Microanatomy of the renal cortex in the domestic fowl

Two aspects of the avian renal cortical microanatomy previously were unclear. The precise in situ folding patterns and orientations of the nephrons with respect to the other cortical elements had not been demonstrated. It also was not known whether certain nephron segments are supplied exclusively by either the arterial or the portal blood flow. In the present study, a new casting compound was developed to allow selective examination of the cortical components by light microscopy. Cortical nephrons at the surface of the kidney were serially sectioned and reconstructed in order to determine: (a) their relationships to the vasculature and collecting ducts; (b) the location and characteristics of the tubule segments; and (c) the primary and secondary folding patterns of the tubules. The anatomical findings were documented individually and then summarized in a comprehensive diagram of the superficial cortical microanatomy. In addition, an in vivo method was used to determine the extent of portal blood distribution to the nephron segments. It was demonstrated that renal portal blood suffuses all of the segments except for the loops of Henle.     

An atypical crista resembling a "tight junction" in bean root mitochondria

The conformation and structure of an atypical crista found in a small percentage of the mitochondria in root tip cells of Phaseolus vulgaris L. have been studied electron microscopically in material fixed in glutaraldehyde followed by osmium tetroxide. In its transformation into an atypical crista, a normal crista elongates, broadens, and flattens, and the inner leaflets of its apposed unit membranes appear to fuse in a manner analogous to the formation of "tight junctions" between certain animal cells. The result is a large platelike, quintuple-layered structure, 240–260 A thick, whose long axis parallels that of the mitochondrion. The outer layers of the "plate," bordering on the mitochondrial matrix, are thickened and exhibit striking patterns in the micrographs. The structure of the plate is compared with that previously described for tight junctions between animal cells.     

PHOTOASSIMILATION OF 14C-ACETATE BY ULVA LACTUCA1

The effect of light on the uptake of ¹⁴C-labeled acetate, glucose, α-ketoglutarate, mannitol, and glycine was investigated in Ulva lactuca var. rigida. Uptake in the light over that in the dark of ¹⁴C-acetale (8-fold) was far higher than that of the other compounds tested. Further study of the phenomenon showed that (1) an increase in light intensity from 60 through 1000 ft-c results in increased ¹⁴C-acetate uptake, the kinetics of which differ from that of ¹⁴CO₂ uptake versus light intensity over the same range: (2) the action spectrum of acetate uptake, between 450 and 730 nm conforms to the action spectrum for photosynthesis in Ulva; (3) the acetate uptake process is sensitive to photosynthetic poisons including N'- (3-4, dichlorophenyl)-N, N-dimethyl urea (DCMU), and phenazine methosulfate (PMS), and inhibitors of the Krebs cycle including sodium monofluoroacetate (MFA) and malonate; (4) uptake of acetate is favored by low CO₂ concentrations; (5) uptake of acetate is not sensitive to 10^?4 M uranyl nitrate; (6) continuous white light, with and without far-red radiation, indicates no significant phytochrome involvement in the process. These results point to an intracellular dependence of the assimilation of acetate on the Krebs cycle in some manner (possibly in cooperation with the glyoxylate cycle) other than simply releasing CO₂ from the acetate moiety with subsequent fixation via the Calvin cycle, and on some product(s) of photo-system 2, eg, NADPH⁺, reduced ferredoxin, or O₂.     

Differential expression of three galaxin-related genes during settlement and metamorphosis in the scleractinian coral Acropora millepora

Background  

The coral skeleton consists of CaCO₃ deposited upon an organic matrix primarily as aragonite. Currently galaxin, from Galaxea fascicularis, is the only soluble protein component of the organic matrix that has been characterized from a coral. Three genes related to galaxin were identified in the coral Acropora millepora.     

Estimation of parameters in large offspring number models and ratios of coalescence times

The ratio of singletons to the total number of segregating sites is used to estimate a reproduction parameter in a population model of large offspring numbers without having to jointly estimate the mutation rate. For neutral genetic variation, the ratio of singletons to the total number of segregating sites is equivalent to the ratio of total length of external branches to the total length of the gene genealogy. A multinomial maximum likelihood method that takes into account more frequency classes than just the singletons is developed to estimate the parameter of another large offspring number model. The performance of these methods with regard to sample size, mutation rate, and bias, is investigated by simulation. The expected value of the ratio of the total length of external branches to the total length of the whole tree is, using simulation, shown to decrease for the Kingman coalescent as sample size increases, but can increase or decrease, depending on parameter values, for Λ coalescents. Considering ratios of tree statistics, as opposed to considering lengths of various subtrees separately, can yield better insight into the dynamics of gene genealogies.