Synaptic Constituents in Health and Disease (eBook)

Proceedings of the Third Meeting of the European Society for Neurochemistry, Bled, August 31st to September 5th, 1980

Herman Bachelard, Miro Brzin, Dusan Sket (Herausgeber)

eBook Download: EPUB

2013 | 1. Auflage
792 Seiten
Elsevier Science (Verlag)
978-1-4831-8970-3 (ISBN)

Infos

Synaptic Constituents in Health and Disease is a collection of papers from the Proceedings of the Third Meeting of the European Society for Neurochemistry held in Yugoslavia, on August 31-September 5, 1980. This collection deals with gene analysis, the diagnosis, and treatment of inherent errors in metabolism. One paper discusses the role of vesicles in cholinergic systems in terms of the vesicle hypothesis or the cytosol hypothesis. Another paper focuses on the molecular organization of chromaffin granulles-the catecholamine-storing vesicles of the adrenal medulla. One author discusses the interaction between antibodies and receptors in receptors such as insulin, TSH, prolactin, or estrogens. Another paper examines the occurrence and postulated functions of trans-synaptic structures to find out whether some kind of structural continuity exists, beyond mere contact, between the plasma membranes of two synapsing neurons. One other paper shows that morphological evidences of damage on nerve cells in some brain areas are found after gerbils inhaling an industrial solvent, trichloroethylene (TCE), The paper also discusses general topics in neurochemistry such as the DNA turnover in rat cerebral cortex. This collection can prove invaluable for biologists, medical and chemical researchers, molecular scientists, and the neuro-chemist investigators.

Textauszug

GENE ANALYSIS AND THE DIAGNOSIS AND TREATMENT OF INBORN ERRORS OF METABOLISM

R. Williamson,     Professor of Biochemistry, St. Mary’s Hospital Medical School, University of London, London, W2 1PG, England

Publisher Summary

This chapter discusses gene analysis and the diagnosis and treatment of inborn errors of metabolism. It has become possible to isolate many gene sequences and to use these as gene-specific probes for the determination of gene organization and the study of specific gene expression. Sequences coding for common proteins made by some tissues in large amounts are first purified and then labeled to high radioactive specific activity either chemically or enzymatically. This technique (through messenger RNA isolation) is by its very nature only applicable to a very small minority of structural genes, those coding for very common tissue-specific proteins. Even for these sequences, the estimates of gene number and of expression are imprecise, because small amounts of contaminating sequences could introduce large errors in the kinetic measurements of nucleic acid reassociation. Gene libraries can be made from human nuclear DNA or from messenger RNA through reverse transcriptase, when only coding sequences specifying proteins will be cloned.

One of the features of molecular biology which makes it extremely powerful scientifically is its philosophical reductionism. To a first approximation the entire determination of both the form and function of a living organism is seen as embodied in the sequence of base pairs in the two sets of chromosomal DNA chains, inherited from the parents. Such a view of biology will appear simplistic, especially to neurobiologists, since it fails to take into account those features of individual and social activity which we understand poorly, but feel are not determined only by gene structure. However, at this moment in scientific history the oversimplified view reigns supreme, and rightly so, for it indicates the directions in which many new answers to the fundamental problems of human genetics will be found.

Until recently, the study of human genetics was the study of the inheritance of phenotypes. The segregation of characters (whether normal, such as height or eye colour, or abnormal, such as haemophilia or Huntington’s Chorea) was studied in such random matings as came the way of the clinician or the biometrician. This situation improved slightly with the visualisation of chromosomes, and the identification of certain regions of chromosomes with particular functions (such as ribosome assembly with the nucleolar organisers). However, the sheer complexity of the human genome defeated attempts to study gene sequences singly -there are approximately five million different pieces of DNA in every cell nucleus, each large enough to code for a protein the size of a globin chain.

During the past ten years, it has become possible to isolate many gene sequences, and to use these as ‘gene-specific probes’ for the determination of gene organisation and the study of specific gene expression. Sequences coding for common proteins made by some tissues in large amounts (such as serum albumen, globin and immunoglobin) were first purified and then labelled to high radioactive specific activity either chemically or enzymatically. This technique (through messenger RNA isolation) is by its very nature only applicable to a very small minority of structural genes, those coding for very common tissue-specific proteins. Even for these sequences, estimates of gene number and of expression were imprecise, because small amounts of contaminating sequences could introduce large errors in the kinetic measurements of nucleic acid reassociation.

The ability to prepare gene recombinants, in which human genes are chemically linked to bacterial viruses (plasmids or phage) and then grown as if part of the virus in clones free from all other human DNA, truly revolutionised our ability to study human genetics. Not only could any identifiable gene sequence be prepared completely pure, it also could replicate in bacteria at a high copy number and in a cell dividing in a laboratory flask. The generation time for human gene multiplication had truly been reduced from twenty years to the same number of minutes.

Gene libraries can be made from human nuclear DNA (in which case all sequences are ‘cloned’ as recombinants, including control sequences, introns, and those for which no function has been assigned) or from messenger RNA through reverse transcriptase, when only coding sequences specifying proteins will be cloned. The efficiency of the cloning systems is now such that in a matter of a few days a complete library can be prepared from ten mls of blood from a single individual. Thus it is not only possible to study human genes singly for their generalised function, but also to study them from one individual, for the particular features that his/her genes have which confer genetic individuality, whether in the normal range or for an inherited disease.

Every genetic disease has its origin in an alteration in the number, organisation or fine base sequence of a region of DNA. Such a disease may be inherited (as for the haemoglobinopathies, or the ‘inborn errors of metabolism’), but it is also useful to consider conditions such as cancer which arise by somatic mutation as genetic disease, for the same principles of gene analysis can then be applied in theory at least. Also, it is useful to divide the simple inherited diseases into those involving a single gene function (whether dominant, recessive or sex-linked) and those where a segment of chromosome is duplicated or deleted (such as Down’s syndrome). Of course, there is also the great range of conditions, ranging from coronary heart disease to diabetes and schizophrenia, which are not inherited in a simple way but where complex genetic factors involving several unlinked genes interact with poorly understood environmental components to lead to pathological states.

At the moment, any disease where a single gene alone is involved can be analysed in principle using ‘genetic engineering’ techniques. This should lead to the virtual elimination of severe single gene inherited diseases within the next couple of decades.

Consider the haemoglobinopathies, which are the most common single gene inherited defects, since they exhibit positive selection as they confer resistance to certain serious forms of malaria. Sickle cell disease and similar structural mutations in the globin chains usually are caused by a single base change in the DNA. Since the globin genes can now be cloned and the base sequence determined directly, this mutation can be demonstrated easily in an individual. So too can many other mutations which do not cause changes in protein sequence, whether because they occur in non-coding portions of the genome or give rise to an equivalent redundant codon. Such mutations are remarkably frequent, and polymorphisms are thought to occur at least once in every hundred or so base pairs along the DNA sequence. This collection of sequence polymorphisms along each genome is the individual evolutionary inheritance of every one of us, and may be said to represent in sum the determinant of genetic individuality.

Of course, sickle cell disease is well understood genetically and biochemically, and both heterozygotes and homozygotes can be identified by blood tests. However, this is difficult for a foetus - obtaining a foetal blood sample at an early age is hazardous, even in a hospital equipped with a large number of technological aids, and is well nigh impossible in a poorly equipped hospital in a third world country, where many of the persons at risk are found. Therefore, direct examination of DNA for the gene defect would be of value in such circumstances for antenatal diagnosis, since foetal cells can be obtained by amniocentesis at an early stage and without major risk to the unborn child. Such cells, although not expressing the globin genes, have them nontheless.

In the case of the haemoglobinopathies, the gene-specific probes are the globin genes themselves, and these have been cloned in bacterial plasmids - the gene sequences for each of the three common chains (α-, β- and γ-globin) are available. However, it is difficult to detect a single base change - and in any case, other ‘silent’ polymorphisms also exist which would be confused with the change causing the malfunctioning globin chain. Kan and Dozy proposed that, instead of looking at the globin gene sequence itself, the surrounding sites for specific bacterial DNases (known as restriction endonucleases) could be studied. Any polymorphismsin such sites would be linked to the defect if it only occured on the mutant chromosome, or if the sites for the parent chromosomes were known.

In the case of sickle cell disease, one restriction site (for HpaI) was found to be commonly linked to the β-gene defect in West Africans; the sickle cell β-globin gene usually gives a DNA fragment 13,000 base pairs in length with this enzyme, while the normal gene gives one approximately 7,000 base pairs long. These fragments, of course, contain much genetic material apart from the β-globin gene; in fact, the critical polymorphic site is about ten genes away from the genetic lesion. We have no idea what its function is, but assume it has merely been selected and inherited with the gene willy-nilly, a piece of genetic detritus suspended in linkage...

Produkt-Details

• Erscheint lt. Verlag: 3.9.2013
• Sprache: englisch
• Themenwelt: Sachbuch/Ratgeber ► Natur / Technik ► Naturführer
• Themenwelt: Naturwissenschaften ► Biologie
• Themenwelt: Technik
• ISBN-10: 1-4831-8970-8 / 1483189708
• ISBN-13: 978-1-4831-8970-3 / 9781483189703