Biomedical subjects

William Y Tsang

Publications and source records attributed to William Y Tsang.

6 recordsLinked to original sources

PubMed2006

CP110 cooperates with two calcium-binding proteins to regulate cytokinesis and genome stability.

The centrosome is an integral component of the eukaryotic cell cycle machinery, yet very few centrosomal proteins have been fully characterized to date. We have undertaken a series of biochemical and RNA interference (RNAi) studies to elucidate a role for CP110 in the centrosome cycle. Using a combination of yeast two-hybrid screens and biochemical analyses, we report that CP110 interacts with two different Ca2+-binding proteins, calmodulin (CaM) and centrin, in vivo. In vitro binding experiments reveal a direct, robust interaction between CP110 and CaM and the existence of multiple high-affinity CaM-binding domains in CP110. Native CP110 exists in large (approximately 300 kDa to 3 MDa) complexes that contain both centrin and CaM. We investigated a role for CP110 in CaM-mediated events using RNAi and show that its depletion leads to a failure at a late stage of cytokinesis and the formation of binucleate cells, mirroring the defects resulting from ablation of either CaM or centrin function. Importantly, expression of a CP110 mutant unable to bind CaM also promotes cytokinesis failure and binucleate cell formation. Taken together, our data demonstrate a functional role for CaM binding to CP110 and suggest that CP110 cooperates with CaM and centrin to regulate progression through cytokinesis.

Calcium-Binding Proteins↗

PubMed2003

The role of mitochondria in the life of the nematode, Caenorhabditis elegans.

Mitochondria are essential organelles involved in energy metabolism via oxidative phosphorylation. They play a vital role in diverse biological processes such as aging and apoptosis. In humans, defects in the mitochondrial respiratory chain (MRC) are responsible for or associated with a bewildering variety of diseases. The nematode Caenorhabditis elegans is a simple animal and a powerful genetic and developmental model system. In this review, we discuss how the nematode model system has contributed to our understanding of mitochondrial dynamics, of the genetics and inheritance of the mitochondrial genome, and of the consequences of nuclear and mitochondrial DNA (mtDNA) mutations. Mitochondrial respiration is vital to energy metabolism but also to other aspects of multicellular life such as aging and development. We anticipate that further significant contributions to our understanding of mitochondrial function in animal biology are forthcoming with the C. elegans model system.

Aging↗

PubMed2003

The mitochondrial prohibitin complex is essential for embryonic viability and germline function in Caenorhabditis elegans.

Prohibitins in eukaryotes consist of two subunits (PHB1 and PHB2) that together form a high molecular weight complex in the mitochondrial inner membrane. The evolutionary conservation and the ubiquitous expression in mammalian tissues of the prohibitin complex suggest an important function among eukaryotes. The PHB complex has been shown to play a role in the stabilization of newly synthesized subunits of mitochondrial respiratory enzymes in the yeast Saccharomyces cerevisiae. We have used Caenorhabditis elegans as model system to study the role of the PHB complex during development of a multicellular organism. We demonstrate that prohibitins in C. elegans form a high molecular weight complex in the mitochondrial inner membrane similar to that of yeast and humans. By using RNA-mediated gene inactivation, we show that PHB proteins are essential during embryonic development and are required for somatic and germline differentiation in the larval gonad. We further demonstrate that a deficiency in PHB proteins results in altered mitochondrial biogenesis in body wall muscle cells. This paper reports a strong loss of function phenotype for prohibitin gene inactivation in a multicellular organism and shows for the first time that prohibitins serve an essential role in mitochondrial function during organismal development.

Amino Acid Sequence↗

PubMed2003

Mitochondrial ATP synthase controls larval development cell nonautonomously in Caenorhabditis elegans.

The mitochondrial respiratory chain is composed of five protein complexes capable of generating cellular energy in the form of ATP. Defects in mitochondrial energy production can result in a wide variety of diseases with tissue-specific effects. We previously have isolated a mutation in the atp-2 gene, which encodes the active site or beta-subunit of complex V in Caenorhabditis elegans. This atp-2(ua2) mutation is lethal, resulting in developmental arrest at the third larval stage (L3). In this report, we use mosaic analysis to identify the tissues in which atp-2 gene activity is dispensable for development past the L3 stage. The loss of atp-2 in any tissue can provoke arrest at the L3 stage. However, animals with a loss of the atp-2 gene in the ABa lineage, which gives rise to neuronal, pharyngeal, and hypodermal cells, and/or the E lineage, which gives rise to the intestinal cells, can occasionally develop past L3. Loss of atp-2 gene function in the lineages that give rise to the body muscles is invariably associated with developmental arrest. This finding suggests that the body muscles may play a key role in regulating development. We conclude that atp-2 functions cell nonautonomously in this developmental process. Our findings suggest that atp-2 is involved in the production or the regulation of a global, developmental signal required for the L3-to-L4 transition.

Animals↗

PubMed2002

Mitochondrial genome content is regulated during nematode development.

Growth and development rely on the mitochondrial respiratory chain (MRC) as the major source of ATP. We measured the mitochondrial DNA (mtDNA) copy number of each of the Caenorhabditis elegans developmental stages. Embryos, L1, L2, and L3 larvae all have approximately 25,000 copies of maternally derived mtDNA. The copy number increases fivefold in L4 larvae and a further sixfold in adult hermaphrodites, but only twofold in adult males. The majority of mtDNA in adult worms is germline associated, and germline-deficient mutants show markedly reduced mtDNA contents. With sperm-deficient or oocyte-deficient mutants, we confirm that mtDNA amplification is primarily associated with oocyte production. When mtDNA replication is inhibited, a quantitative and homogeneous arrest as L3 larvae occurs. Thus, mtDNA amplification is a necessary component of normal development and its regulation may involve an energy-sensing decision or checkpoint that can be invoked when mitochondrial energy generation is impaired.

Animals↗

PubMed2002

Stable heteroplasmy but differential inheritance of a large mitochondrial DNA deletion in nematodes.

Many human mitochondrial diseases are associated with defects in the mitochondrial DNA (mtDNA). Mutated and wild-type forms of mtDNA often coexist in the same cell in a state called heteroplasmy. Here, we report the isolation of a Caenorhabditis elegans strain bearing the 3.1-kb uaDf5 deletion that removes 11 genes from the mtDNA. The uaDf5 deletion is maternally transmitted and has been maintained for at least 100 generations in a stable heteroplasmic state in which it accounts for approximately 60% of the mtDNA content of each developmental stage. Heteroplasmy levels vary between individual animals (from approximately 20 to 80%), but no observable phenotype is detected. The total mtDNA copy number in the uaDf5 mutant is approximately twice that of the wild type. The maternal transmission of the uaDf5 mtDNA is controlled by at least two competing processes: one process promotes the increase in the average proportion of uaDf5 mtDNA in the offspring, while the second promotes a decrease. These two forces prevent the segregation of the mtDNAs to homoplasmy.

Animals↗