Cytoplasmic motors and pollen tube growth

The growth of pollen tubes is characterized by an intense cytoplasmic streaming, during which the movements of smaller organelles (like secretory vesicles) and larger ones (including the generative cell and vegetative nucleus) are precisely coordinated. A well-characterized cytoskeletal apparatus is likely responsible for these intracellular movements. In recent years both microfilament and microtubule-based motor proteins have been identified and assumed to be the translocators of the several organelle categories. Their precise function during pollen tube growth is not yet clear, but apparently an actomyosin-based system is mainly responsible for pollen tube elongation. On the other hand, microtubules and microtubule-based motors have been thought to play a role in the maintenance of cell polarity. Both cytoskeletal systems (and their respective motor activities) could cooperate to ensure a precise regulation of pollen tube growth.     

Teaming up: from motors to people

When I reflect on how I became a cell biologist and why I love being one today, one thing that comes to mind is the many terrific collaborations I have had. The science I am most proud of from my graduate and postdoctoral training would not have been possible without working in teams with other scientists. Now, in my own group, much of our best work is being done collaboratively, both within the lab and with other labs. In this essay, I will highlight my experiences working in teams as a trainee, the role teamwork has played in my own research group, and how important I think collaborative science is for the future of biological research.     

Skewed contraceptive method mix: why it happens, why it matters

Contraceptive prevalence has been central to family planning research over the past few decades, but researchers have given surprisingly little consideration to method mix, a proxy for method availability or choice. There is no 'ideal' method mix recognized by the international community; however, there may be reason for concern when one or two methods predominate in a given country. In this article method skew is operationally defined as a single method constituting 50% or more of contraceptive use in a given country. Of 96 countries examined in this analysis, 34 have this type of skewed method mix. These 34 countries cluster in three groups: (1) sixteen countries in which traditional methods dominate, most of which are in sub-Saharan Africa; (2) four countries in which female sterilization predominates (India, Brazil, Dominican Republic and Panama); and (3) fourteen countries that rely on a single reversible method (the pill in Algeria, Kuwait, Liberia, Morocco, Sudan and Zimbabwe; the IUD in Cuba, Egypt, Kazakhstan, Kyrgyz Republic, Moldova, Turkmenistan and Uzbekistan; and the injectable in Malawi). A review of available literature on method choice in these countries provides substantial insight into the different patterns of method skew. Method skew in some countries reflects cultural preferences or social norms. Yet it becomes problematic if it stems from restrictive population policies, lack of access to a broad range of methods, or provider bias.     

Kinetics: a tool to study molecular motors

Molecular motors are enzymes that couple the energy from nucleoside triphosphate hydrolysis to movement along a filament lattice. The three cytoskeletal motor superfamilies include myosin, dynein, and kinesin. However, in the last decade it has become apparent that the nucleic acid-based enzymes (DNA and RNA polymerases as well as the DNA helicases) share a number of mechanistic features in common with the microtubule and actin motors despite the fact that their cellular functions are so different. This review addresses the mechanistic approaches that have been used to study molecular motors. We discuss the basic biochemical techniques used to characterize a protein preparation, including active site determination and steady-state kinetics. In addition, we present the transient-state kinetic approaches used to define a mechanochemical cycle. We attempt to integrate the information obtained from kinetic studies within the context of motility results to provide a better understanding of the contribution of each approach for dissecting unidirectional force generation.     

Interaction of the molecular motors

A review addresses the up-to-date evidence on the regulation of the organelle transport along microtubules in a very specific aspect of the interaction of the molecular motors of the opposite directions.     

Millennial musings on molecular motors

In a universe that is dominated by increasing entropy, living organisms are a curious anomaly. The organization that distinguishes living organisms from their inanimate surroundings relies upon their ability to execute vectorial processes, such as directed movements and the assembly of macromolecules and organelle systems. Many of these phenomena are executed by molecular motors that harness chemical potential energy to perform mechanical work and unidirectional motion. This article explores how these remarkable protein machines might have evolved and what roles they could play in biological and medical research in the coming decades.     

Millennial musings on molecular motors

In a universe that is dominated by increasing entropy, living organisms are a curious anomaly. The organization that distinguishes living organisms from their inanimate surroundings relies upon their ability to execute vectorial processes, such as directed movements and the assembly of macromolecules and organelle systems. Many of these phenomena are executed by molecular motors that harness chemical potential energy to perform mechanical work and unidirectional motion. This article explores how these remarkable protein machines might have evolved and what roles they could play in biological and medical research in the coming decades.     

Transport characteristics of molecular motors

Properties of transport of molecular motors are investigated. A simplified model based on the concept of Brownian ratchets is applied. We analyze a stochastic equation of motion by means of numerical methods. The transport is systematically studied with respect to its energetic efficiency and quality expressed by an effective diffusion coefficient. We demonstrate the role of friction and non-equilibrium driving on the transport quantifiers and identify regions of a parameter space where motors are optimally transported.     

Millennial musings on molecular motors

In a universe that is dominated by increasing entropy, living organisms are a curious anomaly. The organization that distinguishes living organisms from their inanimate surroundings relies upon their ability to execute vectorial processes, such as directed movements and the assembly of macromolecules and organelle systems. Many of these phenomena are executed by molecular motors that harness chemical potential energy to perform mechanical work and unidirectional motion. This article explores how these remarkable protein machines might have evolved and what roles they could play in biological and medical research in the coming decades.     

Self-organization versus watchmaker: molecular motors and protein translocation

Generation of directional movement at the molecular scale is a phenomenon crucial for biological organization and dynamics. It is traditionally described in mechanistic terms, in consistency with the conventional machine-like image of the cell. The designated and highly specialized protein machines and molecular motors are presumed to bring about most of cellular motion. A review of experimental data suggests, however, that uncritical adherence to mechanistic interpretations may limit the ability of researchers to comprehend and model biology. Specifically, this article illustrates that the interpretation of molecular motors and protein translocation in terms of stochasticity and self-organization appears to provide a more adequate and fruitful conceptual framework for understanding of biological organization at the molecular scale.     

DNA packaging: a new class of molecular motors

DNA is packaged into preformed bacteriophage capsids to liquid crystalline density by the action of a portal protein complex. Single molecule packaging studies indicate that this is a new and extremely powerful class of molecular motors.