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Biomedical subjects

R D Allen

Publications and source records attributed to R D Allen.

At least 253 records · Page 14Linked to original sources
PubMed1969

The morphogenesis of basal bodies and accessory structures of the cortex of the ciliated protozoan Tetrahymena pyriformis.

Dividing cells of Tetrahymena pyriformis were observed by transmission electron microscopy for signs of morphogenesis of cortical structures. The earliest stage of basal body development observed was of a short cylinder of nine single tubules connected by an internal cartwheel structure. This is set perpendicular to the mature basal body at its anterior proximal surface under the transverse microtubules and next to the basal microtubules. Sequential stages show that the single tubules become triplet tubules and that the "probasal bodies" then elongate and tilt toward the organism's surface while maintaining a constant distance of 75-100 mmicro with the "parent." The new basal body after it is fully extended contacts the pellicle, and then assumes a parallel orientation with and moves anterior to the parent basal body. The electron-opaque core in the lumen of the basal body and accessory structures around its outer proximal surface appear after the developing basal body has elongated. These accessory structures associating with their counterparts from other basal bodies and with the longitudinal microtubules may play a role in the final positioning of basal bodies and thus in the maintenance of cortical patterns. Observations on a second sequence of basal body formation suggest that the oral anlage arises by multiple duplication of somatic basal bodies.

Microscopy, Electron↗
PubMed1969

Mechanism of the Seismonastic Reaction in Mimosa pudica.

The efflux of K(+) from the pulvinar cells of Mimosa pudica was shown to increase substantially during the seismonastic reaction. This result is shown to indicate a decrease in sigma (reflection coefficient) of pulvinar cell membrane for potassium salts which could account for the pulvinar cell turgor decrease during the seismonastic reaction.Membrane potentials and concentrations of Ca(2+), K(+), Cl(-), S, and P were measured in the top and bottom halves of pulvini. Pulvinar cells showed a large negative membrane potential, cell vacuole relative to external solution, but no significant difference in membrane potential could be detected between upper and lower pulvinar cells. A large difference in K(+) and Cl(-) concentration between top and bottom pulvinar halves was evident in reactive pulvini but not in unreactive pulvini. The effect of K(+) concentration on plant growth and leaf reactivity was also investigated.

Journal Article↗
PubMed1966

Structure and organization of the living mitotic spindle of Haemanthus endosperm.

New details of mitotic spindle structures in the endosperm of Haemanthus katherinae (Bak) have been demonstrated by differential interference microscopy. Spindle fibers are clearly seen in the living spindle extending from the kinetochores to the polar region. Individual spindle fibers consist of a bundle of smaller filaments which diverge slightly from the kinetochore and intermingle with filaments from other spindle fibers as they approach the polar region. The degree of intermingling increases during metaphase and anaphase. The chromosomes stop moving when the spindle fibers are still 5 to 10microns long; then the fibers disappear. These observations explain some aspects of spindle movements which were difficult to reconcile with earlier concepts of spindle organization.

Cell Division↗
PubMedDate not supplied

Nonclathrin vesicle coats and filament networks in the transition zone and trans-Golgi region of the Golgi complex of Paramecium.

Understanding vesicle trafficking to and through the Golgi stack has been greatly elucidated recently, but the question of what holds the endoplasmic reticulum (ER) and Golgi stack together in many cell types and an explanation of anterograde trafficking in the ER-Golgi transitional zone have not yet been adequately explained. We have studied these problems using both the thin sectioning and the quick-freeze deep-etch (QF-DE) technique on Paramecium cells harvested at different culture ages. Although the Golgi apparatus of Paramecium is made up of many sets of more reduced stacks of cisternae than those of many mammalian cells, the stacks in Paramecium always bear a close relationship to a transitional element of the ER from which non-clathrin-coated transition vesicles arise. In QF-DE replicas two networks of filaments are clearly shown; one is in this ER-Golgi transition zone and the other is on the trans side of the Golgi stack. The network associated with the trans-Golgi region links a number of vesicular elements. The network in the transition zone spans the distance between the ER and the cis-cisterna of the Golgi stack and has branches extending to the coats of the enmeshed nonclathrin-coated transition vesicles. These coats consist of a layer of 11-nm globular elements (the same size as coatomer complexes) which surround the 40-nm-diameter transition vesicles. We conclude that the filamentous network holds the ER and Golgi stack together and prevents the dispersal of the transition vesicles away from this zone. This network may also delineate and stabilize the transitional element within the ER and, finally, help organize anterograde transition vesicle trafficking in this ER-Golgi transition zone.

Animals↗
PubMedDate not supplied

Respiratory distress and neonatal mortality in infants of diabetic and prediabetic mothers.

The 149 live births of 19 insulin-dependent diabetic mothers and 62 prediabetic mothers between 1940 and 1970 were reviewed. The frequency of respiratory distress was 31% in infants of diabetic mothers, 2.6% in infants of prediabetic mothers, and 0.46% in all infants born at the same hospital during the same period. Neonatal mortality during the first month of life was 14% in the infants of diabetic mothers and 3.5% in the infants of prediabetic mothers. Both these rates for neonatal mortality are higher than those reported for live births in the United States and Minnesota between 1950 and 1965. Of the deaths in both groups combined, 77% occurred in the first 3 days of life in infants diagnosed as having respiratory distress. Birth weight and prematurity, gestational age, and toxemia were associated with an increased frequency of respiratory distress in the infants of prediabetic mothers, whereas gestational age, mode of delivery, and weight gain during pregnancy were so associated in infants of insulin-dependent diabetic mothers.

Body Weight↗