Direct interaction of microtubule- and actin-based transport motors.

The microtubule network is thought to be used for long-range transport of cellular components in animal cells whereas the actin network is proposed to be used for short-range transport, although the mechanism(s) by which this transport is coordinated is poorly understood. For example, in sea urchins long-range Ca2+-regulated transport of exocytotic vesicles requires a microtubule-based motor, whereas an actin-based motor is used for short-range transport. In neurons, microtubule-based kinesin motor proteins are used for long-range vesicular transport but microtubules do not extend into the neuronal termini, where actin filaments form the cytoskeletal framework, and kinesins are rapidly degraded upon their arrival in neuronal termini, indicating that vesicles may have to be transferred from microtubules to actin tracks to reach their final destination. Here we show that an actin-based vesicle-transport motor, MyoVA, can interact directly with a microtubule-based transport motor, KhcU. As would be expected if these complexes were functional, they also contain kinesin light chains and the localization of MyoVA and KhcU overlaps in the cell. These results indicate that cellular transport is, in part, coordinated through the direct interaction of different motor molecules.

GTP gamma S inhibits organelle transport along axonal microtubules.

Movements of membrane-bounded organelles through cytoplasm frequently occur along microtubules, as in the neuron-specific case of fast axonal transport. To shed light on how microtubule-based organelle motility is regulated, pharmacological probes for GTP-binding proteins, or protein kinases or phosphatases were perfused into axoplasm extruded from squid (Loligo pealei) giant axons, and effects on fast axonal transport were monitored by quantitative video-enhanced light microscopy. GTP gamma S caused concentration-dependent and time-dependent declines in organelle transport velocities. GDP beta S was a less potent inhibitor. Excess GTP, but not GDP, masked the effects of coperfused GTP gamma S. The effects of GTP gamma S on transport were not mimicked by broad spectrum inhibitors of protein kinases (K-252a) or phosphatases (microcystin LR and okadaic acid), or as shown earlier, by ATP gamma S. Therefore, suppression of organelle motility by GTP gamma S was guanine nucleotide-specific and evidently did not involve irreversible transfer of thiophosphate groups to protein. Instead, the data imply that organelle transport in the axon is modulated by cycles of GTP hydrolysis and nucleotide exchange by one or more GTP-binding proteins. Fast axonal transport was not perturbed by AlF4-, indicating that the GTP gamma S-sensitive factors do not include heterotrimeric G-proteins. Potential axoplasmic targets of GTP gamma S include dynamin and multiple small GTP-binding proteins, which were shown to be present in squid axoplasm. These collective findings suggest a novel strategy for regulating microtubule-based organelle transport and a new role for GTP-binding proteins.

Assay of vesicle motility in squid axoplasm.

Axoplasm prepared as described above will maintain high levels of fast axonal transport for 1-2 hours, although moderate decrements in the average velocity may be noted over time. The organelles and structures that can be detected in isolated axoplasma are as small as the 50-nm synaptic vesicles or 25-nm microtubules, well below the limits of resolution for light microscopy; however, in the center of the axoplasm, where the density of structures is high, individual microtubules are not readily distinguished and individual vesicles can be followed only for short distances before they move out of the plane of focus or are lost in the multitude of neighboring organelles. On the periphery of perfused axoplasm, each of these structures may be readily detected and analyzed, but some information is lost about the role of specific axoplasmic organization in normal transport processes. Fortunately, the juxtaposition in one preparation of essentially structurally intact axoplasm with the extracted individual microtubules transporting organelles provides a unique preparation for molecular dissection of intracellular transport (Brady et al., 1985).

Causes and prognosis in 4,278 cases of paralysis of the oculomotor, trochlear, and abducens cranial nerves.

We collected data from a large series of patients with ocular palsies and compared them with data in previous series from the Mayo Clinic. The largest group of patients among 4,278 cases was that in which the cause was undetermined for a long period of follow-up. The abducens nerve was most commonly affected. The probability of establishing a diagnosis was higher in patients younger than 50 years and among those with associated neurologic findings or multiple ocular palsies. The prognosis for recovery was best in the vascular group but was better than 50% for all groups except those with tumors. Investigation may be tailored to each patient according to clinical findings and probabilities of finding a cause, and judicious clinical judgement should be exercised.

Autosomal dominant crystalline dystrophy.

A black woman was identified with a tapetoretinal degeneration with sparkling intraretinal crystals, retinal pigment epithelial and choroidal atrophy, night blindness, color vision abnormalities, and paracentral scotomas. This constellation of findings is most consistent with the diagnosis of Bietti's crystalline dystrophy. Eight other family members were identified with intraretinal crystals similar to those seen in the proband but in varying degrees of progression. Transmission electron microscopy of circulating lymphocytes in several patients demonstrated crystals and granular osmophilic material of unknown composition contained within abnormal lysosomes. These crystals are similar in appearance and location to those seen in cholesterol ester storage disease. This family demonstrates an autosomal dominant inheritance pattern, as well as other differences from classic Bietti's crystalline dystrophy. The authors, therefore, suggest that this new entity be named autosomal dominant crystalline dystrophy.

Complications of positioning holes in posterior chamber intraocular lenses.

We report our experience with five patients in whom the positioning holes of posterior chamber lenses appeared to cause various complications. The complications included iris chafing with resultant hyphema and pigment loss, iris adhesion to a positioning hole, fibrotic ingrowth into a positioning hole, and fine white deposits of unknown etiology on the lens surface. The possible causes and significance of these findings are discussed.

The effects of nonfixated lower lens haptics of Binkhorst lenses on corneal endothelial cell density.

At specified intervals up to 56 months postoperatively, we took central corneal endothelial cell measurements of 52 patients who had undergone extracapsular cataract extraction (ECCE) with placement of a Heyer-Schulte IC-10 iridocapsular intraocular lens. We then compared the endothelial cell density of patients in whom the lower lens haptic was fixated within the capsule with those in whom it was nonfixated. We found that nonfixation of the lower lens haptic, which in essence converts the irido-capsular lens to an iris-supported lens, does not cause continuing endothelial cell loss.

Fragile X-linked mental retardation: the Martin-Bell syndrome.

Seven members of the original family of sex-linked mental retardation reported by Martin and Bell in 1943 have been re-examined and five of them proved to carry a fragile X chromosome. Some also display the typical facial appearance associated with this anomaly, and some have macro-orchidism. It is proposed that the condition should be designated "The Martin-Bell syndrome."

Creep and flexibility measurements on plastic frames for tissue heart valves.

Measurements on plastic flexible frames for heart valves have shown that the design influences the creep potential of any one plastic material. This has been shown for both in vitro accelerated fatigue tests and after clinical implantation of more than 10 years. The flexibility of the plastic, a polypropylene, was not affected either by fatigue testing, shelf storage or clinical implantation. The possibility of 30 years freedom from creep for a flexible plastic frame for a tissue heart valve has been examined.

Age and mortality trends in residents of an institution for the mentally handicapped.

Ten years' statistics of age and mortality trends in a large institution are reported. It is shown that the residents are still an ageing population and that the higher mortality of the mentally handicapped is largely due to deaths from respiratory causes, as previously reported. Down syndrome is separately analysed and shows a sharp rise in mortality at a considerably earlier age than other mentally handicapped residents.

Blood pressure in Down's syndrome.

Systolic and diastolic blood pressures of a large sample of subjects with Down's syndrome have been compared with those of institutional controls and of the normal population. Subjects with Down's syndrome have the lowest pressures at all ages and institutional controls tend to fall between the two. The rise of blood pressure with age is slight in the two institutional groups and the reported sex difference in the normal population was not observed.

XO/XY mosaicism and non-fluorescing Y chromosome in a male.

An adult male of short stature and with underdeveloped external genitalia is described, who carried out a number of sexual assaults on young women. He proved to have XO/XY mosaicism and a non-fluorescing Y chromosome. It was considered to be a terminal deletion on morphological grounds. It is suggested, on the evidence of the small number of XO/XY mosaics examined by appropriate staining methods, that an abnormal Y chromosome, whether terminally deleted or non-fluorescing owing to an altered chemical state, predisposes to anaphase lagging and non-disjunction. Of eleven reported cases of XO/XY mosaicism with a non-fluorescing Y chromosome, this is the fifth of male phenotype. The severe behaviour disturbance of early onset is considered to be probably causally associated with the chromosome anomaly.