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G Lozano

Publications and source records attributed to G Lozano.

89 records · Page 5Linked to original sources
PubMed1988

The expression of viral and cellular genes in papillomas of the choroid plexus induced in transgenic mice.

A line of transgenic mice that carry the SV40 gene for the large Tumor antigen express this protein during the first two weeks of life in brain tissue. By 30-40 days after birth, independently derived multiple foci of abnormal cells appear throughout the choroid plexus. After 90 days, higher levels of T antigen and rapid tumor growth are detected and all these animals die in a narrow time span, between 100-120 days. In situ hybridization with tissue sections and Northern blot analysis have been employed to follow the steady state levels of SV40 RNA and the p53 oncogene RNA levels in normal and tumor tissues. The level of SV40 RNA is quite variable between tumor cells in a section. This heterogeneity of T antigen mRNA levels could permit the selection of cells (from the multiple foci) expressing higher levels of T antigen and growing more rapidly. The increased levels of p53 RNA observed in tumor cells could then result from the active growth state of these cells or a more direct transcriptional activation. Two cellular genes, transthyretin and the 5-HT1C serotonin receptor, both of which are preferentially expressed in normal choroid plexus cells, were also examined for RNA production in these tumors of the choroid plexus. Both of these genes produced high levels of RNA in tumor tissue indicating the retention of well differentiated gene expression in these tumor tissues. This reflects, at the level of gene expression, the well differentiated morphology of these papillomas of the choroid plexus. Interestingly, as cell lines have been derived from these tumors, both the choroid plexus specific RNA species (for 5-HT1C receptor) and characteristic morphology were lost and an increase in T antigen levels was observed.

Animals↗
PubMed1987

Structure of the glycosaminoglycan domain in the type IX collagen-proteoglycan.

Type IX collagen represents 5-20% of the total collagen in hyaline cartilage. The molecules of this collagen are composed of three genetically distinct polypeptide subunits. One of these subunits, alpha 2(IX), contains covalently bound glycosaminoglycan (chondroitin sulfate or dermatan sulfate). We report here on the structure of the glycosaminoglycan attachment site of type IX collagen-proteoglycan. We show, by a combination of cDNA and peptide sequencing, that the attachment region contains the sequence Gly-Ser-Ala-Asp, located within the noncollagenous domain NC3 of the alpha 2(IX) chain. By comparing the exons encoding the NC3 domain in the alpha 2(IX) and alpha 1(IX) genes, we find that the exon coding for the glycosaminoglycan attachment site in the alpha 2(IX) gene is 48 base pairs long, whereas the homologous alpha 1(IX) exon is 33 base pairs. The NC3 domain is, therefore, five amino acid residues longer in alpha 2(IX) than in alpha 1(IX). The extra sequence in alpha 2(IX), Val-Glu-Gly-Ser-Ala, provides a simple explanation for the kink observed at the NC3 domain of type IX molecules when examined by electron microscopy. The inserted block of amino acid residues also provides the NC3 domain of alpha 2(IX) chains with a serine residue, not present in alpha 1(IX) that serves as attachment site for a glycosaminoglycan side chain. Our data show that the amino acid sequence that surrounds the glycosylated serine residue in type IX collagen-proteoglycan differs from glycosylated sequences in noncollagenous core proteins. The data also provide strong evidence that glycosylation of type IX collagen is not a chance glycosylation of a serine residue in a noncollagenous domain, but is a specific post-translational modification of this unusual collagen molecule.

Amino Acid Sequence↗
PubMed1987

Relationship between simian virus 40 large tumor antigen expression and tumor formation in transgenic mice.

A line of transgenic mice containing the simian virus 40 (SV40) large tumor antigen gene under the control of the viral enhancer-promoter expressed this viral protein in the brains of these mice within the first 2 weeks after birth. Multiple foci of anaplastic cells formed in the choroid plexuses of these mice at 36 to 41 days after birth, and normal tissue coexisted with these transformed foci. Immunoperoxidase staining to detect the SV40 T antigen showed tumor-specific expression of nuclear T antigen at late times in tumor development, approximately 90 to 100 days and thereafter. The level of SV40 T antigen, on a per cell basis, appeared to be lower in the great majority of choroid plexus cells at earlier times in tumor development. These results suggest that low levels of tumor antigen (14 to 36 days) are present before detectable pathology (36 to 41 days) and the level of T antigen per cell is higher in rapidly growing late-stage tumors (older than 90 days).

Animals↗
PubMed1986

Serotonin 5-HT1C receptors are expressed at high density on choroid plexus tumors from transgenic mice.

Choroid plexus tumors develop spontaneously in adult transgenic mice carrying integrated copies of SV40 early region genes. In this communication, we report that these tumors exhibit the highest density of serotonin receptors (6600 fmol/mg protein) found in any tissue. 125I-LSD binding to choroid plexus tumors displays a pharmacological profile that matches the properties of 5-HT1C receptors in normal choroid plexus tissue. Autoradiographic localization of 125I-LSD binding in brain sections from transgenic mice shows high levels of labelling in the tumors, in correlation with immunohistochemical staining for SV40 large T antigen expression. Choroid plexus tumors from these transgenic mice provide an excellent model system for the study of serotonin 5-HT1C receptors.

Animals↗
PubMed1985

Construction and characterization of cDNA encoding the alpha 2 chain of chicken type IX collagen.

We have isolated and characterized a cDNA encoding the carboxy-terminal half of one of the polypeptide subunits of a novel disulfide-bonded collagen found in hyaline cartilage. This collagen has been given the type assignment type IX, and it has several unusual characteristics. First, the polypeptide subunits are shorter than alpha-chains of the fibrillar collagens types I, II, and III. Second, type IX molecules are heterotrimers of three genetically distinct polypeptide subunits. Third, type IX molecules contain three triple-helical collagenous domains interspersed with noncollagenous domains. When chicken cartilage collagens are extracted with pepsin, type IX collagen is cleaved and gives rise to the triple-helical fragments HMW and LMW. The identification of the cDNA reported here is based on a comparison of the amino acid composition of tryptic peptides derived from LMW with the composition of tryptic peptides predicted from the nucleotide sequence of the cDNA. We also show that the amino-terminal sequence of one of the subunits of LMW is identical with the sequence predicted from the nucleotide sequence of the cDNA. Finally, we demonstrate that the amino-terminal amino acid sequence of a tryptic peptide isolated from one of the subunits of HMW is identical with a sequence predicted from the cDNA. We have given the polypeptide chain encoded by the cDNA reported here the name alpha 2(IX), and we show that it is homologous to the alpha 1(IX) chain previously characterized by us.

Amino Acid Sequence↗
PubMed1985

A distinct class of vertebrate collagen genes encodes chicken type IX collagen polypeptides.

Type IX collagen is a disulfide-bonded protein first isolated from hyaline cartilage. The structure of this collagen is unusual in that the molecules contain three triple-helical domains interspersed with noncollagenous regions. The molecules are heterotrimers composed of three genetically distinct polypeptide chains. In our laboratory, cDNAs specific for two of these polypeptide chains have recently been isolated. Here we report on the isolation of genomic clones by use of these cDNAs as probes for screening a chicken genomic library. Nucleotide sequence analysis of these clones shows that the exon structure of type IX collagen genes is fundamentally different from the exon structure of the genes for the fibrillar collagen types I-III. Whereas the sizes of exons in fibrillar collagen genes are related to a basic 54-base-pair coding unit, the exons of type IX collagen genes show a large variation in size and do not appear to be related to a 54-base-pair unit. We propose, therefore, that type IX collagen genes belong to a class of vertebrate collagen genes distinct from that of fibrillar collagens.

Amino Acid Sequence↗
PubMed1983

Procollagen alpha 2(I) mRNA in dermatosparactic fibroblasts: evidence for post-transcriptional regulation.

Dermatosparaxis is a genetic defect of connective tissues found in man and animals. Dermatosparactic sheep fibroblasts fail to cleave off the aminopropeptide of procollagen, this makes the feedback regulation less effective and leads to an elevated production of collagen. We have isolated the total RNA from dermatosparactic and normal sheep fibroblasts and then compared the amount of mRNA sequences complementary to alpha 2(I) genomic DNA. Using methyl mercury gels, the Northern hybridization procedure and dotting hybridization, we were able to show that the levels of mRNA specific for alpha 2(I) collagen were only marginally different in both fibroblast strains. Furthermore, the amount of collagen mRNA translatable in a cell-free translation system was the same in affected and non-affected sheep cells. Our data provide further evidence for a post-transcriptional control of collagen synthesis in fibroblasts.

Animals↗
PubMed1980

Isolation and characterization of genomic DNA coding for alpha 2 type I collagen.

We have isolated and characterized a segment of the chick alpha 2 collagen gene by screening a library of chick genomic fragments using as hybridization probe an alpha 2 collagen cDNA clone. Several clones were isolated and one of them, lambda gCOL 204, was used for further studies. The DNA of lambda gCOL 204 hybridizes to a unique species of mRNA the size of alpha 2 collagen mRNA. This mRNA can be translated into a unique polypeptide which comigrates in SDS-gel electrophoresis with pro-alpha 2 collagen. Electron microscopic analysis by R-loop technique indicates that lambda gCOL 204 contains 7Kb of the alpha 2 collagen gene. This 7 Kb piece constitutes the 3' end of the gene. The same clone also contains 9 Kb of DNA that is immediately adjacent to the 3' end of the alpha 2 collagen gene. The cloned segment of the alpha 2 collagen gene is interrupted by 8 intervening sequences of various lengths. The coding sequences for collagen in this clone add up to approximately 1,800 bp, which correspond to about 1/3 of alpha 2 collagen mRNA. DNA sequence analysis of a small coding segment of lambda g COL 204 reveals a characteristic collagen type sequence which encodes for an amino acid sequence identical to a sequence found in calf alpha 2 collagen. The sequence of this region of the protein has not yet been determined for the chick alpha 2 collagen.

Animals↗
PubMed1980

Renal hydatid cysts: communicating with collecting system.

The clinical and radiological features of five patients with renal hydatid disease communicating with the collecting system are described. Rupture into the renal pelvis of a hydatid cyst gives rise to acute flank pain followed by voiding of scolices or daughter cysts with or without hematuria and/or urinary obstruction. Intravenous urography demonstrates a renal mass frequently involving the collecting system; arteriography shows it to be avascular; sonography reveals a multicystic lesion of mixed echogenicity. When daughter cysts are present, computed tomography establishes the diagnosis.

Adult↗