Rafael Espinosa

Human and rat brain-derived neurotrophic factor and neurotrophin-3: gene structures, distributions, and chromosomal localizations.

The development and maintenance of the vertebrate nervous system depends upon neuronal survival proteins known as neurotrophic factors. Nerve growth factor (NGF) remains the best characterized neurotrophic molecule. Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are two recently cloned neurotrophic factors that are homologous to NGF. Here we describe the molecular cloning of the human and rat genes encoding BDNF, as well as the isolation of the human NT-3 gene. On the basis of comparison of our genomic and cDNA clones with those of previously isolated BDNF and NT-3 genes and cDNAs, we make inferences about the structures of processed transcripts derived from the neurotrophin genes and the protein precursors they encode. We demonstrate that the mature form of BDNF is identical in all mammals examined, and that the same is true of the mature form of NT-3. Furthermore, the respective tissue-distributions and neuronal specificities of NT-3 and BDNF are also conserved among mammals. Finally, we localize the gene encoding human BDNF (gene symbol designated BDNF) to chromosome 11, band p13, and the gene encoding human NT-3 (gene symbol designated NTF3) to chromosome 12, band p13.

Human Glucagon-Like Peptide-1 Receptor Gene: Localization to Chromosome Band 6p21 by Fluorescence In Situ Hybridization and Linkage of a Highly Polymorphic Simple Tandem Repeat DNA Polymorphism to Other Markers on Chromosome 6

Glucagon-like peptide-1 is a fragment of proglucagon secreted by intestinal L-cells. It has potent glucose-dependent insulin secretory effects and also suppresses gastric acid secretion in the stomach. The biological actions of GLP-1 are mediated by the GLP-1 receptor, the structure of which has recently been determined. Defects in insulin secretion are a common feature of NIDDM and as such the GLP-1 receptor is a candidate for contributing to the development of this clinically and genetically heterogeneous disorder. As a first step in determining the role of the GLP-1 receptor in the development of NIDDM, we have isolated the human GLP-1 receptor gene and mapped it to chromosome 6, band p21.1, using the technique of fluorescence in situ hybridization. We also identified a simple tandem repeat DNA polymorphism in the human GLP-1 receptor gene of the form (TG)n. This DNA polymorphism has 14 alleles and a heterozygosity of >0.8. We have used this DNA polymorphism to localize the GLP-1 receptor gene within the genetic map of the short arm of chromosome 6. This DNA polymorphism will facilitate genetic studies of the contribution of the GLP-1 receptor gene to impaired β-cell function and NIDDM.

Abnormalities of Chromosome Band 11q23 and the Mll Gene in Pediatric Myelomonocytic and Monoblastic Leukemias: Identification of the t(9;11) as an Indicator of Long Survival

Purpose and Methods We reviewed the cytogenetic pattern of the malignant cells in 36 patients who were <20 years of age and who had M4 and M5 leukemias, excluding M4Eo cases with inv(16). We performed fluorescence in situ hybridization (FISH) and molecular studies to determine the actual incidence of 11q23/MLL abnormalities in these patients. Results Eighteen patients had 11q23 translocations or insertions detected by cytogenetic analysis (15 cases) or by FISH (3 cases); 10 patients had t(9;11), all of whom had M5a. Eight patients had other 11q23 translocations or insertions not involving chromosome 9 [t(11q23)] (four each had M4 or M5 leukemias). Eighteen cases with M4/M5 did not have 11q23 abnormalities. MLL rearrangements were found in all patients with translocations or insertions of 11q23 who were studied. Clinically, children with t(9; 11) were indistinguishable from other patients with M4-M5 leukemias. In contrast, the t(11q23) group was characterized by extreme hyperleukocytosis, CNS disease, and skin involvement. Patients with the t(9; 11) had a better outcome when compared with patients in the t(11q23) group (EFS ± SE at 3 years, 56 ± 17% versus 10 ± 10%, p = 0.04), and to all the remaining children with M4-M5 leukemias (p = 0.04). Conclusions The combination of cytogenetic, FISH, and molecular analysis provides a highly sensitive strategy for detection of 11q23/MLL gene rearrangements in childhood M4-M5 leukemias. Our more precise classification of these patients allows a more accurate correlation with outcome. The favorable prognostic significance of the t(9; 11) should be confirmed in prospective studies including a larger number of children as well as adults.

Isolation of a cDNA Clone Encoding a KATP Channel–Like Protein Expressed in Insulin-Secreting Cells, Localization of the Human Gene to Chromosome Band 21q22.1, and Linkage Studies With NIDDM

The metabolism of glucose in insulin-secreting cells leads to closure of ATP-sensitive K+ channels (KATP), an event that initiates the insulin secretory process. Defects in insulin secretion are a common feature of non-insulin-dependent diabetes mellitus (NIDDM), and the β-cell KATP that couples metabolism and membrane potential is a candidate for contributing to the development of this clinically and genetically heterogeneous disorder. We screened a hamster insulinoma cDNA library by low-stringency hybridization with a probe coding for the G-protein-coupled inwardly rectifying K+ channel GIRK1/KGA and isolated clones encoding a protein, KATP-2, whose sequence is 90% similar to that of the recently described KATP-1, an ATP-sensitive K+ channel expressed in heart and other tissues. RNA blotting showed that KATP mRNA was present in insulin-secreting cells and brain but not in heart. To assess the contribution of KATP-2 to the development of NIDDM, the human KATP-2 gene (symbol KCNJ7) was isolated and mapped to chromosome band 21q22.1 by fluorescence in situ hybridization. A simple tandem repeat DNA polymorphism, D21S1255, was identified in the region of the KATP-2 gene, and linkage studies between this marker and NIDDM were carried out in a group of Mexican-American sib pairs with NIDDM. There was no evidence for linkage between D21S1255 and NIDDM, indicating that KATP-2 is not a major susceptibility gene in this population.

Analysis of the t(6;11)(q27;q23) in leukemia shows a consistent breakpoint in AF6 in three patients and in the ML‐2 cell line

The t(6;11)(q27;q23) is one of the most common translocations observed in patients with acute myeloid leukemia (AML). The translocation breakpoint involves the MLL gene, which is the human homolog of the Drosophila trithorax gene, at 11q23 and the AF6 gene at 6q27. Reverse transcriptase‐polymerase chain reaction (RT‐PCR) using an MLL sense primer and an AF6 antisense primer detected the MLL/AF6 fusion cDNA from three leukemia patients with the t(6;11) [two AML and one T‐acute lymphoblastic leukemia (ALL)] and one cell line. The fusion point in the AF6 cDNA from these cases is identical, regardless of the leukemia phenotype. The ML‐2 cell line, which was established from a patient with AML that developed after complete remission of T‐cell lymphoma, has retained an 11q23–24 deletion from the lymphoma stage and has acquired the t(6;11) with development of AML. The ML‐2 cells have no normal MLL gene on Southern blot analysis, which indicates that an intact MLL gene is not necessary for survival of leukemic cells. Genes Chromosom Cancer 15:206–216 (1996).

Refinement of the commonly deleted segment in myeloid leukemias with a del(20q)

A deletion of the long arm of chromosome 20 [del(20q)] is a recurring abnormality in a wide spectrum of myeloid disorders. Loss of genetic material from 20q may confer a proliferative advantage to myeloid cells, possibly through loss of function of a tumor suppressor gene. Previously, we analyzed leukemia cells from 19 patients with a del(20q) by fluorescence in situ hybridization (FISH) and identified a segment that was deleted in 95% of all patients examined. The deleted interval extended from 20q11.2 to q12, spanned approximately 13 Mb, and was flanked proximally by RPN2 and distally by D20S17. To narrow the commonly deleted segment and facilitate the identification of candidate genes, we have employed molecular approaches in combination with FISH. By using 21 microsatellite markers positioned in a recently generated physical map of 20q, we performed allele loss studies in myeloid leukemia cells from 23 patients with a del(20q). The results of these studies allowed us to delineate a new proximal border, flanked by marker D20S206. By FISH analysis of additional leukemia samples from patients with a del(20q), we have also delineated a new distal boundary between markers D20S119 and UT654. As a result of the redesignation of both the proximal and distal boundaries, we have successfully narrowed the commonly deleted segment within 20q12 to a region spanning approximately 8 Mb. Identification of the smallest deleted segment will facilitate the eventual cloning of a candidate myeloid tumor suppressor gene. Genes Chromosomes Cancer 21:75–81, 1998.

Chromosomal localization of the genes encoding the p50/p105 subunits of NF-κB (NFKB2) and the IκB/MAD-3 (NFKBI) inhibitor of NF-κB to 4q24 and 14q13, respectively

The regulation of expression of a variety of genes involved in immune function, inflammation, and cellular growth control, as well as control of expression of certain viruses such as the human immunodeficiency virus (HIV), is dependent on the transcription factor NF-kappa B. In many cells, NF-kappa B is found in the cytoplasm where it is associated with an inhibitor protein known as I kappa B. Recently the genes encoding the p50 and p65 subunits of NF-kappa B, as well as one form of I kappa B/MAD-3 (NFKBI), have been cloned. As part of our goal to determine the chromosomal organization of members of the REL/NFKB family, as well as their inhibitors, we localized the NFKBp50/p105 (NFKB2) and I kappa B/MAD-3 (NFKBI) genes to human chromosome bands 4q24 and 14q13, respectively.

Human glutamine: fructose-6-phosphate amidotransferase: characterization of mRNA and chromosomal assignment to 2p13

It has been previously shown that some toxic effects of high concentrations of glucose are mediated by the hexosamine biosynthesis pathway and its rate-limiting enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). We have used the cloned human GFA cDNA to study the chromosomal localization of the gene and tissue distribution of mRNA. The human GFA gene is on chromosome 2, band p13 as determined by fluorescence in situ hybridization. An 8-kb species of GFA mRNA was detected in all rat tissues tested with relatively high expression in testis and smooth muscle; a unique 3-kb mRNA species was found only in testis.

Search for a Third Susceptibility Gene for Maturity-Onset Diabetes of the Young: Studies With Eleven Candidate Genes

Maturity-onset diabetes of the young (MODY) is a model for genetic studies of non-insulin-dependent diabetes mellitus. We have identified 15 MODY families in which diabetes is not the result of mutations in the glucokinase gene. This cohort of families will be useful for identifying other diabetes-susceptibility genes. Nine other candidate genes potentially implicated in insulin secretion or insulin action have been tested for linkage with MODY in these families, including glucokinase regulatory protein, hexokinase II, insulin receptor substrate 1, fatty acid–binding protein 2, glucagon-like peptide-1 receptor, apolipoprotein C-II, glycogen synthase, adenosine deaminase (a marker for the MODY gene on chromosome 20), and phosphoenolpyruvate carboxykinase. None of these loci showed evidence for linkage with MODY, implying that mutations in these genes do not make a major genetic contribution to the development of MODY. In addition to these linkage analyses, one or two affected subjects from each family were screened for the presence of the A to G mutation at nucleotide 3,243 of the mitochondrial tRNALeu(UUR) gene. This mutation was not found in any of these subjects. Finally, we report the localization of the gene encoding the regulatory protein of glucokinase to chromosome 2, band p22.3 and the identification of a restriction fragment length polymorphism at this locus.

Pancreatic Islet Expression Studies and Polymorphic DNA Markers in the Genes Encoding Hepatocyte Nuclear Factor-3α, -3β, -3γ, -4γ, and -6

The genes encoding the functionally related hepatocyte nuclear factors HNF-1α and HNF-4α play a critical role in normal pancreatic β-cell function. Mutations in these liver-enriched transcription factors result in two forms of early-onset type 2 diabetes (maturity-onset diabetes of the young [MODY]), M0DY3 and M0DY1, which are characterized by impaired glucose-stimulated insulin secretion, early disease onset, and autosomal dominant inheritance. The transcriptional hierarchy of HNFs suggests that other proteins of the regulatory cascade might be responsible for other forms of MODY and/or late-onset type 2 diabetes. In this study, we show that HNF-3α, -3β, -3γ, -4γ, and -6 are expressed in pancreatic β-cells. We report the identification and characterization of simple tandem repeat DNA polymorphisms in the genes encoding HNF-3α, -3β, -3γ, -4γ, and -6 and the mapping of HNF-6 to chromosome bands 15q21.1–21.2 by fluorescence in situ hybridization. These markers will be useful to study the role of genetic variation in these genes in the pathogenesis of type 2 diabetes.