Contribution of JAK2 mutations to T-cell lymphoblastic lymphoma development

The JAK-STAT pathway has a substantial role in lymphoid precursor cell proliferation, survival and differentiation. Nonetheless, the contribution of JAK2 to T-cell lymphoblastic lymphoma (T-LBL) development remains poorly understood. We have identified one activating TEL-JAK2 translocation and four missense mutations accumulated in 2 out of 16 T-LBL samples. Two of them are novel JAK2 mutations and the other two are reported for the first time in T-LBL. Notably, R683G and I682T might have arisen owing to RNA editing. Mutated samples showed different mutated transcripts suggesting sub-clonal heterogeneity. Functional approaches revealed that two JAK2 mutations (H574R and R683G) constitutively activate JAK-STAT signaling in γ2A cells and can drive the proliferation of BaF3-EpoR cytokine-dependent cell line. In addition, aberrant hypermethylation of SOCS3 might contribute to enhance the activation of JAK-STAT signaling. Of utmost interest is that primary T-LBL samples harboring JAK2 mutations exhibited increased expression of LMO2, suggesting a mechanistic link between JAK2 mutations and the expression of LMO2, which was confirmed for the four missense mutations in transfected γ2A cells. We therefore propose that active JAK2 contribute to T-LBL development by two different mechanisms, and that the use of pan-JAK inhibitors in combination with epigenetic drugs should be considered in future treatments.

FAS system deregulation in T-cell lymphoblastic lymphoma

The acquisition of resistance towards FAS-mediated apoptosis may be required for tumor formation. Tumors from various histological origins exhibit FAS mutations, the most frequent being hematological malignancies. However, data regarding FAS mutations or FAS signaling alterations are still lacking in precursor T-cell lymphoblastic lymphomas (T-LBLs). The available data on acute lymphoblastic leukemia, of precursor origin as well, indicate a low frequency of FAS mutations but often report a serious reduction in FAS-mediated apoptosis as well as chemoresistance, thus suggesting the occurrence of mechanisms able to deregulate the FAS signaling pathway, different from FAS mutation. Our aim at this study was to determine whether FAS-mediated apoptotic signaling is compromised in human T-LBL samples and the mechanisms involved. This study on 26 T-LBL samples confirms that the FAS system is impaired to a wide extent in these tumors, with 57.7% of the cases presenting any alteration of the pathway. A variety of mechanisms seems to be involved in such alteration, in order of frequency the downregulation of FAS, the deregulation of other members of the pathway and the occurrence of mutations at FAS. Considering these results together, it seems plausible to think of a cumulative effect of several alterations in each T-LBL, which in turn may result in FAS/FASLG system deregulation. Since defective FAS signaling may render the T-LBL tumor cells resistant to apoptotic cell death, the correct prognosis, diagnosis and thus the success of anticancer therapy may require such an in-depth knowledge of the complete scenario of FAS-signaling alterations.

The stromal gene encoding the CD274 antigen as a genetic modifier controlling survival of mice with γ-radiation-induced T-cell lymphoblastic lymphomas

Using an inter-specific subcongenic strain, Nested Recombinant Haplotype 3 (NRH3), generated between two mouse strains showing extreme differences in γ-radiation-induced thymic lymphoma susceptibility (SEG/Pas and C57BL/6J), we have identified a critical region on chromosome 19 that regulates survival of mice suffering from T-cell lymphoblastic lymphomas. Mapped on this region, the gene encoding the Cd274 ligand is able to trigger an inhibitory effect that modulates T-cell receptor (TCR) signalling and affects thymocyte maturation. Interestingly, this gene shows differential expression between thymic stromal cells from both strains in early response to a single sublethal γ-ray dose, but is inhibited in T-cell lymphoblastic lymphomas. Furthermore, we have identified several polymorphisms in the complementary DNA sequence of this gene that affect the affinity for its Cd279 receptor and are able to induce a differential rate of thymocyte apoptosis. Taken together, our data are consistent with Cd274 acting as a genetic modifier that influences the survival of γ-radiation-induced T-cell lymphoma-bearing mice. The data similarly support the idea of a co-evolution of tumour cells and associated stromal cells to generate a favourable microenvironment for T-cell lymphoma growth.

Functional Fas (Cd95/Apo-1) promoter polymorphisms in inbred mouse strains exhibiting different susceptibility to gamma-radiation-induced thymic lymphoma

The Fas death receptor is a cell surface molecule involved in apoptosis as well as in proliferative or activating signals of many cells types, including T lymphocytes. Using quantitative real-time reverse transcription-PCR analysis, we confirm that expression of this gene is scarcely perceptible in thymic lymphomas induced by gamma-irradiation in C57BL/6J mice. Notably, we also demonstrate for the first time that Fas expression is significantly upregulated in vivo both after single high dose of radiation and in thymic lymphoma-free mice. In addition, we determined its levels of expression in five mouse strains exhibiting different degrees of susceptibility (SPRET/Ei, SEG/Pas, BALB/cJ, C57BL/6J and RF/J). Interestingly, we found the highest levels of expression in SPRET/Ei and SEG/Pas strains (both derived from the Mus spretus species), which are known to have the most resistant phenotype, and the lowest levels in the most susceptible strains C57BL/6J and RF/J. DNA sequencing of the Fas promoter in all five strains showed many polymorphisms that can be classified into three functional haplotypes by using luciferase assays: (1) C57BL/6J and RF/J, (2) BALB/cJ and (3) SPRET/Ei and SEG/Pas. Promoter activities in response to single high doses of radiation correlated well with the levels of Fas expression and are consistent with the degree of strain susceptibility.

Lack of correlation between DNA copy number and mRNA expression levels ofc-myc in γ-radiation-induced mouse thymic lymphomas by using quantitative real-time PCR

BACKGROUND

It is well documented that over-expression of the c-myc proto-oncogene occurs in the vast majority of mouse thymic lymphomas induced by gamma-irradiation, evidencing the importance of this gene in T-cell lymphomagenesis. However, it remains unknown whether elevated levels of c-myc expression are driven by extra c-myc copy numbers.

MATERIALS AND METHODS

Here we use a quantitative test on the basis of real-time PCR to determine the cellular copy number of c-myc in a set of 14 g-radiation- induced thymic lymphomas obtained from (C57BL/6J x BALB/cJ) F1 hybrid mice with increased mRNA c-myc expression.

RESULTS

Since 5 out of 14 (35.7%) cases had no extra copy numbers of c-myc, gene amplification was obviously not the cause of c-myc over-expression in these tumours. In the remaining 9 tumours, c-myc over-expression was also accompanied with extra DNA copy numbers. Therefore, c-myc amplification might be a consequence of the genomic instability subsequent to the up-regulation of c-myc. However, linear regression analysis showed a lack of correlation between increasing DNA copy numbers and mRNA over expression of c-myc in these tumours (r = 0.029, p = 0.94).

CONCLUSION

De-regulation of c-myc does not necessarily imply amplification of this gene in these tumours. This report is, to our knowledge, the first one comparing c-myc amplification with expression in lymphomas of the T-cell lineage.

Tumorigenic activity of p21Waf1/Cip1 in thymic lymphoma

The cell cycle inhibitor p21Waf1/Cip1 is among the most important mediators of the tumor suppressor p53. However, there is increasing evidence indicating that p21 could favor tumorigenesis in specific cell types. In particular, the absence of p21 delays the development of thymic lymphomas induced either by ataxia-telangiectasia mutated deficiency or by ionizing irradiation. Here, we extend these observations to the context of p53-deficient mice. The absence of p21 results in a significant extension of the lifespan of p53-null and p53-haploinsufficient mice, and this effect can be attributed exclusively to a decrease in the incidence of spontaneous thymic lymphomas. Specifically, despite the occurrence of a variety of tumor types in the context of p53 deficiency, the only tumors that were significantly impaired by the absence of p21 were thymic lymphomas. Moreover, the absence of p21 also delays the incidence of radiation-induced thymic lymphomas in p53-deficient mice. Interestingly, p21-deficient lymphomas have a higher apoptotic rate than p21-proficient lymphomas, and this could be on the basis of the delayed incidence of thymic lymphomas in the absence of p21. Together, our results indicate that p21 plays an oncogenic role restricted to thymic lymphomas that is mechanistically independent of p53 and associated to a lower tumor apoptotic rate.

Epigenetic silencing of E- and N-cadherins in the stroma of mouse thymic lymphomas

Aberrant expression of some tumour suppressor genes and oncogenes by thymocytes had been involved in the development of primary thymic lymphomas induced by gamma-irradiation, but genetic alterations affecting critical genes expressed by stromal cells have not been yet explored. This paper analyzes a series of such tumours induced in C57BL/6J and in F1 hybrids of BALB/c and C57BL/6J mouse strains. As expected, hystopathological analyses revealed profound disorganizations within the thymus with a poor demarcation of the cortical and medullar areas. Immunological and quantitative on-line RT-PCR analyses confirm that E-cadherin (Cdh1) is essentially expressed by stromal cells of the thymus, while evidencing that the expression of this gene is significantly reduced in all tumours. In addition, and contrary to what one would expect, N-cadherin (Cdh2) that is exclusively expressed by stromal cells is likewise down-regulated in most of the thymic lymphomas. Although hypermethylation of the promoter region appears to be involved in the inactivation of Cdh2 in all tumours, additional epigenetic mechanisms mediated by repressors such as Snai1 may also play a role in Cdh1 silencing. These results represent the first reported case for tumour-associated gene alterations occurring not in the tumour cells per se, but in the stromal cells of primary thymic lymphomas. Additionally, since the expression of both genes is significantly up-regulated after a single high dose of gamma-radiation, but remained unchanged in treated thymic-lymphoma-free-mice, epigenetic down-regulation of E- and N-cadherin appears to occur concomitantly with the progression towards the most advanced stages of gamma-radiation-induced thymic lymphomas.

Defective expression of Notch1 and Notch2 in connection to alterations of c-Myc and Ikaros in -radiation-induced mouse thymic lymphomas

Gamma-radiation-induced thymic lymphomas constitute a heterogeneous group of T-cell lymphomas. Some tumour suppressor genes and oncogenes have been shown to be defective in a fraction of such lymphomas, yet a considerable number of these remain elusive in terms of gene alterations. In the present work we present evidence that gamma-radiation-induced thymic lymphomas in (C57BL/6 J x BALB/c) F1 hybrid mice often exhibit increased levels of Notch1 expression, but, contrary to what was expected, they also exhibit a clearly reduced Notch2 mRNA expression, suggesting a cooperative antagonism of these genes. These results represent the first reported instance for the involvement of Notch2 inactivation in the development of thymic primary tumours while confirming the role of Notch1 as an activated oncogene. Additional analyses revealed that c-Myc over-expression and partial inactivation of Znfn1a1/Ikaros appear to be relevant events some how coupled to alterations in Notch genes inducing these kinds of tumours.

Psychiatric comorbidity in pathological gamblers seeking treatment

OBJECTIVE

The authors' goal was to determine the frequency of psychiatric comorbidity among treatment-seeking pathological gamblers, compare the severity of gambling and psychological problems in gamblers with and without comorbid disorders, and investigate differences between gamblers with and without comorbid disorders in the dopamine D(2) receptor gene (DRD(2)).

METHOD

Sixty-nine pathological gamblers who consecutively applied to a specialized outpatient treatment program were evaluated with structured interviews, self-report questionnaires, and psychological scales and were genotyped for a DRD(2) polymorphism.

RESULTS

A comorbid psychiatric disorder was present in 43 (62.3%) of the gamblers. The most frequent diagnoses were personality disorders (N=29 [42.0%]), alcohol abuse or dependence (N=23 [33.3%]), and adjustment disorders (N=12 [17.4%]). Gamblers with comorbid psychiatric disorders had gambling scores and psychological scale scores indicating greater severity of gambling and psychopathology. Significant differences in DRD(2) allele distribution were found in gamblers with and without comorbid disorders.

CONCLUSIONS

Psychiatric comorbidity is common among pathological gamblers and is associated with greater severity of clinical problems. The DRD(2) gene could be a liability genetic factor for psychiatric comorbidity in pathological gambling.

Evidence of a possible epigenetic inactivation mechanism operating on a region of mouse chromosome 19 in γ-radiation-induced thymic lymphomas

Loss of heterozygosity (LOH) analysis, performed in 68 gamma-radiation-induced primary thymic lymphomas of F1 hybrid mice, provided evidence of significant LOH on chromosome 19 in a region defined by the D19Mit106 (22 cM) and D19Mit100 (27 cM) markers (Thymic Lymphoma Suppressor Region 8, TLSR8). Cd95 and Pten, two genes mapped at this region, were inactivated in a vast majority of these tumors (85.3% for Cd95 and 61.8% for Pten). Moreover, altered expression of Cd95 and Pten occurred concomitantly in 34 of 68 (50%) thymic lymphomas suggesting a coordinated mechanism of inactivation of these genes. Surprisingly, we also found that Jak2, a proto-oncogene located between Cd95 and Pten, was simultaneously inactivated in a significant fraction of the tumors analysed (24 of 34, 70.6%). Taken together these findings and the lack of mutations in the coding sequences of the mentioned genes clearly suggest a possible regional epigenetic inactivation mechanism on mouse chromosome 19 operating during the development of these tumors.

Characterization of the murine p19(ARF) promoter CpG island and its methylation pattern in primary lymphomas

The INK4a/ARF locus encodes two different proteins involved in cell cycle control. Both molecules, p16(INK4a) and p19(ARF), inhibit cell cycle progression and have been shown to act as tumor suppressors in a variety of models. Their expression is controlled by separate promoters responding to different stimuli and they therefore show independent transcriptional regulation. We have cloned and characterized a 2.5 kb region upstream of the murine p19(ARF) gene to determine the role of DNA methylation in suppressing p19(ARF) transcription in a wide panel of murine primary T cell lymphomas. This region contains a DNA fragment with the characteristics of a CpG island similar to those described for the murine p16(INK4a) and p15(INK4b) genes. Expression of p19(ARF) is decreased in a significant number (20%) of the murine lymphomas analyzed. Overexpression of the p19(ARF) transcript is also frequent, suggesting alterations in molecules of the retinoblastoma or p53 pathways that are involved in p19(ARF) regulation. Although hypermethylation of the INK4a and INK4b promoters is frequently involved in murine lymphomas, the p19(ARF) CpG island is infrequently methylated in the murine primary lymphomas studied in this work. Since loss of p19(ARF) expression cannot be explained as the result of homozygous deletions or hypermethylation of the ARF gene, other regulatory mechanisms seem to be altered in these malignancies.

Cooperative alterations of Rb pathway regulators in mouse primary T cell lymphomas

Alterations in the Rb pathway have been described in many different tumors. In order to study this cell cycle regulatory mechanism in murine T cell lymphomas, we have analyzed the RNA and protein expression of the cyclin D1, cdk4 and retinoblastoma genes in primary tumor samples. We have detected overexpression of the cyclin D1 gene and deficient expression of the retinoblastoma gene in 42 and 28% of these tumors, respectively. The immunohistochemical analysis showed that these RT-PCR results are correlated with a significant increase in the number of positive cells for cyclin D1 and a moderate decrease in the expression of Rb protein, respectively. The analysis of cyclin D1, Rb, p15(INK4b) and p16(INK4a) showed that 75% of lymphomas had alterations in these genes and indicates that the Rb pathway is frequently altered in mouse primary T cell lymphomas. Moreover, 31% of lymphomas presented simultaneous alterations in at least two of these genes, suggesting the importance of concurrent alteration of different Rb pathway regulators. In addition, we have characterized these samples for mutational status of the N-ras and K-ras genes. We have only detected mutations in codon 12 of K-ras in six of 49 lymphomas (12%). Interestingly, five of these lymphomas also showed alterations in at least one of the Rb pathway regulators analyzed here. Taken together, these data suggest that deregulation of the Rb pathway regulators and/or oncogenic activation of K-ras may represent a common important clue in progression of murine T cell lymphomas.

Loss of heterozygosity at the proximal-mid part of mouse chromosome 4 defines two novel tumor suppressor gene loci in T-cell lymphomas

Recent studies in our laboratory reported frequent loss of heterozygosity (LOH) on mouse chromosome 4 in T-cell lymphomas, identifying three candidate tumor suppressor regions (TLSR1-3). To determine the possible existence of other tumor suppressor gene loci on the proximal-mid part of chromosome 4 and to clarify whether the p16(INK4a) (alpha and beta) and p15(INK4b) genes are the inactivation targets of deletion at TLSR1, we have tested 73 gamma-radiation-induced T-cell lymphomas of F1 hybrid mice by LOH analysis. Frequent LOH was found at the INK4a and INK4b loci and the surrounding markers D4Mit77, D4Mit245 and D4Wsm1. In addition, we identified two distinct regions of significant allelic losses in the proximal-mid part of chromosome 4, defined by the markers D4Mit116 (TLSR4) and D4Mit21 (TLSR5). Taken together, this evidence and our previous data indicate the existence of at least five different candidate sites for tumor suppressor genes on chromosome 4, thus revealing a main role for this chromosome in the development of mouse T-cell lymphomas.

Mouse p73 gene maps to the distal part of chromosome 4 and might be involved in the progression of gamma-radiation-induced T-cell lymphomas

We have isolated and sequenced a DNA fragment of about 12 kb that comprises exons 5-14 of the mouse p73 gene. We have identified four polymorphic markers, and one of them has been used to genetically map p73 to the distal part of chromosome 4. Previously, we have reported that gamma-radiation-induced T-cell lymphomas undergo frequent loss of heterozygosity around marker D4Mit205b at the distal part of chromosome 4. Based on this, we have performed loss of heterozygosity analysis in a set of T-cell lymphomas, and we have found allelic losses of p73 in 32.6% (16 of 49) of the tumors analyzed. Interestingly, allelic losses occur concurrently at both p73 and D4Mit205b, thus suggesting that p73 could be specifically inactivated in radiation-induced T-cell lymphomas.

Analysis of the INK4a/ARF locus in non-Hodgkin's lymphomas using two new internal microsatellite markers

Inactivation of the INK4a/ARF locus is a frequent event in non-Hodgkin's lymphomas (NHLs), which may be attributed to deletion, point mutation, and 5' CpG methylation at its promoter region. In the present study we evaluated the occurrence of deletions and genetic instability of INK4a/ARF locus in 30 paired normal and tumor samples of B cell NHLs by conducting an allelotypic analysis with two new polymorphic markers, one located at the intron 1 of p16INK4a gene and the other one placed downstream exon 1beta of p19ARF. Comparison of these results with those obtained in a previous paper using flanking markers (D9S171, D9S942, D9S958 and IFNA) allowed us to detect two new cases of microsatellite instability (L-446 and L-442), and to confirm the occurrence of LOH at the INK4a/ARF locus in one tumor (M-3770). On the contrary, this locus is not affected in three different tumors (L-421, L-272 and L-159) which exhibited LOH at some of the flanking markers.

A new candidate site for a tumor suppressor gene involved in mouse thymic lymphomagenesis is located on the distal part of chromosome 4

In a previous work we provided preliminary evidence of the existence of a putative tumor suppressor gene region on the distal part of chromosome 4 in gamma-radiation-induced T-cell lymphomas of (C57BL/6J x RF/J) F1 hybrid mice. This region, named as TLSR2 (Thymic Lymphoma Suppressor Region 2), was located centered at D4Mit54. A more detailed allelotype analysis in the mentioned tumors with new informative microsatellites on distal chromosome 4 region, as well as in thymic lymphomas induced with gamma-rays in F1 hybrids generated from reciprocal crosses between the strains C57BL/6J and BALB/cJ, and having in mind the new map position of D4Mit205b, allowed us to confirm the existence of TLSR2 and to define it more precisely as centered at D4Mit205b. In addition, we identified a new candidate region, named as TLSR3 (Thymic Lymphoma Suppressor Region 3), located between the Mom-1 locus and D4Mit68, as the site of another putative tumor suppressor region involved in thymic lymphomagenesis.

An AC-repeat adjacent to mouse Cdkn2B allows the detection of specific allelic losses in the p15INK4b and p16INK4a tumor suppressor genes

The cyclin-dependent kinase inhibitors p15INK4b and p16INK4a are involved in the development of a wide range of human and murine tumors. These tumor suppressor genes are inactivated by deletions frequently associated to point mutations in the coding regions or hypermethylation of their promoters. In this work, we describe a simple-sequence length polymorphism located in mouse Chromosome (Chr) 4, between the Cdkn2B (p15INK4b) and Cdkn2A (p16INK4a) genes, only 700 bp downstream of the Cdkn2B locus. This DNA region was analyzed in different inbred strains showing a variable AC-repetitive DNA sequence. We used this microsatellite to detect loss of heterozygosity of the Cdkn2A and Cdkn2B loci in gamma-irradiation-induced thymic lymphomas of C57BL/6J x RF/J F1 hybrids. Using this specific marker, we were able to locate additional allelic losses not detected by other microsatellites. Since the allelic losses can be detected by a simple PCR amplification, this AC-repetitive sequence is specially useful as a genetic marker for these Cdkn2 genes and specifically for the p15INK4b cell cycle inhibitor.

Instability of the D4Mit12 microsatellite marker in C57BL/6J x BALB/cJF1 hybrid mice is independent of the tumor phenotype

We examined the stability of different types of DNA microsatellite markers in gamma-radiation-induced thymic lymphomas as well as normal, nontumorous tissues of F1 hybrid mice derived from the parental strains C57BL/6J, RF/J, and BALB/cJ. Surprisingly, the D4Mit12 microsatellite showed genomic instability in a significant fraction of DNAs of the (C57BL/6J x BALB/cJ) F1 hybrids with independence of the tumor phenotype. This instability was not found in the reciprocal F1 DNAs, in DNAs of the parental strains, or in DNAs of (C57BL/6J x RF/J) F1 hybrid mice. These results suggest that the instability of the D4Mit 12 microsatellite is dependent on its repeat length, the genetic background of F1 hybrids, and the maternal origin of the C57BL/6J allele.

Genetic association study between pathological gambling and a functional DNA polymorphism at the D4 receptor gene

A Spanish sample consisting of 68 Caucasian pathological gambling patients (47 males and 21 females) and 68 unaffected controls were screened by the molecular analysis of a functional DNA polymorphism in the locus for the D4 dopamine receptor gene. Our results are consistent with the existence of a significant association between genetic variants at a DRD4 gene polymorphism and pathological gambling (chi 2 = 11.82; P = 0.037). This association seems to be sex-influenced, since there was no significant association when only males were considered (chi 2 = 9.45; P = 0.09), but there was a more significant association if we only considered female subjects (chi 2 = 8.73; P = 0.033). Individuals with the longest allele (D7) were the most frequent in affected females (chi 2 = 4.50; P = 0.033). This work provides a new evidence of the implication of the dopaminergic reward pathways, now through the involvement of DRD4, in the aetiology of this impulsive disorder.

Frequent allelic losses of 9p21 markers and low incidence of mutations at p16(CDKN2) gene in non-Hodgkin lymphomas of B-cell lineage

We present an allelotype analysis of 35 cases of non-Hodgkin lymphomas and normal pairs using four microsatellite markers that flank the region occupied by the CDKN2 gene locus at 9p21. Frequent allelic losses (LOH) were detected in B-cell lineage NHLs, including Burkitt lymphoma (33.3% of total, if we only consider high grade tumors). In five of these tumors LOH did not include the CDKN2 gene. Mutational analysis of exon 1 and 2 of CDKN2 (SSGP and sequencing of abnormal bands) revealed a nonsense mutation (Arg72Ter) in one tumor (case 10), where the second hit of the Knudson's model consisted of the elimination of the wild type allele. In view of these results, the hypothesis of two different candidate tumor suppressor gene regions around the CDKN2 locus remains an intriguing possibility.

A study of genetic association between manic-depressive illness and a highly polymorphic marker from the GABRbeta-1 gene

We report on an association study between a tetranucleotide repeat polymorphism in the GABR beta1 gene and manic-depressive illness in a Spanish population. This gene may be an important candidate for bipolar affective disorders since severe GABergic alterations have been described in patients. Although our results do not reveal a clear evidence for association between manic-depressive illness and GABR beta1, we have found significant differences between patients and controls in the female subpopulation.

Inactivation of the cyclin-dependent kinase inhibitor p15INK4b by deletion and de novo methylation with independence of p16INK4a alterations in murine primary T-cell lymphomas

A wide panel of murine induced T-cell lymphomas have been analysed for p16INK4a or p15INK4b alterations. Only one gamma-radiation-induced lymphoma showed p16INK4a homozygous deletion and no other intragenic mutations were found in these INK4 genes. However, de novo methylation of the 5' CpG islands of the murine p15INK4b and p16INK4a genes was found to be highly frequent. While p16INK4a hypermethylation was found in 36% of the neutron-radiation-induced lymphomas and 15% of the gamma-radiation-induced lymphomas, de novo methylation of p15INK4b occurs in 88% and 42% of these tumors respectively, correlating with deficient expression of the corresponding mRNA and allelic losses in the p15INK4b and p16INK4a chromosome location. These data represent, to our knowledge, the first report on the significant involvement of hypermethylation of these INK4 genes in murine primary tumors. Moreover, they show the importance of allelic losses and CpG island methylation of p15INK4b gene inactivation and support a tumor suppressor role for p15INK4b in T-cell lymphomas independent of p16INK4a.

Allelic losses on chromosome 4 suggest the existence of a candidate tumor suppressor gene region of about 0.6 cM in gamma-radiation-induced mouse primary thymic lymphomas

Mouse chromosome 4 was investigated to assess the involvement of tumor suppressor genes in primary thymic lymphomas induced by gamma-irradiation. PCR analysis using microsatellite DNA polymorphic markers was performed in F1 animals generated from a cross between the strains C57BL/6J and RF/J. Microsatellite markers were selected with focus on chromosome 4 around the region containing the interferon alpha gene cluster (D4Mit17, D4Wsm1, D4Mit9, and D4Mit205 and a more distal region (D4Mit12, D4Mit54, and D4Mit13). Allelic losses were detected in 21/47 (44.7%) gamma-radiation-induced thymic lymphomas. Analysis of markers located on six other chromosomes as well as on the proximal region of chromosome 4 illustrates the specificity of the occurrences of LOH appearing on the former markers. This analysis clearly suggests the existence of a candidate tumor suppressor gene region on mouse chromosome 4 of about 0.6 cM between the markers D4Wsm1 and D4Mit9 (TLSR1, Thymic Lymphoma Suppressor Region 1). In addition, another more distal region centered at the marker D4Mit54 could be also exist (TLSR2). In most tumors, allelic losses on these chromosome regions involved the paternal RF/J allele (19 of 20).

No association between particular DRD3 and DAT gene polymorphisms and manic-depressive illness in a Spanish sample

We have carried out an association study of a polymorphism in the 3'UTR of the dopamine transporter gene (DAT) and a polymorphism in the coding region of the D3 receptor gene (DRD3) in Spanish patients with manic depression and in controls. No significant differences in allelic and genotypic frequencies of either of these polymorphisms was found in patients compared with controls.

Lack of association between manic-depressive illness and a highly polymorphic marker from GABRA3 gene

We have carried out an association study between a dinucleotide repeat polymorphism in GABRA3 gene and manic-depressive illness in a Spanish population. This may be an important candidate gene for bipolar affective disorders since it is located in the Xq28 region, previously implicated in linkage studies. In addition, severe GABergic alterations have been reported in patients. We have not found significant differences between controls and patients in allele frequencies or genotypes.

A weak association between TH and DRD2 genes and bipolar affective disorder in a Spanish sample

Genetic factors play an important role in the aetiology of bipolar affective disorder (BP). So far, results of linkage studies have been largely disappointing. We have searched for a possible association between polymorphic DNA markers of two candidate genes (tyrosine hydroxylase, TH; dopamine D2 receptor gene, DRD2) and BP in a population from central Spain. Our results are consistent with the existence of a weak association between these two genes and BP, in such a way that TH and DRD2 could be considered as minor genes contributing to susceptibility.

Eight new polymorphic microsatellites in mouse gene loci

Eight mouse gene loci (Atp1b2, Epo, Kit, Krt2, Mor1, Ren1, Pdgfb, and Wnt1) that contain unidentified microsatellites were selected to detect simple sequence-length polymorphisms on genomic DNAs from two laboratory strains (C57BL/6J and RF/J) and strains recently derived from the Mus musculus species complex (CAST/Ei, MOLF/Ei, CZECH II, and M. m. domesticus) and from M. spretus (SPRET/Ei). All microsatellite DNA sequences varied in size among some of the seven mouse strains tested. These new polymorphisms might be useful in the search for tumor suppressor genes involved in specific cancers.

Molecular and cytological evidence of S-adenosyl-L-homocysteine as an innocuous undermethylating agent in vivo

Undermethylating agents are frequently used in the study of DNA methylation. However, the drugs of choice to induce experimental DNA undermethylation, 5-azacytidine and 5-aza-2'-deoxycytidine, are known to be cytotoxic. We report on S-adenosyl-L-homocysteine (SAH) as an alternative agent for inducing undermethylation of human DNA in vivo. The molecular and cytological evidence presented in this paper clearly suggests that SAH could be even more efficient than the cytidine analogs; in addition, SAH does not exhibit the secondary toxic effects that cripple the usefulness of cytidine analogs.

No association between dopamine D4 receptor polymorphism and manic depressive illness

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S-adenosyl-L-homocysteine: a non-cytotoxic hypomethylating agent

The cytotoxic effect caused by the hypomethylating agent S-adenosyl-L- homocysteine (SAH) was compared with that of two drugs commonly used to induce DNA hypomethylation, 5-azacytidine and 5-aza-2'-deoxycytidine. Two in vitro cytotoxicity tests, the tetrazolium MTT assay and the intracellular lactate dehydrogenase (LDH) activity test, suggest that SAH induces hypomethylation without causing any cytotoxic effect. We propose the use of SAH as a non-cytotoxic agent which may be more suitable for inducing experimental DNA hypomethylation.

An adaptation of the Maxam and Gilbert sequencing method to the study of human metaphase chromosomes

We have adapted the chemical DNA sequencing method developed by Maxam and Gilbert to study human metaphase chromosomes. Particularly, the in situ cytosine-specific chemical cleavage has been assayed. After exhaustive treatments, a C-like banding pattern was consistently shown. Since methyl groups interfere with the cytosine-specific chemical cleavage reaction, we assume that heterochromatin remains resistant as a result of the high level of methylation. On the other hand when moderate treatments are applied, T-bands remain as resistant regions, implying that these domains would be the most intensely methylated regions within euchromatin.

Dynamic mosaicism involving an unstable supernumerary der(22) chromosome in cat eye syndrome

We have studied a girl, her sister and her mother who had a supernumerary marker chromosome in mosaicism. The marker was studied by cytogenetic methods and non-isotopic in situ hybridization with the single D22S9 DNA probe which maps to 22q11. The supernumerary chromosome was derived from a chromosome 22 and it did not present the same morphology in all the cells. At least 5 distinct types of the marker chromosome were detected and some of them were probably derived from each other (dynamic mosaicism). The proposita had an MCA pattern consistent with mild cat eye syndrome, while her sister and her mother had some of the manifestations described in this syndrome. A specific correlation could be established between phenotype and karyotype.

Distribution of DYZ2 repetitive sequences on the human Y chromosome

The distribution of the 2000 copies of the Y-specific repetitive family DYZ2 is controversial since previous reports have mapped these sequences to different sites of the Yqh region. In this work, we have performed non-radioactive in situ hybridization of a cloned DYZ2 fragment at higher stringency conditions on 5-aza-cytidine-enlarged Y chromosomes; the results suggest a non-uniform distribution of these sequences, which are preferentially located at the proximal and distal parts of Yqh, including the C+/Q- heterochromatin at the boundary with the euchromatic region.

Induction of G- and R-banding in human chromosomes by the demethylating agent S-adenosyl-L-homocysteine

In this report we describe the procedure of growing human lymphocytes with the demethylating agent S-adenosyl-L-homocysteine (SAH). After this treatment, which is not toxic for cell survival, both R- and G-banding were obtained by new experimental procedures: R-bands have been directly demonstrated with the GC-specific fluorochrome chromomycin A3 without the necessity of any AT-specific counterstaining agent; simultaneous G-banding and active nucleolar organizer regions have been obtained by silver impregnation of chromosomes and subsequent Giemsa staining. These results suggest a possible relationship between local differences in DNA methylation and the determination of the banded chromosome structure.

Cytogenetic analysis of a human familial 15p+ marker chromosome

An extreme variant of a human 15p+ marker chromosome is described in a human family. The short arm of this variant is greatly enriched in ribosomal RNA genes, and there are up to three secondary constrictions potentially active for rRNA transcription. These sites are hypomethylated, whereas the rest of rDNA is highly methylated, as shown by the isoschizomer pair HpaII-MspI. This chromosome variant is similar to others previously described for chromosomes 14 and 22, but some differences have been found after C-banding and after treatments with AluI and Sau3AI.

Identification of human esterase D subunits from the homodimeric and heterodimeric forms of five phenotypes by a new two-dimensional isoelectric focusing method

A new two-dimensional isoelectric focusing method was developed to identify the human esterase D (EsD) subunits from the homodimeric and heterodimeric forms of five EsD phenotypes. EsD polymorphism was also analyzed by one-dimensional isoelectric focusing under reducing and mild denaturing conditions to study the influence of dithiothreitol and low concentrations of urea on the focusing pattern of the EsD dimers.

Cryptic variants of acrocentric human chromosomes as analysed by restriction endonucleases

Ten phenotypically normal human individuals have been analysed by in situ treatments with restriction endonucleases in order to obtain a better characterization of some cryptic variants of acrocentric chromosomes. Treatments with AluI, NdeII and Sau3AI confirm the existence of two cryptic amplified regions on the short arms of both one chromosome 15 and one chromosome 22, in one female. These amplifications seem to be of different origin involving the nucleolar organizer region of chromosome 15 and the satellite of chromosome 22.

Longitudinal differentiation of the human Yq heterochromatin as revealed by the restriction enzyme TaqI

The restriction endonuclease TaqI cleaves DNA at TCGA sites which are very common in human satellite DNAs. However, this enzyme was not used successfully up to now to digest constitutive heterochromatin of human chromosomes, where those highly repetitive DNAs are preferentially located. In this work, we show that TaqI is able to cut and extract DNA from the major heterochromatic regions on chromosomes 1, 9, 15, and 16 which appear as unstained gaps. Yq heterochromatin displays moderate digestion along its entire length but a middle region can be distinguished which is usually more affected. Complete digestion of Yq heterochromatin can be achieved when this block has been previously undercondensed by treating cell cultures with the cytidine analog, 5-azacytidine. Thus, it may be deduced that some factors related to chromatin organization might be involved in the action of TaqI. These results come to reinforce previous data about heterogeneity of Yq heterochromatin, and allow us to subdivide it into three different regions according to their differential response to TaqI digestion.

Genetic polymorphism of alpha-2-HS-glycoprotein in a Spanish population

The genetic polymorphism of alpha-2-HS-glycoprotein (AHSG) was analyzed in 489 unrelated individuals living in Madrid (central Spain), by isoelectric focusing in miniaturized polyacrylamide gels followed by immunoblotting. The allele frequencies were estimated to be 0.7147 and 0.2771 for AHSG*1 and AHSG*2, respectively. In addition to the common alleles, 3 rare variants (AHSG*3, AHSG*10 and AHSG*11) have been found in this study.

Visualization of R-bands in human metaphase chromosomes by the restriction endonuclease MseI

Human metaphase chromosomes were treated with the restriction endonuclease MseI, which cuts DNA at TTAA sequences. This enzyme preferentially cuts and extracts DNA from G-bands and thus is the first restriction endonuclease allowing direct R-band visualization. Specific patterns ranging from R+C-like to C-like banding can be induced, depending on the concentration of the enzyme. At intermediate concentrations, only a subset of R-bands are produced, corresponding to GC-rich bands that are especially resistant to heat denaturation (so-called T-bands). These results suggest that compositional differences between chromosomal regions determine the different rates of cleavage by MseI, not only between R- and G-bands but also among different R-bands.

New distinctions between regions of centromeric heterochromatin in human chromosomes by treatments with the isoschizomers NdeII-Sau3AI

The isoschizomers NdeII-Sau3AI (decreases GATC) have been used to characterize heterochromatic regions in human chromosomes. The findings with NdeII are identical with those previously published with MboI, but the results with Sau3AI provide evidence for new distinctions of centromeric heterochromatin in chromosomes 5 and 6. The results are discussed in relation to the chromatin organization at these regions an the mechanisms of the action of restriction endonucleases.

Characterization of human catalase by isoelectric focusing in presence of urea

Human catalase from erythrocytes and liver were analyzed by polyacrylamide gel isoelectric focusing in presence and absence of urea using two different pH gradients, namely pH 6-8 and pH 6.7-7.7. In presence of urea, human catalase focused in the pH range 6.75-7.0, slightly anodal to that of hemoglobin A. In narrow pH gradients, human erythrocyte catalase was microheterogeneous. Neuraminidase from different sources and peptide-N-glycosidase F were applied to investigate the presence of sialic acid and/or carbohydrate chains in human catalase. A shift in the focusing pattern of both erythrocyte and liver catalase towards the anode was observed after treatment with one of the commercially available neuroaminidase preparations. This unusual result could be related to a contaminating protease since no effect was observed when the catalases were treated in presence of a serine protease inhibitor. In contrast, bovine liver and Macaca erythrocyte catalase did not display any detectable change in their focusing patterns after treatment with any of the neuraminidase preparations.

Haptoglobin subtyping by isoelectric focusing in miniaturized polyacrylamide gels rehydrated in presence of 2-mercaptoethanol

A fast isoelectric focusing method for routine haptoglobin (Hp) subtyping is presented. This method is based on isoelectric focusing, under reducting conditions, of neuraminidase-treated plasma samples by using dry miniaturized (interelectrode distance: 55 mm) polyacrylamide gel, rehydrated in presence of 2-mercaptoethanol and a mixture of pharmalyte carrier ampholytes (pH 4-6.5 and pH 6-8) followed by immunoblotting. The presence of 2-mercaptoethanol in the gel prevented refolding of the Hp alpha and Hp beta chains during focusing, making it possible to obtain a sharp Hp band pattern with a clear separation of the different Hp alpha allelic products (1S, 1F, 2FS, 2SS and 2FF). A population study carried out with 250 unrelated individuals living in Central Spain is also presented.

Nucleolar dominance in interracial hybrids of the Steropleurus martorelli complex

Two new chromosomal races (V and VI) of the Steropleurus martorelli complex, as well as the corresponding natural interracial hybrids, have been found in a region in southern Spain. Hybrids can be easily distinguished because they are heterozygous for a large L2 pair (submetacentric–telocentric), which in addition carries the major nucleolar organizer region (NOR). Silver staining reveals that the chromosomal rearrangement involved in the origin of these two chromosomal races does not affect the expression of the major active NOR in the parental homozygous races, but a nucleolar dominance phenomenon can be detected in the heterozygous hybrids, which tends to suppress NOR activity in the telocentric L2 chromosome from race VI.Key words: Steropleurus martorelli complex, nucleolar organizer region activity, nucleolar dominance, interracial hybrid.

Breaking up the chromosomes of Baetica ustulata by in situ treatments with restriction endonucleases

Fixed chromosomes of Baetica ustulata were treated with restriction endonucleases and subsequently stained with either Giemsa or the DNA-specific dye propidium iodide. Each enzyme produces a specific banding pattern with both dyes, which demonstrates the value of restriction endonucleases for chromosome banding in this species. The results obtained agree with the hypothesis that the action of restriction enzymes is based on cutting and extraction of DNA and is essentially determined by DNA base composition rather than by chromatin structure. However, strictly centric bands could be an exception. At least nine chromatin types can be distinguished in B. ustulata according to their different response to enzyme digestion and to the fluorescence banding patterns. Differential digestion of specific heterochromatic areas in band 4.4 and in the supernumerary segment of M5 by the HpaII – MspI enzyme pair suggests a high level of DNA methylation at these regions. The distribution of the different classes of DNA repeated sequences in the chromosome complement of B. ustulata indicates that some bands seem to follow the general principles of heterochromatin equilocality, while conceited evolution of heterochromatic DNA in other regions might have different rates of convergence in this species.Key words: restriction endonucleases, chromatin heterogeneity, methylated bands, equilocality, concerted evolution.