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Biomedical subjects

M O Díaz

Publications and source records attributed to M O Díaz.

8 recordsLinked to original sources
PubMed1997

Changes in telomerase activity and telomere length during human T lymphocyte senescence.

It has been proposed that telomeres shorten with every cell cycle because the normal mechanism of DNA replication cannot replicate the end sequences of the lagging DNA strand. Telomerase, a ribonucleoprotein enzyme that synthesizes telomeric DNA repeats at the DNA 3' ends of eukaryotic chromosomes, can compensate for such shortening, by extending the template of the lagging strand. Telomerase activity has been identified in human germline cells and in neoplastic immortal somatic cells, but not in most normal somatic cells, which senesce after a certain number of cell divisions. We and others have found that telomerase activity is present in normal human lymphocytes and is upregulated when the cells are activated. But, unlike the immortal cell lines, presence of telomerase activity is not sufficient to make T cells immortal and telomeres from these cells shorten continuously during in vitro culture. After senescence, telomerase activity, as detected by the TRAP technique, was downregulated. A cytotoxic T lymphocyte (CTL) cell line that was established in the laboratory has very short terminal restriction fragments (TRFs). Telomerase activity in this cell line is induced during activation and this activity is tightly correlated with cell proliferation. The level of telomerase activity in activated peripheral blood T cells, the CTL cell line, and two leukemia cell lines does not correlate with the average TRF length, suggesting that other factors besides telomerase activity are involved in the regulation of telomere length.

Adult↗
PubMed1996

Type I interferon genes and proteins.

The large number of type I interferon genes in mammalian species could be explained by simple redundancy, by different functions for different interferons, or by different spatial or temporal patterns of expression. Different functions would require different receptors for each interferon, while different patterns of expression would require different transcriptional or postranscriptional regulatory mechanisms. It is also necessary to explain when and how this diversity was achieved. Information on comparative genetics of the interferon system, cloning of new interferon genes, studies on receptor interactions and studies on gene expression are accrued at each of the annual meetings of the ISICR. The last meeting held on October 2-7, 1994, at Budapest was not an exception, and this review summarizes some of this year's reports.

Animals↗
PubMed1994

Mapping a putative tumor suppressor gene on chromosome 9 bands p21-p22 with microdissection probes.

Deletions of the short arm of chromosome 9 have been observed in a number of malignant cell lines and primary tumor samples using cytogenetic and molecular techniques. These tumors include acute lymphoblastic leukemias, lymphomas, gliomas, melanomas, mesotheliomas, bladder cancer, and lung cancer. The smallest region of overlap (SRO) of these deletions is thought to contain a tumor suppressor gene. A microdissection library was constructed from bands 9p21-p23 to obtain DNA probes that would be useful in further defining the limits of the deletions. Eight single-copy probes were found to be homozygously deleted in at least 1 of the 10 cell lines examined. The mapping of these 8 clones using a panel of cell lines with deletions revealed that 3 probes mapped telomeric to the SRO and 5 clones mapped centromeric to the SRO.

Base Sequence↗
PubMed1994

Structure of the human type-I interferon gene cluster determined from a YAC clone contig.

A map of the type-I interferon gene cluster located on the short arm of human chromosome 9 (9p) has been constructed using a contig of YAC clones. This map contains 26 interferon (IFN) genes and pseudogenes, and it accounts for all, except one, of the IFN sequences previously reported by other authors, plus a new IFNW pseudogene. The most distal gene on 9p is IFNB, and the most proximal one is IFNWP19. The direction of transcription for the 20 most distal IFN sequences is toward the telomere and for the 6 most proximal sequences, toward the centromere. Several regions of the cluster show evidence of ancestral duplication events. Some of these events may be explained by unequal crossing over between adjacent tandem genes. The location of several breakpoints within the cluster, from deletions associated with leukemias and gliomas, was also determined.

Base Sequence↗
PubMed1994

Breakpoint junctions of chromosome 9p deletions in two human glioma cell lines.

Interstitial deletions of the short arm of chromosome 9 are associated with glioma, acute lymphoblastic leukemia, melanoma, mesothelioma, lung cancer, and bladder cancer. The distal breakpoints of the deletions (in relation to the centromere) in 14 glioma and leukemia cell lines have been mapped within the 400 kb IFN gene cluster located at band 9p21. To obtain information about the mechanism of these deletions, we have isolated and analyzed the nucleotide sequences at the breakpoint junctions in two glioma-derived cell lines. The A1235 cell line has a complex rearrangement of chromosome 9, including a deletion and an inversion that results in two breakpoint junctions. Both breakpoints of the distal inversion junction occurred within AT-rich regions. In the A172 cell line, a tandem heptamer repeat was found on either side of the deletion breakpoint junction. The distal breakpoint occurred 5' of IFNA2; the 256 bp sequenced from the proximal side of the breakpoint revealed 95% homology to long interspersed nuclear elements. One- and two-base-pair overlaps were observed at these junctions. The possible role of sequence overlaps, and repetitive sequences, in the rearrangement is discussed.

Base Sequence↗
PubMed1994

Sequence-independent amplification and labeling of yeast artificial chromosomes for fluorescence in situ hybridization.

We have developed a method that allows reliable construction of high quality FISH probes from yeast artificial chromosomes (YACs) based on the separation of YACs by pulse-field gel electrophoresis and a rapid sequence-independent amplification procedure (SIA). These probes can be used to localize YACs on metaphase chromosomes and also with high efficiency, in interphase nuclei.

Base Sequence↗
PubMed1992

A method for the rapid sequence-independent amplification of microdissected chromosomal material.

We have developed a simple, efficient method by which microdissected material can be amplified directly in the collection container in a few hours. The procedure involves two initial rounds of DNA synthesis with T7 DNA polymerase, using a primer that contains a random pentanucleotide sequence at its 3' end and a defined sequence at its 5' end, followed by PCR amplification with the defined sequence as the primer. The resulting products can be biotinylated and used for fluorescence in situ hybridization (FISH) to confirm their chromosomal location. As few as 17 dissected chromosomal regions provide sufficient material for a specific FISH signal on the appropriate band of metaphase chromosomes. We have obtained a chromosome 6q25-qter-specific painting probe in this way.

Base Sequence↗