Studies on the origin of milk fat. A further study of bovine serum lipoproteins and an estimation of their contribution to milk fat

1. Tritium-labelled palmitic acid combined in olive-oil triglycerides was introduced into the rumen of a lactating cow and the specific radioactivity of the lipids of milk and of the lipoproteins of both jugular and mammary venous serum was measured. 2. As previously found in a similar experiment with [(3)H]stearic acid, the specific radioactivity of the triglyceride fraction of the dextran sulphate-precipitable lipoproteins reached a maximum earlier and greater than that of the milk fat. 3. This fraction was the only lipid separated that had a significant arteriovenous difference in concentration, and is therefore identified as the main circulating lipid precursor of milk fat. 4. Although the non-esterified fatty acids showed no arteriovenous difference in concentration, they showed a negative difference in specific radioactivity that could have occurred only at the expense of the triglycerides of the precipitable lipoproteins. 5. The mean specific radioactivity of the triglycerides immediately after removal from the blood is calculated and shown to be very close in value to that of the corresponding fraction in mammary venous serum. 6. By comparison of the mean specific radioactivities of milk fat and of this precursor, its contribution is calculated as 36%. 7. This value is discussed with reference to the concentration of C(16) and C(18) fatty acids in milk fat and it is concluded that substantial amounts of these acids must have been derived from a source other than preformed circulating lipids.     

Exploring the assumptions underlying genetic variation in host nematode resistance (Open Access publication)

The wide range of genetic parameter estimates for production traits and nematode resistance in sheep obtained from field studies gives rise to much speculation. Using a mathematical model describing host – parasite interactions in a genetically heterogeneous lamb population, we investigated the consequence of: (i) genetic relationships between underlying growth and immunological traits on estimated genetic parameters for performance and nematode resistance, and (ii) alterations in resource allocation on these parameter estimates. Altering genetic correlations between underlying growth and immunological traits had large impacts on estimated genetic parameters for production and resistance traits. Extreme parameter values observed from field studies could only be reproduced by assuming genetic relationships between the underlying input traits. Altering preferences in the resource allocation had less pronounced effects on the genetic parameters for the same traits. Effects were stronger when allocation shifted towards growth, in which case worm burden and faecal egg counts increased and genetic correlations between these resistance traits and body weight became stronger. Our study has implications for the biological interpretation of field data, and for the prediction of selection response from breeding for nematode resistance. It demonstrates the profound impact that moderate levels of pleiotropy and linkage may have on observed genetic parameters, and hence on outcomes of selection for nematode resistance.     

The distribution of GAWK-like immunoreactivity in neuroendocrine cells of the human gut, pancreas, adrenal and pituitary glands and its co-localisation with chromogranin B

GAWK is a recently discovered peptide isolated from extracts of human pituitary gland and subsequently shown to be identical to sequence 420-493 of human chromogranin B. The distribution of this peptide was studied in human gut, pancreas, adrenal and pituitary glands using antisera to two portions of the 74 amino acid peptide (sequences 1-17 and 20-38). In addition, the co-existence of GAWK immunoreactivity with other peptides and chromogranin B was investigated using comparative immunocytochemistry. In the gut, GAWK was localised mainly to serotonin-containing cells of the mucosal epithelium, where electron microscopy showed it to be stored in typical electron-dense (250 nm diameter) granules, and to a moderate population of nerve fibres in the gut wall. Considerable quantities of GAWK-like immunoreactivity were measured in the gut, up to 36.3 +/- 18 pmol GAWK 1-17/g wet weight of tissue (mean +/- SEM) and 12.4 +/- 2.9 pmol GAWK 20-38/g. Chromatography of gut extracts revealed several GAWK-like immunoreactive peaks. GAWK-like immunoreactivity was also detected in endocrine cells of pancreas, pituitary gland and adrenal medulla, where the highest concentrations of GAWK-like immunoreactivity were measured (GAWK 1-17 2071.8 +/- 873.2 and GAWK 20-38 1292.7 +/- 542.7 pmol/g). Endocrine cells containing GAWK-like immunoreactivity were found also to be immunoreactive for chromogranin B. Our results define a discrete distribution of GAWK immunoreactivity in human endocrine cells and nerves and provide morphological support for the postulated precursor-product relationship between chromogranin B and GAWK. Details of the functions of this peptide are awaited.     

Nucleic acid and protein sequence databases

Nucleic acid and protein sequences contain a wealth of informationof interest to molecular biologists. The advent of molecularsequence databases provides a unique opportunity for the computeranalysis of all available sequences. Sequence databases servetwo main functions: (i) to facilitate comparisons with newlydetermined sequences, and (ii) to act as a source of data forthe generation and testing of hypotheses concerning molecularsequence organisation and evolution. The large amounts of sequencedata now becoming available require that algorithms for databasesearching be fast and efficient and considerable progress isbeing made in this area.     

Genomic imprinting of chromatin inDrosophila melanogaster

During gametogenesis, chromosomes may become imprinted with information which facilitates proper expression of the DNA in offspring. We have used a position effect variegation mutant as a reporter system to investigate the possibility of imprinting inDrosophila melanogaster. Genetic crosses were performed in which the variegating gene and a strong modifier of variegation were present either within the same parental genome or in opposite parental genomes in all possible combinations. Our results indicate that the presence of the variegating chromosome and a modifier chromosome in the same parental genome can alter the amount of variegation formed in progeny. The genomic imprinting we observed is not determined by the parental origin of the variegating chromosome but is instead determined by the genetic background the variegating chromosome is subjected to during gametogenesis.