Induction and modulation of cell-type-specific gene expression in Dictyostelium

We have identified genes that are expressed preferentially in either prestalk or prespore cells in Dictyostelium. The prestalk mRNAs are detectable at 7.5 hr prior to the completion of cell aggregation, while the prespore mRNAs are not detectable until approximately 15 hr of development. Exogenous cAMP in the absence of sustained cell contact is sufficient to induce prestalk-specific gene expression, while multicellularity is required for the induction of prespore-specific genes. A gene expressed equally in both cell types, which has the same developmental kinetics as the prestalk genes, is induced in shaking culture in the absence of either cAMP or stable cell associations. Dissociation of aggregates results in the rapid loss of prespore- and prestalk-specific mRNAs, and these can be induced to reaccumulate with the addition of cAMP. We conclude that there are substantial differences in the timing and requirements for tissue-specific gene expression in Dictyostelium.

Merkel cell carcinoma

Merkel cell carcinoma is a malignant neuroendocrine tumor with features of epithelial differentiation. Biologically aggressive, it may be difficult to diagnose and, particularly in its late stages, even more difficult to treat effectively. This article addresses what is known and what is still controversial about the histogenesis, diagnosis, and management of Merkel cell carcinoma and the structure and function of the Merkel cell from which it is believed to be derived. The incidence, clinical presentation and diagnosis, ultrastructure, immunocytochemistry, treatment, and prognosis of this tumor will be discussed.

Mohs micrographic surgery for the treatment of dermatofibrosarcoma protuberans. Results of a multiinstitutional series with an analysis of the extent of microscopic spread

BACKGROUND

Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft-tissue tumor of the skin; its microscopic extent of invasion beyond the grossly visible tumor is frequently difficult to appreciate. Although wide local excision has been the standard treatment of DFSP, recurrence rates range from 11% to 53%. Because Mohs micrographic surgery allows the extent of excision to be tailored to the microscopic extent of tumor, we evaluated this technique for the treatment of primary and recurrent DFSP.

OBJECTIVE

Our purpose was to determine the local recurrence rate and microscopic extent of spread of primary and recurrent DFSP after treatment with Mohs micrographic surgery.

METHODS

The records of 58 patients with primary and recurrent DFSP treated with Mohs micrographic surgery at three institutions were reviewed and the macroscopic and microscopic extents of tumor were recorded.

RESULTS

One patient with a twice-recurrent DFSP had another recurrence after Mohs micrographic surgery, for an overall local recurrence rate of 2% (zero for primary tumors and 4.8% for recurrent tumors). There were no cases of regional or distant metastases. Macroscopic tumor size ranged from 0.3 x 0.6 cm to 30 x 20 cm, whereas microscopic (postoperative) size ranged from 1.8 x 1.0 cm to 35 x 40 cm. We calculated the likelihood that a given width of excision around the macroscopic tumor would clear the entire microscopic extent of tumor. Standard wide excision with a width of 1 cm around the primary tumor would have left microscopic residual tumor in 70.7%; a width of 2 cm, 39.7%; 3 cm, 15.5%; and 5 cm, 5.2%. Even an excision width of 10 cm would not have cleared the microscopic extent of some tumors, despite taking a huge excess of normal tissue.

CONCLUSION

Treatment of primary and recurrent DFSP by Mohs micrographic surgery results in a low recurrence rate because of the ability of the technique to permit the detection and excision of microscopic tumor elements in even the most asymmetric tumors. Whatever type of surgery is chosen to treat DFSP, it is necessary to assess the entire perimeter of the tumor for microscopic extension and to achieve tumor-free margins in all directions.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Universal PCR amplification of mouse immunoglobulin gene variable regions: the design of degenerate primers and an assessment of the effect of DNA polymerase 3' to 5' exonuclease activity

Degenerate primers were designed for PCR amplification of unknown mouse immunoglobulin (Ig) light (L) and heavy (H) chain variable (V) genes. Each subgroup of mouse Ig gene sequences [Kabat, E.A., Wu, T. T., Perry, H.H., Gottesman, K.S., Foeller, C., 1991. Sequences of Proteins of Immunological Interest, 5th edn. US Department of Health and Human Services, Public Health Service, NIH.] was analyzed, and highly degenerate primers in the framework one (FR1) region were designed. A single highly degenerate FR1 primer sufficed for the amplification of light chains; for heavy chains, a series of FR1 primers was used. At the same time, we assessed the effect of 3' to 5' exonuclease activity of DNA polymerase on the utilization of these degenerate primers. Using Taq polymerase, which lacks 3' to 5' exonuclease activity, we successfully amplified the Ig VL and VH genes expressed in more than a hundred monoclonal hybridoma cell lines reactive against a phosphonamidate hapten. Sequence analysis of the cloned VL and VH genes, 52 of each, showed that they are derived from multiple germline families (10 of the 17 VL families and 9 of the 14 VH families) as recently defined [Martinez, C., Lefranc, M., 1998. The mouse (Mus musculus) immunoglobulin kappa variable (IGKV) genes and joining (IGKJ) segments. Exp. Clin. Immunogenet. 15, 184.]. The universality of our primers was also demonstrated by successful amplification of other mouse hybridoma cell lines that are specific to different antigens.

High-intensity double-pulse X-ray free-electron laser

The X-ray free-electron laser has opened a new era for photon science, improving the X-ray brightness by ten orders of magnitude over previously available sources. Similar to an optical laser, the spectral and temporal structure of the radiation pulses can be tailored to the specific needs of many experiments by accurately manipulating the lasing medium, that is, the electron beam. Here we report the generation of mJ-level two-colour hard X-ray pulses of few femtoseconds duration with an XFEL driven by twin electron bunches at the Linac Coherent Light Source. This performance represents an improvement of over an order of magnitude in peak power over state-of-the-art two-colour XFELs. The unprecedented intensity and temporal coherence of this new two-colour X-ray free-electron laser enable an entirely new set of scientific applications, ranging from X-ray pump/X-ray probe experiments to the imaging of complex biological samples with multiple wavelength anomalous dispersion.

Two-colour X-ray pulses from free-electron lasers can be used to probe ultrafast dynamics, but the total power is a fraction of the saturation power. Here, Marinelli et al. use twin electron bunches to reach full saturation power and increase the two-colour intensity by an order of magnitude at hard-X-ray energies.

Skin grafting. From here to there

Free skin grafts for soft tissue reconstruction can be classified into four types: full-thickness skin grafts, split-thickness skin grafts, composite grafts, and free cartilage grafts. The indications, techniques, donor site considerations, and postoperative complications of each type of skin graft are reviewed.

Soft tissue reconstruction with skin grafting

Free skin grafts for soft tissue reconstruction can be classified into three types: full-thickness skin grafts, split-thickness skin grafts, and composite grafts. The indications, techniques, donor site considerations, and postoperative complications of each type of skin graft are reviewed.

Perineural spread of basal cell carcinomas treated with Mohs micrographic surgery

BACKGROUND

Perineural spread is a well-documented feature of cutaneous tumors and may portend a more aggressive course. The incidence of perineural invasion in basal cell carcinoma (BCC) is reportedly 1%. The authors sought to determine whether perineural spread occurs more commonly than previously thought.

METHODS

The authors prospectively evaluated 434 patients with BCC treated with Mohs surgery, assessing the presence or absence of perineural inflammation and invasion in tumors requiring more than one stage of surgery. They also documented the demographic features, clinical characteristics, histologic subtype, and operative data in each case.

RESULTS

Seventy-eight BCCs required more than one stage of Mohs surgery. Perineural inflammation, perineural tumor invasion, or both were present in 29 of the 78 tumors (37%), or 6.7% of all 434 prospectively evaluated cases. Twenty-one of the 78 tumors (26.9%) exhibited perineural inflammation, 3 (3.8%) demonstrated perineural invasion, and 5 (6.4%) exhibited both. Tumors with perineural invasion required 5.3 surgical stages on average for clearance, in contrast to tumors without perineural invasion, which required 2.2 stages. Tumors with perineural inflammation, inflammation plus tumor invasion, and invasion alone were, respectively, 138%, 149%, and 194% greater in area preoperatively than tumors without perineural involvement, and their mean defect areas after Mohs surgery were, respectively, 151%, 121%, and 605% larger than those of tumors without perineural involvement.

CONCLUSIONS

The incidence of perineural invasion among cases of BCC appears higher than previously recognized. Tumor aggressiveness appears to correlate with the presence of perineural invasion. Surgery with horizontal frozen-section margin control enables easy detection of perineural involvement and should therefore be strongly considered for the treatment of high risk BCC patients.

The uses of digital photography in dermatology

Digital photography is a powerful tool that is transforming the specialty of dermatology by integrating patient and practice management. The fundamentals of digital imaging are discussed, and an approach to the selection of a digital camera and its associated hardware and software is provided. The applications of this technology to patient and practice management are addressed, and the ethical implications of digital tampering are also discussed.

Comparison of differentiating Dictyostelium discoideum cell types separated by an improved method of density gradient centrifugation

During the migrating slug stage of development of the cellular slime mold Dictyostelium discoideum, the precursor cells of the mature spores and stalk are known to differ from each other. In order to explore these differences on a variety of levels, we have improved existing methods for the isopyknic purification of the precursor types. Prespore and prestalk amoebae obtained from mechanically dissociated slugs were separated by centrifugation on preformed Percoll density gradients. The isolated precursor cells are greater than 90-95% pure, show good viability and developmental competence, and can be obtained in relatively large amounts. We have performed initial comparisons of the differentiating amoebae with respect to their location within the slug, protein composition, and developmental capabilities. Density centrifugation reveals heterogeneity among posterior slug cells: The majority of these cells have the expected prespore characteristics, but there is also a minor (lighter) density fraction resembling anterior, prestalk amoebae. Thirty polypeptides synthesized preferentially by prespore or prestalk slug cells were detected by two-dimensional gel electrophoresis and fluorography. Some of these proteins are equally cell-specific when their accumulation is measured by silver staining; others are remarkably non-specific when stained. When the isolated precursor populations were allowed to complete development, they differed in terms of developmental territory size and timing, and in ways which suggest differences in cell cohesion and chemotaxis.

Cutaneous laser resurfacing

Cutaneous resurfacing with the new generation of carbon dioxide and erbium lasers has recently come into favor for the treatment of facial rhytides, photodamage, and scarring. The precise control of these resurfacing lasers over the extent of tissue vaporization minimizes thermal damage to the skin while maximizing therapeutic efficacy. Proper use of resurfacing lasers is contingent upon a complete understanding of their clinical, histologic, and ultrastructural effects, as well as an appreciation of the principles of laser safety. An organized approach to the preoperative, intraoperative, and postoperative management of the patient undergoing laser resurfacing will be provided, including a discussion of prevention and treatment of postoperative side effects and complications. (J Am Acad Dermatol 1999;41:365-89.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the clinical, histologic, and ultrastructural effects of resurfacing lasers and be able to discuss the preoperative, intraoperative, and postoperative management of patients undergoing laser resurfacing.

Merkel cell carcinoma in the setting of HIV infection

Merkel cell carcinoma has been found to have an increased incidence among immunosuppressed patients, specifically organ transplant recipients receiving immunosuppressive therapy. HIV similarly depresses the immune response of infected persons. We report a case of Merkel cell carcinoma (MCC) in an HIV-infected patient who died from liver metastases 2 years after his tumor was diagnosed. The purpose of this report is to describe the possible relationship between HIV and MCC and to emphasize the importance of early diagnosis and aggressive management of MCC.

Melanoma in solid organ transplant recipients

This manuscript outlines estimated risk and clinical course of pretransplant MM, donor-transmitted MM and de novo MM posttransplantation and includes an analysis of risk factors for metastasis, data from clinical studies and current and proposed management. MM in situ and thin melanoma (<1 mm) in the transplant population has similar recurrence and survival estimates to those in the general population. A minimum wait time of 2 years prior to transplantation is suggested for MM with a Breslow depth <1 mm and no clinical evidence of metastasis. More advanced MM may adopt a more aggressive course in transplant recipients. Sentinel lymph node biopsy may be of additional prognostic benefit. Revision of immunosuppression in the management of de novo melanoma in collaboration with the transplant team should be considered. Larger studies utilizing uniform staging criteria or at minimum Breslow depth, are required to assess true risk and outcome of MM in the immunosuppressed transplant population. Emphasis remains on patient education and regular screening to provide early detection of MM.

PTCH mutations in squamous cell carcinoma of the skin

Ultraviolet light exposure is the major risk factor for the development of squamous cell carcinoma in Caucasians. Mutations in the tumor suppressor gene p53 have been identified in both squamous cell carcinomas and basal cell carcinomas. The human homolog of the Drosophila patched gene, has been shown to be mutated in sporadic basal cell carcinomas; however, mutations in the patched gene have not been found in squamous cell carcinoma. In this study, we screened a total of 20 squamous cell carcinoma samples for mutations in the patched gene. Using polymerase chain reaction-single strand conformation polymorphism as an initial screening method, we identified one non-sense mutation, two mis-sense mutations and three silent mutations in five squamous cell carcinoma samples. In one squamous cell carcinoma sample, we identified a tandem GG-->AA transitional change at nucleotide 3152 in exon 18 of the patched gene that resulted in a premature stop codon at codon 1051. The three squamous cell carcinoma samples containing non-sense and mis-sense mutations were isolated from individuals with histories of multiple basal cell carcinoma. Sequence analysis of the p53 gene in these five squamous cell carcinoma samples identified one CC-->TT and three C-->T ultraviolet-specific nucleotide changes. Our study provides evidence that the patched gene is mutated in squamous cell carcinoma from individuals with a history of multiple basal cell carcinoma. The identification of ultraviolet-specific nucleotide changes in both tumor suppressor genes supports the notion that ultraviolet exposure plays an important part in the development of squamous cell carcinoma.

Experimental demonstration of a soft x-ray self-seeded free-electron laser

The Linac Coherent Light Source has added a self-seeding capability to the soft x-ray range using a grating monochromator system. We report the demonstration of soft x-ray self-seeding with a measured resolving power of 2000-5000, wavelength stability of 10(-4), and an increase in peak brightness by a factor of 2-5 across the photon energy range of 500-1000 eV. By avoiding the need for a monochromator at the experimental station, the self-seeded beam can deliver as much as 50-fold higher brightness to users.

Role of PTCH and p53 genes in early-onset basal cell carcinoma

Basal cell carcinoma (BCC) is the most common skin cancer in the Western world. Ultraviolet (UV) exposure, race, age, gender, and decreased DNA repair capacity are known risk factors for the development of BCC. Of these, UVB irradiation from sunlight is the most significant risk factor. The incidence of sporadic BCC increases in individuals older than age 55, with the greatest incidence reported in individuals who are older than 70, and is rare in individuals who are younger than 30. In this study, we analyzed 24 BCC samples from individuals who had BCC diagnosed by the age of 30. Fifteen single-stranded conformation polymorphism variants in the PTCH gene were identified in 13 BCC samples. Sequence analysis of these single-stranded conformation polymorphism variants revealed 13 single nucleotide changes, one AT insertion, and one 15-bp deletion. Most of these nucleotide changes (nine of 15) were predicted to result in truncated PTCH proteins. Fifteen p53 mutations were also found in 11 of the 24 BCC samples. Thirty-three percent (five of 15) and 60% (nine of 15) of the nucleotide changes in the PTCH and p53 genes, respectively, were UV-specific C-->T and CC-->TT nucleotide changes. Our data demonstrate that the p53 and PTCH genes are both implicated in the development of early-onset BCC. The identification of UV-specific nucleotide changes in both tumor suppressor genes suggests that UV exposure is an important risk factor in early onset of BCC.

Electron Ghost Imaging

In this Letter we report a demonstration of electron ghost imaging. A digital micromirror device directly modulates the photocathode drive laser to control the transverse distribution of a relativistic electron beam incident on a sample. Correlating the structured illumination pattern to the total sample transmission then retrieves the target image, avoiding the need for a pixelated detector. In our example, we use a compressed sensing framework to improve the reconstruction quality and reduce the number of shots compared to raster scanning a small beam across the target. Compressed electron ghost imaging can reduce both acquisition time and sample damage in experiments for which spatially resolved detectors are unavailable (e.g., spectroscopy) or in which the experimental architecture precludes full frame direct imaging.

Blinded vs. unblinded peer review of manuscripts submitted to a dermatology journal: a randomized multi-rater study

BACKGROUND

Submissions to medical and scientific journals are vetted by peer review, but peer review itself has been poorly studied until recently. One concern has been that manuscript reviews in which the reviewer is unblinded (e.g. knows author identity) may be biased, with an increased likelihood that the evaluation will not be strictly on scientific merits.

OBJECTIVES

The purpose of this study was to compare the outcomes of blinded and unblinded reviews of manuscripts submitted to a single dermatology journal via a randomized multi-rater study.

MATERIALS AND METHODS

Forty manuscripts submitted to the journal Dermatologic Surgery were assessed by four reviewers, two of whom were randomly selected to be blinded and two unblinded regarding the identities of the manuscripts' authors. The primary outcome measure was the initial score assigned to each manuscript by each reviewer characterized on an ordinal scale of 1-3, with 1 = accept; 2 = revise (i.e. minor or major revisions) and 3 = reject. Subgroup analysis compared the primary outcome measure across manuscripts from U.S. corresponding authors and foreign corresponding authors. The secondary outcome measure was word count of the narrative portion (i.e. comments to editor and comments to authors) of the reviewer forms.

RESULTS

There was no significant difference between the scores given to manuscripts by unblinded reviewers and blinded reviewers, both for manuscripts from the U.S. and for foreign submissions. There was also no difference in word count between unblinded and blinded reviews.

CONCLUSIONS

It seems, at least in the case of one dermatology journal, that blinding during peer review does not appear to affect the disposition of the manuscript. To the extent that review word count is a proxy for review quality, there appears to be no quality difference associated with blinding.

Pilot ultrastructural evaluation of human preauricular skin before and after high-energy pulsed carbon dioxide laser treatment

BACKGROUND

Carbon dioxide laser resurfacing has recently come into favor for the treatment of photodamaged skin. While the clinical and histologic effects of high-energy short-pulse carbon dioxide lasers on human skin have been investigated, the ultrastructural effects of these lasers have not been documented. Our objective was to study the ultrastructural effects of a high-energy pulsed carbon dioxide laser on photodamaged human skin.

OBSERVATIONS

Before laser surgery, the ultrastructural changes characteristic of photodamaged skin were evident. Immediately after treatment, there was extensive coagulation necrosis of the epidermis and papillary dermis. Thirty days after treatment, there was no evidence of intercellular or intracellular edema, and ordered differentiation of the epidermal keratinocytes, with a loss of keratinocyte dysplasia, was seen. Increased numbers of desmosomes and tonofibrils were noted. New deposition of collagen was present in the papillary dermis. The ultrastructural findings seen at 90 days after treatment were similar to those seen at 30 days, apart from increased organization of collagen fibers in the papillary dermis.

CONCLUSIONS

Treatment with the high-energy pulsed carbon dioxide laser appears to reverse the epidermal and dermal changes of photoaging on an ultrastructural level. These changes appear morphologically to be consistent with previously described clinical and histologic changes following laser resurfacing.