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Biomedical subjects

A B Fulton

Publications and source records attributed to A B Fulton.

At least 55 records · Page 3Linked to original sources
PubMed1993

Vimentin mRNA location changes during muscle development.

The mRNAs for some cytoskeletal proteins are localized, suggesting that mRNA for these proteins may concentrate at sites appropriate for assembly. To test this hypothesis, we observed vimentin mRNA in developing chicken muscle cultures by in situ hybridization with a digoxigenin-labeled DNA probe to vimentin, detected by confocal microscopy using fluorescent anti-digoxigenin antibody. This method has submicrometer resolution. In developing muscle, vimentin mRNA was bipolar in young myoblasts, somewhat perinuclear in elongated myoblasts and spread fibroblasts, and diffuse in young and developing myotubes. In mature myotubes, vimentin mRNA occurred at costameres with vimentin protein. Localization of mRNA may prove important for assembling and maintaining differentiated cytoskeletal structures, as it is for organizing the embryo.

Animals↗
PubMed1993

Natural course of visual functions in the Bardet-Biedl syndrome.

OBJECTIVE: To determine the course of visual functions in patients with Bardet-Biedl syndrome. PATIENTS AND METHODS: The 21 patients with Bardet-Biedl syndrome seen at Children's Hospital, Boston, Mass, had optotype and grating acuities and dark-adapted thresholds measured over time. Their ages at first visit ranged from 2 weeks to 23 years (median age, 6 years). The courses of the visual functions were analyzed with a random-effects model. RESULTS: Substantial declines in visual functions were found. On average, grating and optotype acuities declined 0.09 log units (roughly 1 line) per year, and thresholds increased about 0.19 log units per year. The rates at which these visual functions were lost and the predicted level of the visual functions at ages 11 to 12 years (the mean ages of measurement) varied among individuals. CONCLUSIONS: The visual prognosis for children with Bardet-Biedl syndrome is poor. The course of both central and peripheral visual functions is variable.

Adolescent↗
PubMed1993

Spatial organization of the synthesis of cytoskeletal proteins.

The cytoskeleton of most cells is complex and spatially diverse. The mRNAs for some cytoskeletal proteins are localized, suggesting that synthesis of these proteins may occur at sites appropriate for function or assembly. mRNA concentrations were first observed for several oocyte and embryonic mRNAs. Some insight has been gained into the mechanisms that help to position these mRNAs. More surprising to some, many cytoskeletal mRNAs are also localized. Among them are mRNAs for actin, tubulin, intermediate filaments, and a variety of associated proteins. Different mRNAs in the same cell can be located in different places; the same mRNA can be located in different places; the same mRNA can be located differently at different times of development. For example, we observed vimentin mRNA in developing chicken muscle cultures by fluorescent in situ hybridization. We found that vimentin mRNA takes on a variety of positions during myogenesis, ending up located with its cognate protein at costameres. This last pattern is significant because it is too finely structured to have a function in the soluble phase and probably reflects cotranslational assembly of this particular protein. Analogies can be made between oocyte or embryonic positions (animal/vegetal poles, oocyte cortex, and interior) and somatic cell positions (anterior/posterior and cell cortex/cell center). These analogies may point to conserved mechanisms for moving and retaining mRNA. Localization of cytoskeletal synthesis, through the mRNA or by other means, may prove as important for assembling and maintaining differentiated cytoskeletal structures and somatic cells as mRNA location is for organizing the embryo. Mechanisms that permit mRNA localization are likely to be conserved.

Animals↗
PubMed1993

Specific and quantitative immunoprecipitation of tropomyosin and other cytoskeletal proteins by magnetic separation.

Immunoprecipitation is a powerful technique for purifying many proteins for which specific antibodies exist. Magnetic separation has recently been demonstrated to be effective in the immunoprecipitation of cell-surface proteins. We have used magnetic separation with anti-immunoglobulin or protein A bound to magnetic particles to immunoprecipitate labeled muscle tropomyosin and several other cytoskeletal proteins for which specific antibodies exist. We have not found it necessary to bind antigen-specific antibody to the magnetic particles, increasing the versatility of the technique. The quantitative recovery of tropomyosin from muscle cultures using magnetic separation is superior to Staph A (protein A-positive Staphylococcus aureus cells). The specificity of magnetic separation also compares favorably with Staph A for immunoprecipitation of muscle tropomyosin. Fibroblast tropomyosin, vimentin (from muscle and osteoblast) and myosin heavy chain are other cytoskeletal proteins that are easily recovered with magnetic separation. Magnetic separation, therefore, appears to be a valuable technique for the immunoprecipitation of cytoskeletal proteins from various cell types.

Animals↗
PubMed1992

Association of titin and myosin heavy chain in developing skeletal muscle.

To understand molecular interactions that organize developing myofibrils, we examined the biosynthesis and interaction of titin and myosin heavy chain in cultures of developing muscle. Use of pulse-labeling, immunoprecipitation, and a reversible cross-linking procedure demonstrates that within minutes of synthesis, titin and myosin heavy chain can be chemically cross-linked into very large, detergent-resistant complexes retaining many features of intact myotubes. These complexes, predominantly of titin and myosin, occur very early in myofibrillogenesis as well as later. These data suggest that synthesis and assembly of titin and myosin are temporally and spatially coordinated in nascent myofibrils and support the hypothesis that titin molecules help to organize sarcomere formation.

Animals↗
PubMed1992

The effect of light adaptation on scotopic spatial summation in 10-week-old infants.

Psychophysical area-intensity functions of individual 10-week-old human infants and adults were obtained in the dark adapted state, and in the presence of a steady background that elevated threshold 1 log unit above the dark adapted level. For dark adapted infants, the mean diameter for complete spatial summation (4.42 degrees; SD: 1.67 degrees) was significantly larger than that of adults (2.32 degrees; SD: 0.09 degrees). The background reduced the mean critical diameter to 2.67 degrees for infants (SD: 0.64 degrees) and to 1.16 degrees for adults (SD: 0.08 degrees). Spatial probability summation has similar effects on infant and adult thresholds, and, therefore, does not appear to account for the developmental decrease in critical diameters. Rather, decreases in receptive field size are suspected.

Adaptation, Ocular↗
PubMed1992

Effects of halothane on children's electroretinograms.

BACKGROUND: At times, anesthesia is necessary to test children's electroretinographic (ERG) responses. Halothane, an anesthetic commonly used for pediatric patients, affects some aspects of ERG responses, but it is unknown if halothane affects ERG parameters evaluated by contemporary clinical protocols. METHODS: Scotopic and photopic ERG responses were recorded from children when awake and then under halothane. RESULTS: Halothane has no effect on scotopic b-wave stimulus/response parameters, including amplitude, sensitivity, and implicit time. Scotopic a-wave amplitudes, implicit times, model parameters, and ratio of a- to b-wave amplitudes are unaffected by halothane. The amplitudes and implicit times of photopic responses to red flashes and 30 Hz flickering white light are not altered by halothane. Halothane causes no significant change in amplitudes and implicit times of the oscillatory potential wavelets. CONCLUSION: These results suggest that significant departures of ERG responses (studied with the protocol described herein) from a laboratory's normal values cannot be attributed to halothane.

Adolescent↗
PubMed1992

The rod sensitivity of dark adapted human infants.

The determinants of infants' low scotopic visual sensitivity are controversial. Some interpret infants' scotopic vision as indicative of immature rod photoreceptor function while others attribute infantile sensitivities mainly to post receptoral immaturities. To date the rod photoreceptor sensitivity of human infants has not actually been measured. In the work reported herein, electroretinographic a-wave responses, which represent the rod photoresponse, were recorded from dark adapted 10-week old infants and adult control subjects. Rod isolated a-waves indicate that 10-week-old infants' rods are less sensitive than adults'. Thus, any explanation of infants' scotopic visual sensitivity must take into account this fundamental property of infants' rods, low sensitivity.

Adult↗
PubMed1991

Titin, a huge, elastic sarcomeric protein with a probable role in morphogenesis.

Titin, the largest protein identified to date (over 1 micron long, almost 3 million daltons in mass) is the third most abundant component of the sarcomere. In the mature myofibril, titin molecules span from M line to Z line, forming a third filament system which provides sarcomeric alignment and elastic recoil. In the developing sarcomere, accumulating evidence from studies both in vivo and in vitro implicates titin as part of a morphogenetic scaffolding, upon which critical events in myofibrillogenesis are coordinated in a time- and space-dependent manner.

Animals↗
PubMed1991

Dark adapted thresholds in young RCS rats.

The dark adapted thresholds of black-eyed RCS rats and cogenic controls were measured using a new psychophysical procedure that permits determination of thresholds at earlier ages than previously possible. Rats were tested longitudinally between about ages 1 and 3 months. At all ages, thresholds of RCS rats were higher than those of controls. Thresholds did not change systematically with age for either RCS rats or controls. At age 3 months, when the RCS rats' b-wave is no longer recordable, RCS thresholds are about 2.2 log units higher than those of controls.

Aging↗
PubMed1991

Temporal summation in dark-adapted 10-week old infants.

The effect of stimulus duration on the b-wave and psychophysical responses of dark-adapted 10-week-old infants and adult control subjects is reported. Both infant and adult b-wave sensitivities vary with stimulus duration, show summation for brief duration stimuli, critical durations estimated at 88-155 msec, and little variation in sensitivity for longer durations. There are however, substantial differences between the infant and adult psychophysical temporal summation functions. The infant function is described by a straight line, slope about -0.5, across all flash durations while adults show summation at durations less than 100 msec and critical durations of 136 to 151 msec. Adult, but not infant, b-wave integration times and b-wave rise and fall times show duration-dependent changes. Thus, both ERG and psychophysical measures demonstrate immaturities in the rod mediated function of the infant retina.

Adult↗
PubMed1991

Electroretinographic assessment of background adaptation in 10-week-old human infants.

Full field, scotopic b-wave stimulus/response functions of 10-week-old infants and adults were measured in the dark-adapted condition, and in the presence of steady backgrounds. Dark adapted b-wave sensitivity (log sigma) differed significantly between infants and adults; the median dark adapted sensitivity of infants was 0.50 log unit less than that of adults. The median eigengraus of infants (-1.32 log scot. td) and adults (-1.55 log scot. td) did not differ significantly. The median slope of the linear portion of the background adaptation function was about 0.9 for infants and adults. These results argue for post-receptoral immaturities, but do not rule out receptoral immaturities.

Adaptation, Ocular↗
PubMed1991

Visual development of infants with severe ocular disorders.

Among 11 patients who presented as blind in early infancy, with Leber's congenital amaurosis (5 patients), optic nerve hypoplasia (4 patients), or macular colobomata (2 patients), 8 developed visually guided behavior and measurable grating acuity by age 5 to 46 months. All children with measurable grating acuity demonstrated visually guided mobility. Grating acuity was predictive of later visual performance in 10 of 11 patients by age 12 to 16 months. The best grating acuity attained by 7 months was 1.3 to 3.0 cycles/degrees (20/460 to 20/200) and 0.13 cycles/degrees (20/4700) by month 8. Two patients with Leber's congenital amaurosis and one with optic nerve hypoplasia remained blind. No clinical features existed to differentiate these three patients from the eight whose visual status improved. Posterior visual pathway maturation may underlie the improvement.

Child↗
PubMed1991

The quantity of rhodopsin in young human eyes.

The rhodopsin content of 20 eyes of infants and children ages 27 weeks gestation to 8 years (11 donors) was assayed and compared to the rhodopsin content of adults (36 eyes; 19 donors). Infants have significantly lower rhodopsin contents than adults. On average the rhodopsin content of young infants is about a third of adults. Previously reported full-field b-wave sensitivity of young infants is about 0.5 log units, that is about a third, less than adults. Thus, as previously found in infant rats, photon capture by rhodopsin appears to limit the dark adapted sensitivity of young human infants.

Adolescent↗