Das Deutsche Netzwerk für mitochondriale Erkrankungen (mitoNET)

Das mitoNET wurde als interdisziplinäres, deutschlandweites Netzwerk mit dem Ziel konzipiert, eine Verbesserung der Patientenversorgung auf dem Gebiet der mitochondrialen Erkrankungen zu erreichen. Das horizontale klinische Netzwerk des mitoNET umfasst 8 neurologische und 13 pädiatrische Kliniken, die für die Patientenrekrutierung, deren Phänotypisierung und die Erfassung des natürlichen Verlaufs im Rahmen von jährlichen Kontrolluntersuchungen zuständig sind. Die Speicherung der erhobenen Daten erfolgt in einer eigens entwickelten webbasierten Registerdatenbank. Das Netzwerk betreibt 2 Biobanken zur Asservierung von DNA, RNA, Plasma sowie von diagnostisch gewonnenen Fibro- und Myoblasten. Vier Forschungsprojekte zielen auf eine Verbesserung des diagnostischen Spektrums durch Etablierung neuer Methoden, und ein Teilprojekt beschäftigt sich mit der Überprüfung neuer Therapiemöglichkeiten. Das mitoNET wird seit Anfang 2009 vom Bundesministerium für Bildung und Forschung (BMBF, Förderkennzeichen 01GM1113A) gefördert.

CEDNIK syndrome results from loss-of-function mutations in SNAP29

BACKGROUND

CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis and keratoderma) syndrome is a rare genodermatosis which was shown 5 years ago in one family to be associated with a loss-of-function mutation in SNAP29, encoding a member of the SNARE family of proteins. Decrease in SNAP29 expression was found to result in abnormal lamellar granule maturation leading to aberrant epidermal differentiation and ichthyosis.

OBJECTIVES

To delineate the molecular consequences of disease-causing mutations in SNAP29.

METHODS

We used direct sequencing, in vitro mutagenesis and three-dimensional organotypic cell cultures.

RESULTS

We identified a novel homozygous insertion in SNAP29 (c.486insA) in two sibs presenting with ichthyosis and dysgenesis of the corpus callosum. In vitro transfection experiments indicated that this mutation results in SNAP29 loss-of-function. Further substantiating this notion, we could replicate histological features typical for CEDNIK syndrome in three-dimensional primary human keratinocyte organotypic cell cultures downregulated for SNAP29.

CONCLUSIONS

The identification of a second mutation in SNAP29 in the present study definitely establishes a causal relationship between defective function of SNAP29 and the pleiotropic manifestations of CEDNIK syndrome. Our present and previous data position SNAP29 as an essential component of the epidermal differentiation machinery.

Antiviral prophylaxis may prevent human herpesvirus-6 reactivation in bone marrow transplant recipients

Human herpesvirus-6 (HHV-6) infects the majority of children under the age of 2 years causing roseola infantum. Following short self-limited disease, the virus enters into a latency phase in peripheral blood lymphocytes (PBL). It has been previously reported that HHV-6 reactivation from latency, in immunocompromised patients undergoing bone marrow transplantation (BMT), could result in febrile illness, pneumonitis, meningitis, and/or encephalitis. In our study, 14 BMT patients received two different antiviral prophylactic therapies: 8 patients received acyclovir, whereas 6 patients received ganciclovir. Clinical manifestations and virus recovery were monitored pre- and post-BMT by polymerase chain reaction tests of cord blood cells cultured with the patients' PBL. No HHV-6 recovery was shown in the 6 patients treated with ganciclovir, whereas 3 of the 8 acyclovir-treated patients experienced virus reactivation 20-21 days post-BMT. One of the 3 patients was asymptomatic but had late engraftment; the second patient had prolonged fever, skin rash, and hemorrhage; the third patient experienced prolonged fever, pneumonitis, marrow rejection, and fatal encephalitis. It is concluded that viral reactivation may be prevented by prophylactic treatment with ganciclovir. Our observation awaits further documentation in prospective randomized trials in high-risk BMT recipients.

Structural requirements of Tom40 for assembly into preexisting TOM complexes of mitochondria

Tom40 is the major subunit of the translocase of the outer mitochondrial membrane (the TOM complex). To study the assembly pathway of Tom40, we have followed the integration of the protein into the TOM complex in vitro and in vivo using wild-type and altered versions of the Neurospora crassa Tom40 protein. Upon import into isolated mitochondria, Tom40 precursor proteins lacking the first 20 or the first 40 amino acid residues were assembled as the wild-type protein. In contrast, a Tom40 precursor lacking residues 41 to 60, which contains a highly conserved region of the protein, was arrested at an intermediate stage of assembly. We constructed mutant versions of Tom40 affecting this region and transformed the genes into a sheltered heterokaryon containing a tom40 null nucleus. Homokaryotic strains expressing the mutant Tom40 proteins had growth rate defects and were deficient in their ability to form conidia. Analysis of the TOM complex in these strains by blue native gel electrophoresis revealed alterations in electrophoretic mobility and a tendency to lose Tom40 subunits from the complex. Thus, both in vitro and in vivo studies implicate residues 41 to 60 as containing a sequence required for proper assembly/stability of Tom40 into the TOM complex. Finally, we found that TOM complexes in the mitochondrial outer membrane were capable of exchanging subunits in vitro. A model is proposed for the integration of Tom40 subunits into the TOM complex.

Assembly of Tom6 and Tom7 into the TOM core complex of Neurospora crassa

Translocation of preproteins across the mitochondrial outer membrane is mediated by the translocase of the outer mitochondrial membrane (TOM) complex. We report the molecular identification of Tom6 and Tom7, two small subunits of the TOM core complex in the fungus Neurospora crassa. Cross-linking experiments showed that both proteins were found to be in direct contact with the major component of the pore, Tom40. In addition, Tom6 was observed to interact with Tom22 in a manner that depends on the presence of preproteins in transit. Precursors of both proteins are able to insert into the outer membrane in vitro and are assembled into authentic TOM complexes. The insertion pathway of these proteins shares a common binding site with the general import pathway as the assembly of both Tom6 and Tom7 was competed by a matrix-destined precursor protein. This assembly was dependent on the integrity of receptor components of the TOM machinery and is highly specific as in vitro-synthesized yeast Tom6 was not assembled into N. crassa TOM complex. The targeting and assembly information within the Tom6 sequence was found to be located in the transmembrane segment and a flanking segment toward the N-terminal, cytosolic side. A hybrid protein composed of the C-terminal domain of yeast Tom6 and the cytosolic domain of N. crassa Tom6 was targeted to the mitochondria but was not taken up into TOM complexes. Thus, both segments are required for assembly into the TOM complex. A model for the topogenesis of the small Tom subunits is discussed.

Recognition of preproteins by the isolated TOM complex of mitochondria

A multisubunit complex in the mitochondrial outer membrane, the TOM complex, mediates targeting and membrane translocation of nuclear-encoded preproteins. We have isolated the TOM holo complex, containing the preprotein receptor components Tom70 and Tom20, and the TOM core complex, which lacks these receptors. The interaction of recombinant mitochondrial preproteins with both types of soluble TOM complex was analyzed. Preproteins bound efficiently in a specific manner to the isolated complexes in the absence of chaperones and lipids in a bilayer structure. Using fluorescence correlation spectroscopy, a dissociation constant in the nanomolar range was determined. The affinity was lower when the preprotein was stabilized in its folded conformation. Following the initial binding, the presequence was transferred into the translocation pore in a step that required unfolding of the mature part of the preprotein. This translocation step was also mediated by protease-treated TOM holo complex, which contains almost exclusively Tom40. Thus, the TOM core complex, consisting of Tom40, Tom22, Tom6 and Tom7, is a molecular machine that can recognize and partially translocate mitochondrial precursor proteins.

The dorsal cutaneous branch of the ulnar nerve. An anatomic clarification with six case reports

We studied the anatomy and pathology of the dorsal cutaneous branch of the ulnar nerve by dissecting 10 fresh cadaver upper limbs and reviewing 6 cases of injury or entrapment of the dorsal cutaneous branch of the ulnar nerve. In all of the cadavers and in our series of cases, several anatomical features were apparent: 1) the dorsal cutaneous branch of the ulnar nerve arises from the main ulnar nerve an average of 5.5 centimeters proximal to the head of the ulna; 2) the dorsal cutaneous branch of the ulnar nerve reaches the dorsum of the hand after coursing volar to the ulnar head; 3) there was no communication between the dorsal cutaneous branch of the ulnar nerve and the superficial sensory branch of the radial nerve; and 4) no volar branches were noted. Based on our experience, disorders of this nerve are more prevalent than previously reported. This clarification of the anatomy will help prevent unnecessary injury during surgery and will be valuable in the diagnosis of disorders of the dorsal cutaneous branch of the ulnar nerve.

Tamplicon-7, a novel T-lymphotropic vector derived from human herpesvirus 7

We describe the derivation of a novel T-cell-defective virus vector employing the human herpesvirus 7 (HHV-7). The new vector, designated Tamplicon-7, replicates in CD4(+) T cells. The system is composed of a helper virus and defective virus genomes derived by the replication of the input Tamplicon vector. There are two cis-acting functions required for the replication and packaging of the defective virus genomes in the presence of the helper virus: the viral DNA replication origin and the composite cleavage and packaging signal, which directs the cleavage and packaging of defective virus genomes. Viral DNA replication is compatible with the rolling circle mechanism, producing large head-to-tail concatemers of the Tamplicon vector. Thus, in the presence of the helper virus, the replicated vectors are packaged and secreted into the medium. Furthermore, we have shown that the vector can be employed to express a foreign gene, encoding the green fluorescent protein, in the T cells infected with the HHV-7 helper virus. We predict that the Tamplicon-7 vector might be potentially useful for gene therapy of diseases affecting the human CD4(+) T cells, including autoimmune diseases, T-cell lymphomas, and AIDS.

Dynamics of the TOM complex of mitochondria during binding and translocation of preproteins

Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. This complex consists of receptor components for the initial contact with preproteins at the mitochondrial surface and membrane-embedded proteins which promote transport and form the translocation pore. In order to understand the interplay between the translocating preprotein and the constituents of the TOM complex, we analyzed the dynamics of the TOM complex of Neurospora crassa and Saccharomyces cerevisiae mitochondria by following the structural alterations of the essential pore component Tom40 during the translocation of preproteins. Tom40 exists in a homo-oligomeric assembly and dynamically interacts with Tom6. The Tom40 assembly is influenced by a block of negatively charged amino acid residues in the cytosolic domain of Tom22, indicating a cross-talk between preprotein receptors and the translocation pore. Preprotein binding to specific sites on either side of the outer membrane (cis and trans sites) induces distinct structural alterations of Tom40. To a large extent, these changes are mediated by interaction with the mitochondrial targeting sequence. We propose that such targeting sequence-induced adaptations are a critical feature of translocases in order to facilitate the movement of preproteins across cellular membranes.

Fzo1p is a mitochondrial outer membrane protein essential for the biogenesis of functional mitochondria in Saccharomyces cerevisiae

Fzo1p is a novel component required for the biogenesis of functional mitochondria in the yeast Saccharomyces cerevisiae. The protein is homologous to Drosophila Fzo, the first known protein mediator of mitochondrial fusion. Deletion of the FZO1 gene results in a petite phenotype, loss of mitochondrial DNA, and a fragmented mitochondrial morphology. Fzo1p is an integral protein of the mitochondrial outer membrane exposing its major part to the cytosol. It is imported into the outer membrane in a receptor-dependent manner. Fzo1p is part of a larger protein complex of 800 kDa, and presumably is the first identified component of the yeast mitochondrial fusion machinery.

Role of the negative charges in the cytosolic domain of TOM22 in the import of precursor proteins into mitochondria

TOM22 is an essential mitochondrial outer membrane protein required for the import of precursor proteins into the organelles. The amino-terminal 84 amino acids of TOM22 extend into the cytosol and include 19 negatively and 6 positively charged residues. This region of the protein is thought to interact with positively charged presequences on mitochondrial preproteins, presumably via electrostatic interactions. We constructed a series of mutant derivatives of TOM22 in which 2 to 15 of the negatively charged residues in the cytosolic domain were changed to their corresponding amido forms. The mutant constructs were transformed into a sheltered Neurospora crassa heterokaryon bearing a tom22::hygromycin R disruption in one nucleus. All constructs restored viability to the disruption-carrying nucleus and gave rise to homokaryotic strains containing mutant tom22 alleles. Isolated mitochondria from three representative mutant strains, including the mutant carrying 15 neutralized residues (strain 861), imported precursor proteins at efficiencies comparable to those for wild-type organelles. Precursor binding studies with mitochondrial outer membrane vesicles from several of the mutant strains, including strain 861, revealed only slight differences from binding to wild-type vesicles. Deletion mutants lacking portions of the negatively charged region of TOM22 can also restore viability to the disruption-containing nucleus, but mutants lacking the entire region cannot. Taken together, these data suggest that an abundance of negative charges in the cytosolic domain of TOM22 is not essential for the binding or import of mitochondrial precursor proteins; however, other features in the domain are required.

Efficacy of hyperthermic isolated limb perfusion for extremity-confined recurrent melanoma

BACKGROUND

Recurrent melanoma of the extremity has been treated by local excision, systemic chemotherapy, amputation, or a combination of these approaches. Hyperthermic isolated limb perfusion (HILP) provides a method of limb preservation through isolation, allowing the administration of chemotherapy in higher doses than is possible through systemic treatment.

METHODS

An experimental group of 59 HILP patients with melanoma recurrences of the extremity was studied prospectively. A control group of 248 melanoma patients with similar recurrences was excluded from HILP because their recurrences were in non-extremity locations. The experimental group underwent HILP and excision; the control group had excision only. The experimental procedure consisted of vascular isolation of the affected extremity and a 1-hour perfusion with melphalan. Temperatures were maintained at 40 degrees C in the perfusion circuit.

RESULTS

The HILP patients had a lower rate of locoregional recurrence (P=.028) and demonstrated increased survival (P=.026) compared to the control group. In multivariate regression analysis, which included age, ulceration and thickness of the primary, and the treatment variable of perfusion, age (P=.02) and perfusion for the treatment of recurrence (P=.006) were significant predictors of survival.

CONCLUSIONS

HILP improves prognosis by sterilizing the treated extremity, controlling locoregional disease, and perhaps preventing metastasis, thus having a positive impact on overall survival.

The DNA sequence of the RK strain of human herpesvirus 7

The complete DNA sequence of human herpesvirus-7 (HHV-7) strain RK was determined following direct cloning of virion DNA fragments into a sequencing vector. The sequence was compared with the previously published complete sequences of HHV-7 strain JI and human herpesvirus-6 (HHV-6) strain U1102. Despite a very close relationship between the two HHV-7 strains, differences are apparent in regions containing tandem reiterations, particularly in the "telomeric" reiterations located near the termini of the large direct repeat at the genome ends, and in a total of 179 additional positions distributed throughout the genome (i.e., about one nucleotide difference per kbp). This extent of divergence implies that the two strains arose from an ancestral virus several thousands of years ago. Differences that affect coding potential do not cluster in particular protein-coding regions, indicating that specific HHV-7 genes have not been measurably subject to unusual evolutionary pressures since divergence. Reassessments of genetic content indicated that the HHV-7 genome contains 84 different genes, whereas the HHV-6 genome contains 85. All HHV-7 genes but 1 have direct HHV-6 counterparts, and all but 2 HHV-6 genes have HHV-7 homologues. Sequence comparisons between HHV-7 and HHV-6 provided evidence that the protein-coding regions of 11 genes are expressed by splicing.

cis and trans sites of the TOM complex of mitochondria in unfolding and initial translocation of preproteins

Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. Our previous studies led to the concept of two preprotein binding sites acting in series, the surface-exposed cis site and the trans site exposed to the intermembrane space. We report here that preproteins are bound to the cis site in a labile fashion even at low ionic strength, whereas intermediates arrested at the trans site remained firmly bound at higher salt concentration. The stability of the trans site intermediate results from interactions of both the presequence and unfolded parts of the mature part of the preprotein with the TOM complex. Binding to the trans site proceeded at rates comparable with those of unfolding of the mature domain and appeared to be kinetically limited by the unfolding reaction. Efficient binding to the trans site and unfolding were observed with both outer membrane vesicles and intact mitochondria whose membrane potential, DeltaPsi, was dissipated. Upon re-establishing DeltaPsi, trans site-bound preprotein resumed translocation into the matrix. The rates of unfolding and binding to the trans site were the same as those for translocation into intact energized mitochondria. We conclude that preprotein unfolding in intact mitochondria can take place without the involvement of the translocation machinery of the inner membrane and, in particular, the matrix Hsp70 chaperone. Further, preprotein unfolding at the outer membrane can be a rate-limiting step for formation of the trans site intermediate and for the entire translocation reaction.

Mitochondrial protein import. Tom40 plays a major role in targeting and translocation of preproteins by forming a specific binding site for the presequence

During preprotein transport across the mitochondrial outer membrane, the N-terminal presequence initially binds to a surface-exposed site, termed cis site, of the protein translocation complex of this membrane (the TOM complex). The presequence then moves into the translocation pore and becomes exposed at the intermembrane space side. Membrane passage is driven by specific interaction of the presequence with the trans site. We have used chemical cross-linking to identify components in the vicinity of the translocating presequence. Preproteins bound to the surface-exposed cis site can be cross-linked via their N-terminal presequence to Tom20 and Tom22, demonstrating their direct association with this part of the preprotein. In addition, the presequence establishes an early contact to Tom40, a membrane-embedded protein of the TOM complex. Upon further entry of the preprotein into the translocation pore, the presequence loses its contact with Tom20/Tom22, but remains in firm association with Tom40. Our study suggests that Tom40 plays an important function in guiding the presequence of a preprotein across the mitochondrial outer membrane. We propose that Tom40 forms a major part of the trans presequence binding site.

Fusion peptides derived from the HIV type 1 glycoprotein 41 associate within phospholipid membranes and inhibit cell-cell Fusion. Structure-function study

The fusion domain of human immunodeficiency virus (HIV-1) envelope glycoprotein (gp120-gp41) is a conserved hydrophobic region located at the N terminus of the transmembrane glycoprotein (gp41). A V2E mutant has been shown to dominantly interfere with wild-type envelope-mediated syncytium formation and virus infectivity. To understand this phenomenon, a 33-residue peptide (wild type, WT) identical to the N-terminal segment of gp41 and its V2E mutant were synthesized, fluorescently labeled, and characterized. Both peptides inhibited HIV-1 envelope-mediated cell-cell fusion and had similar alpha-helical content in membrane mimetic environments. Studies with fluorescently labeled peptide analogues revealed that both peptides have high affinity for phospholipid membranes, are susceptible to digestion by proteinase-K in their membrane-bound state, and tend to self- and coassemble in the membranes. In SDS-polyacrylamide gel electrophoresis the WT peptide formed dimers as well as higher order oligomers, whereas the V2E mutant only formed dimers. The WT, but not the V2E mutant, induced liposome aggregation, destabilization, and fusion. Moreover, the V2E mutant inhibited vesicle fusion induced by the WT peptide, probably by forming inactive heteroaggregates. These data form the basis for an explanation of the mechanism by which the gp41 V2E mutant inhibits HIV-1 infectivity in cells when co-expressed with WT gp41.

Lymphatic mapping and sentinel node biopsy in patients with malignant melanoma

Intra-operative sentinel lymph node (SLN) mapping and biopsy is a procedure that accurately stages the regional lymph node basin. Defined patterns of lymphatic drainage allow intra-operative determination of the first (sentinel) lymph node in the regional basin, and the absence of metastatic disease in the SLN accurately reflects the absence of melanoma in the remaining regional nodes. The use of a radiocolloid and a handheld gamma probe together with a vital blue dye provides optimal results, and allows for the successful identification of the SLN(s) in over 98 percent of the procedures. Close collaboration between surgeons, nuclear radiologists and pathologists is required to ensure optimal results. Surgical excision of the SLN allows for a more thorough and focused pathological examination of one or two nodes. Examination of serially sectioned SLNs by H&E staining, immunohistochemical staining and perhaps RT-PCR should reduce the number of patients with missed microscopic melanoma in the regional lymph nodes. Recently reported survival data from the Intergroup Melanoma Trial suggest that patients may benefit from identification and removal of regional lymph nodes that contain metastatic melanoma. Furthermore, the survival benefit recently reported in patients with melanoma metastatic to regional nodes prospectively randomized to receive high dose Interferon alfa-2b signals that the surgeons should aggressively examine patients for the presence of occult regional melanoma metastases. Intra-operative SLN mapping and SLN biopsy is a cost-effective procedure that allows accurate identification of regional lymph nodes that contain metastatic melanoma.

Florida's undeclared epidemic: malignant melanoma

Contrary to the trend of early diagnosis observed in other parts of the world, in Florida melanoma is still being discovered in the more advanced stages. This is characterized by thicker lesions at diagnosis, which are hallmarked by bleeding, itching, ulceration, and increased vertical growth. In a study of 1,626 cutaneous melanoma patients at the H. Lee Moffitt Cancer Center in Florida, three prognostic factors, tumor thickness, Clark level, and presence of ulceration in the primary tumor, have remained relatively constant over an eight-year period (1987-1994). Despite the lack of change in tumor thickness in the last four years, mortality rate is decreasing, possibly due to more effective treatments. Regardless of these apparent improvements in mortality rates, definite progress must be made in the early detection of malignant melanoma through the initiation of statewide programs of lay public and professional education. In addition, it is proposed that the establishment of statewide screening programs of the Caucasian population with skin phenotypes 1 and 2 will also facilitate the early diagnosis of melanoma in the future, improve the outlook for these patients, and begin to address a major public health problem in the state of Florida.

Investment in new technology research can save future health care dollars

OBJECTIVE

To perform a cost analysis of the emerging technology of lymphatic mapping for patients with malignant melanoma.

DESIGN

A retrospective, computer-aided chart and financial cost and charge review of consecutive patients with the diagnosis of melanoma registered at a cancer center from December, 1995 to March, 1996.

PARTICIPANTS

73 consecutive patients with the diagnosis of Stage 1 and 2 melanoma (cutaneous disease only) had nodal staging of their disease with either a sentinel node (SLN) biopsy or an elective complete node dissection (ELND). This was determined largely by patient choice and the protocol in operation at the time of the presentation of the patient to the clinic.

OUTCOMES MEASURED

There were no deaths in the series. Patient morbidity endpoints included rates of infection, incidence of extremity lymphedema, development of a seroma in the regional nodal basin wound and wound healing. Clinical outcome was measured by the ability to obtain complete nodal staging information with the new lymphatic mapping technology, and recurrence rates in the nodal basin after a negative SLN biopsy. Total charges, direct costs and total costs were calculated from all hospital, OR, pathology and lab charges. Professional fees were included in the analysis.

RESULTS

Group 1 patients (50) had melanomas greater than 0.76 mm in thickness treated with a wide local excision (WLE), lymphatic mapping and SLN biopsy under general anesthesia. Five patients (Group 2) had their procedure performed under a straight local anesthesia. Group 3 patients (18) had nodal staging performed with an elective node dissection. In Groups 1 and 2, if the SLN was positive for micrometastases, the patients were taken back to the OR for a complete node dissection. The total charges per patient were $13,835, $6,853 and $19,285, respectively. Significant dollar savings were achieved if the nodal staging could be accomplished with the lymphatic mapping technology (p = 0.001). Morbidity was significantly less in Groups 1 and 2 compared to Group 3. After a mean follow-up of three years, only one patient has recurred in a SLN negative basin.

CONCLUSIONS

With 38,300 new cases of melanoma diagnosed each year in the United States, a projected savings of $172 million per year (general anesthesia) and $350 million per year (local anesthesia) could be realized if this new mapping technology could be incorporated into the care of the melanoma patient. Patient morbidity is minimized, nodal staging is complete and patients return to work sooner. Recently approved adjuvant therapy can be applied in a selective fashion, treating only those patients in which a documented benefit has been obtained, saving the health care system more dollars. Initial investment in defining the technology was minimal.

Redefining cutaneous lymphatic flow: the necessity of preoperative lymphoscintigraphy in the management of malignant melanoma

OBJECTIVE

The purpose of this study is to emphasize the instrumental role of preoperative lymphoscintigraphy in the surgical treatment of patients with malignant melanoma.

SUMMARY BACKGROUND DATA

The efficacy of lymphoscintigraphy is reflected in its ability to reveal cutaneous lymphatic drainage to regional nodal basins that are at risk for melanoma metastases but not necessarily discernable to be at risk through standard historical anatomical guidelines or clinical experience. This preoperative lymphatic mapping technique has contributed greatly to the accuracy and efficiency of staging procedures including sentinel node biopsy and elective lymph node dissection.

PATIENTS AND METHODS

After informed consent, a selected series of four patients with primary melanomas located in watershed areas of the body (left neck, right mid-abdomen, right scapula, left back) and two patients with extremity melanomas (right distal forearm and left ankle) underwent pre-operative lymphoscintigraphy to identify all basins for metastases.

RESULTS

In all of the cases, lymphatic drainage occurred in an unusual and unexpected basin that could not have been predicted clinically and in three of the cases the resected basins contained positive sentinel nodes. If not for the preoperative lymphoscintigraphy, these nodal basins would not have been resected and metastatic disease would have been left behind. In addition, the staging of the melanoma patient would have been inaccurate.

CONCLUSION

If the sentinel node biopsy of elective lymph node dissection (ELND) were based on clinical predictions only, nodes equally at risk for metastatic disease would not have been resected and in some cases, nodal basins not at risk for metastases would have been resected unnecessarily. Without lymphoscintigraphy, the validity and efficacy of the ELND or the sentinel node biopsy for nodal staging is greatly compromised. These six case studies illustrate the difficulty of predicating lymphatic drainage from primary sites located on the head and neck, truck and even the extremities and demonstrate the indispensability of preoperative lymphoscintigraphy in the management of malignant melanoma.

Multiple primary melanomas: implications for screening and follow-up programs for melanoma

BACKGROUND

Once individuals are diagnosed with malignant melanoma, they are at an increased risk of developing another melanoma when compared with the normal population.

METHODS

To determine the impact of an intensive follow-up protocol on the stage of disease at diagnosis of subsequent primary melanomas, a retrospective query was performed of an electronic medical record database of 2,600 consecutively registered melanoma patients.

RESULTS

Sixty-seven patients (2.6%) had another melanoma diagnosed at the time of presentation to the clinic or within 2 months (synchronous) and another 44 patients (1.7%) developed a second primary melanoma during the follow-up period (metachronous). For the 44 patients diagnosed with metachronous lesions, the Breslow mean tumor thickness for the first invasive melanoma was 2.27 mm compared with 0.90 mm for the second melanoma. The first melanomas diagnosed are thicker by an average of 3.8 mm (p = 0.008). The mean Clark level for the initial melanoma was greater than the mean level for subsequently diagnosed melanomas (p = 0.002). Twenty-three percent of the initial melanomas were ulcerated, whereas only one of the second primary lesions showed this adverse prognostic factor (p = 0.002).

CONCLUSIONS

Once individuals are diagnosed with melanoma, they are in a high-risk population for having other primary site melanomas diagnosed and should be placed in an intensive follow-up protocol consisting of a complete skin examination.

Evaluation of new putative tumor markers for melanoma

BACKGROUND

The early diagnosis of recurrent melanoma can contribute to better outcome if the disease can be surgically resected or if the metastases are responsive to systemic therapies. Lipid-associated sialic acid (LASA-P) and the S-100 protein (S-100) were evaluated as tumor markers for melanoma with the goal of early detection of recurrence.

METHODS

Sixty-seven patients were identified who had levels of S-100 and LASA-P drawn during their clinical course. A multivariate regression analysis was performed to determine the significance of the serum markers in relation to other prognostic factors for melanoma.

RESULTS

After a median follow-up of 30 months, 58 patients had recurrences, and 49 patients died of disease. LASA-P elevation was not associated with the time to recurrence (p = 0.2176) or survival (p = 0.2507). S-100 positivity was a significant predictor of recurrence (p < 0.0001) and survival (p = 0.0059). The median time to recurrence for S-100-positive and S-100-negative patients was 7.6 and 33.8 months, respectively. The median survival time was 59.2 months for S-100-negative patients and 29.6 months for patients positive for S-100.

CONCLUSIONS

Serum S-100 shows significant correlations to both time to recurrence and survival and could be useful in the clinical detection of malignant melanoma.

The use of intraoperative radiolymphoscintigraphy for sentinel node biopsy in patients with malignant melanoma

BACKGROUND

Selective lymphadenectomy or "sentinel node" biopsy has been introduced recently by Morton and colleagues (Arch Surg 1992;127:392-9) to stage patients with intermediate and thick malignant melanomas. It has proven to be an effective way to identify nodal basins at risk for metastasis without the morbidity of a complete lymph node dissection. The majority of biopsies can be performed under local anesthesia with small incisions, but technical difficulties occasionally result in unsuccessful explorations. Identification of the sentinel node can be enhanced by a intraoperative radiolymphoscintigraphy, a technique introduced Alex and Krag (Surg Oncol 1993;137-43) that uses radiolabeled sulfur colloid and a hand-held gamma probe.

OBJECTIVE

We used intraoperative radiolymphoscintigraphy in conjunction with 1% lymphazurin blue dye to define the sentinel node(s) in 148 patients with greater than 0.76 mm in thickness or Clark level IV melanomas. Sentinel lymph nodes were isolated, harvested, and examined using conventional histopathology, and immunohistochemistry for S-100 and HMB-45 antibodies.

RESULTS

The overall success rate of sentinel lymph node localization was 97% using a combination of the two techniques. Twenty-one (14%) patients had micrometastasis, and 17 of these subsequently underwent complete lymph node dissection. A total of 220 of 275 (80%) sentinel nodes harvested were radioactive or "hot" compared with 165 of 275 (60%) with the blue dye alone. Four of the patients with micrometastasis had sentinel nodes positive by gamma probe, but negative by blue dye mapping techniques.

CONCLUSION

Our results suggest that intraoperative radiolymphoscintigraphy using a hand-held gamma detecting probe improves the identification of sentinel lymph nodes during selective lymphadenectomy. This may reduce the number of "unsuccessful explorations" using the vital blue dye technique for lymphatic mapping, and appeal to a greater variety of surgeons, including dermatologic surgeons.

Reversible surface aggregation in pore formation by pardaxin

The mechanism of leakage induced by surface active peptides is not yet fully understood. To gain insight into the molecular events underlying this process, the leakage induced by the peptide pardaxin from phosphatidylcholine/ phosphatidylserine/cholesterol large unilamellar vesicles was studied by monitoring the rate and extent of dye release and by theoretical modeling. The leakage occurred by an all-or-none mechanism: vesicles either leaked or retained all of their contents. We further developed a mathematical model that includes the assumption that certain peptides become incorporated into the vesicle bilayer and aggregate to form a pore. The current experimental results can be explained by the model only if the surface aggregation of the peptide is reversible. Considering this reversibility, the model can explain the final extents of calcein leakage for lipid/peptide ratios of > 2000:1 to 25:1 by assuming that only a fraction of the bound peptide forms pores consisting of M = 6 +/- 3 peptides. Interestingly, less leakage occurred at 43 degrees C, than at 30 degrees C, although peptide partitioning into the bilayer was enhanced upon elevation of the temperature. We deduced that the increased leakage at 30 degrees C was due to an increase in the extent of reversible surface aggregation at the lower temperature. Experiments employing fluorescein-labeled pardaxin demonstrated reversible aggregation of the peptide in suspension and within the membrane, and exchange of the peptide between liposomes. In summary, our experimental and theoretical results support reversible surface aggregation as the mechanism of pore formation by pardaxin.

Intraoperative radio-lympho-scintigraphy improves sentinel lymph node identification for patients with melanoma

BACKGROUND

The sentinel lymph node (SLN), the first node draining the primary tumor site, has been shown to reflect the histologic features of the remainder of the lymphatic basin in patients with melanoma. Intraoperative localization of the SLN, first proposed by Morton and colleagues, has been accomplished with the use of a vital blue dye mapping technique. Technical difficulties resulting in unsuccessful explorations have occurred in up to 20% of the dissections.

OBJECTIVES

The authors aimed to define the SLN using gamma detection probe mapping and to determine whether intraoperative radiolymphoscintigraphy using technetium sulfur colloid and a hand-held gamma-detecting probe could be used to improve detection of all SLNs for patients with melanoma.

METHODS

To ensure that all initial nodes draining the primary site were removed at the time of selective lymphadenectomy, the authors used intraoperative radiolymphoscintigraphy to confirm the location of the SLN, which was determined initially with the preoperative lymphoscintigram and the intraoperative vital blue dye injection.

PATIENT POPULATION

The patient population consisted of 106 consecutive patients who presented with cutaneous melanomas larger than 0.75 mm in all primary site locations.

RESULTS

The preoperative lymphoscintigram revealed that 22 patients had more than one lymphatic basin sampled. Two hundred SLNs and 142 neighboring non-SLNs were harvested from 129 basins in 106 patients. After the skin incision was made, the mean ratio of hot spot to background activity was 8.5:1. The mean ratio of ex vivo SLN-to-non-SLN activity for 72 patients who had SLNs harvested was 135.6:1. When correlated with the vital blue dye mapping, 139 of 200 (69.5%) SLNs demonstrated blue dye staining, whereas 167 of 200 (83.5%) SLNs were hot according to radioisotope localization. With the use of both intraoperative mapping techniques, identification of the SLN was possible for 124 of the 129 (96%) basins sampled. Micrometastases were identified in SLNs of 16 of the 106 (15%) patients by routine histologic analysis.

CONCLUSION

The use of intraoperative radiolymphoscintigraphy can improve the identification of all SLNs during selective lymphadenectomy.

The tumor biology of melanoma nodal metastases

Approximately 20 per cent of melanomas greater than 0.76 mm in thickness will metastasize to the regional lymph nodes if treated with wide local excision alone (WLE). Elective lymph node dissection (ELND) is associated with significant morbidity, which includes lymphedema, wound complications, and paresthesias of the extremity. An alternative operative approach uses selective lymphadenectomy with the identification of the sentinel node, defined as the first node in the lymphatic basin that drains the primary cutaneous site. This study consisted of 132 patients with melanomas greater than 0.76 mm. One hundred nine patients (83%) had histologic negative sentinel nodes, and 23 patients (17%) had one or more sentinel nodes positive for disease. In patients with metastatic disease, 30/35 (86%) sentinel nodes were positive, and 25/357 (7%) nonsentinel nodes were positive (P < 0.001). In 18 patients (78%) of the 23 patients with metastatic disease, the sentinel node was the only node positive, strongly suggesting that there is an orderly progression of metastases. Two patients developed metastatic nodal disease after removal of a negative sentinel node (false negative rate = 1.5). The mean follow-up was 1 year. Sentinel node histology reflects the histology of the remainder of the nodes in the lymphatic basin and "skip" metastases, defined as a negative sentinel node but positive nodes higher in the regional chain positive for metastases or an axillary recurrence after a negative sentinel node biopsy, are rare for malignant melanoma. Harvesting the sentinel node in patients with intermediate or greater thickness melanoma will, therefore, identify a subset of patients with metastatic disease who have the most to benefit from a complete node dissection. This surgical approach allows for complete pathological staging and therapeutic management of patients while significantly reducing expense and overall morbidity.

A synthetic peptide corresponding to a conserved heptad repeat domain is a potent inhibitor of Sendai virus-cell fusion: an emerging similarity with functional domains of other viruses

A series of peptides derived from three domains within the fusion protein of Sendai virus was synthesized and examined for their potential to inhibit the fusion of the virus with human red blood cells. These domains include the 'fusion peptide' and two heptad repeats, one adjacent to the fusion peptide (SV-163) and the other to the transmembrane domain (SV-473). Of all the peptides tested, only SV-473 was highly inhibitive. Using fluorescently-labelled peptides, the mechanism through which the SV-473 peptide inhibits the haemolytic activity of the virus was investigated. The results suggest that interactions of the active peptide with virion elements and lipid membranes are involved. Since it has recently been found that synthetic peptides corresponding to putative coiled-coil domains of the human immunodeficiency virus (HIV) type 1 transmembrane protein gp41 are potent inhibitors of HIV, we discuss the general property of virus-derived coiled-coil peptides as inhibitors of viral infection.

Accurate Nodal Staging of Malignant Melanoma

The incidence of malignant melanoma is increasing at a faster pace than that of any other cancer in the United States. It is estimated that people born in the year 2000 will have a 1:75 risk of developing melanoma sometime during his or her lifetime. Stimulated by novel lymphatic mapping techniques, the surgical care of the melanoma patient is evolving toward more conservative resections that can provide the same staging information but without the added morbidity of more radical surgeries. This approach promises to yield positive results in the age of health care reform, outcome measurements, and cost:benefit considerations.

The identification and mapping of melanoma regional nodal metastases: minimally invasive surgery for the diagnosis of nodal metastases

The most controversial part of melanoma surgical care involves the role of elective lymph node dissection (ELND). Whereas proponents cite retrospective studies demonstrating the ability to control regional metastases and more accurate staging, opponents cite the unnecessary morbidity of a complete node dissection for the majority of patients. The technology of sentinel node mapping and selective lymphadenectomy, defined as the identification and removal of the first node into which the primary melanoma drains, may revolutionize melanoma care. If the sentinel node is negative, then theoretically the remainder of the nodes should also be negative (no "skip" metastases), and a complete lymphadenectomy would not be required to control occult nodal disease. The location of the sentinel node may be variable in the lymphatic basin. Ideally, the surgeon needs a map of the position of the sentinel node in reference to the other nodes in the basin in order to do the procedure under local anesthesia with small incisions. In this way, patients are subjected to minimal morbidity and the procedure can be performed as an out-patient. Twenty-nine patients with clinically negative nodes and melanomas greater than 0.76 mm in thickness were judged to be candidates for ELND. Preoperative lymphoscintigraphy in two planes was used to mark the sentinel node, and the patients were taken to the operating room for intraoperative lymphatic mapping and sentinel node biopsy followed by complete dissection.(ABSTRACT TRUNCATED AT 250 WORDS)

Capacities of pardaxin analogues to induce fusion and leakage of negatively charged phospholipid vesicles are not necessarily correlated

Peptide-induced vesicle fusion is frequently accompanied by leakage of vesicle contents. To determine the correlation between these two processes, we studied the interaction of the amphiphilic peptide pardaxin and two of its analogues with large unilamellar vesicles composed of phosphatidylserine. A pardaxin analogue with a positive charge at both its C- and N-termini induced significantly more fusion but less leakage than the parent peptide. Fusion and leakage were studied with large unilamellar vesicles of two sizes. Aggregation of vesicles was found to be the rate-limiting step in the overall fusion process induced by the peptides. The rates and extents of fusion, determined by membrane mixing, increase in vesicle size, and mixing of aqueous contents, were significantly enhanced in the presence of 2.5-5 mM Mg2+ which promoted vesicle aggregation. Model calculations showed that increasing the peptide to lipid ratio resulted in a parallel increase in the fusion rate constants. As the average vesicle diameter was increased, the extent of leakage was enhanced, as more peptide molecules were bound to each vesicle. The mode of leakage induced by the peptides was also investigated. Our results suggest that the potency of a peptide to induce vesicle fusion is not necessarily associated with its capacity to induce leakage, and we further elucidate how these capacities depend on the structures of the peptides.

Interaction of fluorescently labeled analogues of the amino-terminal fusion peptide of Sendai virus with phospholipid membranes

A peptide representing the NH2-terminal (33 amino acid residues) of the fusion protein (F) of Sendai virus, as well as its Gly12-->Ala12 mutant, were synthesized, fluorescently labeled, and spectroscopically and functionally characterized. Peptide-induced vesicle fusion was demonstrated by a combination of increased visible absorbance, lipid mixing assay, and electron microscopy. Both peptides, with the mutant peptide being significantly more potent, were shown to induce membrane fusion and bilayer perturbation of negatively charged phospholipid vesicles. These results are consistent with a previous study that showed that a similar mutation in the homologous NH2-terminal segment of simian virus 5 greatly enhanced syncytium formation (Horvath, C. M., and Lamb, R. A. (1992) J. Virol. 66, 2443-2455). Circular dichroism spectroscopy revealed similar high alpha-helical contents of both peptides in methanol and in trifluoroethanol. Using fluorescently labeled peptide analogues we found that (i) the peptides' membrane partition coefficients are in the range of 10(5) M-1; (ii) the NH2 terminus of the wild-type peptide is located within the lipid bilayer, whereas that of the variant peptide lies on the surface; and (iii) both peptides tend to self-associate in their membrane-bound state. The results support a model in which an alpha-helical secondary structure and self-aggregation of peptides are necessary conditions for membrane fusion. The observed differences in the peptides' fusogenic abilities are hypothesized to result from differences in the peptides' degree of penetration into the membrane, induction of membrane destabilization, and ability to cause vesicles to aggregate. The data support Sendai virus-cell fusion models in which the fusion peptide plays a crucial role in fusion induction by destabilizing the bilayer and by triggering the association of viral fusion protein molecules.

Dp71, the nonmuscle product of the Duchenne muscular dystrophy gene is associated with the cell membrane

The 70.8 kDa protein, Dp71, is the major Duchenne muscular dystrophy (DMD) gene product in many nonmuscle tissues including the brain. Dp71 shares most of the C-terminal and cysteine-rich domains with the dystrophins but lacks the entire large rod shaped domain of spectrin-like repeats, and the N-terminal actin-binding domain. The function of Dp71 is unknown. Using subcellular fractionation and immunostaining we show that Dp71 is associated with the plasma membrane. Dp71 is also associated with the plasma membrane in mdx myogenic cells transfected with a vector expressing Dp71.

Somatosensory cortical plasticity in adult humans revealed by magnetoencephalography

Microelectrode recordings in adult mammals have clearly demonstrated that somatosensory cortical maps reorganize following peripheral nerve injuries and functional modifications; however, such reorganization has never been directly demonstrated in humans. Using magnetoencephalography, we have been able to demonstrate the somatotopic organization of the hand area in normal humans with high spatial precision. Somatosensory cortical plasticity was detected in two adults who were studied before and after surgical separation of webbed fingers (syndactyly). The presurgical maps displayed shrunken and nonsomatotopic hand representations. Within weeks following surgery, cortical reorganization occurring over distances of 3-9 mm was evident, correlating with the new functional status of their separated digits. In contrast, no modification of the somatosensory map was observed months following transfer of a neurovascular skin island flap for sensory reconstruction of the thumb in two subjects in whom sensory transfer failed to occur.

pH- and ionic strength-dependent fusion of phospholipid vesicles induced by pardaxin analogues or by mixtures of charge-reversed peptides

The fusogenic properties of the neurotoxin paradaxin and eight of its analogues with small unilamellar vesicles (SUV), composed of egg phosphatidylcholine and phosphatidylserine (PC/PS), were investigated. Fusion was demonstrated by a lipid-mixing assay and by an increase in vesicle size as revealed by electron microscopy. The lipid-mixing assay was performed at either neutral (pH 6.8) or acidic (pH 4.5) conditions, in solutions containing either high or low salt concentrations. A low level of fusion could be induced at neutral pH only by pardaxin derivatives with amino groups at both the peptide's backbone and N-terminus. However, a marked enhancement in the fusogenic activity occurred when amino groups were present also in the C-terminus. Pardaxin analogues in which amino groups were substituted by carboxylic groups induced elevated levels of fusion only at high salt concentrations where enhancement of aggregation occurs, and acidic pH, which increased alpha-helicity. The influence of mutual interactions between pardaxin's analogues possessing complementary charges on the lipid-mixing process was also studied. At neutral pH and high salt, an inactive acidic analogue increased the fusogenic activity of a complementary-charged basic peptide. However, such mutual interactions at low salt concentrations reduced the fusogenic activity of the pardaxin analogues. Analogues containing D-amino acids were not fusogenic, thus demonstrating the structural specificity of these observations. The results indicate that the charge, alpha-helical structure, and aggregation of peptide monomers play an important role in the fusogenic ability of polypeptides.

Interaction of antimicrobial dermaseptin and its fluorescently labeled analogues with phospholipid membranes

Dermaseptin, a 34 amino-acid residue antimicrobial polypeptide [Mor, A., Nguyen, V. H., Delfour, A., Migliore-Samour, D., & Nicolas, P. (1991) Biochemistry 30, 8824-8830] was synthesized and selectively labeled at its N-terminal amino acid with either 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD), rhodamine, or fluorescein. The fluorescent emission spectra of the NBD-labeled dermaseptin displayed a blue-shift upon binding to small unilamellar vesicles (SUV), reflecting the relocation of the fluorescent probe to an environment of increased apolarity. Titrations of solutions containing NBD-labeled dermaseptin with SUV composed of zwitterionic or acidic phospholipids were used to generate binding isotherms, from which were derived surface partition constants of (0.66 +/- 0.06) x 10(4) M-1 and (2.8 +/- 0.3) x 10(4) M-1, respectively. The shape of the binding isotherms, as well as fluorescence energy transfer measurements, suggests that some aggregation of membrane-bound peptide monomers occurs in acidic but not in zwitterionic vesicles. The preferential susceptibility of the peptide to proteolysis when bound to zwitterionic but not to acidic SUV suggests that these aggregates might then penetrate a relatively short distance into the hydrophobic region of the acidic membrane. Furthermore, the results provide good correlation between the peptide's strong binding and its ability to permeate membranes composed of acidic phospholipids, as revealed by a dissipation of diffusion potential and a release of entrapped calcein from SUV.

Different mosaicism frequencies for proximal and distal Duchenne muscular dystrophy (DMD) mutations indicate difference in etiology and recurrence risk

In about 65% of the cases of Duchenne muscular dystrophy (DMD) a partial gene deletion or duplication in the dystrophin gene can be detected. These mutations are clustered at two hot spots: 30% at the hot spot in the proximal part of the gene and about 70% at a more distal hot spot. Unexpectedly we observed a higher frequency of proximal gene rearrangements among proved "germ line" mosaic cases. Of the 24 mosaic cases we are aware of, 19 (79%) have a proximal mutation, while only 5 (21%) have a distal mutation. This finding indicates that the mutations at the two hot spots in the dystrophin gene differ in origin. Independent support for the different mosaicism frequency was found by comparing the mutation spectra observed in isolated cases of DMD and familial cases of DMD. In a large two-center study of 473 patients from Brazil and the Netherlands, we detected a significant difference in the deletion distribution of isolated (proximal:distal ratio 1:3) and familial cases (ratio 1:1). We conclude from these data that proximal deletions most likely occur early in embryonic development, causing them to have a higher chance of becoming familial, while distal deletions occur later and have a higher chance of causing only isolated cases. Finally, our findings have important consequences for the calculation of recurrence-risk estimates according to the site of the deletion: a "proximal" new mutant has an increased recurrence risk of approximately 30%, and a "distal" new mutant has a decreased recurrence risk of approximately 4%.

Expression of the Duchenne muscular dystrophy gene products in embryonic stem cells and their differentiated derivatives

Three protein products of the Duchenne muscular dystrophy (DMD) gene were identified so far. These include the two very similar muscle and brain type dystrophins, which are encoded by 14-kilobase (kb) mRNAs, and Dp71, which is much smaller. Dp71 is encoded by a 6.5-kb mRNA, which is transcribed from approximately 6% of the giant dystrophin gene. The present investigation shows that Dp71 is the first product of the DMD gene detectable during development. It is already expressed in the pluripotent embryonic stem cells. The two 14-kb mRNAs encoding the dystrophins are detectable only after differentiation of specialized cell types. The possible implication of these findings with regard to the ontogenetic activation and the evolution of the DMD gene are discussed.

Membrane interactions of the sodium channel S4 segment and its fluorescently-labeled analogues

A 24-amino acid peptide corresponding to the S4 segment of the sodium channel was synthesized. In order to perform fluorescence energy transfer measurements and to monitor the interaction of the peptide with lipid vesicles, the peptide was selectively labeled with fluorescence probes at either its N- or C-terminal amino acids. The fluorescent emission spectra of 7-nitrobenz-2-oxa-1,3-diazol-4- yl-(NBD-)labeled analogues displayed blue shifts upon binding to small unilamellar vesicles (SUV), reflecting the relocation of the fluorescent probe to an environment of increased apolarity. The results revealed that both the N- and C-terminus of the S4 segment are located within the lipid bilayer. Titration of solutions containing NBD-labeled peptides with SUV was used to generate binding isotherms, from which surface partition constants, in the range of 10(4) M-1, were derived. The shape of the binding isotherms as well as fluorescence energy transfer measurements suggest that aggregation of peptide monomers within the membrane readily occurs in acidic but not in zwitterionic vesicles. Furthermore, the results provide good correlation between the incidence of aggregation in PC/PS vesicles and the ability of the peptides to permeate the vesicle's membrane. However, a transmembrane diffusion potential had no detectable effect on the location of the peptide within the lipid bilayer or on its aggregation state.(ABSTRACT TRUNCATED AT 250 WORDS)

Aggregation and organization of pardaxin in phospholipid membranes. A fluorescence energy transfer study

Fluorescence resonance energy transfer has been used to study the aggregation and organization of pardaxin and its analogues within lipid membranes. Peptide molecules labeled with 5- (and 6-) carboxyfluorescein at their N-terminal amino acid served as donors in these energy transfer measurements, whereas peptides labeled with 5- (and 6-) carboxytetramethylrhodamine at either their N- or C-terminal amino acid, served as acceptors. The membrane-permeating activity of the native molecule was maintained in the labeled peptides. Upon aggregation of the labeled peptides, fluorescence energy transfer was detected as a quenching of the donor fluorescence (520 nm), as well as an enhancement of the acceptor fluorescence (575 nm). Correlation exists between self-aggregation of the different analogues within membranes and their poreforming abilities. A comparison of the degrees of fluorescence energy transfer from N1-donor-labeled pardaxin to N1-acceptor-labeled pardaxin with the transfer efficiency observed in the interaction between the same donor and C1-acceptor-labeled pardaxin suggests that aggregates are formed in an ordered manner, with a preferentially parallel orientation of monomers within the aggregate. The extent of hetero-oligomer formation, i.e. complexes composed of two different analogue species, revealed that complementary charges contribute to peptide-peptide recognition within the lipid bilayer. Taken together, these results provide further support for the barrel stave model, involving parallel organization of monomers within the aggregate, as a description of the pore formation mechanism of pardaxin and its analogues.

Characterization and cell type distribution of a novel, major transcript of the Duchenne muscular dystrophy gene

Previously we identified a novel 6.5 kb mRNA transcribed from the Duchenne muscular dystrophy (DMD) gene. This mRNA differs in coding content and tissue distribution from the known muscle type and brain type 14 kb DMD mRNAs which code for dystrophin. The novel transcript shares with dystrophin most of the sequence coding for the cysteine-rich and C-terminal domains. Here we used cDNA cloning to identify the divergence point between the common region and the sequence unique to the novel mRNA at the 5' end of the sequence encoding the cysteine-rich domain of dystrophin. This unique sequence containing the translation initiation site is located in a new exon in the intron between exons 62 and 63 of the dystrophin gene. Using probes containing RNA sequences specific to the novel mRNA, we investigated the expression of this mRNA in various tissues and cell types. The study reveals that this mRNA is the main DMD gene product detectable in a variety of nonmuscle tissues including brain cells. The amount of this mRNA in some tissues is comparable to the amount of dystrophin mRNA in the muscle. The expression of the 6.5 kb mRNA is down-regulated during differentiation of myogenic cells; it is present in small amounts in proliferating myoblasts but is undetected in differentiated muscle cultures depleted of mononucleated cells.

Changes in the expression of mRNAs for myogenic factors and other muscle-specific proteins in experimental autoimmune myasthenia gravis

The regulation of genes for acetylcholine receptor (AChR), myogenic factors and other muscle-specific proteins has been analyzed in experimental autoimmune myasthenia gravis (EAMG) and following denervation. The levels of the transcripts for the myogenic factors, MyoD1, myogenin and MRF4, were measured using Northern blot analysis. Myogenin and MRF4 transcript levels were observed to be 3.1- and 2.6-fold higher in muscle of rats with EAMG than in controls, respectively. MyoD1 levels, however, remained unchanged. The increases in AChR, myogenin and MRF4 mRNAs were one order of magnitude higher in 2-week denervated muscle than in the myasthenic muscle. The levels of muscle creatine kinase (MCK), alpha-actin and muscle dystrophin transcripts were also analyzed. Dystrophin levels were found to be 1.7- and 4.7-fold higher in EAMG and denervated muscle, respectively, than in controls; in contrast, MCK and alpha-actin levels remained unchanged.

A deletion including the brain promoter of the Duchenne muscular dystrophy gene is not associated with mental retardation

A total of 161 unrelated Duchenne (DMD) and Becker muscular dystrophy (BMD) patients were screened for deletions in the brain promoter region of the dystrophin gene. Southern blot analysis using a probe for the brain promoter detected a deletion in this region in only one of the DMD families, in a patient with normal intelligence. This deletion also included the promoter of the muscle-type dystrophin and the exons encoding the actin-binding and part of the spectrin-like domains. Our data suggest that deletions in the brain promoter region are rare in DMD and are compatible with normal intelligence.