premature termination of bud enlargement preceding the appearance of the next bud. Cortical actin, the septin ring, Cla4p-green fluorescent protein (GFP), and GFP-Cdc24p all predominantly localized to one bud at a time per multibudded cell. These data suggest that Cdc42(D38E)p triggers a morphogenetic defect post-bud emergence, leading to cessation of bud growth and reorganization of the budding machinery to another random budding site, indicating that Cdc42p is involved in prevention of the initiation of supernumerary buds during the cell cycle.
Mol Cell Biol 2000 Nov
PMID:Saccharomyces cerevisiae cdc42p GTPase is involved in preventing the recurrence of bud emergence during the cell cycle. 1104 50

The Saccharomyces cerevisiae p21-activated kinases, Ste20p and Cla4p, have individual functions but appear to share an essential function(s) as well because a strain lacking both kinases is inviable. To learn more about the shared function, we sought new mutations that were lethal in the absence of CLA4. This approach led to the identification of at least 10 complementation groups designated NCS (need CLA4 to survive). As for ste20 cla4-75 mutants, most ncs cla4-75 double mutants were defective for septin localization during budding. One group, NCS1/RRD1 (YIL153w), did not confer this defect, however, and we investigated its function further. ncs1Delta cla4Delta cells arrested with elongated buds and short mitotic spindles. The morphological defects and lethality were suppressed by mutations that abrogate the cell cycle morphogenetic checkpoint, CDC28Y19F or swe1Delta. The connection to the cell cycle may be direct, as we detected a Cla4p-Cdc28p complex. NCS1 encodes a protein with significant similarity to a mammalian phosphotyrosyl phosphatase activator (PTPA) regulatory subunit for type 2A protein phosphatases (PP2As). Genetic and biochemical evidence suggested that the phosphatase Sit4p is a target for Ncs1p. First, CLA4 and SIT4 were synthetically lethal. Second, Ncs1p and its yeast paralog, Noh1p (Rrd2p), bound to the catalytic domain of Sit4p in vitro, and Ncs1p could be immunoprecipitated with Sit4p but not with another PP2A (Pph21p) from yeast cell extracts. Strains lacking both NCS1 and NOH1 were inviable and arrested as unbudded cells, implying that PTPA function is required for proper G(1) progression.
Mol Cell Biol 2001 Jan
PMID:The phosphotyrosyl phosphatase activator, Ncs1p (Rrd1p), functions with Cla4p to regulate the G(2)/M transition in Saccharomyces cerevisiae. 1113 37

The highly conserved small GTPase Cdc42p is a key regulator of cell polarity and cytoskeletal organization in eukaryotic cells. Multiple effectors of Cdc42p have been identified, although it is unclear how their activities are coordinated to produce particular cell behaviors. One strategy used to address the contributions made by different effector pathways downstream of small GTPases has been the use of "effector-loop" mutants of the GTPase that selectively impair only a subset of effector pathways. We now report the generation and preliminary characterization of a set of effector-loop mutants of Saccharomyces cerevisiae CDC42. These mutants define genetically separable pathways influencing actin or septin organization. We have characterized the phenotypic defects of these mutants and the binding defects of the encoded proteins to known yeast Cdc42p effectors in vitro. The results suggest that these effectors cannot account for the observed phenotypes, and therefore that unknown effectors exist that affect both actin and septin organization. The availability of partial function alleles of CDC42 in a genetically tractable system serves as a useful starting point for genetic approaches to identify such novel effectors.
Mol Biol Cell 2001 May
PMID:Isolation and characterization of effector-loop mutants of CDC42 in yeast. 1135 19

In Saccharomyces cerevisiae, entry into mitosis requires activation of the cyclin-dependent kinase Cdc28 in its cyclin B (Clb)-associated form. Clb-bound Cdc28 is susceptible to inhibitory tyrosine phosphorylation by Swe1 protein kinase. Swe1 is itself negatively regulated by Hsl1, a Nim1-related protein kinase, and by Hsl7, a presumptive protein-arginine methyltransferase. In vivo all three proteins localize to the bud neck in a septin-dependent manner, consistent with our previous proposal that formation of Hsl1-Hsl7-Swe1 complexes constitutes a checkpoint that monitors septin assembly. We show here that Hsl7 is phosphorylated by Hsl1 in immune-complex kinase assays and can physically associate in vitro with either Hsl1 or Swe1 in the absence of any other yeast proteins. With the use of both the two-hybrid method and in vitro binding assays, we found that Hsl7 contains distinct binding sites for Hsl1 and Swe1. A differential interaction trap approach was used to isolate four single-site substitution mutations in Hsl7, which cluster within a discrete region of its N-terminal domain, that are specifically defective in binding Hsl1. When expressed in hsl7Delta cells, each of these Hsl7 point mutants is unable to localize at the bud neck and cannot mediate down-regulation of Swe1, but retains other functions of Hsl7, including oligomerization and association with Swe1. GFP-fusions of these Hsl1-binding defective Hsl7 proteins localize as a bright perinuclear dot, but never localize to the bud neck; likewise, in hsl1Delta cells, a GFP-fusion to wild-type Hsl7 or native Hsl7 localizes to this dot. Cell synchronization studies showed that, normally, Hsl7 localizes to the dot, but only in cells in the G1 phase of the cell cycle. Immunofluorescence analysis and immunoelectron microscopy established that the dot corresponds to the outer plaque of the spindle pole body (SPB). These data demonstrate that association between Hsl1 and Hsl7 at the bud neck is required to alleviate Swe1-imposed G2-M delay. Hsl7 localization at the SPB during G1 may play some additional role in fine-tuning the coordination between nuclear and cortical events before mitosis.
Mol Biol Cell 2001 Jun
PMID:Dynamic localization of the Swe1 regulator Hsl7 during the Saccharomyces cerevisiae cell cycle. 1140 75

The location of the septin ring in the germ tubes of Candida albicans hyphae and pseudohyphae was studied using an antibody to Saccharomyces cerevisiae Cdc11p. In pseudohyphae induced by growth at 35 degrees C in YEPD or Lee's medium, a septin ring formed at or near (mean 1.8 microm) the neck between the mother cell and the germ tube. This became double later in the cycle, and the first mitosis took place across the plane of this double ring. A septin ring also formed at the germ tube neck of developing hyphae induced by serum or growth on Lee's medium at 37 degrees C. However, at later times, this ring became disorganized and disappeared. A second double ring then appeared 10-15 microm (mean 12.5 microm) along the length of the germ tube. The nucleus subsequently migrated out of the mother cell into the germ tube, and the first mitosis took place across the plane of this second septin ring. The relocation of the septin ring in developing hyphae provides a clear-cut molecular distinction between hyphae and pseudohyphae. Commitment to one type of septin localization and mitosis was shown to occur early in the first mitotic cycle, well before evagination. Germ tubes of hyphae and pseudohyphae also have different widths. A point of commitment to germ tube width was also demonstrated, but occurred later in the cycle, approximately coincident with the time of evagination.
Mol Microbiol 2001 Jul
PMID:The germ tubes of Candida albicans hyphae and pseudohyphae show different patterns of septin ring localization. 1145 97

Budding cells of the yeast Saccharomyces cerevisiae possess a ring of septin filaments of unknown biochemical nature that lies under the inner surface of the plasma membrane in the neck that connects the mother cell to its bud. Mutants, defective in any of the four genes (CDC3, CDC10, CDC11, CDC12), lack these septin filaments and display a pleiotropic phenotype that involves abnormal bud growth and an inability to complete cytokinesis. The cloned CDC10 was fused to bacterial genes to generate antibodies specific for the CDC10 product was a constituent of the septin filaments. Cdc10p-specific antibodies for septin staining and actin-specific rhodamine-phalloidine were used to investigate the timing of the localization of septin and actin at the budding site using the immunofluorescence microscopic technique. In wild-type cells, the timing of the appearance and disappearance of these proteins was indistinguishable. In addition, the cdc10 mutant did not prevent actin localization at the budding site. The mutant that was blocked in the actin function also did not prevent the septin localization of the Cdc10p. This result may suggest an organizational independence between these proteins in the bud formation. Finally, the localization of septin and actin in the cdc24 mutant cell was examined. It was found that the CDC24 function was necessary for the organization of septin and actin at the budding site.
Mol Cells 2001 Aug 31
PMID:Characterization of the CDC10 product and the timing of events of the budding site of Saccharomyces cerevisiae. 1156 33

The Saccharomyces cerevisiae mitotic exit network (MEN) is a conserved set of genes that mediate the transition from mitosis to G(1) by regulating mitotic cyclin degradation and the inactivation of cyclin-dependent kinase (CDK). Here, we demonstrate that, in addition to mitotic exit, S. cerevisiae MEN gene MOB1 is required for cytokinesis and cell separation. The cytokinesis defect was evident in mob1 mutants under conditions in which there was no mitotic-exit defect. Observation of live cells showed that yeast myosin II, Myo1p, was present in the contractile ring at the bud neck but that the ring failed to contract and disassemble. The cytokinesis defect persisted for several mitotic cycles, resulting in chains of cells with correctly segregated nuclei but with uncontracted actomyosin rings. The cytokinesis proteins Cdc3p (a septin), actin, and Iqg1p/ Cyk1p (an IQGAP-like protein) appeared to correctly localize in mob1 mutants, suggesting that MOB1 functions subsequent to actomyosin ring assembly. We also examined the subcellular distribution of Mob1p during the cell cycle and found that Mob1p first localized to the spindle pole bodies during mid-anaphase and then localized to a ring at the bud neck just before and during cytokinesis. Localization of Mob1p to the bud neck required CDC3, MEN genes CDC5, CDC14, CDC15, and DBF2, and spindle pole body gene NUD1 but was independent of MYO1. The localization of Mob1p to both spindle poles was abolished in cdc15 and nud1 mutants and was perturbed in cdc5 and cdc14 mutants. These results suggest that the MEN functions during the mitosis-to-G(1) transition to control cyclin-CDK inactivation and cytokinesis.
Mol Cell Biol 2001 Oct
PMID:Saccharomyces cerevisiae Mob1p is required for cytokinesis and mitotic exit. 1156 80

The ability to switch between yeast and hyphal morphologies is an important virulence factor for the opportunistic pathogen Candida albicans. Although the kinetics of appearance of the filamentous ring that forms at the incipient septum differ in yeast and cells forming hyphae (germ tubes) (), the molecular mechanisms that regulate this difference are not known. Int1p, a C. albicans gene product with similarity in its C terminus to Saccharomyces cerevisiae Bud4p, has a role in hyphal morphogenesis. Here we report that in S. cerevisiae, Int1p expression results in the growth of highly polarized cells with delocalized chitin and defects in cytokinesis and bud-site selection patterns, phenotypes that are also seen in S. cerevisiae septin mutant strains. Expression of high levels of Int1p in S. cerevisiae generated elaborate spiral-like structures at the periphery of the polarized cells that contained septins and Int1p. In addition, Int1p coimmunoprecipitated with the Cdc11p and Cdc12p septins, and Cdc12p is required for the establishment and maintenance of these Int1p/septin spirals. Although Swe1p kinase contributes to INT1-induced filamentous growth in S. cerevisiae, it is not required for the formation of ectopic Int1p/septin structures. In C. albicans, Int1p was important for the axial budding pattern and colocalized with Cdc3p septin in a ring at the mother-bud neck of yeast and pseudohyphal cells. Under conditions that induce hyphae, both Cdc3p and Int1p localized to a ring distal to the junction of the mother cell and germ tube. Thus, placement of the Int1p/septin ring with respect to the mother-daughter cell junction distinguishes yeast/pseudohyphal growth from hyphal growth in C. albicans.
Mol Biol Cell 2001 Nov
PMID:Candida albicans Int1p interacts with the septin ring in yeast and hyphal cells. 1169 87

Velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) is a congenital anomaly disorder associated with hemizygous 22q11 deletions. We previously showed that bacterial artificial chromosome (BAC) transgenic mice overexpressing four transgenes, PNUTL1, (CDCrel-1), GP1B beta, TBX1 and WDR14, had reduced viability, cardiovascular malformations and thymus gland hypoplasia. Since these are hallmark features of VCFS/DGS, we analyzed the mice for additional anomalies. We found that the mice have important defects in the middle and inner ear that are directly relevant to the disorder. The most striking defect was the presence of chronic otitis media, a common finding in VCFS/DGS patients. In addition, the mice had a hyperactive circling behavior and sensorineural hearing loss. This was associated with middle and inner ear malformations, analogous to Mondini dysplasia in humans reported to occur in VCFS/DGS patients. We propose that overexpression of one or more of the transgenes is responsible for the etiology of the ear defects in the mice. Based upon its pattern of expression in the ear and functional studies of the gene, TbX1 likely plays a central role. Haploinsufficiency of TBX1 may be responsible for ear disorders in VCFS/DGS patients.
Hum Mol Genet 2001 Oct 15
PMID:Mice overexpressing genes from the 22q11 region deleted in velo-cardio-facial syndrome/DiGeorge syndrome have middle and inner ear defects. 1170 42


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