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Bruce Bowerman

Publications and source records attributed to Bruce Bowerman.

At least 19 recordsLinked to original sources
PubMed2026

The Small but Versatile Cyclin-Dependent Kinase Subunit CKS: C. elegans CKS-1 Regulates Anaphase Onset and Is Required for Anaphase B During Oocyte Meiosis.

The cyclin-dependent kinase subunit (CKS) remains the least well-understood component of the tripartite cyclin-dependent kinase (CDK) complexes that specify the proper sequence of events required to duplicate and segregate genomes during eukaryotic cell division. Our recent investigation of CKS requirements during Caenorhabditis elegans oocyte meiosis I and II documents an essential role for CKS in the execution of anaphase B and expands the known range of CKS influence on cell cycle regulation to a third class of E3 ligases. Our findings also further document how C. elegans oocytes use very different mechanisms to progress through these two sequential cell divisions that ultimately produce a haploid oocyte. In this Think Again article, we discuss our findings as they relate to previous studies of CKS in different model systems.

Animals↗
PubMed2007

Caenorhabditis elegans SAND-1 is essential for RAB-7 function in endosomal traffic.

The small rab-GTPase RAB-7 acts in endosome and endosome to lysosome traffic. We identified SAND-1 as a protein required for RAB-7 function based on similarities between SAND-1 and RAB-7 RNAi phenotypes. Although the initial uptake of yolk protein in oocytes, or of soluble secreted (ss) GFP in coelomocytes, appeared normal, further transport along the endocytic traffic route was delayed in the absence of SAND-1 function, and yolk proteins failed to reach yolk granules efficiently. Moreover, in coelomocytes, ssGFP and BSA-Texas-Red were endocytosed but not transported to lysosomes. We show that SAND-1 is essential for RAB-7 function at the transition from early to late endosomes, but not for RAB-7 function at lysosomes.

Animals↗
PubMed2006

Left-right asymmetry: making the right decision early.

A left-right asymmetry in neuronal function is specified surprisingly early during embryogenesis in Caenorhabditis elegans. Do early cues influence left-right asymmetries in other animals? How are early cues remembered until late in development?

Animals↗
PubMed2006

The puromycin-sensitive aminopeptidase PAM-1 is required for meiotic exit and anteroposterior polarity in the one-cell Caenorhabditis elegans embryo.

In the nematode Caenorhabditis elegans, sperm entry into the oocyte triggers the completion of meiosis and the establishment of the embryonic anteroposterior (AP) axis. How the early embryo makes the transition from a meiotic to a mitotic zygote and coordinates cell cycle changes with axis formation remains unclear. We have discovered roles for the C. elegans puromycin-sensitive aminopeptidase PAM-1 in both cell cycle progression and AP axis formation, further implicating proteolytic regulation in these processes. pam-1 mutant embryos exhibit a delay in exit from meiosis: thus, this peptidase is required for progression to mitotic interphase. In addition, the centrosomes associated with the sperm pronucleus fail to closely associate with the posterior cortex in pam-1 mutants, and the AP axis is not specified. The meiotic exit and polarity defects are separable, as inactivation of the B-type cyclin CYB-3 in pam-1 mutants rescues the meiotic exit delay but not the polarity defects. Thus PAM-1 may regulate CYB-3 during meiotic exit but presumably targets other protein(s) to regulate polarity. We also show that the pam-1 gene is expressed both maternally and paternally, providing additional evidence that sperm-donated gene products have important roles during early embryogenesis in C. elegans. The degradation of proteins through ubiquitin-mediated proteolysis has been previously shown to regulate the cell cycle and AP axis formation in the C. elegans zygote. Our analysis of PAM-1 requirements shows that a puromycin-sensitive aminopeptidase is also required for proteolytic regulation of the oocyte to embryo transition.

Amino Acid Sequence↗
PubMed2006

Conditional dominant mutations in the Caenorhabditis elegans gene act-2 identify cytoplasmic and muscle roles for a redundant actin isoform.

Animal genomes each encode multiple highly conserved actin isoforms that polymerize to form the microfilament cytoskeleton. Previous studies of vertebrates and invertebrates have shown that many actin isoforms are restricted to either nonmuscle (cytoplasmic) functions, or to myofibril force generation in muscle cells. We have identified two temperature-sensitive and semidominant embryonic-lethal Caenorhabditis elegans mutants, each with a single mis-sense mutation in act-2, one of five C. elegans genes that encode actin isoforms. These mutations alter conserved and adjacent amino acids predicted to form part of the ATP binding pocket of actin. At the restrictive temperature, both mutations resulted in aberrant distributions of cortical microfilaments associated with abnormal and striking membrane ingressions and protrusions. In contrast to the defects caused by these dominant mis-sense mutations, an act-2 deletion did not result in early embryonic cell division defects, suggesting that additional and redundant actin isoforms are involved. Accordingly, we found that two additional actin isoforms, act-1 and act-3, were required redundantly with act-2 for cytoplasmic function in early embryonic cells. The act-1 and -3 genes also have been implicated previously in muscle function. We found that an ACT-2::GFP reporter was expressed cytoplasmically in embryonic cells and also was incorporated into contractile filaments in adult muscle cells. Furthermore, one of the dominant act-2 mutations resulted in uncoordinated adult movement. We conclude that redundant C. elegans actin isoforms function in both muscle and nonmuscle contractile processes.

Actin Cytoskeleton↗
PubMed2006

Degrade to create: developmental requirements for ubiquitin-mediated proteolysis during early C. elegans embryogenesis.

The ubiquitin protein conjugation system tags proteins with the small polypeptide ubiquitin. Most poly-ubiquitinated proteins are recognized and degraded by the proteasome, a large multi-subunit protease. Ubiquitin-dependent protein degradation is used as a regulatory tool for many essential processes, the best studied of which is eukaryotic cell cycle progression. More recently, genetic studies in C. elegans have identified multiple roles for the ubiquitin system in early development, where ubiquitin-dependent protein degradation governs such diverse events as passage through meiosis, cytoskeletal regulation and cell fate determination.

Animals↗
PubMed2005

MOM-5 frizzled regulates the distribution of DSH-2 to control C. elegans asymmetric neuroblast divisions.

Asymmetric cell divisions produce all 302 neurons of the C. elegans hermaphrodite. Here, we describe a role for a C. elegans Dishevelled homolog, DSH-2, in an asymmetric neuroblast division. In dsh-2 mutants, neurons normally descended from the anterior neuroblast daughter of the ABpl/rpppa blast cell were frequently duplicated, while non-neuronal cells produced by the posterior daughter cell were often missing. These observations indicate that in the absence of dsh-2 function, the posterior daughter cell was transformed into a second anterior-like cell. Loss of mom-5, a C. elegans frizzled homolog, produced a similar phenotype. We also show that the DSH-2 protein localized to the cell cortex in most cells of the embryo. In the absence of MOM-5/Fz, DSH-2 was localized to the cytoplasm, suggesting that MOM-5 regulates asymmetric cell division by controlling the localization of DSH-2. Although all neurons in C. elegans are produced by an invariant pattern of cell divisions, our results indicate that cell signaling may contribute to asymmetric neuroblast division during embryogenesis.

Animals↗
PubMed2005

The conserved protein DCN-1/Dcn1p is required for cullin neddylation in C. elegans and S. cerevisiae.

SCF-type E3 ubiquitin ligases are multi-protein complexes required for polyubiquitination and subsequent degradation of target proteins by the 26S proteasome. Cullins, together with the RING-finger protein Rbx1, form the catalytic core of the ligase, and recruit the substrate-recognition module. Cycles of covalent modification of cullins by the ubiquitin-like molecule Nedd8 (neddylation) and removal of Nedd8 by the COP9 signalosome (deneddylation) positively regulate E3 ligase activity. Here we report the identification and analysis of a widely conserved protein that is required for cullin neddylation in the nematode Caenorhabditis elegans and the yeast Saccharomyces cerevisiae. C. elegans DCN-1 and S. cerevisiae Dcn1p (defective in cullin neddylation) are characterized by a novel UBA-like ubiquitin-binding domain and a DUF298 domain of unknown function. Consistent with their requirements for neddylation, DCN-1 and Dcn1p directly bind Nedd8 and physically associate with cullins in both species. Moreover, overexpression of Dcn1p in yeast results in the accumulation of Nedd8-modified cullin Cdc53p. Both in vivo and in vitro experiments indicate that Dcn1p does not inhibit deneddylation of Cdc53p by the COP9 signalosome, but greatly increases the kinetics of the neddylation reaction.

Adenosine Triphosphatases↗
PubMed2004

A spindle checkpoint functions during mitosis in the early Caenorhabditis elegans embryo.

During mitosis, chromosome segregation is regulated by a spindle checkpoint mechanism. This checkpoint delays anaphase until all kinetochores are captured by microtubules from both spindle poles, chromosomes congress to the metaphase plate, and the tension between kinetochores and their attached microtubules is properly sensed. Although the spindle checkpoint can be activated in many different cell types, the role of this regulatory mechanism in rapidly dividing embryonic animal cells has remained controversial. Here, using time-lapse imaging of live embryonic cells, we show that chemical or mutational disruption of the mitotic spindle in early Caenorhabditis elegans embryos delays progression through mitosis. By reducing the function of conserved checkpoint genes in mutant embryos with defective mitotic spindles, we show that these delays require the spindle checkpoint. In the absence of a functional checkpoint, more severe defects in chromosome segregation are observed in mutants with abnormal mitotic spindles. We also show that the conserved kinesin CeMCAK, the CENP-F-related proteins HCP-1 and HCP-2, and the core kinetochore protein CeCENP-C all are required for this checkpoint. Our analysis indicates that spindle checkpoint mechanisms are functional in the rapidly dividing cells of an early animal embryo and that this checkpoint can prevent chromosome segregation defects during mitosis.

Alleles↗
PubMed2004

Mutations in Caenorhabditis elegans cytoplasmic dynein components reveal specificity of neuronal retrograde cargo.

We describe Caenorhabditis elegans dynein complex mutants, which misaccumulate synaptic proteins at the ends of neuronal processes. Ultrastructural analysis revealed irregularly sized vesicles that likely represent accumulation of cargo. We propose that synaptobrevin, synaptotagmin, and UNC-104 are specific cargoes of the dynein complex. Many cargoes link to dynein via interactions between dynactin and vesicle-associated spectrin. However, loss of spectrin results in only mild and occasional defects in synaptobrevin localization. Thus, the dynein-dynactin complex shows neuronal cargo selectivity without spectrin being a critical component of cargo binding. We observed parallels to progressive motor neuron disease symptoms in these animals. With age, neuronal misaccumulations increase in size and frequency; locomotion becomes progressively slower; and life span is shortened. These mutants provide a model to assess whether defects in transport of specific cargo mediate neuronal dysfunction.

Aging↗
PubMed2004

Maternally expressed and partially redundant beta-tubulins in Caenorhabditis elegans are autoregulated.

The mitotic spindle, which partitions replicated chromosomes to daughter cells during cell division, is composed of microtubule assemblies of alpha/beta-tubulin heterodimers. Positioning of the mitotic spindle influences the size and location of daughter cells, and can be important for the proper partitioning of developmental determinants. We describe two semi-dominant mis-sense mutations in tbb-2, one of two C. elegans beta-tubulin genes that are maternally expressed and together are required for microtubule-dependent processes in the early embryo. These mutations result in a posteriorly displaced and misoriented mitotic spindle during the first cell division. In contrast, a probable tbb-2 null allele is recessive, and when homozygous results in less severe spindle positioning defects and only partially penetrant embryonic lethality. Two of the tbb-2 mutations result in reduced levels of TBB-2 protein, and increased levels of a second maternally expressed beta-tubulin, TBB-1. However, levels of TBB-1 are not increased in a tbb-2 mutant with an allele that does not result in reduced levels of TBB-2 protein. We conclude that feedback regulation influences maternal beta-tubulin expression in C. elegans, but cannot fully restore normal microtubule function in the absence of one beta-tubulin isoform.

Alleles↗
PubMed2004

Roles for two partially redundant alpha-tubulins during mitosis in early Caenorhabditis elegans embryos.

The Caenorhabditis elegans genome encodes multiple isotypes of alpha-tubulin and beta-tubulin. Roles for a number of these tubulins in neuronal development have been described, but less is known about the isoforms that function during early embryonic development. Microtubules are required for multiple events after fertilization produces a one-cell zygote in C. elegans, including pronuclear migration, mitotic spindle assembly and function, and proper spindle positioning. Here we describe a conditional and dominant mis-sense mutation in the C. elegans alpha-tubulin gene tba-1 that disrupts pronuclear migration and positioning of the first mitotic spindle, and results in a highly penetrant embryonic lethality, at the restrictive temperature of 26 degrees C. Our analysis of the dominant tba-1 (or346ts) allele suggests that TBA-1 assembles into microtubules in early embryonic cells. However, we also show that reduction of tba-1 function using RNA interference results in defects much less severe than those caused by the dominant or346ts mutation, due to partial redundancy of TBA-1 and another alpha-tubulin called TBA-2. Reducing the function of both TBA-1 and TBA-2 results in severe defects in microtubule-dependent processes. We conclude that microtubules in the early C. elegans embryo are composed of both TBA-1 and TBA-2, and that the dominant tba-1(or346ts) mutation disrupts MT assembly or stability. Cell Motil.

Animals↗
PubMed2004

Multiple Wnt signaling pathways converge to orient the mitotic spindle in early C. elegans embryos.

How cells integrate the input of multiple polarizing signals during division is poorly understood. We demonstrate that two distinct Caenorhabditis elegans Wnt pathways contribute to the polarization of the ABar blastomere by differentially regulating its duplicated centrosomes. Contact with the C blastomere orients the ABar spindle through a nontranscriptional Wnt spindle alignment pathway, while a Wnt/beta-catenin pathway controls the timing of ABar spindle rotation. The three C. elegans Dishevelled homologs contribute to these processes in different ways, suggesting that functional distinctions may exist among them. We also find that CKI (KIN-19) plays a role not only in the Wnt/beta-catenin pathway, but also in the Wnt spindle orientation pathway as well. Based on these findings, we establish a model for the coordination of cell-cell interactions and distinct Wnt signaling pathways that ensures the robust timing and orientation of spindle rotation during a developmentally regulated cell division event.

Alleles↗