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Biomedical subjects

J A Maynard

Publications and source records attributed to J A Maynard.

At least 19 recordsLinked to original sources
PubMed2001

A novel all helix fold of the AP180 amino-terminal domain for phosphoinositide binding and clathrin assembly in synaptic vesicle endocytosis.

Clathrin-mediated endocytosis plays a major role in retrieving synaptic vesicles from the plasma membrane following exocytosis. This endocytic process requires AP180 (or a homolog), which promotes the assembly and restricts the size of clathrin-coated vesicles. The highly conserved 33 kDa amino-terminal domain of AP180 plays a critical role in binding to phosphoinositides and in regulating the clathrin assembly activity of AP180. The crystal structure of the amino-terminal domain reported herein reveals a novel fold consisting of a large double layer of sheets of ten alpha helices and a unique site for binding phosphoinositides. The finding that the clathrin-box motif is mostly buried and lies in a helix indicates a different site and mechanism for binding of the domain to clathrins than previously assumed.

Adaptor Proteins, Vesicular Transport↗
PubMed2000

CD44 expression in the developing and growing rat intervertebral disc.

CD44 has been identified at the time of extracellular matrix formation and expansion in several sites of the developing embryo (Wheatley et al. [1993] Development 119:295-306). The nucleus pulposus, consisting of a hydrated extracellular matrix tissue at birth, not previously closely analyzed, was examined for expression of CD44 in the developing and aging rat intervertebral disc. CD44 was identified solely on notochordal cells from the first onset of intervertebral disc formation (day 15 embryo) through the loss of notochordal cells from the nucleus pulposus (12-24 months of age). No CD44 expression was found in the notochordal cells prior to disc formation or in any cells other than the notochordal cells in the annulus fibrosus or nucleus pulposus of the intervertebral disc. Using reverse transcriptase-polymerase chain reaction methodology, the single 365 amino acid CD44 standard, CD44s, open reading frame was amplified from notochordal cells isolated from the nucleus pulposus. Western blot analysis of a cultured nucleus pulposus notochordal cells total protein extract identified a single CD44 species devoid of chondroitin sulfate with a mass of approximately 85 kDa, characteristic of CD44s. Cell surface detection for CD44 was co-localized with hyaluronan and proteoglycans at first appearance of disc formation in the nucleus pulposus.

Animals↗
PubMed1998

Spatial and temporal expression of CD44 isoforms in the developing and growing joints of the rat limb.

Hyaluronan is an integral component of proteoglycan-rich extracellular matrices such as hyaline cartilage. Hyaluronan is commonly found in embryonic tissue and is important in the formation of hydrated matrices that allow cellular expansion and migration. Cell surface hyaluronan-binding proteins such as CD44 are presumed to be important in the cellular interactions with hyaluronan in both of these processes. The primary aim of this study was to document the spatial and temporal expressions of CD44 isoforms during the development and growth of the diarthrodial joints of rat limbs. With use of in situ hybridization and immunohistochemistry, the CD44s isoform is selectively identified as localized to a single cell layer on opposing sides of the joint at the first appearance of joint cavitation (on the 18th day of gestation). After joint formation in the neonate, the expression of the CD44s isoform in the cells at the joint surface is lost. These findings suggest that the CD44s isoform has a role in the development of the diarthrodial joint, presumably through interaction with hyaluronan.

Animals↗
PubMed1998

Rhizoremediation of trichloroethylene by a recombinant, root-colonizing Pseudomonas fluorescens strain expressing toluene ortho-monooxygenase constitutively.

Trichloroethylene (TCE) was removed from soils by using a wheat rhizosphere established by coating seeds with a recombinant, TCE-degrading Pseudomonas fluorescens strain that expresses the tomA+ (toluene o-monooxygenase) genes from Burkholderia cepacia PR1(23)(TOM23C). A transposon integration vector was used to insert tomA+ into the chromosome of P. fluorescens 2-79, producing a stable strain that expressed constitutively the monooxygenase at a level of 1.1 nmol/min.mg of protein (initial TCE concentration, 10 microM, assuming that all of the TCE was in the liquid) for more than 280 cell generations (36 days). We also constructed a salicylate-inducible P. fluorescens strain that degraded TCE at an initial rate of 2.6 nmol/min.mg of protein in the presence of 10 microM TCE [cf. B. cepacia G4 PR1(23) (TOM23C), which degraded TCE at an initial rate of 2.5 nmol/min.mg of protein]. A constitutive strain, P. fluorescens 2-79TOM, grew (maximum specific growth rate, 0.78 h-1) and colonized wheat (3 x 10(6) CFU/cm of root) as well as wild-type P. fluorescens 2-79 (maximum specific growth rate, 0.77 h-1; level of colonization, 4 x 10(6) CFU/cm of root). Rhizoremediation of TCE was demonstrated by using microcosms containing the constitutive monooxygenase-expressing microorganism, soil, and wheat. These closed microcosms degraded an average of 63% of the initial TCE in 4 days (20.6 nmol of TCE/day.plant), compared to the 9% of the initial TCE removed by negative controls consisting of microcosms containing wild-type P. fluorescens 2-79-inoculated wheat, uninoculated wheat, or sterile soil.

Biodegradation, Environmental↗
PubMed1998

Effects of 2 weeks hypergravity on the composition of the intervertebral disc.

BACKGROUND: The effects of loading on connective tissues similar to the intervertebral disk have primarily been studied using articular cartilage organ culture in vitro techniques. The effects of in vivo loading on the intervertebral disk are less well documented. METHODS: The lumbar annuli of rats centrifuged at 2G for 2 wk were compared with those of similar rats kept under analogous conditions at 1G. The studies involved the water, hydroxyproline (collagen), and uronic acid (proteoglycan, PG) content of the L4-5 and L5-6 annuli. Comparisons were also made between the 2G animals and the previous Cosmos 2044 spaceflight animals at 0G. RESULTS: The water content of annuli did not differ between the control and 2G annuli; however, the PG content of the tissue was decreased in the 2G animals and the collagen content slightly increased, resulting in an increased collagen-PG ratio in the 2G animals. When the annuli were immersed in water for 2 h, more PG leached from the annuli of the 2G animals than the control animals, suggesting an alteration in the nature of the PG population comprising the annuli. Interestingly, the direction of changes in the 2G annuli was identical to that of the previous Cosmos 2044 0G animals when they were compared with their respective controls. Therefore, directly opposite experimental conditions (2G and 0G) produced similar results. CONCLUSION: Previous studies regarding PG synthesis and content in cartilaginous tissues suggest alterations in intratissue pH and hydration to be among the factors involved in controlling the PG population. If the observed changes are permanent, they may affect the integrity of the intervertebral disk although it is likely they are totally reversible on return to 1G after an interim period, providing injuries are avoided.

Adaptation, Physiological↗
PubMed1995

Morphological and biochemical effects of strenuous exercise on immature long bones.

To determine the effects of intense exercise on the growth of long bones in immature animals, young male white leghorn chickens were run five days per week starting at four weeks of age on motor-driven treadmills. Work intensity was determined on the basis of maximal oxygen consumption (VO2 max) with the exercise intensity maintained at 70-80 percent VO2 max. Young animals ran continuously for 30 minutes, older animals 45 to 60 minutes each day. Runners and controls (10 animals per group) were sacrificed at 8, 12, 14 and 20 weeks of age. The lengths of the femurs and tibiotarsus were significantly stunted at 8-, 12- and 14 weeks in the runners but had nearly recovered at 20 weeks of age. Both bones also demonstrated significantly decreased total cross-sectional areas in 8-, 12- and 14 week-old runners as well as decreased cortical cross-sectional areas. The tibiotarsus also remained significantly smaller in the 20-week-old runners, but the femur had recovered in terms of radial growth. Intermolecular pyridinoline collagen crosslinks were identical in amount in the two groups with the femur collagen significantly less cross-linked than the tibiotarsus. The delayed growth of the exercised avian young bone is consistent with data obtained from children and young mammalian models. The osteogenic response to exercise that produces an increased bone mass in adult tissue appears either suppressed or overcome in young avian bone indicating that it may be erroneous to assume that data obtained from adult tissue are also applicable to young growing bone.

Animals↗
PubMed1994

The effects of space flight on the composition of the intervertebral disc.

The lumbar annuli of rats flown on a COSMOS space flight were compared with those of three control groups and a ground antigravity tail suspension model. The wet and dry weights of the space flight annuli were significantly smaller than the three control groups. In addition, the collagen-to-proteoglycan ratio was significantly greater in the flight group due to a proportional increase in collagen and a decrease in proteoglycan. Finally, it appears microgravity may have altered the nature of the proteoglycan population as more proteoglycans leached from the annuli of flight animals than control animals when immersed in water.

Animals↗
PubMed1993

Anatomy of the oblique retinacular ligament of the index finger.

The available literature includes conflicting descriptions of the anatomy and function of the oblique retinacular ligament. We have studied this ligament in the index finger to better define its presence, configuration, points of attachment, length, and relationship to the proximal interphalangeal joint axis. Twenty fresh frozen index fingers were dissected. Five additional specimens were decalcified, mounted, sectioned transversely at 1 mm intervals and studied under the microscope. An oblique retinacular ligament was identified on the radial side of the index finger in 95% and on the ulnar side in 90% of the specimens. The radial oblique retinacular ligament was usually longer and more developed than the ulnar oblique retinacular ligament. Proximally, the ligament arose from the middle third of the proximal phalanx and the A-2 pulley whereas, distally, it inserted into the lateral extensor band with a fan-shaped expansion centered 4 to 6 mm distal to the proximal interphalangeal joint line. In 70% of the specimens, the oblique retinacular ligament was supplemented by a contribution from the proximal cruciform pulley (C-1). Histologic cross sections also confirmed the presence of the oblique retinacular ligament but not the supplemental contribution arising from the C-1 pulley. The relationship of the oblique retinacular ligament to the proximal interphalangeal joint axis is dependent on the proximal interphalangeal joint position; the ligament lies palmar to the proximal interphalangeal joint axis only when the proximal interphalangeal joint is flexed.

Cadaver↗
PubMed1992

Effects of microgravity on the composition of the intervertebral disk.

The lumbar annuli of rats flown on COSMOS 2044 were compared with those of three control groups and a tail-suspension experimental model. The wet and dry weights of the annuli were significantly smaller (P less than 0.05) in the flight group than in three control groups. The collagen-to-proteoglycan ratio was significantly greater (P less than 0.001) in the flight group than in the three control groups, but there were no detectable changes in the relative proportions of type I and II collagen or in the number of pyridinoline cross-links. When the annuli were immersed in water for 2 h, more proteoglycans (P less than 0.001) leached from the annuli of flown rats than from the tissue of control animals, suggesting abnormal or smaller proteoglycans. Safranin-O indicated a normal spatial distribution of the proteoglycans within the annulus. Tail suspension did not affect the size of the annuli, but more proteoglycans (P less than 0.05) leached from the tissue of suspended animals than from the normal annuli. The reasons for smaller disks and the abnormal ratio between the fibrous collagenous network and the proteoglycan gel in the flight group are unknown at this time. It is, however, probable that these changes may affect the biomechanical functions of the annulus, although they may be temporary and totally reversible if injuries are avoided in the interim period.

Animals↗
PubMed1990

Muscle spindles in the velopharyngeal musculature of humans.

Seven muscles in the velopharyngeal region of humans were studied histologically to determine the presence of muscle spindles. Typical spindles were found in palatoglossus and tensor veli palatini with a greater number in the latter. Spindles were not found in levator veli palatini, palatopharyngeus, musculus uvulae, salpingopharyngeus, or the superior pharyngeal constrictor.

Adult↗
PubMed1989

A microvascular anastomotic device: Part II. A histologic study in arteries and veins.

This study analyzes the histology associated with the polyethylene ring-pin device. The device was placed in 20 rabbit femoral arteries and 20 femoral veins. Specimens were harvested at 24-hour and 3-week postoperative intervals and were analyzed using light, scanning electron, and transmission electron microscopy. Generally, the reparative process in the arteries and veins was similar. In 24-hour artery and vein specimens, the endothelial cells were absent, the media tapered within the device, but smooth muscle cells (SMC) remained partially viable. In 3-week specimens, the device junction was well healed and reendothelialized. Subintimal hyperplasia was present, the internal elastic lamina was not reconstituted, and the SMCs were partially viable. Small vascular channels formed at the device junction, and small venous valves were noted near the device. Macrophages lined the margins of the device. The early reparative process proceeds favorably, by histologic criteria, after vessel repair with the polyethylene ring-pin device.

Anastomosis, Surgical↗
PubMed1988

Response of immature chicken meniscus to strenuous exercise: biochemical studies of proteoglycan and collagen.

Male white Leghorn chickens were exercised on a treadmill at 70-80% of their maximal oxygen consumption starting at 4 weeks and continuing up to 20 weeks of age. The effect of the strenuous exercise regime on the extracellular matrix of menisci was followed through studies of proteoglycans and collagen. Avian menisci contain type I collagen, chondroitin sulfate proteoglycans, which increase with age in amount and degree of aggregation, and dermatan sulfate proteoglycans, which decrease with age. Five weeks of exercise cause a premature decrease of dermatan sulfate proteoglycans, while the chondroitin sulfate-containing molecules become significantly more aggregated than those of the tissue of age-matched controls. Strenuous exercise also causes a significant decrease in the number of pyridinoline crosslinks per mole of collagen in the menisci of young runners. The exercise-induced changes of proteoglycan and collagen occur only during the period of active growth, and all parameters return to normal when the animals reach skeletal maturity. The early proteoglycan aggregation and dermatan sulfate decrease induced by exercise are probably an adaptation to the increased loading. Although the mechanism by which strenuous exercise reduces or delays the formation of collagen pyridinoline crosslinks in menisci of skeletally immature animals is unknown, their decrease could negatively affect the mechanical properties of the tissue during the period of active growth.

Adaptation, Physiological↗
PubMed1988

Suture extrusion in small arteries and veins.

One longitudinally orientated microsuture was implanted in the femoral artery and vein of 40 rats and harvested at 4 different time intervals (2, 8, 12, 18 weeks). The tissue section containing the most luminal portion of suture loop was chosen and submitted for analysis. Two parameters, one estimating the suture location in the vessel wall relative to the internal elastic lamina (IEL) and a second, estimating the magnitude of the intimal response at the suture site were addressed. Average suture location changed significantly over time. The suture tended to be exteriorized or extruded from its once luminal location within the intima to a position located within the adventitia. Veins exhibited a greater incidence of suture extrusion than arteries. The maximum magnitude of the intimal cellular response occurred in the 2 week time interval. Significant decreases (p less than 0.05) in the thickness of the intima was observed in each subsequent time interval for both arteries and veins. The results of this experiment indicate that the cellular response and reparative processes occurring in small arteries and veins modifies the luminal papillary projection and extrudes nylon suture material.

Animals↗
PubMed1986

Structural and mechanical adaptation of immature bone to strenuous exercise.

To investigate the adaptive responses of immature bone to increased loads, young (3-wk-old) White Leghorn roosters were subjected to moderately intense treadmill running for 5 or 9 wk. The training program induced significant increases in maximal O2 consumption and muscle fumarase activity in the 12-wk-old birds, demonstrating that growing chickens have the ability to enhance their aerobic capacity. The structural and mechanical properties of the runners' tarsometatarsus bones were compared with sedentary age-matched controls at 8 and 12 wk of age. Suppression of circumferential growth occurred with exercise at both ages, whereas exercise enhanced middiaphysial cortical thickening, especially on the bones' concave surfaces. Although cross-sectional area moments of inertia did not change with exercise, significant decreases in bending stiffness, energy to yield, and energy to fracture were observed. It was concluded that strenuous exercise may retard long-bone maturation, resulting in more compliant bones.

Adaptation, Physiological↗
PubMed1985

Morphological and biochemical effects of sodium morrhuate on tendons.

The purpose of this study was to determine some of the morphological and biochemical effects of sodium morrhuate injections into intact rabbit patellar tendons and Achilles tendons. The effects of one, three, and five 100 microliters injections of sodium morrhuate on tendon circumference, cell content, collagen fibril diameter, collagen-proteoglycan relationships, water content, amino sugar content, and hydroxyproline content were investigated over periods of 1, 4, and 9 weeks. In general, sodium morrhuate injected tendons were larger in diameter and contained more cells, smaller collagen fibrils, increased water and amino sugar content, and reduced hydroxyproline content compared with their contralateral controls. As a sclerosing agent, sodium morrhuate appears to mimic the early stages of an injury-repair sequence when injected directly into intact tendons. Whether sodium morrhuate may hasten repair responses or improve joint laxity remains to be determined.

Achilles Tendon↗