Interdependent MHC-DRB exon-plus-intron evolution in artiodactyls

Exon 2 sequences of an expressed MHC-DRB locus from sheep were examined for polymorphisms in both the antigen-binding regions and the adjacent intronic mixed simple tandem repeat. Twenty-one novel exon 2 Ovar-DRB alleles were identified. Short nucleotide motifs are extensively shared between certain exon 2 regions of Ovar-DRB alleles. The simple repeat variations, the number of different amino acids at usually polymorphic sites, and the number of silent substitutions were reduced in the intraspecies analyses of sheep DRB sequences, compared with those of cattle and goats. It was paradoxical that the abundance of different sheep alleles was similar to that of cattle and goats. This paradox may be explained by postulating a relatively small number of "ancient" alleles, with the present-day Ovar-DRB alleles being generated by reciprocal exchange of nucleotide motifs. At the antigen-binding sites, new combinations of amino acids were maintained in Ovar-DRB alleles by strong positive selection. In sheep--and less pronounced in goats and cattle--the DRB alleles can be divided into two groups. In one group, silent substitutions are increased when compared with the other. This suggests separate evolutionary pathways for certain groups of DRB alleles within a species. The simple repetitive sequences are also discussed with respect to the evolution of DRB alleles.      

Protein metabolism and survival of rat hepatocytes in early culture

Rat hepatocytes, cultured in a serum- and hormone-free medium on a substratum of adsorbed fibronectin, are in negative protein balance throughout the first 24 h of culture. The rate of protein loss at all times equals the difference between the high rate of protein degradation and the low rate of protein synthesis. A continuous decline in the rate of protein degradation gradually reduces the loss of protein, probably the result of medium conditioning as well as progressive culture deterioration. Inhibition of lysosomal protein degradation by amino acids and the protease inhibitor, leupeptin, reduces the protein loss considerably, but does not prevent cell death. The protein balance per se thus does not seem to be the limiting factor for the survival of cultured hepatocytes.     

Negative regulation of airway responsiveness that is dependent on gammadelta T cells and independent of alphabeta T cells.

The mechanisms regulating airway function are complex and still poorly understood. In diseases such as asthma, involvement of immune-dependent mechanisms has been suggested in causing changes in airway responsiveness to bronchoconstrictors. We now demonstrate that gammadelta T cells can regulate airway function in an alphabeta T cell-independent manner, identifying them as important cells in pulmonary homeostasis. This function of gammadelta T cells differs from previously described immune-dependent mechanisms and may reflect their interaction with innate systems of host defense.     

Major morphological effects of a regulatory gene: Pgm1-t in rainbow trout

We have investigated the morphological effects of a genetic locus, Pgm1- t, that affects the expression of a phosphoglucomutase locus (Pgm1) in liver of rainbow trout (Salmo gairdneri). We have previously shown that embryos with liver Pgm1 expression hatch earlier than those without liver Pgm1 expression. We predicted that this difference in developmental rate should cause a reduction in meristic counts in the more rapidly developing fish with liver Pgm1 expression. Eight meristic (countable) characters in nine full-sib groups segregating for the presence or absence of liver Pgm1 expression are in agreement with this prediction. In eight of the nine families, there is a significant difference in the multivariate distribution of the eight meristic counts between full sibs with and without liver Pgm1 expression. This separation in multivariate space is based on a tendency for lower meristic counts in fish with liver Pgm1 expression. The magnitude of these morphological differences is similar to that between two subspecies of cutthroat trout (Salmo clarki) that show substantial genetic divergence at structural loci encoding enzymes (Nei's D = 0.34). These data support the view that small changes in the developmental process caused by genetic differences at regulatory genes can have large effects on morphology.      

Abscisic acid biosynthesis and catabolism and their regulation roles in fruit ripening

Abscisic acid (ABA) plays a series of significant physiology roles in higher plants including but not limited to promote bud and seed dormancy, accelerate foliage fall, induce stomatal closure, inhibit growth and enhance resistance. Recently, it has been revealed that ABA also has an important regulator role in the growth, development and ripening of fruit. In higher plants ABA is produced from an indirect pathway from the cleavage products of carotenoids. The accumulation of endogenous ABA levels in plants is a dynamic balance controlled by the processes of biosynthesis and catabolism, through the regulation of key ABA biosynthetic gene and enzyme activities. It has been hypothesized that ABA levels could be part of the signal that trigger fruit ripening, and that ABA may play an important role in the regulation of ripening and senescence of both non-climacteric and climacteric fruit. The expensive costs of natural ABA and labile active ABA for its chemical synthesis limit its application in scientific research and agricultural production. These findings that ABA has various of important roles in the regulation of growth and development, quality formation, coloring and softening, ripening and senescence of fruit, are providing opportunities and challenges for Horticultural Science. This is to elucidate the specific mechanism of response and biosynthesis, signal transduction, and receptor recognition of ABA in fruit, employing comprehensive research methods, such as molecular biology, plant physiology and molecular genetics. Further and more in-depth research about ABA has a great, realistic significance for knowing the mechanisms behind the process of fruit ripening.     

Local CD11c+ MHC class II- precursors generate lung dendritic cells during respiratory viral infection, but are depleted in the process

Increases in numbers of lung dendritic cells (DC) observed during respiratory viral infections are assumed to be due to recruitment from bone marrow precursors. No local production has been demonstrated. In this study, we isolated defined populations of murine lung cells based on CD11c and MHC class II (MHC II) expression. After culture for 12 days with GM-CSF, we analyzed cell numbers, DC surface markers, and Ag-presenting capacity. Only CD11c+ MHC II- cells from naive mice proliferated, yielding myeloid DC, which induced Ag-specific proliferation of naive T cells. After respiratory syncytial virus (RSV) infection, numbers of pulmonary CD11c+ MHC II- precursor cells were significantly reduced and DC could not be generated. Moreover, RSV infection prevented subsequent in vivo expansion of pulmonary DC in response to influenza infection or LPS treatment. These results provide direct evidence of local generation of fully functional myeloid DC in the lung from CD11c+ MHC II(-) precursor cells that are depleted by RSV infection, leading to an inability to expand lung DC numbers in response to subsequent viral infection or exposure to bacterial products. This depletion of local DC precursors in respiratory viral infections may be important in explaining complex interactions between multiple and intercurrent pulmonary infections.     

Interaction of hexane phosphonic acid diethyl ester with phospholipids in hepatic microsomes and reconstituted liposomes as studied by 31P-NMR

By use of 31P-NMR, quasi-elastic light scattering and freeze-fracture electron microscopy it is shown that hexane phosphonic acid diethyl ester (PAE) is incorporated in hepatic microsomes without any alteration of the bilayer structure at two different sites. These findings proved that PAE can be used as molecular 31P-NMR probe in microsomes to get information about lipid-protein interactions. Extensive studies on reconstituted liposomal systems which contained cytochrome P-450 and cytochrome P-450 reductase showed that both proteins influence the localization of incorporated PAE. The results indicate a specific interaction of phosphatidylethanolamine (PE) with cytochrome P-450 in microsomes.     

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