An assessment of validation techniques for estimating chlorophyll-a concentration from airborne multispectral imagery

Accurate estimates of chlorophyll-a levels in coastal waters are required for the assessment of waters potentially subject to eutrophication. Traditional laboratory analysis of water samples does not offer the required spatial or temporal density of sampling. Remote sensing methods have been suggested as a more appropriate representation of the variability in chlorophyll a concentration encountered in UK coastal waters. This paper examines the use of two established techniques for the calibration of airborne multispectral imagery to determine chlorophyll-a concentration: the blue/green ratio and Fluorescence Line Height methods. These methods have been developed for use in oceanic or Canadian coastal waters. The errors incurred in the use of these techniques for calibration of data of UK coastal waters have not previously been addressed. This paper describes a rigorous assessment of the errors incurred, allowing the limitations of the techniques to be established. This has resulted in recommendations for chlorophyll-a measurement in the coastal zone.     

The substitution of proline 35 by alanine in Rhodobacter capsulatus cytochrome c2 affects the overall protein stability but not the alkaline transition

It was shown by Koshy et al. [1990, Proc. Natl Acad. Sci USA, 87, 8697- 8701; 1994, Biochem. J., 299, 347-350] that the substitution of proline 30 by alanine (P30A) of Drosophila melanogaster and rat cytochromes c exhibited decreased stabilities in both the heme iron-methionine sulfur (Fe-S) bond and overall protein conformation. Now we have found that the stability properties of the equivalent mutant of Rhodobacter capsulatus cytochrome c2 (P35A) are somewhat different. Based on optical and NMR spectroscopies, the Rb.capsulatus P35A alkaline transition (pKalk) was found to be unchanged with respect to the wild type, suggesting that the mutation in Rb.capsulatus cytochrome c2 has little effect on the stability of the Fe-S bond. However, Rb.capsulatus conformational stability was found to be decreased by 1.6 kcal/mol in the oxidized state. The difference in the stability properties of the equivalent proline to alanine substitutions in various species underscores the importance of studying mutations in more than one species before drawing generalizations about the role of conserved residues in protein structure and function.      

Immunohistochemical localization of xanthine oxidase in human retina

Xanthine oxidase has been established as an important source of oxygen free radicals in ischemia-reperfusion injury. It has been localized in many different tissues such as heart and intestine, but it has not yet been localized in the eye. Xanthine oxidase was detected using immunohistochemistry on paraformaldehyde/glutaraldehyde fixed cryosections. Antibodies used included rabbit antibovine xanthine oxidase antibody and rabbit antihuman xanthine oxidase antibody. Xanthine oxidase was detected in the capillary endothelium cells of blood vessels in the retina of bovine and post mortem human eyes. Whole mount preparation of human retinas showed xanthine oxidase present throughout the small capillary network. Furthermore, whole mounts showed that xanthine oxidase was present in cones. This was confirmed by using mouse anticalbindin antibody for co-labelling. It is possible that xanthine oxidase can be a source of oxidative damage in the retina following ischemia-reperfusion injury.     

Late-onset pseudarthrosis of the dysplastic tibia

Eleven children in whom a tibial fracture occurred after minor trauma had pre-existing dysplastic changes evident radiographically. These changes included cortical tapering, sclerosis, and formation of a cyst in the region of the medullary canal. Ten of the eleven patients had had no more fractures an average of fifteen years after the most recent fracture. Six of the fractures healed following prolonged immobilization in a cast, but four of the six tibiae were abnormally bowed anteriorly, and it was thought that a stress fracture could occur in the future. Four of the patients had a clinically straight tibia and radiographic evidence of thick cortices following corrective osteotomy, intramedullary fixation with bone-grafting, and prolonged immobilization in a cast. At the most recent follow-up examination, the eleventh patient had a persistent pseudarthrosis despite several operative procedures. While there were too few patients in this series for us to draw definite conclusions, our findings suggest that late-onset pseudarthrosis of a dysplastic tibia has a better prognosis than does congenital pseudarthrosis.     

Detection of hepatitis A virus in oysters

A digoxigenin-labelled RNA probe with a sensitivity of 800 50% tissue culture infectious dose (TCID₅₀) was used to detect Hepatitis A Virus (HAV) in oysters. We studied the influence of extraction methodology on riboprobe detection. Oyster samples obtained by four methods of extraction and extraction-concentration were spiked with HAV (CF53 strain). There was no correlation between protein concentration and turbidity of samples, and anti-digoxigenin antibodies showed a non specific reaction. Background noise was independent of protein concentration and disappeared when HAV RNA isolation by phenol/chloroform extraction was introduced, but HAV RNA could not be detected by this technique. In the presence of Acid Guanidinium Thiocyanate (AGT), RNA from HAV suspension was detected following phenolic extraction with a detection threshold of 8.10⁴ TCID₅₀ of spotted virus. HAV detection in oyster extract by a digoxigenin-labelled riboprobe appeared useful in shellfish virology, at least for a primary screening of samples.     

Tests and estimates of allelic association in complex inheritance

Family-based procedures such as the transmission disequilibrium test (TDT) were motivated by concern that sample-based methods to map disease genes by allelic association are not robust to population stratification, migration, and admixture. Other factors to consider in designing a study of allelic association are specification of gene action in a weakly parametric model, efficiency, diagnostic reliability for hypernormal individuals, interest in linkage and imprinting, and sibship composition. Family-based samples lend themselves to the TDT despite its inefficiency compared with cases and unrelated normal controls. The TDT has an efficiency of 1/2 for parent-offspring pairs and 2/3 for father-mother-child trios. Against cases and hypernormal controls, the efficiency is only 1/6 on the null hypothesis. Although dependent on marker gene frequency and other factors, efficiency for hypernormal controls is always greater than for random controls. Efficiency of the TDT is increased in multiplex families and by inclusion of normal sibs, approaching a case-control design with normal but not hypernormal controls. Isolated cases favor unrelated controls, and only in exceptional populations would avoidance of stratification justify a family-based design to map disease genes by allelic association.     

Morphologically docked synaptic vesicles are reduced in synaptotagmin mutants of Drosophila

Nerve terminal specializations include mechanisms for maintaining a subpopulation of vesicles in a docked, fusion-ready state. We have investigated the relationship between synaptotagmin and the number of morphologically docked vesicles by an electron microscopic analysis of Drosophila synaptotagmin (syt) mutants. The overall number of synaptic vesicles in a terminal was reduced, although each active zone continued to have a cluster of vesicles in its vicinity. In addition, there was an increase in the number of large vesicles near synapses. Examining the clusters, we found that the pool of synaptic vesicles immediately adjacent to the presynaptic membrane, the pool that includes the docked population, was reduced to 24 +/- 5% (means +/- SEM) of control in the sytnull mutation. To separate contributions of overall vesicle depletion and increased spontaneous release from direct effects of synaptotagmin on morphological docking, we examined syt mutants in an altered genetic background. Recombining syt alleles onto a second chromosome bearing an as yet uncharacterized mutation resulted in the expected decrease in evoked release but suppressed the increase in spontaneous release frequency. Motor nerve terminals in this genotype contained more synaptic vesicles than control, yet the number of vesicles immediately adjacent to the presynaptic membrane near active zones was still reduced (33 +/- 4% of control). Our findings demonstrate that there is a decrease in the number of morphologically docked vesicles seen in syt mutants. The decreases in docking and evoked release are independent of the increase in spontaneous release. These results support the hypothesis that synaptotagmin stabilizes the docked state.     

The molecular basis of long QT syndrome and prospects for therapy

Long QT syndrome (LQT) is a cardiac disorder that causes sudden death from ventricular tachyarrhythmias, specifically torsade de pointes. Two types of LQT have been reported, autosomal-dominant LQT (Romano-Ward syndrome) and autosomal-recessive LQT (Jervell and Lange-Nielsen syndrome); Jervell and Lange-Nielsen syndrome is also associated with deafness. Four LQT genes have been identified for autosomal-dominant LQT: K+ channel genes KVLQT1 on chromosome 11p15.5, HERG on 7q35-36 and minK on 21q22, and the cardiac Na+ channel gene SCN5A on chromosome 3p21-24. Two genes, KVLQT1 and minK, have been identified for Jervell and Lange-Nielsen syndrome. Genetic testing and gene-specific therapies are available for some LQT patients.