Biomedical subjects

K H Cheung

Publications and source records attributed to K H Cheung.

At least 19 recordsLinked to original sources

PubMed2004

Regulation of epididymal principal cell functions by basal cells: role of transient receptor potential (Trp) proteins and cyclooxygenase-1 (COX-1).

The epithelia lining the epididymides of many species including the human are known to consist of several cell types. Among them, the principal cells are the most abundant and their functions most extensively studied. There are other cell types such as the narrow cells, clear cells, halo cells and basal cells which are scattered along the duct in lesser number. Although these minority cell types have not been studied to the same extent as the principal cells, it is conceivable that their presence are essential to the integrated functions of the epididymis. In the intact epididymis, basal cells can be seen adhering to the basement membrane forming close contact with the principal cells above them. Work in our laboratory has provided evidence that through local formation of prostaglandins, basal cells may regulate electrolyte and water transport by the principal cells. This regulatory process involves two proteins which are exclusively expressed by the basal cells. They are the transient receptor potential (Trp) proteins, which serve as transmembrane pathways for Ca(2+) influx, and cyclooxygenase 1 (COX-1), a key enzyme in the formation of prostaglandins. The role of the two proteins in the integrated functions of the basal cells as humoral regulators of principal cells is discussed.

Animals↗

PubMed2004

Secretin controls anion secretion in the rat epididymis in an autocrine/paracrine fashion.

There is growing evidence that secretin, the first hormone discovered in our history, has functions in the brain other than in the gastrointestinal tract. This article reports for the first time that secretin and its receptor mRNAs are produced in distinct cell types within the epididymis. To test if secretin affects electrolyte transport in the epididymis, we measured short-circuit current (Isc) in cultured epididymal epithelia and found secretin dose-dependently stimulated Isc. Ion substitution experiments and use of pharmacological agents inferred that the stimulated Isc is a result of concurrent electrogenic chloride and bicarbonate secretion. It is further shown that secretin and pituitary adenylate cyclase-activating polypeptide (PACAP) function via totally different mechanisms: 1) PACAP works only from the apical side of the epithelium to stimulate chloride and not bicarbonate secretion, while secretin acts on the apical and basolateral sides to stimulate chloride and bicarbonate secretion. 2) the stimulation by PACAP but not secretin requires local prostaglandin synthesis. By immunocytochemical staining, secretin is localized in the principal cells of the initial segment and caput epididymidis, whereas secretin receptor is present in the principal cells of the proximal as well as the distal part of the epididymis. This pattern of distribution appears to be consistent with the idea that secretin is secreted by the proximal epididymis and acts on the proximal and distal epididymis in an autocrine and paracrine fashion. Its function is to control secretion of electrolytes and water.

Adenylyl Cyclase Inhibitors↗

PubMed2004

Twin births in Singapore: a population-based study using the National Birth Registry.

INTRODUCTION: Twin studies are a most effective method to analyse gene and environment interactions. Using data from the Singapore National Registry of Births and Deaths (SNRBD), this paper describes the number of twin and multiple births among different ethnic populations in Singapore. MATERIALS AND METHODS: All births recorded in the SNRBD from 1 January 1986 to 31 December 2001 were analysed. Outcomes measured were twin and triple birth rates (per 1000 maternities) of the 3 main ethnic groups in Singapore (Chinese, Malays and Asian Indians). Further outcomes were calculated using Weinberg's differential rule to estimate the number of monozygotic and dizygotic twins. RESULTS: Overall twin birth rates have steadily increased across all ethnic groups (7 to 9/1000). The largest increase in multiple births among the ethnic groups were twins born to Asian Indian fathers (6.9 to 9.9/1000) and Malay mothers (5.9 to 9.8/1000). A significant difference in birth rates between the ethnic groups was found during the years 1994 to 1997, where Chinese parents had the lowest multiple birth rates and Asian Indians the highest. Estimation and ratios of monozygotic and dizygotic twin births differed among the ethnic groups: Asian Indians had the highest ratios, followed by the Chinese and, lastly, the Malays. CONCLUSION: The SNRBD has provided an overview of multiple births in Singapore, although the establishment of a national twin register would enable more detailed analysis of genetic and environmental effects in multiple births.

Asian People↗

PubMed2003

Reduction of chromate (CrO4(2-)) by an enrichment consortium and an isolate of marine sulfate-reducing bacteria.

An enrichment consortium and an isolate (isolate TKW) of sulfate-reducing bacteria (SRB) have been obtained from metal-contaminated marine sediments of Tokwawan, Hong Kong SAR. These bacteria are capable of reducing highly toxic and soluble hexavalent chromium (Cr6+) enzymatically into less toxic and insoluble trivalent chromium (Cr3+) under anaerobic conditions. The enrichment consortium almost completely (98.5%) reduced 0.6 mM Cr6+ in 168 h and the rate of reduction was 0.5 g (Cr6+) g(protein)(-1)h(-1). In comparison, with Cr6+ as the sole electron acceptor (as a surrogate for SO4(2-)), isolate TKW reduced 94.5% of the initially added Cr6+ (0.36 mM) in 288 h, with the rate of 0.26 g (Cr6+) g(protein)(-1)h(-1). Adsorption by these bacteria was not the major mechanism contributing to the transformation or removal of Cr6+. The biomass and Cr3+ in the cultures increased simultaneously with the reduction of Cr6+. These indigenous SRB might have potential application in bioremediation of metal contaminated sediments.

Adsorption↗

PubMed2002

Synergistic effects of cystic fibrosis transmembrane conductance regulator and aquaporin-9 in the rat epididymis.

The cystic fibrosis transmembrane conductance regulator (CFTR) and aquaporin-9 (AQP-9) are present in the luminal membrane of the epididymis, where they play an important role in formation of the epididymal fluid. Evidence is accumulating that CFTR regulates other membrane transport proteins besides functioning as a cAMP-activated chloride channel. We have explored the possible interaction between epididymal CFTR and AQP-9 by cloning them from the rat epididymis and expressing them in Xenopus oocytes. The effects of the expressed proteins on oocyte water permeability were studied by immersing oocytes in a hypo-osmotic solution, and the ensuing water flow was measured using a gravimetric method. The results show that AQP-9 alone caused an increase in oocyte water permeability, which could be further potentiated by CFTR. This potentiation was markedly reduced by phloretin and lonidamine (inhibitors of AQP-9 and CFTR, respectively). The regulation of water permeability by CFTR was also demonstrated in intact rat epididymis luminally perfused with a hypo-osmotic solution. Osmotic water reabsorption across the epididymal tubule was reduced by phloretin and lonidamine. Elevation of intracellular cAMP with 3-isobutyl-1-methylxanthine increased osmotic water permeability, whereas inhibiting protein kinase A with H-89 (N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline sulfonamide hydrochloride) reduced it. These results are consistent with a role for CFTR in controlling water permeability in the epididymis in vivo. We conclude that this additional role of CFTR in controlling water permeability may have an impact on the genetic disease cystic fibrosis, in which men with a mutated CFTR gene have abnormal epididymis and infertility.

Absorption↗

PubMed2002

Indazole inhibition of cystic fibrosis transmembrane conductance regulator Cl(-) channels in rat epididymal epithelial cells.

Previous studies have shown that two indazole compounds, lonidamine [1-(2,4-dichlorobenzyl)-indazole-3-carboxylic acid] and its analogue AF2785 [(1-(2,4-dichlorobenzyl)-indazol-3-acrylic acid], suppress fertility in male rats. We also found that these compounds inhibit the cystic fibrosis transmembrane conductance regulator chloride (CFTR-Cl(-)) current in epididymal epithelial cells. To further investigate how lonidamine and AF2785 inhibit the current, we used a spectral analysis protocol to study whole-cell CFTR current variance. Application of lonidamine or AF2785 to the extracellular membrane of rat epididymal epithelial cells introduced a new component to the whole-cell current variance. Spectral analysis of this variance suggested a block at a rate of 3.68 micro mol(-1)/sec(-1) and an off rate of 69.01 sec(-1) for lonidamine, and an on rate of 3.27 micro mol(-1)/sec(-1) and an off rate of 108 sec(-1) for AF2785. Single CFTR-Cl(-) channel activity using excised inside-out membrane patches from rat epididymal epithelial cells revealed that addition of lonidamine to the intracellular solution caused a flickery block (a reduction in channel-open time) at lower concentration (10 micro M) without any effect on open channel probability or single-channel current amplitude. At higher concentrations (50 and 100 micro M), lonidamine showed a flickery block and a decrease in open-channel probability. The flickery block by lonidamine was both voltage-dependent and concentration-dependent. These results suggest that lonidamine and AF2785, which are open-channel blockers of CFTR at low concentrations, also affect CFTR gating at high concentrations. We conclude that these indazole compounds provide new pharmacological tools for the investigation of CFTR. By virtue of their interference with reproductive processes, these drugs have the potential for being developed into novel male contraceptives.

Animals↗

PubMed2002

A BK(Ca) to K(v) switch during spermatogenesis in the rat seminiferous tubules.

Spermatogenesis is a complex cellular event during which the diploid germ cells differentiate and divide by mitosis and meiosis at specific time points along the spermatogenic cycle to generate the haploid spermatozoa. For this complex event to go in an orderly manner, cell differentiation and division must be precisely controlled by signals arising from within and outside the seminiferous tubules. Changes in the membrane potential of the germ cells are likely to be an important part of the signaling mechanism. We have applied the whole-cell patch clamp technique to identify and characterize ion channels in different spermatogenic cells from immature and mature rat testes fractionated by discontinuous Percoll gradient. A voltage- and Ca(2+)- dependent, outwardly rectifying current with gating and pharmacologic properties resembling the large conductance K(+) channels (BK(Ca)) was recorded from the spermatogonia and primary spermatocytes. Another voltage-dependent, outwardly rectifying current that was sensitive to 4-aminopyridine, a K(v) channel blocker, was detected in spermatocytes and early spermatids. This current is likely caused by the smaller conductance, voltage-sensitive K(+) channels (K(v)). In some spermatogonia, both the BK(Ca) channels and the K(v) channels could be simultaneously detected in the same cell. It appears that during the course of spermatogenesis, there is up-regulation of K(v) but down-regulation of BK(Ca). Reverse transcription-polymerase chain reaction, Western blot analysis, and immunohistochemistry further confirmed the differential expression of the ion channels in different spermatogenic cells. We conclude that these ion channels may play an important role in the control of spermatogenesis.

Animals↗

PubMed2001

ALFRED: an allele frequency database for diverse populations and DNA polymorphisms--an update.

ALFRED (the ALelle FREquency Database) is designed to store and disseminate frequencies of alleles at human polymorphic sites for multiple populations, primarily for the population genetics and molecular anthropology communities. Currently ALFRED has information on over 180 polymorphic sites for more than 70 populations. Since our initial release of the database we have focussed on increasing the quantity and quality of data, making reciprocal links between ALFRED and other related databases, and providing useful tools to make the data more comprehensible to the end user. ALFRED is accessible from the Kidd Lab home page (http://info.med.yale. edu/genetics/kkidd/) or from ALFRED directly (http://alfred.med.yale. edu/alfred/index.asp).

Alleles↗

PubMed2001

Expression of cystic fibrosis transmembrane conductance regulator in rat efferent duct epithelium.

The expression of cystic fibrosis transmembrane conductance regulator (CFTR) was studied in rat efferent ducts. Under whole-cell patch-clamp condition, efferent duct cells responded to intracellular cAMP with a rise in inward current. The cAMP-activated current exhibited a linear I-V relationship and time- and voltage-independent characteristics. The current was inhibited by the Cl(-) channel blocker diphenylamine 2,2'-dicarboxylic acid (DPC) in a voltage-dependent manner and reversed at 24 +/- 0.5 mV, close to the equilibrium potential for Cl(-) (30 mV), suggesting that the current was Cl(-) selective. The cAMP-activated current displayed a permeability sequence of Br(-) > Cl(-) > I(-). Short-circuit current measurement in cultured rat efferent duct epithelia also revealed a cAMP-activated inward current inhibitable by DPC. These electrophysiological properties of the cAMP-activated Cl(-) conductance in the efferent duct were consistent with those reported for CFTR. In support of the functional studies, reverse transcription polymerase chain reaction revealed the presence of CFTR message in cultured efferent duct epithelium. Immunohistochemical studies in intact rats also demonstrated CFTR protein at the apical membrane of the principal cells of efferent duct. CFTR may play a role in modulating fluid transport in the efferent duct.

Animals↗

PubMed2001

Expression of the cystic fibrosis transmembrane conductance regulator in rat spermatids: implication for the site of action of antispermatogenic agents.

To establish whether cystic fibrosis transmembrane conductance regulator (CFTR) is functionally expressed in the testis, we subjected spermatogenic cells from rat testes to analysis of CFTR mRNA, protein and channel activity. CFTR mRNA was detected in the testes of mature but not immature rats using reverse transcription-polymerase chain reaction analysis. Western blot analysis performed with a CFTR specific antibody revealed immunoreactivity in the membrane extract of spermatogenic cells. Immunohistochemical studies localized CFTR in round and elongated spermatids, but not in the fully developed spermatozoa. Using a whole-cell patch clamp technique, we recorded an inward current activated by intracellular cAMP (100 micromol/l) in round spermatids. The current displayed a linear I / V relationship and was inhibited by diphenylamine-2-carboxylate (DPC), a chloride channel blocker. Transfection of the rat germ cell CFTR cDNA into human embryonic kidney (HEK) 293 cells caused the expression of a cAMP-activated chloride current with CFTR characteristics. The current was completely blocked by the antispermatogenic agents 1-(2,4-dichlorobenzyl)-indazole-3-carboxylic acid, lonidamine (500 micromol/l) and 1-(2,4-dichlorobenzyl)-indazole-3-acrylic acid, AF2785 (250 micromol/l). These results taken together provide evidence that CFTR is differentially expressed in spermatids during spermiogenesis. We speculate that CFTR may interact with aquaporin to bring about cytoplasmic volume contraction which is an essential feature of spermiogenesis.

Animals↗

PubMed2001

Na+ reabsorption in cultured rat epididymal epithelium via the Na+/nucleoside cotransporter.

The effect of nucleoside on Na+ reabsorption via Na+/nucleoside cotransporter in cultured rat epididymal epithelia was studied by short-circuit current (Isc) technique. Guanosine added apically stimulated Isc in a dose-dependent manner, with a median effective concentration (EC50) of 7 +/- 2 microM (mean +/- SEM). Removal of Na+ from the apical bathing solution or pretreatment with a nonspecific Na+/nucleoside cotransporter inhibitor, phloridzin, completely blocked the Isc response to guanosine. Moreover, the guanosine response was abolished by pretreatment of the tissue with ouabain, a Na+/K+-ATPase inhibitor, suggesting the involvement of Na+/nucleoside cotransporter on the apical side and Na+/K+-ATPase on the basolateral side in Na+ reabsorption. In contrast, the Isc response to guanosine was not affected after desensitization of purinoceptors by ATP. Addition of the Na+/K+/2Cl- symport inhibitor bumetanide to the basolateral side or the nonspecific Cl- channel blocker diphenylamine-2-carboxylate to the apical side showed no effect on the Isc response to guanosine, excluding stimulation of Cl- secretion by guanosine as the cause of the guanosine-induced Isc. The Isc response to purine nucleoside (guanosine and inosine) was much higher than that to pyrimidine nucleoside (thymidine and cytidine). Consistent with substrate specificity, results of reverse transcription-polymerase chain reaction revealed mRNA for concentrative nucleoside transporter (CNT2), which is a purine nucleoside-selective Na+/nucleoside cotransporter in the epididymis, but not for CNT1. It is suggested that the Na+/nucleoside cotransporter (i.e., CNT2) may be one of the elements involved in Na+ and fluid reabsorption in the epididymis, thereby providing an optimal microenvironment for the maturation and storage of spermatozoa.

Absorption↗

PubMed2001

A metadata framework for interoperating heterogeneous genome data using XML.

The rapid advances in the Human Genome Project and genomic technologies have produced massive amounts of data populated in a large number of network-accessible databases. These technological advances and the associated data can have a great impact on biomedicine and healthcare. To answer many of the biologically or medically important questions, researchers often need to integrate data from a number of independent but related genome databases. One common practice is to download data sets (text files) from various genome Web sites and process them by some local programs. One main problem with this approach is that these programs are written on a case-by-case basis because the data sets involved are heterogeneous in structure. To address this problem, we define metadata that maps these heterogeneously structured files into a common eXtensible Markup Language (XML) structure to facilitate data interoperation. We illustrate this approach by interoperating two sets of essential yeast genes that are stored in two yeast genome databases (MIPS and YPD).

Databases, Genetic↗

PubMed2000

ALFRED: an allele frequency database for diverse populations and DNA polymorphisms.

We have developed a publicly accessible database (ALFRED, the ALlele FREquency Database) that catalogues allele frequency data for a wide range of population samples and DNA polymorphisms. This database is web-accessible through our laboratory (Kidd Lab) Web site: http://info.med.yale.edu/genetics/kkidd. ALFRED currently contains data on 60 populations and 156 genetic systems including single nucleotide polymorphisms (SNPs), short tandem repeat polymorphisms (STRPs), variable number of tandem repeats (VNTRs) and insertion-deletion polymorphisms. While data are not available for all population-DNA polymorphism combinations, over 2000 allele frequency tables have been entered. Our database is designed (i) to address our specific research requirements as well as broader scientific objectives; (ii) to allow researchers and interested educators to easily navigate and retrieve data of interest to them; and (iii) to integrate links to other related public databases such as dbSNP, GenBank and PubMed.

Alleles↗

PubMed2000

TRIPLES: a database of gene function in Saccharomyces cerevisiae.

Using a novel multipurpose mini-transposon, we have generated a collection of defined mutant alleles for the analysis of disruption phenotypes, protein localization, and gene expression in Saccharomyces cerevisiae. To catalog this unique data set, we have developed TRIPLES, a Web-accessible database of TRansposon-Insertion Phenotypes, Localization and Expression in Saccharomyces. Encompassing over 250 000 data points, TRIPLES provides convenient access to information from nearly 7800 transposon-mutagenized yeast strains; within TRIPLES, complete data reports of each strain may be viewed in table format, or if desired, downloaded as tab-delimited text files. Each report contains external links to corresponding entries within the Saccharomyces Genome Database and International Nucleic Acid Sequence Data Library (GenBank). Unlike other yeast databases, TRIPLES also provides on-line order forms linked to each clone report; users may immediately request any desired strain free-of-charge by submitting a completed form. In addition to presenting a wealth of information for over 2300 open reading frames, TRIPLES constitutes an important medium for the distribution of useful reagents throughout the yeast scientific community. Maintained by the Yale Genome Analysis Center, TRIPLES may be accessed at http://ycmi.med.yale.edu/ygac/triples.htm

DNA Transposable Elements↗

PubMed2000

An integrated web interface for large-scale characterization of sequence data.

Large-scale genome projects require the analysis of large amounts of raw data. This analysis often involves the application of a chain of biology-based programs. Many of these programs are difficult to operate because they are non-integrated, command-line driven, and platform-dependent. The problem is compounded when the number of data files involved is large, making navigation and status-tracking difficult. To demonstrate how this problem can be addressed, we have created a platform-independent Web front end that integrates a set of programs used in a genomic project analyzing gene function by transposon mutagenesis in Saccharomyces cerevisiae. In particular, these programs help define a large number of transposon insertion events within the yeast genome, identifying both the precise site of transposon insertion as well as potential open reading frames disrupted by this insertion event. Our Web interface facilitates this analysis by performing the following tasks. Firstly, it allows each of the analysis programs to be launched against multiple directories of data files. Secondly, it allows the user to view, download, and upload files generated by the programs. Thirdly, it indicates which sets of data directories have been processed by each program. Although designed specifically to aid in this project, our interface exemplifies a general approach by which independent software programs may be integrated into an efficient protocol for large-scale genomic data processing.

Clinical Laboratory Information Systems↗

PubMed2000

ALFRED: a Web-accessible allele frequency database.

We present a Web-accessible database (ALFRED) that allows public access to gene frequency data for a diverse set of population samples and genetic systems. The data in ALFRED are modeled based on the experience and needs of a single laboratory, but with the expectation that the database will meet the needs of a much broader scientific community that needs population-specific gene frequency estimates. Our database currently contains data on more than 40 populations representing most major regions of the world and data on more than 150 genetic systems including SNPs, STRPs, and insertion-deletion polymorphisms. While data are not available for all population-genetic system combinations, over 2000 allele frequency tables already exist. In this paper, we enumerate the broad needs in the scientific domain, describe their significance, and describe how we have designed the database to meet those needs. We compare our database with dbSNP, the NCBI database that has a broader but overlapping purpose.

Alleles↗

PubMed2000

Graphically-enabled integration of bioinformatics tools allowing parallel execution.

Rapid analysis of large amounts of genomic data is of great biological as well as medical interest. This type of analysis will greatly benefit from the ability to rapidly assemble a set of related analysis programs and to exploit the power of parallel computing. TurboGenomics, which is a software package currently in its alpha-testing phase, allows integration of heterogeneous software components to be done graphically. In addition, the tool is capable of making the integrated components run in parallel. To demonstrate these abilities, we use the tool to develop a Web-based application that allows integrated access to a set of large-scale sequence data analysis programs used by a transposon-insertion based yeast genome project. We also contrast the differences in building such an application with and without using the TurboGenomics software.

Computational Biology↗

PubMed1999

Large-scale analysis of the yeast genome by transposon tagging and gene disruption.

Economical methods by which gene function may be analysed on a genomic scale are relatively scarce. To fill this need, we have developed a transposon-tagging strategy for the genome-wide analysis of disruption phenotypes, gene expression and protein localization, and have applied this method to the large-scale analysis of gene function in the budding yeast Saccharomyces cerevisiae. Here we present the largest collection of defined yeast mutants ever generated within a single genetic background--a collection of over 11,000 strains, each carrying a transposon inserted within a region of the genome expressed during vegetative growth and/or sporulation. These insertions affect nearly 2,000 annotated genes, representing about one-third of the 6,200 predicted genes in the yeast genome. We have used this collection to determine disruption phenotypes for nearly 8,000 strains using 20 different growth conditions; the resulting data sets were clustered to identify groups of functionally related genes. We have also identified over 300 previously non-annotated open reading frames and analysed by indirect immunofluorescence over 1,300 transposon-tagged proteins. In total, our study encompasses over 260,000 data points, constituting the largest functional analysis of the yeast genome ever undertaken.

Algorithms↗