Gene Function & Disease最新文献

The mammalian auditory sense organ is subdivided into three principle compartments, the outer-, middle- and inner ear. The main task of the outer- and middle ear is to channel sound waves towards the cochlea within the inner ear. The inner ear also contains the vestibule, the end organ for the perception of gravity and acceleration. Hair cells within the sensory epithelia of the cochlea and the vestibule contain stereocilia that harbor mechanically gated ion channels. These ion channels open or close upon deflection of the stereocilia leading to changes in cell polarization and the rate of neurotransmitter release from hair cells onto sensory neurons. In this way, mechanical signals evoked by sound waves or head movement are transformed into electrochemical signals. The positional cloning of human disease genes and the analysis of mouse mutants has led to the identification of numerous genes that cause deafness and balance disorders. These findings provide insights into the molecular and cellular requirements for mechanosensory transduction and establish an entry point to understand deafness at the molecular level. We will summarize results that have shed light on the function of extracellular matrix glycoproteins, cell adhesion molecules, and components of the actin cytoskeleton in the inner ear.

Farnesyltransferase inhibitors (FTIs) represent a novel class of anti-cancer drugs with preferential effects on transformed cells. FTIs are currently evaluated in clinical trials. They are developed with the idea to inhibit farnesylation and membrane association of proteins such as Ras. In support of this idea, FTIs are effective in interfering with phenotypes due to H-ras activation, although K-ras activated events are resistant to FTIs. Recent studies on farnesylated proteins also raised the possibility that FTIs affect farnesylated proteins other than H-ras. To gain insight into this possibility, we have examined cellular effects of FTIs on human cancer cells. We, as well as others, have observed that FTIs cause enrichment of G0/G1-phase cells with a number of cancer cells. In addition, FTIs affect proteins involved in cell cycle regulation, such as retinoblastoma protein, p21^Waf1/Cip1 and cyclins. With some cancer cell lines, FTI causes G2/M enrichment. Proteins, such as farnesylated Rho proteins and centromere binding proteins CENP-E/F may play roles in these cell cycle effects.

RNA binding proteins are involved in a diverse array of biological functions including mRNA transport, splicing, localization, stability and translation. Jerky is an RNA binding protein, complexed with mRNAs in neurons, that regulates mRNA utilization and consequently translation. The mouse line defective in the jerky gene shows recurrent seizures; a hallmark of epilepsy. Lack of FMRP (Fragile X Mental Retardation Protein), another RNA binding protein involved in mRNA processing and translation, also results in seizures in mice. This finding is consistent with the high incidence of epilepsy in fragile X syndrome. These two mutant mice are examples of a seizure condition elicited by a deficiency in RNA binding proteins. It is hypothesized that lack of Jerky and FMRP results in the abnormal translation of target-RNAs compromising the development and/or function of neurons. It is known that perturbation of neuronal development/function can result in recurrent seizures. The seizure phenotype of Jerky and FMRP deficient mice raises the possibility that a dysfunction in RNA binding proteins may be a more general disease mechanism in epilepsy.

The elucidation of the pathogenesis of inherited and acquired disorders will stimulate the design of novel therapies. Somatic gene therapy may become a very interesting alternative or addition to many drug-based treatment modalities. Efficient and non-toxic gene delivery is critical for a successful implementation of somatic gene therapy. High-capacity adeno�viral (HC-Ad) vectors have some features that make them very promising reagents to achieve this goal. With low toxicity, they can efficiently transduce different primary cell types in vitro and in vivo. In addition, they can deliver DNA fragments with sizes of up to 35 kb which allows the simultaneous expression of several genes or the tight control of gene expression by including regulatory control elements. Preclinical studies in mice suggest that long-term gene expression can be achieved from this vector type. Thus, safety, duration of expression, and versatility is considerably improved compared to previous-generation adenoviral vectors.

Genomic imprinting is a curious manifestation of epigenetic inheritance that defies normal Mendelian genetics. Most vertebrate genes are expressed from both, the paternal and maternal alleles. However, a subset of mammalian genes is monoallelically expressed in a parent-of-origin manner due to imprinting mechanisms that confer a parent-specific memory to individual cells. Epigenetically correct inheritance of imprinted genes requires appropriate germ-line specific chromosomal modifications like histone acetylation or DNA methylation. Some of these modified, imprinted genes are organized in clusters as exemplified by the 2 Mb domain on human chromosome 15q11-q13. Deletion, uniparental disomy (UPD), or inappropriate imprinting of this chromosomal region results in the neurogenetic disorders Prader-Willi syndrome (PWS) and Angelman syndrome (AS), respectively. Recently, new genes and regulatory mechanisms that contribute to imprint regulation within the affected regions have been characterized. This review focuses on the role of these imprinted genes on human chromosome 15q11-13, imprinting center elements, and epigenetic mechanisms in the development of specific regions of the mammalian brain.

Monoamine oxidases A and B (MAOA and MAOB) have been suggested to be involved in human behavior and neuropsychiatric disorders. These observations were supported by several lines of evidence provided by pharmacological studies as well as enzyme deficiency investigations in humans and model animals. Numerous allelic association studies have attempted to detect a link between different alleles of the genes encoding monoamine oxidases and certain complex human traits. Many of these studies have reported contradictory findings, probably due to population stratification and limitations of the experimental and statistical designs used in the studies. Here, we review all the genetic variants described for the MAO genes, we summarize the allelic associations found with different traits, and we discuss these results in the context of the factors that affect detection of allelic association. Finally, we discuss the advantages of the use of haplotypes for studying associations with human traits.

β-D-N-acetylhexosaminidases A (Hex A, αβ) and B (Hex B, ββ) cleave N-acetylglucosamine and N-acetylgalactosamine termini of glycoconjugates. Hex B hydrolyzes neutral substrates whereas Hex A also hydrolyzes electronegative substrates, including GM₂ ganglioside, which accumulates in the neurons of patients with Tay-Sachs disease (TSD). We hypothesized that enzyme-substrate electrostatic interactions influence substrate specificities of the two isozymes. Among seven positively charged candidate residues in Hex A, at which substitution for the homolgous β residue was performed, only the α424R→L mutation resulted in loss of activity toward the electronegative substrate 4-methylumbellifery-N-acetylglucosamine-6-sulfate (4MUGS). The substitution L→R at the homolgous β position 453 increased Hex B activity to 4MUGS 5-fold. αR453 projects into the α-subunit substrate cavity opposite three active site amino acids. The adjacent residue, βD452, may repel negatively charged substrates. Double substitution, βL453R and βD452→N (the α-subunit homologue), increases 4MUGS hydrolysis by 22-fold relative to wild type Hex B. These results indicate that the homology model for hexosaminidase gives an accurate picture of the active site region and may furnish other candidate residues to test as determinants of the unique substrate specificity of Hex A.

The I269L (c.805A→C) and R270K (c.809G→A) mutations in exon 7 of the human phenylalanine hydroxylase (PAH) gene were identified in the Portuguese phenylketonuric (PKU) population with a frequency of 0.4 % and 6.2 %, respectively. To confirm that these changes at the DNA level are responsible for the PKU phenotype presented by those patients, and to establish a correlation between the genotype and the presented phenotype, these two mutations were produced in a prokaryotic expression system and characterized. In the present study we show that, using the pTrcHis system, the R270K mutation results in a severe loss of PAH enzyme activity and that mutation I269L only causes a moderate reduction in the specific activity of the enzyme. The obtained results are compatible with the clinical/metabolic phenotype of the affected patients.

In the intestinal tract of mammals, the organism is constantly being exposed to a large amount of foreign DNA in the food supply. The intestinal wall contains one of the largest defence systems of the organism. For a number of projects in biomedical research, investigations on the DNA recovered from the contents of the gastrointestinal tract have become increasingly important. In the present report, different methods for the purification of DNA from the gut contents have been compared for the efficacy of extraction and for the quality of DNA obtained. We have also initiated studies on the influence of the fiber content in the daily food supply on the fate of food-ingested DNA in the intestinal tract of mice.