Solvent cage effects: the influence of radical mass and volume on the recombination dynamics of radical cage pairs generated by photolysis of [CpCH2CH2N(CH3)C(O)(CH2)nCH3Mo(CO)3]2 (n = 3, 8, 13, 18) (Cp = eta 5-C5H4) complexes

The photochemistry of the [(CpR)Mo(CO)(3)](2) molecules, where CpR = eta(5)-C(5)H(4)(CH(2))(2)C(O)NCH(3)(CH(2))(n)CH(3) (n = 3, 8, 13, and 18), was examined using femtosecond pump-probe transient absorption spectroscopy. The goal of this study was to investigate the importance of radical size and mass on the dynamics and efficiency of geminate radical-radical recombination. The femtosecond results demonstrated the lack of any size/mass dependence of the recombination efficiency. This finding contrasts with results from a prior study that did find a size/mass dependence using a steady-state photochemical technique. To explain these conflicting results, it is proposed that the femtosecond pump-probe results are a measurement of the efficiency of primary geminate recombination whereas the steady-state method results are a measurement of the sum of primary and secondary geminate recombination efficiencies. The size/mass dependence is evident in the latter because secondary geminate recombination is a slower diffusive recombination process and therefore depends on the steric properties of the radicals. Although the existence of primary and secondary recombination channels is often taken for granted, experimental differentiation of primary and secondary caging has proven to be difficult because it is not possible for a single experimental technique to span the entire timescale for recombination of a radical cage pair and adequately resolve these recombination pathways.     

Ciliary receptors associated with the mouth and pharynx of Acoela (Acoelomorpha): a comparative ultrastructural study

The ultrastructure and distribution of receptor cells near the mouth and (where present) the pharynx of Hofstenia miamia, Proporus bermudensis, Conaperta thela, and Convoluta convoluta (Acoela) were investigated by transmission electron microscopy and confocal laser scanning microscopy of specimens stained with a fluorescence marker for actin. Five types of monociliary receptors were identified: (1) non‐collared receptors with a single long and narrow ciliary rootlet; (2) non‐collared receptors with a wide main ciliary rootlet and a smaller posterior rootlet; (3) non‐collared receptors with a single wide and hollow ciliary rootlet with a granulated core; (4) Collar (?) receptors with obliquely radial filament bundles in the cell apex and with a single hollow ciliary rootlet composed of numerous strand‐like elements; and (5) Collar receptors lacking a striated rootlet but with a granular body (swallow's nest rootlet). While H. miamia bears the first two receptor types, P. bermudensis has receptors of type 1, 3 and 5, and Cona. thela and Conv. convoluta have receptors of type 3, 4 and 5. The density of receptors is generally highest at the anterior body tip, regardless of where the mouth is located. Most receptor types occur scattered over the whole body but type 2 receptors of H. miamia are restricted to the pharynx and mouth region. The lack of a common receptor type specific for the mouth and pharynx of the investigated species points to an independent origin of the pharynges in Hofsteniidae and in Proporidae and of the mouth tube in Convolutidae. Moreover, the homology of the so‐called collar receptors in Acoela with typical collar receptors in other invertebrates is questioned.     

Presymptomatic testing for Huntington's disease in the United Kingdom. The United Kingdom Huntington's Disease Prediction Consortium.

OBJECTIVE--To evaluate the United Kingdom Huntington''s disease presymptomatic testing programme. DESIGN--Postal questionnaire survey to collect data on all tests performed by clinical genetics centres between 1987 and 1990. SETTING--Genetic centres providing presymptomatic testing in the United Kingdom. SUBJECTS--248 subjects at risk of Huntington''s disease who had presymptomatic testing at their request. MAIN OUTCOME MEASURES--Sex, age, prior risk, and risk after testing. RESULTS--The risk of carrying the Huntington disease gene was reduced for 151 (61%) of the applicants and raised for 97 (39%). 158 (64%) of the subjects were female and 90 (36%) male. The median age at which the results were given was 32.5 years. CONCLUSIONS--The demand for testing was lower than expected and may have reached its peak in 1990. The excess of low risk results was not fully explained by the age effect. All the genetics centres concerned have agreed a common service protocol which requires extensive pre-test counselling and post-test follow up. The worth of the procedure remains to be decided. The availability of a large body of pooled data from all the United Kingdom testing centres, which individually are likely to have only a few results, will form a valuable resource for monitoring the long term psychosocial impact of testing.     

Morphogenesis of the respiratory bronchiole in rhesus monkey lungs

The epithelium of the respiratory bronchiole in the adult rhesus monkey consists of two populations: a pseudostratified epithelium with basal, mucous goblet, and ciliated cells located near the pulmonary artery (PA); and a simple cuboidal epithelium composed only of nonciliated bronchiolar epithelial (or Clara) cells in areas away from the PA. This study describes the pattern of differentiation of these two epithelial populations, and their relationship to the PA and to the time of appearance of alveoli in the respiratory bronchiole of the rhesus monkey during the period of 90-125 days gestational age (DGA). These events were related to changes in the adjacent parenchyma. Dissected airways of infusion-fixed, critical-point-dried lungs were evaluated by scanning microscopy followed by light microscopy of the same airways. At 54% of gestation (90 DGA), the distal airway was lined by a mixture of ciliated and nonciliated cells. By 67% of gestation (110 DGA), the ciliated cells were confined to the epithelium over the PA. The underlying connective tissue initially was cellular containing few fibers but was fibrous by 76% of gestation (125 DGA). Alveolarization began near the most distal cartilage at 57% of gestation (95 DGA), the same period at which secondary septation occurred in the distal acinus. Thus, alveolarization occurred simultaneously in two centers: 1) the proximal centriacinar region in the vicinity of the most distal cartilage and 2) the distal lung parenchyma. The duration of centriacinar alveolarization was short, approximately 5 days.     

Genetic basis for altered pathogenesis of an immune-selected antigenic variant of reovirus type 3 (Dearing).

In this paper we provide a step by step comparison of the pathogenesis of murine infection caused by reovirus type 3 (Dearing) and an antigenic variant (K) selected by its resistance to neutralization with a monoclonal antibody (G5) directed against the T3 hemagglutinin. To show that specific changes in the biologic properties of variant K were due to mutation in the S1 double-stranded RNA segment (gene), which encodes the viral hemagglutinin, we generated a reassortant virus ("1 HA K") containing the variant K S1 gene and compared its properties to variant K and to a reassortant ("1 HA 3") containing the T3 (Dearing) S1 gene. These studies, in conjunction with our previous nucleotide sequence analysis of the S1 genes of variant K and T3 (Dearing) [R. Bassel-Duby, A. Jayasuriya, D. Chatterjee, N. Sonenberg, J. V. Maizel, Jr., and B. N. Fields, Nature (London) 315:421-423, 1985; R. Bassel-Duby, D. R. Spriggs, K. L. Tyler, and B. N. Fields, submitted for publication], indicate that a single amino acid change in the T3 hemagglutinin can alter viral growth and tropism within the central nervous system without affecting either its primary replication in the intestine or its pattern of spread to or within the central nervous system.     

Growth of Acinetobacter sp. strain HO1-N on n-hexadecanol: physiological and ultrastructural characteristics.

The growth of Acinetobacter sp. strain HO1-N on hexadecanol results in the formation of intracytoplasmic membranes and intracellular rectangular inclusions containing one of the end products of hexadecanol metabolism, hexadecyl palmitate. The intracellular inclusions were purified and characterized as "wax ester inclusions" consisting of 85.6% hexadecyl palmitate, 4.8% hexadecanol, and 9.6% phospholipid, with a phospholipid-to-protein ratio of 0.42 mumol of lipid phosphate per mg of inclusion protein. The cellular lipids consisted of 69.8% hexadecyl palmitate, 22.8% phospholipid, 1.9% triglyceride, 4.7% mono- and diglyceride, 0.1% free fatty acid, and 0.8% hexadecanol, as compared with 98% hexadecyl palmitate and 1.9% triglyceride, which comprised the extracellular lipids. Cell-associated hexadecanol represented 0.05% of the exogenously supplied hexadecanol, with hexadecyl palmitate accounting for 14.7% of the total cellular dry weight. Acinetobacter sp. strain HO1-N possesses a mechanism for the intracellular packaging of hexadecyl palmitate in wax ester inclusions, which differ in structure and chemical composition from "hydrocarbon inclusions" isolated from hexadecane-grown cells.     

The snapping strength of the egg shells of various orders of birds

A study of the snapping strength (S) of egg shells and its relationship to the square of the thickness (T²) has been made on seven orders of birds and also in respect of a few shells of ratite birds, domestic fowl and guinea fowl.
There are considerable differences in strength between the egg shells of different orders of birds and when shells are snapped outwards the egg shells of Sphenisciformes are almost twice as strong as those of Podicipitiformes for a given thickness. The shells of the guinea fowl are very strong and those of the domestic fowl weak compared with the seven orders when they are snapped inwards.
Comparisons of the strength of shells with and without the outside chalky cover, which occurs on the egg shells of Sphenisciformes, Pelecaniformes and Podicipitiformes, show very variable relationships, while comparisons of inward and outward snapping strength indicate that in some orders the difference is great but that in others it is negligible.
The presence or absence of a cover on the shell could not explain any difference in snapping strength, nevertheless, a few tests on Pelecanus shells using impact strength showed that then the cover adds considerably to the strength. No other shell characteristics could explain the differences in snapping strength.