SARS CoV subunit vaccine: antibody-mediated neutralisation and enhancement

1. A SARS vaccine was produced based on recombinant native full-length Spike-protein trimers (triSpike) and efficient establishment of a vaccination procedure in rodents. 2. Antibody-mediated enhancement of SARS-CoV infection with anti-SARS-CoV Spike immune-serum was observed in vitro. 3. Antibody-mediated infection of SARS-CoV triggers entry into human haematopoietic cells via an FcγR-dependent and ACE2-, pH-, cysteine-protease-independent pathways. 4. The antibody-mediated enhancement phenomenon is not a mandatory component of the humoral immune response elicited by SARS vaccines, as pure neutralising antibody only could be obtained. 5. Occurrence of immune-mediated enhancement of SARS-CoV infection raises safety concerns regarding the use of SARS-CoV vaccine in humans and enables new ways to investigate SARS pathogenesis (tropism and immune response deregulation).

Cytogenetic and fluorescence in situ hybridization monitoring in Ph+ Chronic Myeloid Leukemia patients treated with imatinib mesylate

Imatinib mesylate determines a favorable clinical course in most Ph positive Chronic Myeloid Leukemia (CML) patients in the chronic phase. Cytogenetic response is usually evaluated by analyzing 20-25 bone marrow metaphases using standard banding techniques. Since this methodology has very low sensitivity, we compared the results obtained by standard banding techniques to the ones obtained by fluorescent in situ hybridization (FISH). This was also done to identify any possible discrepancies between the two techniques. We analyzed 40 Ph+ CML patients in the chronic phase who had previously been treated with interferon alpha (IFNalpha) and who were receiving imatinib. The studies were performed by utilizing the same BM cell samples fixed in acetic acid/methanol, before imatinib therapy and then quarterly. Comparison of cytogenetic results to FISH results at 3 and 6 months of imatinib treatment showed that some patients who had achieved major cytogenetic response (i.e.<35% of examined metaphases showing Ph), showed retention of a higher number of persisting Ph+ cells when examined by FISH, and they did not achieve major FISH response (i.e. <35% of examined interphase cells show the BCR-ABL fusion signal). The discrepancy we found between the results that were obtained by analyzing metaphases and interphase cells disappeared in the subsequent examinations. Moreover, we found that 4 patients (10%) were still Ph+ in all the metaphases we examined even though they achieved excellent clinical response. On the basis of this small series of patients, we suggest that cytogenetic evaluation of patients on imatinib therapy should be performed by utilizing the classic banding technique (metaphase examination), but also by using the FISH technique (interphase examination), since the two methodologies may provide different results.

Identification and functional expression of HCx31.9, a novel gap junction gene

By combining in silico and bench molecular biology methods we have identified a novel human gap junction gene that encodes a protein designated HCx31.9. We have determined its human chromosomal location and gene structure, and we have identified a putative mouse ortholog, mCx30.2. We have observed the presence of HCx31.9 in human cerebral cortex, liver, heart, spleen, lung, and kidney and the presence of mCx30.2 in mouse cerebral cortex, liver and lung. Moreover, preliminary data on the electrophysiological properties of HCx31.9 have been obtained by functional expression in paired Xenopus oocytes and in transfected N2A cells.

Functional analysis of a dominant mutation of human connexin26 associated with nonsyndromic deafness

Cx26 has been implicated in dominant (DFNA3) and recessive (DFNB1) forms of nonsyndromic sensorineural deafness. While most homozygous DFNB1 Cx26 mutations result in a simple loss of channel activity, it is less clear how heterozygous mutations in Cx26 linked to DFNA3 cause hearing loss. We have tested the ability of one dominant mutation (W44C) to interfere with wild-type human Cx26 (HCx26wt). HCx26wt induced robust electrical conductance between paired oocytes, and facilitated dye transfer between transfected HeLa cells. In contrast, oocyte pairs injected with only W44C were not electrically coupled above background levels, and W44C failed to dye couple transfected HeLa cells. Moreover, W44C dramatically inhibited intercellular conductance of HCx26wt when co-expressed in an equal ratio, and the low levels of residual conductance displayed altered gating properties. A nonfunctional recessive mutation (W77R) did not inhibit the ability of HCx26wt to form functional channels when co-injected in the same oocyte pairs, nor did it alter HCx26wt gating. These results provide evidence for a functional dominant negative effect of the W44C mutant on HCx26wt and explain how heterozygous Cx26 mutations could contribute to autosomal dominant deafness, by resulting in a net loss, and/or alteration, of Cx26 function.

Loss-of-function and residual channel activity of connexin26 mutations associated with non-syndromic deafness

Connexins are the protein subunits of gap junction channels that allow a direct signaling pathway between networks of cells. The specific role of connexin channels in the homeostasis of different organs has been validated by the association of mutations in several human connexins with a variety of genetic diseases. Several connexins are present in the mammalian cochlea and at least four of them have been proposed as genes causing sensorineural hearing loss. We have started our functional analysis by selecting nine mutations in Cx26 that are associated with non-syndromic recessive deafness (DFNB1). We have observed that both human Cx26 wild-type (HCx26wt) and the F83L polymorphism, found in unaffected controls, generated electrical conductance between paired Xenopus oocytes, which was several orders of magnitude greater than that measured in water-injected controls. In contrast, most recessive Cx26 mutations (identified in DFNB1 patients) resulted in a simple loss of channel activity. In addition, the V37I mutation, originally identified as a polymorphism in heterozygous unaffected individuals, was devoid of function and thus may be pathologically significant. Unexpectedly, we have found that the recessive mutation V84L retained functional activity in both paired Xenopus oocytes and transfected HeLa cells. Furthermore, both the magnitude of macroscopic junctional conductance and its voltage-gating properties were indistinguishable from those of HCx26wt. The identification of functional differences of disease causing mutations may lead to define which permeation or gating properties of Cx26 are necessary for normal auditory function in humans and will be instrumental in identifying the molecular steps leading to DFNB1.

Altered gene expression in Schwann cells of connexin32 knockout animals

The discovery that the dominant X-linked form of Charcot-Marie-Tooth disease (CMTX), a genetic disease of the peripheral nervous system (PNS), is associated with mutations in connexin32 (Cx32) has brought attention to the importance of connexins in glial cell biology. To gain further insight into the consequences of Cx32 deficiency, we have undertaken a detailed characterization of the gene expression profile of Schwann cells isolated from the sciatic nerve of wild-type and Cx32-null mice. Schwann cells exhibit two distinct phenotypes, myelinating and nonmyelinating, which are defined by their different morphology with respect to axons and by their unique profile of gene expression. Our findings show that, regardless of the mouse genotype, cultured Schwann cells express similar levels of messages for a number of connexins and for genes characteristic of both the myelinating and the nonmyelinating phenotypes. Furthermore, we have identified Cx36, a member of the gamma subclass of connexins, which are preferentially expressed in neuronal cells of mouse brain and retina, as an additional connexin present in Schwann cells. Mice lacking Cx32, however, exhibited a marked up-regulation of glial fibrillary acidic protein (GFAP), a cytoskeletal protein usually synthesized only by nonmyelinating Schwann cells. This observation was extended to the PNS in vivo and did not reflect a general perturbation of the expression of other nonmyelinating Schwann cell genes. These findings demonstrate that the absence of Cx32 results in a distinct pattern of gene dysregulation in Schwann cells and that Schwann cell homeostasis is critically dependent on the correct expression of Cx32 and not just any connexin. Identifying the relationship between increased GFAP expression and the absence of Cx32 could lead to the definition of specific roles for Cx32 in the control of myelin homeostasis and in the development of CMTX.

First genetic evidence of GABA(A) receptor dysfunction in epilepsy: a mutation in the gamma2-subunit gene

Major advances in the identification of genes implicated in idiopathic epilepsy have been made. Generalized epilepsy with febrile seizures plus (GEFS+), benign familial neonatal convulsions and nocturnal frontal lobe epilepsy, three autosomal dominant idiopathic epilepsies, result from mutations affecting voltage-gated sodium and potassium channels, and nicotinic acetylcholine receptors, respectively. Disruption of GABAergic neurotransmission mediated by gamma-aminobutyric acid (GABA) has been implicated in epilepsy for many decades. We now report a K289M mutation in the GABA(A) receptor gamma2-subunit gene (GABRG2) that segregates in a family with a phenotype closely related to GEFS+ (ref. 8), an autosomal dominant disorder associating febrile seizures and generalized epilepsy previously linked to mutations in sodium channel genes. The K289M mutation affects a highly conserved residue located in the extracellular loop between transmembrane segments M2 and M3. Analysis of the mutated and wild-type alleles in Xenopus laevis oocytes confirmed the predicted effect of the mutation, a decrease in the amplitude of GABA-activated currents. We thus provide the first genetic evidence that a GABA(A) receptor is directly involved in human idiopathic epilepsy.

Learning the language of cell-cell communication through connexin channels

A report on the Ninth International Gap Junction Conference, Honolulu, USA, 4-9 August 2001.

Molecular and functional diversity of neural connexins in the retina

Electrical synapses (gap junctions) in neuronal circuits have become a major focus in the study of network properties such as synchronization and oscillation (Galarreta and Hestrin, 1999; Gibson et al., 1999). Despite the recent progress made in unraveling the contribution of gap junctions to network behavior, little is known about the molecular composition of the junctional constituents. By cloning gap junction proteins [connexins (Cxs)] from zebrafish retina and through functional expression, we demonstrate that the retina possesses a high degree of connexin diversity, which may account for differential functional properties of electrical synapses. Three new Cxs, designated as zebrafish Cx27.5 (zfCx27.5), zfCx44.1, and zfCx55.5, and the carp ortholog of mammalian Cx43 were cloned. By in situ hybridization and in situ RT-PCR, we demonstrate that the four fish connexin mRNAs show differential localization in the retina. Transient functional expression in paired Xenopus oocytes and in the neuroblastoma N2A cell line indicate an extreme range of electrophysiological properties of these connexins in terms of voltage dependence and unitary conductance. For instance, the new zfCx44.1 exhibited high sensitivity to voltage-induced closure with currents decaying rapidly for transjunctional potentials >10 mV, whereas zfCx55.5 channels showed an opposite voltage dependence in response to voltage steps of either polarity. Moreover, although zfCx44.1 channels showed unitary conductance as high as any previously reported for junctional channels (nearly 300 pS), zfCx55. 5 and zfCx27.5 exhibited much lower unitary conductances (<60 pS).

Gap junctions: fates worse than death?

The reasons for the molecular heterogeneity of connexin channels in vivo remain unclear. Functional replacement of one connexin gene with another has now revealed unexpected phenotypes and shows that cellular homeostasis depends not simply on cell-cell communication but also on the correct types of connexin.

Intercellular communication in the eye: clarifying the need for connexin diversity

In the vertebrate eye, virtually every cell type is directly coupled to its neighbors by intercellular channels present in gap junctions. Although these structures share the common property of allowing adjacent cells to directly exchange ions, second messengers and small metabolites, intercellular channels in the eye also play a specific role in distinct functions such as neuronal transmission at electrotonic synapses in the retina, and the maintenance of homeostasis in the avascular lens. The structural proteins comprising these channels, the connexins (Cx), are a multigene family of which many members are expressed in the eye, even in the same cell type. This molecular heterogeneity poses the crucial question of whether and how a diversity in gap junctional structural proteins influences intercellular communication in ocular tissues. This review will focus on two recent advances in the understanding of connexin diversity in regard to the eye. First, connexin knockouts have demonstrated that postnatal development and homeostasis in the lens requires multiple connexin proteins. Secondly, functional characterization of new connexins that are abundantly expressed in the retina has revealed biophysical properties that mimic those recorded from retinal neurons.

Connexin channels in Schwann cells and the development of the X-linked form of Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease comprises a group of genetically heterogenous disorders of the peripheral nervous system. The X-linked form of Charcot-Marie-Tooth (CMTX) is associated with mutations in the gene encoding the gap junction protein connexin32 (Cx32), which is expressed in Schwann cells. Immunocytochemical evidence suggests that Cx32 is localized to the incisures of Schmidt-Lanterman and the paranodes of myelinating Schwann cells, where it appears to form reflexive gap junctions. It is currently thought that this cytoplasmic continuity provides a much shorter diffusion pathway for the transport of ions, metabolites and second messenger molecules through intracellular channels between the adaxonal and peri-nuclear regions of Schwann cells, across the myelin sheath. This review summarizes our current understanding of the role of connexins in Schwann cells and focuses on the lessons for channel function and disease pathophysiology derived from the functional analysis of Cx32 mutations. One of the most intriguing aspects emerging from this work is that several mutations retain functional competence, although the mutated channels exhibit altered gating properties. This suggests that partial and/or selective disruption of the radial communication pathway formed by Cx32 is sufficient to cause a functional deficit and lead to the development of CMTX. The next challenge will be to define, at the molecular level, the sequence of events involved in the disease process. The presence of a group of functional mutations should help understand the cellular basis of CMTX, by allowing the identification of the specific molecules that need to be exchanged through Cx32 channels, but are excluded from the mutated ones.

Functional properties, developmental regulation, and chromosomal localization of murine connexin36, a gap-junctional protein expressed preferentially in retina and brain

Retinal neurons of virtually every type are coupled by gap-junctional channels whose pharmacological and gating properties have been studied extensively. We have begun to identify the molecular composition and functional properties of the connexins that form these 'electrical synapses,' and have cloned several that constitute a new subclass (gamma) of the connexin family expressed predominantly in retina and brain. In this paper, we present a series of experiments characterizing connexin36 (Cx36), a member of the gamma subclass that was cloned from a mouse retinal cDNA library. Cx36 has been localized to mouse chromosome 2, in a region syntenic to human chromosome 5, and immunocytochemistry showed strong labeling in the ganglion cell and inner nuclear layers of the mouse retina. Comparison of the developmental time course of Cx36 expression in mouse retina with the genesis of the various classes of retinal cells suggests that the expression of Cx36 occurs primarily after cellular differentiation is complete. Because photic stimulation can affect the gap-junctional coupling between retinal neurons, we determined whether lighting conditions might influence the steady state levels of Cx36 transcript in the mouse retina. Steady-state levels of Cx36 transcript were significantly higher in animals reared under typical cyclic-light conditions; exposure either to constant darkness or to continuous illumination reduced the steady-state level of mRNA approximately 40%. Injection of Cx36 cRNA into pairs of Xenopus oocytes induced intercellular conductances that were relatively insensitive to transjunctional voltage, a property shared with other members of the gamma subclass of connexins. Like skate Cx35, mouse Cx36 was unable to form heterotypic gap-junctional channels when paired with two other rodent connexins. In addition, mouse Cx36 failed to form voltage-activated hemichannels, whereas both skate and perch Cx35 displayed quinine-sensitive hemichannel activity. The conservation of intercellular channel gating contrasts with the failure of Cx36 to make hemichannels, suggesting that the voltage-gating mechanisms of hemichannels may be distinct from those of intact intercellular channels.

Complex chromosome rearrangements may locate the bcr/abl fusion gene sites other than 22q11

BACKGROUND AND OBJECTIVE

From 5-8% of Philadelphia (Ph) positive patients with chronic myeloid leukemia (CML) show variant translocations in which at least a third chromosome in addition to 9q34 and 22q11 is involved. The formation mechanisms and clinical significance of variant Ph translocations are still unclear. The BCR/ABL chimeric gene encoding for chimeric proteins is always present and maps on the 22q- regardless of the type of translocation. We studied two apparently Ph negative CML patients with unusual karyotypes both showing a typical b3a2 rearrangement.

DESIGN AND METHODS

Dual-color fluorescence in situ hybridization (FISH) can visualize BCR and ABL genes and localize the BCR/ABL fusion gene. We used FISH to study the formation mechanisms of variant Ph translocations in two patients.

RESULTS

The chimeric BCR/ABL gene was located on a locus other than the expected 22q11 in both patients. In the first case the fusion signal was present on the 9q34 band whereas in the second patient it was detected on chromosome 8, involved in masked Ph formation.

INTERPRETATION AND CONCLUSIONS

The location of the hybrid BCR/ABL gene on chromosomes other than 22q- is a rare event which can only be observed using the FISH technique. When these unusual translocations occur the hypothesis most often put forward is that several consecutive cytogenetic events have taken place. The factors which regulate the formation of these breakpoints have yet to be clarified. The FISH technique allows the identification of chromosome rearrangements that could not otherwise be detected by conventional banding procedures. The location of the hybrid BCR/ABL gene on sites other than 22q11 represents a rare type of variant Ph translocation. The real frequency and clinical significance of such rearrangements need to be investigated.

Functional characteristics of skate connexin35, a member of the gamma subfamily of connexins expressed in the vertebrate retina

Retinal neurons are coupled by electrical synapses that have been studied extensively in situ and in isolated cell pairs. Although many unique gating properties have been identified, the connexin composition of retinal gap junctions is not well defined. We have functionally characterized connexin35 (Cx35), a recently cloned connexin belonging to the gamma subgroup expressed in the skate retina, and compared its biophysical properties with those obtained from electrically coupled retinal cells. Injection of Cx35 RNA into pairs of Xenopus oocytes induced intercellular conductances that were voltage-gated at transjunctional potentials >/= 60 mV, and that were also closed by intracellular acidification. In contrast, Cx35 was unable to functionally interact with rodent connexins from the alpha or beta subfamilies. Voltage-activated hemichannel currents were also observed in single oocytes expressing Cx35, and superfusing these oocytes with medium containing 100 microm quinine resulted in a 1.8-fold increase in the magnitude of the outward currents, but did not change the threshold of voltage activation (membrane potential = +20 mV). Cx35 intercellular channels between paired oocytes were insensitive to quinine treatment. Both hemichannel activity and its modulation by quinine were seen previously in recordings from isolated skate horizontal cells. Voltage-activated currents of Cx46 hemichannels were also enhanced 1. 6-fold following quinine treatment, whereas Cx43-injected oocytes showed no hemichannel activity in the presence, or absence, of quinine. Although the cellular localization of Cx35 is unknown, the functional characteristics of Cx35 in Xenopus oocytes are consistent with the hemichannel and intercellular channel properties of skate horizontal cells.

Different TBX5 interactions in heart and limb defined by Holt-Oram syndrome mutations

To better understand the role of TBX5, a T-box containing transcription factor in forelimb and heart development, we have studied the clinical features of Holt-Oram syndrome caused by 10 different TBX5 mutations. Defects predicted to create null alleles caused substantial abnormalities both in limb and heart. In contrast, missense mutations produced distinct phenotypes: Gly80Arg caused significant cardiac malformations but only minor skeletal abnormalities; and Arg237Gln and Arg237Trp caused extensive upper limb malformations but less significant cardiac abnormalities. Amino acids altered by missense mutations were located on the three-dimensional structure of a related T-box transcription factor, Xbra, bound to DNA. Residue 80 is highly conserved within T-box sequences that interact with the major groove of target DNA; residue 237 is located in the T-box domain that selectively binds to the minor groove of DNA. These structural data, taken together with the predominant cardiac or skeletal phenotype produced by each missense mutation, suggest that organ-specific gene activation by TBX5 is predicated on biophysical interactions with different target DNA sequences.

Complex structural involvement of chromosome 7 in primary myelodysplastic syndromes determined by fluorescence in situ hybridization

Cytogenetic analysis of 72 consecutive de novo myelodysplastic syndrome patients revealed monosomy 7 in 12 cases. In 4 of these cases, the -7 was the only abnormality, whereas the remaining 8 cases showed additional chromosomal aberrations. Fluorescence in situ hybridization (FISH) utilizing chromosome 7 alpha-satellite and painting probes and other specific probes, when necessary, provided evidence of unusual and unsuspected structural rearrangements involving chromosome 7. FISH analysis showed that the small fragment found in one patient and the ring found in each of two other patients were chromosome 7-derived rings. FISH also revealed the insertion of chromosome 7 sequences into autosomes in three other patients and unusual translocations in the remaining two patients. By comparing the results obtained by using banding techniques to those obtained by using the FISH technique, we deduced the involvement of chromosome 7 with partial deletion of the short arm in all eight examined patients. Our study confirms the ability of FISH to detect chromosomal aberrations that would otherwise not be identified and the tendency of chromosome 7 to be involved in many different rearrangements. From a clinical point of view, we confirm that patients affected by myelodysplastic syndromes with complex karyotypes involving chromosome 7 do not respond to treatment and have a poor prognosis.

Cloning and expression of two related connexins from the perch retina define a distinct subgroup of the connexin family

We have cloned cDNAs for two closely related connexins (Cx), Cx35 and Cx34.7, from a perch retinal cDNA library. Sequencing of PCR products from genomic DNA revealed that both connexins have an intron 71 bp after the translation initiation site; in Cx35, the intron is 900 bp in length, whereas in Cx34.7 it is approximately 20 kb. Southern blots of genomic DNA suggest that the two connexins represent independent single copy genes. In Northern blots, Cx35 and Cx34.7 transcripts were detected in retina and brain; Cx34.7 also showed a weak signal in smooth muscle (gut) RNA. Antibodies against Cx35 labeled a 30 kDa band on a Western blot of retinal membranes, and in histological sections, the pattern of antibody recognition was consistent with labeling of bipolar cells and unidentified processes in the inner plexiform and nerve fiber layers. When expressed in Xenopus oocytes, Cx35 and Cx34.7 formed homotypic gap junctions, but the junctional conductance between paired oocytes expressing Cx35 was 10-fold greater than that recorded for gap junctional channels formed by Cx34.7. The homotypic gap-junctional channels were closed in a voltage-dependent manner but with relatively weak voltage sensitivity. Heterotypic gap junctions formed by Cx35 and Cx34.7 displayed junctional conductances similar to those of Cx34.7 homotypic pairs and showed a slightly asymmetric current-voltage relationship; the side expressing Cx35 exhibited a higher sensitivity to transjunctional potentials. An analysis of the sequence and gene structure of the connexin family revealed that perch Cx35 and Cx34.7, skate Cx35, and mouse Cx36 constitute a novel gamma subgroup.

Connexin32 mutations associated with X-linked Charcot-Marie-Tooth disease show two distinct behaviors: loss of function and altered gating properties

The X-linked form of Charcot-Marie-Tooth disease (CMTX) is associated with mutations in the gene encoding connexin32 (Cx32), which is expressed in Schwann cells. We have compared the functional properties of 11 Cx32 mutations with those of the wild-type protein by testing their ability to form intercellular channels in the paired oocyte expression system. Although seven mutations were functionally incompetent, four others were able to generate intercellular currents of the same order of magnitude as those induced by wild-type Cx32 (Cx32wt). In homotypic oocyte pairs, CMTX mutations retaining functional activity induced the development of junctional currents that exhibited changes in the sensitivity and kinetics of voltage dependence with respect to that of Cx32wt. The four mutations were also capable of interacting in heterotypic configuration with the wild-type protein, and in one case the result was a marked rectification of junctional currents in response to voltage steps of opposite polarity. In addition, the functional CMTX mutations displayed the same selective pattern of compatibility as Cx32wt, interacting with Cx26, Cx46, and Cx50 but failing to do so with Cx40. Although the functional mutations exhibited sensitivity to cytoplasmic acidification, which induced a >/=80% decrease in junctional currents, both the rate and extent of channel closure were enhanced markedly for two of them. Together, these results indicate that the functional consequences of CMTX mutations of Cx32 are of two drastically distinct kinds. The presence of a functional group of mutations suggests that a selective deficit of Cx32 channels may be sufficient to impair the homeostasis of Schwann cells and lead to the development of CMTX.

High frequency of trisomy 8 in acute promyelocytic leukemia: a fluorescence in situ hybridization study

Correct diagnosis of acute promyelocytic leukemia (APL) requires proof of the translocation (15;17)(q24;q11), which appears to be absolutely specific for this particular type of myeloid disorder. We studied the karyotypes of 29 consecutive APL patients at diagnosis: in 5 of them banding techniques failed to detect the t(15;17). In these seemingly cytogenetically negative cases, fluorescence in situ hybridization (FISH) with a chromosome 17 painting probe detected a high percentage of mitoses with 3 hybridization signals: one derived from the intact chromosome 17, and 2 from the rearranged chromosomes 15 and 17. Trisomy 8 (+8) as a secondary chromosomal abnormality was observed in 8 cases (27.5%), confirming that the t(15;17) favors the acquisition of an extra chromosome 8. One of these 8 cases showed a marker that was interpreted by FISH analysis as der(8) with duplication of a segment of the long arm carrying the c-MYC allele. Clinical features of patients with t(15;17) and +8 were no different from patients with t(15;17) alone. The usefulness of FISH to standard banding techniques in the detection of specific structural and/or numerical chromosomal abnormalities is confirmed in this report.

Amplified c-MYC sequences localized by fluorescence in-situ hybridization on double minute chromosomes in acute myeloid leukemias

Double minute chromosomes (dmin) are small acentric fragments frequently observed when karyotyping human tumor cells. They are considered the cytogenetic manifestation of gene amplification. The finding of dmin in leukemia is a rare event usually associated with progression of the disease and unfavorable prognosis. We present four patients affected by myeloid disorders with an abnormal karyotype and a variable number of dmin. In an attempt to clarify the origin of the dmin and the amplified gene, we utilized a fluorescent in-situ hybridization (FISH) technique and a panel of specific probes. The results of the analysis indicate that, although chromosomes 8 are apparently uninvolved, dmin retained c-MYC sequencs in three cases. By observing previously reported cases, we found that the majority of patients with myeloid disorders and dmin showed an amplified c-MYC gene, regardless of the chromosomal abnormalities. The FISH technique proved to be informative in demonstrating gene amplification in both metaphase and interphase cells. Finally, in the one patient carrying a 20q deletion, FISH allowed the detection of a previously unreported translocation between a 16p and the 20q-, confirming the ability of the technique to understand complex karyotypes.

Gap junctions: getting the message through

Connexin proteins make intercellular channels - gap junctions - which provide a direct pathway for cell-cell signaling in vertebrates. Studies of mice lacking connexin genes have demonstrated the need for intercellular transfer of messenger molecules and are uncovering the specific functions of each connexin.

Duplication of the der(13)t(12;13)(p13;q14) in chronic myelomonocytic leukemia

A case of chronic myelomonocytic leukemia with a reciprocal translocation (12;13)(p13;q14) and other numerical and structural abnormalities is described. Most of the metaphases examined showed duplication of the der(13)t(12;13), leading to trisomy of the translocated segment of chromosome 12. Using fluorescence in situ hybridization we observed that the breakpoint on chromosome 13 is centromeric to the retinoblastoma gene. Since other cases with apparently similar t(12;13) have recently been reported, we conclude that this structural rearrangement may be a rare but non random event in hematologic disorders.

Connexins, gap junctions and cell-cell signalling in the nervous system

Connexins form a multigene family of polytopic membrane proteins that, in vertebrates, are the constitutive subunits of intercellular channels and provide the structural basis for electrical coupling. The appearance of electrical coupling in the nervous system is developmentally regulated and restricted to distinct cell types. Electrical coupling between neurons persists after the establishment of chemical transmission, thus suggesting that this form of cell-cell signalling may be functionally interrelated with, rather than alternative to chemical transmission. Furthermore, evidence for the possible role of gap junctions in human neurological diseases is also mounting, following the discovery that the X-linked form of Charcot-Marie-Tooth syndrome, a demyelinating neuropathy of the peripheral nervous system, is associated with mutations in a connexin gene. These findings raise new questions on the significance of connexin diversity and on their functional role in the nervous system.

Dominant inhibition of intercellular communication by two chimeric connexins

1. The physiological significance of communication through gap junction channels has been difficult to assess because channel activity cannot be experimentally modulated in a specific manner. To address this problem we have constructed chimeric connexins that function as dominant-negative inhibitors of intercellular channel activity.

Granulocytes with segmented nucleus retain normal chromosomes 17 in Philadelphia chromosome-positive chronic myeloid leukemia with i(17q) and pseudo-Pelger anomaly. A case report studied with fluorescence in situ hybridization

Previous reports suggested a correlation between the deletion of the terminal region of the short arm of a chromosome 17 and the appearance of dysgranulopoiesis in myeloproliferative disorders. Using the dual-color fluorescence in situ hybridization technique we analyzed the bone marrow and peripheral blood cells of a Philadelphia chromosome-positive chronic myeloid leukemia (CML) patient showing at the onset of transformation into blastic crisis both metaphases with the i(17q) as well as granulocytes without nuclear segmentation. This phenomenon is defined as pseudo-Pelger-Huët anomaly. Using two probes, one specific for 17p and one for 17q, we determined the presence or absence of the i(17q) in both metaphase and interphase cells. Moreover, we observed that all cells with a polysegmented nucleus typical of mature granulocytes did not have i(17q) but had two normal chromosomes 17. This observation confirmed the correlation between 17p deletion and the appearance of pseudo-Pelger anomaly. This finding may also be useful from a clinical point of view: the appearance of pseudo-Pelger cells in CML indicates that 17p deletion actually occurred. This event implies a negative prognosis.

The cellular Internet: on-line with connexins

Most cells communicate with their immediate neighbors through the exchange of cytosolic molecules such as ions, second messengers and small metabolites. This activity is made possible by clusters of intercellular channels called gap junctions, which connect adjacent cells. In terms of molecular architecture, intercellular channels consist of two channels, called connexons, which interact to span the plasma membranes of two adjacent cells and directly join the cytoplasm of one cell to another. Connexons are made of structural proteins named connexins, which compose a multigene family. Connexin channels participate in the regulation of signaling between developing and differentiated cell types, and recently there have been some unexpected findings. First, unique ionic- and size-selectivities are determined by each connexin; second, the establishment of intercellular communication is defined by the expression of compatible connexins; third, the discovery of connexin mutations associated with human diseases and the study of knockout mice have illustrated the vital role of cell-cell communication in a diverse array of tissue functions.

Multiple connexin proteins in single intercellular channels: connexin compatibility and functional consequences

In vertebrates, the protein subunits of intercellular channels found in gap junctions are encoded by a family of genes called connexins. These channels span two plasma membranes and result from the association of two half channels, or connexons, which are hexameric assemblies of connexins. Physiological analysis of channel formation and gating has revealed unique patterns of connexin-connexin interaction, and uncovered novel functional characteristics of channels containing more than one type of connexin protein. Structure-function studies have further demonstrated that unique domains within connexins participate in the regulation of different functional properties of intercellular channels. Thus, gap junctional channels can contain more than one connexin, and this structural heterogeneity has functional consequences in vitro. Moreover, emerging evidence for the existence of intercellular channels containing multiple connexins in native tissues suggests that the functional diversity generated by connexin-connexin interaction could contribute to complex communication patterns that have been observed in vivo.

Loss of telomeric sequences in a ring derived from chromosome 8 in refractory anemia with excess of blasts in transformation

Using the fluorescence in situ hybridization technique, we analyzed a ring chromosome that appeared as a karyotype evolution in a patient affected by refractory anemia with excess of blasts in transformation. Metaphases hybridized with a chromosome-8-specific centromeric probe indicated that the ring retained the centromere of chromosome 8. Successively, utilizing a probe specific for all human telomeres, we observed that the ring lost telomeric sequences. This study demonstrated that the formation of a ring chromosome in hematologic disorders can cause loss of genetic material not revealed by banding techniques and therefore providing further proof of the advantages of molecular cytogenetic techniques.

Connections with connexins: the molecular basis of direct intercellular signaling

Adjacent cells share ions, second messengers and small metabolites through intercellular channels which are present in gap junctions. This type of intercellular communication permits coordinated cellular activity, a critical feature for organ homeostasis during development and adult life of multicellular organisms. Intercellular channels are structurally more complex than other ion channels, because a complete cell-to-cell channel spans two plasma membranes and results from the association of two half channels, or connexons, contributed separately by each of the two participating cells. Each connexon, in turn, is a multimeric assembly of protein subunits. The structural proteins comprising these channels, collectively called connexins, are members of a highly related multigene family consisting of at least 13 members. Since the cloning of the first connexin in 1986, considerable progress has been made in our understanding of the complex molecular switches that control the formation and permeability of intercellular channels. Analysis of the mechanisms of channel assembly has revealed the selectivity of inter-connexin interactions and uncovered novel characteristics of the channel permeability and gating behavior. Structure/function studies have begun to provide a molecular understanding of the significance of connexin diversity and demonstrated the unique regulation of connexins by tyrosine kinases and oncogenes. Finally, mutations in two connexin genes have been linked to human diseases. The development of more specific approaches (dominant negative mutants, knockouts, transgenes) to study the functional role of connexins in organ homeostasis is providing a new perception about the significance of connexin diversity and the regulation of intercellular communication.

Fluorescence in situ hybridization provides evidence for two-step rearrangement in a masked Ph chromosome formation

A chronic myelogenous leukemia (CML) patient with a masked Ph chromosome due to the translocation (9;10;22)(q34;q24;q11) is reported. Banding analysis showed a 9q+ chromosome typical of standard t(9;22)(q34;q11), and fluorescence in situ hybridization studies confirmed the involvement of a chromosome 10 in the masked Ph formation and also the presence of 3' ABL-DNA sequences in the der(22). This complex rearrangement could be explained by two consecutive translocations: the first, a standard t(9;22) (q34;q11), the second, a translocation between a chromosome 10 and the der(22) with a breakpoint in sequences derived from chromosome 9 telomeric to the ABL gene. By reverse transcription polymerase chain reaction (RT-PCR), we studied the BCR/ABL transcript junction: a chimeric m-RNA b3-a2, indicating a breakpoint within the major breakpoint cluster region, was found.