The Chlamydomonas flagellar membrane glycoprotein FMG-1B is necessary for expression of force at the flagellar surface.

In addition to bend propagation for swimming, Chlamydomonas cells use their flagella to glide along a surface. When polystyrene microspheres are added to cells, they attach to and move along the flagellar surface, thus serving as a proxy for gliding that can be used to assay for the flagellar components required for gliding motility. Gliding and microsphere movement are dependent on intraflagellar transport (IFT). Circumstantial evidence suggests that mechanical coupling of the IFT force-transducing machinery to a substrate is mediated by the flagellar transmembrane glycoprotein FMG-1B. Here, we show that cells carrying an insertion in the 5'-UTR of the FMG-1B gene lack FMG-1B protein, yet assemble normal-length flagella despite the loss of the major protein component of the flagellar membrane. Transmission electron microscopy shows a complete loss of the glycocalyx normally observed on the flagellar surface, suggesting it is composed of the ectodomains of FMG-1B molecules. Microsphere movements and gliding motility are also greatly reduced in the 5'-UTR mutant. Together, these data provide the first rigorous demonstration that FMG-1B is necessary for the normal expression of force at the flagellar surface in ChlamydomonasThis article has an associated First Person interview with authors from the paper.

Sensory reception is an attribute of both primary cilia and motile cilia.

A recent cluster of papers has shown that motile cilia in the respiratory and reproductive tracts of humans and other mammals can exhibit sensory functions, a function previously attributed primarily to non-motile primary cilia. This leads to a new paradigm that all cilia and flagella (both motile and primary) can mediate sensory functions. However, examination of the literature shows that evidence of sensory functions of motile cilia and flagella is widespread in studies of invertebrates, and extends as back as far as 1899. In this Opinion article, I review the recent and historical findings that motile cilia have a variety of sensory functions, and discuss how this concept has in fact been evolving for the past century.

The reciprocal coordination and mechanics of molecular motors in living cells.

Molecular motors in living cells are involved in whole-cell locomotion, contractility, developmental shape changes, and organelle movement and positioning. Whether motors of different directionality are functionally coordinated in cells or operate in a semirandom "tug of war" is unclear. We show here that anterograde and retrograde microtubule-based motors in the flagella of Chlamydomonas are regulated such that only motors of a common directionality are engaged at any single time. A laser trap was used to position microspheres on the plasma membrane of immobilized paralyzed Chlamydomonas flagella. The anterograde and retrograde movements of the microsphere were measured with nanometer resolution as microtubule-based motors engaged the transmembrane protein FMG-1. An average of 10 motors acted to move the microsphere in either direction. Reversal of direction during a transport event was uncommon, and quiescent periods separated every transport event, suggesting the coordinated and exclusive action of only a single motor type. After a jump to 32 degrees C, temperature-sensitive mutants of kinesin-2 (fla10) showed exclusively retrograde transport events, driven by 7 motors on average. These data suggest that molecular motors in living cells can be reciprocally coordinated to engage simultaneously in large numbers and for exclusive transport in a single direction, even when a mixed population of motors is present. This offers a unique model for studying the mechanics, regulation, and directional coordination of molecular motors in a living intracellular environment.

Prey capture in protists utilizing microtubule filled processes and surface motility.

Surface motility, which can be visualized by the movement of live prey organisms, polystyrene microspheres or other inert particles, has been shown to occur in a wide variety of microtubule-filled extensions of the protistan cell surface, although the associated functions remain enigmatic. This article integrates an extensive but poorly known body of literature showing that surface motility, associated with microtubule-filled cell extensions such as flagella, axopodia, actinopodia, reticulopodia, and haptonema, plays a crucial role in protistan prey capture. Surface motility has been most extensively studied in Chlamydomonas where it is responsible for flagella-dependent whole cell gliding motility. The force transduction machinery for gliding motility in Chlamydomonas is intraflagellar transport. Other than in Chlamydomonas, this field has not moved far beyond the descriptive to the mechanistic because of technical challenges associated with many of the protistan organisms that utilize surface motility for prey capture. The purpose of this article is to rekindle interest in the protistan systems that utilize surface motility for prey capture at a time when newly emerging molecular tools for working with protists are poised to reinvigorate a field that has been quiescent too long.

Trends in histology laboratory teaching in United States medical schools.

Owing to competition for faculty time among the three major missions of today's academic medical centers, as well as the rapid development of computer-based instructional technologies, laboratory instruction in medical schools in the United States has been undergoing dramatic change. In order to determine recent trends in histology laboratory instruction at U.S. medical schools, a detailed Web survey was administered to histology course directors, with about two-thirds of schools responding. The survey was designed to identify trends in the number of hours of histology laboratory instruction that each medical student receives, the amount of faculty effort devoted to histology laboratory instruction, and the use of various computer-based technologies (including virtual microscopy and virtual slides) in histology laboratory instruction. Consistent with the long-term trend of declining total laboratory teaching hours in U.S. medical schools, there is an ongoing reduction in the number of hours of faculty-directed histology laboratory instruction that each medical student receives, with a concomitant reduction in hours of faculty time devoted to histology laboratory instruction. In terms of the tools used in the histology laboratory, there has been a dramatic increase in the use of various forms of computer-aided instruction (including virtual slides). The large increase in the number of schools using computer-aided instruction has not been accompanied by an equivalent decrease in the number of schools that utilize microscopes and glass slides. Rather, the clear trend has been toward a blending of the new computer-based instructional technologies with the long-standing use of microscopes and glass slides.

Laser trap measurements of flagellar membrane motility.

In addition to swimming motility, which is driven by propagation of bends along the flagellum, the unicellular green alga Chlamydomonas exhibits an unusual and alternative form of whole cell locomotion, called gliding motility. In gliding motility, a large flagellar membrane glycoprotein mediates flagellar membrane adhesion to solid substrates. This in turn activates a transmembrane signaling system that initiates the movement of a cross-linked cluster of glycoproteins within the plane of the flagellar membrane by activating and/or recruiting isoforms of the motor proteins kinesin and dynein. Flagellar membrane motility can be visualized through the bidirectional movement of microspheres adherent to the flagellar surface. This microsphere motility offers a unique, noninvasive experimental system for measuring the in vivo dynamics and regulation of microtubule-dependent molecular motors by using a laser trap transducer to capture and manipulate microspheres as they move along the flagellar surface. Detailed procedures for conducting such analyses are provided.

The future of ciliary and flagellar membrane research.

There has been a dramatic shift of attention from the ciliary axoneme to the ciliary membrane, much of this driven by the appreciation that cilia play a widespread role in sensory reception and cellular signaling. This Perspective focuses attention on some of the poorly understood aspects of ciliary membranes, including the establishment of ciliary and periciliary membrane domains, the trafficking of membrane components into and out of these membrane domains, the nonuniform distribution of ciliary membrane components, the regulation of membrane morphogenesis, functional collaboration between the axoneme and the membrane, and the evolving field of therapeutics targeted at the ciliary membrane.

Active learning: A small group histology laboratory exercise in a whole class setting utilizing virtual slides and peer education.

Histology laboratory instruction is moving away from the sole use of the traditional combination of light microscopes and glass slides in favor of virtual microscopy and virtual slides. At the same time, medical curricula are changing so as to reduce scheduled time for basic science instruction as well as focusing on student-centered learning approaches such as small group active learning and peer-instruction. It is important that medical schools resist the temptation to respond to this conjunction of events by turning histology into a self-study activity. This article describes a lymphoid histology laboratory exercise, occurring in a specially equipped Learning Studio housing an entire medical class that utilizes virtual slides in the context of small group active learning and peer instruction.

From central to rudimentary to primary: the history of an underappreciated organelle whose time has come. The primary cilium.

For the first time, the history of the central flagellum/primary cilium has been explored systematically and in depth. It is a long and informative story about the course of scientific discovery, memory loss and rediscovery. The progress of our story is saltatory, pushed onward by innovations in technology and retarded by socio-scientific issues of linguistic and temporal chauvinism. Over one hundred and fifty years passed between the discovery of this organelle and full appreciation of its important functions. The main character in our story is an organelle that was relegated to a very minor role in the cellular opera for a very long time, until its rather sudden promotion to a central role in orchestrating many of the sensory and signaling events of the cell. Although early investigators speculated on just such a role for the primary cilium as early as 1898, it was over one hundred years before proof for this hypothesis was forthcoming.

A change to pass/fail grading in the first two years at one medical school results in improved psychological well-being.

PURPOSE: To measure the impact of a change in grading system in the first two years of medical school, from graded (A, B, C, D, F) to pass/fail, on medical students' academic performance, attendance, residency match, satisfaction, and psychological well-being. METHOD: For both the graded and pass/fail classes, objective data were collected on academic performance in the first- and second-year courses, the clerkships, United States Medical Licensing Examination (USMLE) Steps 1 and 2 Clinical Knowledge (CK), and residency placement. Self-report data were collected using a Web survey (which included the Dupuy General Well-Being Schedule) administered each of the first four semesters of medical school. The study was conducted from 2002 to 2007 at the University of Virginia School of Medicine. RESULTS: The pass/fail class exhibited a significant increase in well-being during each of the first three semesters of medical school relative to the graded class, greater satisfaction with the quality of their medical education during the first four semesters of medical school, and greater satisfaction with their personal lives during the first three semesters of medical school. The graded and pass/fail classes showed no significant differences in performance in first- and second-year courses, grades in clerkships, scores on USMLE Step 1 and Step 2CK, success in residency placement, and attendance at academic activities. CONCLUSIONS: A change in grading from letter grades to pass/fail in the first two years of medical school conferred distinct advantages to medical students, in terms of improved psychological well-being and satisfaction, without any reduction in performance in courses or clerkships, USMLE test scores, success in residency placement, or level of attendance.

Targeting proteins to the ciliary membrane.

Most vertebrate cell types display solitary nonmotile cilia on their surface that serve as cellular antennae to sense the extracellular environment. These organelles play key roles in the development of mammals by coordinating the actions of a single cell with events occurring around them. Severe defects in cilia lead to midgestational lethality in mice while more subtle defects lead to pathology in most organs of the body. These pathologies range from cystic diseases of the kidney, liver, and pancreas, to retinal degeneration, to bone and skeletal defects, hydrocephaly, and obesity. The sensory functions of cilia rely on proteins localized specifically to the ciliary membrane. Even though the ciliary membrane is a subdomain of the plasma membrane and is continuous with the plasma membrane, cells have the ability to specifically localize proteins to this domain. In this chapter, we will review what is currently known about the structure and function of the ciliary membrane. We will further discuss ongoing work to understand how the ciliary membrane is assembled and maintained, and discuss protein machinery that is thought to play a role in sorting or trafficking proteins to the ciliary membrane.

The ultrastructure of Pyrsonympha and its associated microorganisms.

The termite gut flagellates are of interest because of their unusual motile organelles, their ability to digest cellulose, and their symbiotic relationship with prokaryotes inhabiting the insect gut. This report provides a detailed ultrastructural description of Pyrsonympha from the hind-gut of Reticulitermes flavipes. The motile axostyle is composed of 2,000-4,000 microtubules connected by cross-bridges. At its anterior end, the axostyle is associated with a "primary row" of microtubules which is associated with a fibrous network. The "primary row" is embedded in a large mass of amorphous, electron-dense material occupying the furthest anterior end of the cell. The basal bodies of the eight flagella are also embedded in this presumptive microtubule-organizing center. The flagella are associated with the cell surface throughout their length. Isolation and reactivation of the axostyle has demonstrated that although ATP dependent motility is inherent in the structure of the axostyle, its proper control may be mediated by the attachment of the axostyle to structures at the anterior end of the cell. Pyrsonympha lacks morphologically distinguishable mitochondria and Golgi complexes. The cell surface is covered by unique, previously underscribed, tubular specializations. Symbiotic microorganisms are observed associated with the cell surface and within the cytoplasm. Wood particles are taken up from the gut fluid by large phagocytic vacuoles formed at the posterior end of the cell. Even during the process of breakdown, the wood is always enclosed within the membrane of the phagocytic vacuole. The Pyrsonympha from Reticulitermes flavipes are not attached to the lining of the hind-gut and do not contain an attachment organelle, unlike the Pyrsonympha from other species of Reticulitermes.