3D Whole-body skin imaging for automated melanoma detection

BACKGROUND

Existing artificial intelligence for melanoma detection has relied on analysing images of lesions of clinical interest, which may lead to missed melanomas. Tools analysing the entire skin surface are lacking.

OBJECTIVES

To determine if melanoma can be distinguished from other skin lesions using data from automated analysis of 3D-images.

METHODS

Single-centre, retrospective, observational convenience sample of patients diagnosed with melanoma at a tertiary care cancer hospital. Eligible participants were those with a whole-body 3D-image captured within 90 days prior to the diagnostic skin biopsy. 3D-images were obtained as standard of care using VECTRA WB360 Whole Body 3-dimensional Imaging System (Canfield Scientific). Automated data from image processing (i.e. lesion size, colour, border) for all eligible participants were exported from VECTRA DermaGraphix research software for analysis. The main outcome was the area under the receiver operating characteristic curve (AUC).

RESULTS

A total of 35 patients contributed 23,538 automatically identified skin lesions >2 mm in largest diameter (102-3021 lesions per participant). All were White patients and 23 (66%) were males. The median (range) age was 64 years (26-89). There were 49 lesions of melanoma and 22,489 lesions that were not melanoma. The AUC for the prediction model was 0.94 (95% CI: 0.92-0.96). Considering all lesions in a patient-level analysis, 14 (28%) melanoma lesions had the highest predicted score or were in the 99th percentile among all lesions for an individual patient.

CONCLUSIONS

In this proof-of-concept pilot study, we demonstrated that automated analysis of whole-body 3D-images using simple image processing techniques can discriminate melanoma from other skin lesions with high accuracy. Further studies with larger, higher quality, and more representative 3D-imaging datasets would be needed to improve and validate these results.

Dermoscopy of Linear Basal Cell Carcinomas, a Potential Mimicker of Linear Lesions: a Descriptive Case-series

Introduction

Among the various widely recognized basal cell carcinoma (BCC) clinical patterns, linear basal cell carcinoma (LBCC) is an uncommon morphologic variant of BCC.

Objectives

Describe the clinical and dermoscopic characteristics of LBCC.

Methods

Retrospective study including LBCC cases from 5 dermatology centers in North and South America. Biopsy-proven primary BCCs, that presented with at least 3:1 length:width ratio on physical examination, irrespective of tumor subtype or location, were included. Clinical and dermoscopic analysis were performed by 2 experts in dermoscopy.

Results

Eighteen cases of LBCC met our inclusion criteria and were included in the study. Median age at diagnosis was 86.0 years, 10 patients (58.8%) were males. Regarding anatomic location, 11/18 (61.1%) were located on the head and neck, 5/18 (27.7%) cases were found on the trunk, and 2 on lower extremities (11.1%). Under dermoscopy, 15/18 (83.3%) of LBCC were pigmented. All tumors displayed at least one of the BCC-specific dermoscopic criteria the most common being blue-grey globules (72.2%).

Conclusions

Dermoscopy might be useful in the differentiation of LBCC from other diagnoses presenting as linear lesions such as scars, scratches/erosions, and tattoos, among others. Some of these lesions might be confused by naked eye examination alone.

Consent and Deidentification of Patient Images in Dermatology Journals: Observational Study

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Prevalence and Age-Related Patterns in Health Information-Seeking Behaviors and Technology Use Among Skin Cancer Survivors: Survey Study

Background

Information is an unmet need among cancer survivors. There is a paucity of population-based data examining the health information-seeking behaviors and attitudes of skin cancer survivors.

Objective

We aimed to identify the prevalence and patterns of health information-seeking behaviors and attitudes among skin cancer survivors across age groups.

Methods

We analyzed population-based data from the 2019 Health Information National Trends Survey 5 (Cycle 3).

Results

The 5438 respondents included 346 (6.4%) skin cancer survivors (mean age 65.8 years); of the 346 skin cancer survivors, the majority were White (96.4% [weighted percentages]), and 171 (47.8%) were men. Most reported having ever looked for health- (86.1%) or cancer-related (76.5%) information; 28.2% stated their last search took a lot of effort, and 21.6% were frustrated. The internet was most often cited as being the first source that was recently used for health or medical information (45.6%). Compared to skin cancer survivors younger than 65 years old, those 65 years of age or older were more likely to see a doctor first for important health information (≥65 years: 68.3%;<65 years: 36.2%; P<.001) and less likely to have health and wellness apps (≥65 years: 26.4%; <65 years: 54.0%, P=.10), to have watched a health-related YouTube video (≥65 years: 13.3%; <65 years: 27.4%; P=.02), and to have used electronic means to look for information (≥65 years: 61.4%;<65 years: 82.3%, P<.001).

Conclusions

Searches for health information are common among skin cancer survivors, but behaviors and attitudes are associated with age, which highlights the importance of access to doctors and personalized information sources.

Association between the dermoscopic morphology of peripheral globules and melanocytic lesion diagnosis

BACKGROUND

The presence of peripheral globules is associated with enlarging melanocytic lesions; however, there are numerous patterns of peripheral globules distribution and it remains unknown whether specific patterns can help differentiate enlarging naevi from melanoma.

OBJECTIVE

To investigate whether morphological differences exist between the peripheral globules seen in different subsets of naevi and in melanoma.

METHODS

A cross-sectional study of clinical notes that mentioned peripheral globules, in addition to all melanoma images with peripheral globules on the International Skin Imaging Collaboration archive. Dermoscopic images were reviewed and annotated. Associations between diagnosis and categorical features were measured with odds ratios. Non-parametric tests were used for continuous factors.

RESULTS

184 lesions with peripheral globules from our clinic were included in the analysis; only 6 of these proved to be melanoma. 109 melanomas with peripheral globules from the International Skin Imaging Collaboration archive were added to the analysis. Melanomas were more common on the extremities and among older individuals. Melanomas were more likely to display atypical, tiered and/or focal peripheral globules. Only 5% of melanomas lacked dermoscopic melanoma-specific structures compared to 48% of naevi.

CONCLUSIONS

Melanocytic lesions with atypical or asymmetrically distributed peripheral globules, especially when located on the extremities, should raise suspicion for malignancy. Melanocytic lesions with typical and symmetrically distributed peripheral globules, and with no other concerning dermoscopic features, are unlikely to be malignant.

Performance of a deep neural network in teledermatology: a single-centre prospective diagnostic study

BACKGROUND

The use of artificial intelligence (AI) algorithms for the diagnosis of skin diseases has shown promise in experimental settings but has not been yet tested in real-life conditions.

OBJECTIVE

To assess the diagnostic performance and potential clinical utility of a 174-multiclass AI algorithm in a real-life telemedicine setting.

METHODS

Prospective, diagnostic accuracy study including consecutive patients who submitted images for teledermatology evaluation. The treating dermatologist chose a single image to upload to a web application during teleconsultation. A follow-up reader study including nine healthcare providers (3 dermatologists, 3 dermatology residents and 3 general practitioners) was performed.

RESULTS

A total of 340 cases from 281 patients met study inclusion criteria. The mean (SD) age of patients was 33.7 (17.5) years; 63% (n = 177) were female. Exposure to the AI algorithm results was considered useful in 11.8% of visits (n = 40) and the teledermatologist correctly modified the real-time diagnosis in 0.6% (n = 2) of cases. The overall top-1 accuracy of the algorithm (41.2%) was lower than that of the dermatologists (60.1%), residents (57.8%) and general practitioners (49.3%) (all comparisons P < 0.05, in the reader study). When the analysis was limited to the diagnoses on which the algorithm had been explicitly trained, the balanced top-1 accuracy of the algorithm (47.6%) was comparable to the dermatologists (49.7%) and residents (47.7%) but superior to the general practitioners (39.7%; P = 0.049). Algorithm performance was associated with patient skin type and image quality.

CONCLUSIONS

A 174-disease class AI algorithm appears to be a promising tool in the triage and evaluation of lesions with patient-taken photographs via telemedicine.

Human surface anatomy terminology for dermatology: a Delphi consensus from the International Skin Imaging Collaboration

BACKGROUND

There is no internationally vetted set of anatomic terms to describe human surface anatomy.

OBJECTIVE

To establish expert consensus on a standardized set of terms that describe clinically relevant human surface anatomy.

METHODS

We conducted a Delphi consensus on surface anatomy terminology between July 2017 and July 2019. The initial survey included 385 anatomic terms, organized in seven levels of hierarchy. If agreement exceeded the 75% established threshold, the term was considered 'accepted' and included in the final list. Terms added by the participants were passed on to the next round of consensus. Terms with <75% agreement were included in subsequent surveys along with alternative terms proposed by participants until agreement was reached on all terms.

RESULTS

The Delphi included 21 participants. We found consensus (≥75% agreement) on 361/385 (93.8%) terms and eliminated one term in the first round. Of 49 new terms suggested by participants, 45 were added via consensus. To adjust for a recently published International Classification of Diseases-Surface Topography list of terms, a third survey including 111 discrepant terms was sent to participants. Finally, a total of 513 terms reached agreement via the Delphi method.

CONCLUSIONS

We have established a set of 513 clinically relevant terms for denoting human surface anatomy, towards the use of standardized terminology in dermatologic documentation.

Outpatient dermatology consultations for oncology patients with acute dermatologic adverse events impact anticancer therapy interruption: a retrospective study

BACKGROUND

Dermatologic adverse events (dAEs) of anticancer therapies may negatively impact dosing and quality of life. While therapy interruption patterns due to dAEs have been studied in hospitalized cancer patients, similar outcomes in outpatient oncodermatology are lacking.

OBJECTIVES

To analyse the therapy interruption patterns, clinico-histopathologic characteristics and management outcomes of outpatient dermatology consultations for acute dAEs attributed to the most frequently interrupted class of oncologic agents.

METHODS

We performed a retrospective cohort study of all cancer patients who received a same-day outpatient dermatology consultation for acute dAEs at our institution from 1 January to 30 June 2015. Relevant data were abstracted from electronic medical records, including demographics, oncologic history and explicit recommendations by both the referring clinician and consulting dermatologist on anticancer therapy interruption. Consultations with the most frequently interrupted class of oncologic treatment were characterized according to clinico-histopathologic features, dermatologic management and clinical outcomes.

RESULTS

There were 426 same-day outpatient dermatology consultations (median age 59, 60% female, 30% breast cancer), of which 295 (69%) had systemic anticancer therapy administered within 30 days prior. There was weak inter-rater agreement between referring clinicians and consulting dermatologists on interruption of anticancer treatment (n = 150, κ = 0.096; 95% CI -0.02 to 0.21). Seventy-three (25%) consultations involved interruption by the referring clinician, most commonly targeted therapy (24, 33%). Maculopapular rash was commonly observed in 23 consultations with 25 dAEs attributed to targeted agents (48%), and topical corticosteroids were most frequently utilized for management (22, 38%). The majority (83%) of consultations with targeted therapy-induced dAEs responded to dermatologic treatment and 84% resumed oncologic therapy, although three (19%) at a reduced dose. Rash recurred only in two instances (13%).

CONCLUSIONS

A high frequency of positive outcomes in the management of targeted therapy-induced dAEs by outpatient consulting dermatologists and low recurrence of skin toxicity suggests impactful reductions in interruption of anticancer therapy.

Accuracy of tele-consultation on management decisions of lesions suspect for melanoma using reflectance confocal microscopy as a stand-alone diagnostic tool

BACKGROUND

Diagnostic accuracy of reflectance confocal microscopy (RCM) as a stand-alone diagnostic tool for suspect skin lesions has not been extensively studied.

OBJECTIVE

Primary aim was to measure experts' accuracy in RCM-based management decisions. Secondary aim was to identify melanoma-specific RCM features.

METHODS

The study enrolled patients ≥18 years that underwent biopsy of skin lesions clinically suspected to be melanoma. One hundred lesions imaged by RCM were randomly selected from 439 lesions prospectively collected at four pigmented lesion clinics. The study data set included 23 melanomas, three basal cell and two squamous cell carcinomas, 11 indeterminate melanocytic lesions and 61 benign lesions including 50 nevi. Three expert RCM evaluators were blinded to clinical or dermoscopic images, and to the final histopathological diagnosis. Evaluators independently issued a binary RCM-based management decision, 'biopsy' vs. 'observation'; these decisions were scored against histopathological diagnosis, with 'biopsy' as the correct management decision for malignant and indeterminate lesions. A subset analysis of 23 melanomas and 50 nevi with unequivocal histopathological diagnosis was performed to identify melanoma-specific RCM features.

RESULTS

Sensitivity, specificity and diagnostic accuracy were 74%, 67% and 70% for reader 1, 46%, 84% and 69% for reader 2, and 72%, 46% and 56% for reader 3, respectively. The overall kappa for management decisions was 0.34. Readers had unanimous agreement on management for 50 of the 100 lesions. Non-specific architecture, non-visible papillae, streaming of nuclei, coarse collagen fibres and abnormal vasculature showed a significant association with melanoma in the evaluation of at least two readers.

CONCLUSIONS

Reflectance confocal microscopy tele-consultation of especially challenging lesions, based on image review without benefit of clinical or dermoscopy images, may be associated with limited diagnostic accuracy and interobserver agreement. Architectural and stromal criteria may emerge as potentially useful and reproducible criteria for melanoma diagnosis.

Dermoscopic features and patterns of poromas: a multicentre observational case-control study conducted by the International Dermoscopy Society

BACKGROUND

Poromas are benign cutaneous sweat gland tumours that are challenging to identify. The dermoscopic features of poromas are not well characterized.

OBJECTIVE

To determine the clinical-dermoscopic features of poromas.

METHODS

Cross-sectional, observational study of 113 poromas and 106 matched control lesions from 16 contributors and eight countries. Blinded reviewers evaluated the clinical and dermoscopic features present in each clinical and dermoscopic image.

RESULTS

Poromas were most commonly non-pigmented (85.8%), papules (35.4%) and located on non-acral sites (65.5%). In multivariate analysis, dermoscopic features associated with poroma included white interlacing areas around vessels (OR: 7.9, 95% CI: 1.9-32.5, P = 0.004), yellow structureless areas (OR: 2.5, 95% CI: 1.1-6.0, P = 0.04), milky-red globules (OR: 3.9, 95% CI: 1.4-11.1, P = 0.01) and poorly visualized vessels (OR: 33.3, 95% CI: 1.9-586.5, P = 0.02). The presence of branched vessels with rounded endings was positively associated with poromas but did not reach statistical significance (OR: 2.4, 95% CI: 0.8-6.5, P = 0.10). The presence of any of these five features was associated with a sensitivity and specificity of 62.8% and 82.0%, respectively.

CONCLUSION

We identified dermoscopic features that are specific to the diagnosis of poroma. Overall, however, the prevalence of these features was low. Significant clinical and dermoscopic variability is a hallmark of these uncommon tumours, which are most prevalent on non-acral sites.

A case report of disappearing pigmented skin lesions associated with pembrolizumab treatment for metastatic melanoma

Pembrolizumab is an immune checkpoint inhibitor that targets the programmed cell death (PD)-1 receptor. Common cutaneous adverse side-effects of PD-1 inhibitors include maculopapular rash, pruritus, vitiligo and lichenoid skin and mucosal reactions. Here we describe a man in his sixties with metastatic melanoma treated with pembrolizumab who subsequently developed fading or disappearance of pigmented skin lesions, lightening of the skin, and poliosis of the eyebrows, eyelashes and scalp and body hair. Compared with baseline high-resolution three-dimensional total-body photography, we observed fading or disappearance of solar lentigines, seborrhoeic keratoses and melanocytic naevi, suggesting that PD-1 inhibitors may affect the evolution of these benign skin lesions. With dermatoscopic follow-up, altered lesions showed either blue-grey peppering/granularity or fading in colour without other identifiable features. No halo lesions or lesions with surrounding inflammation were identified. One changed pigmented lesion that showed blue-grey peppering/granularity on dermoscopy was biopsied and interpreted as a macular seborrhoeic keratosis with melanophages. Further studies are required to elucidate the effects of PD-1 inhibition on benign skin lesions.

Cutaneous involvement of disseminated adenovirus infection in an allogeneic stem cell transplant recipient

Infection by human adenoviruses can lead to significant morbidity and mortality in immunocompromised hosts, such as allogeneic stem cell transplant (SCT) recipients, with limited effective treatment options. Specific cutaneous manifestations of disseminated adenovirus infection are not well described. We report a woman in her twenties who received an allogeneic T-cell-depleted peripheral blood SCT for the treatment of severe aplastic anaemia and, 5 months post-transplant, was hospitalized for severe systemic adenovirus infection with progressive involvement of the colon, liver and lungs. Despite therapy with intravenous cidofovir, oral brincidofovir and intravenous immunoglobulin, she had progression of adenoviraemia and dissemination of adenoviral disease. The patient developed a progressive rash characterized by keratotic papules that began on the palms and soles and spread to the entire body. Histopathological examination of skin biopsies of individual skin lesions from the palm and abdomen showed focal acantholytic dyskeratosis and keratinocytes with hyperchromatic nuclei. Several keratinocyte nuclei were immunoreactive for adenovirus. The patient was further treated with ribavirin and adenovirus-specific cytotoxic T lymphocytes but experienced multisystem progression of adenovirus infection culminating in death.

Cross-sectional analysis of the dermoscopic patterns and structures of melanocytic naevi on the back and legs of adolescents

BACKGROUND

Junctional (flat) naevi predominate on the extremities, whereas dermal (raised) naevi are found primarily on the head, neck and trunk. Few studies have investigated the anatomical site prevalence of melanocytic naevi categorized using dermoscopy.

OBJECTIVES

To identify the prevalence of dermoscopic patterns and structures of naevi from the back and legs of adolescents.

METHODS

Dermoscopic images of acquired melanocytic naevi were obtained from the back and legs of students from a population-based cohort in Framingham, Massachusetts. Naevi were classified into reticular, globular, homogeneous or complex dermoscopic patterns. Multinomial logistic regression modelling assessed the associations between dermoscopic pattern and anatomical location.

RESULTS

In total 509 participants (mean age 14 years) contributed 2320 back naevi and 637 leg naevi. Compared with homogeneous naevi, globular and complex naevi were more commonly observed on the back than the legs [odds ratio (OR) 29·39, 95% confidence interval (CI) 9·53-90·65, P < 0·001 and OR 6·8, 95% CI 2·7-17·14, P < 0·001, respectively], whereas reticular lesions were less likely to be observed on the back than on the legs (OR 0·67, 95% CI 0·54-0·84, P = 0·001). Naevi containing any globules were more prevalent on the back than on the legs (25% vs. 3·6%, P < 0·001). Naevi containing any network were more prevalent on the legs than on the back (56% vs. 40·6%, P < 0·001).

CONCLUSIONS

These findings add to a robust body of literature suggesting that dermoscopically defined globular and reticular naevi represent biologically distinct naevus subsets that differ in histopathological growth pattern, age- and anatomical-site-related prevalence, molecular phenotype and aetiological pathways.

Genetic factors associated with naevus count and dermoscopic patterns: preliminary results from the Study of Nevi in Children (SONIC)

BACKGROUND

Melanocytic naevi are an important risk factor for melanoma. Naevi with distinct dermoscopic patterns can differ in size, distribution and host pigmentation characteristics.

OBJECTIVES

We examined MC1R and 85 other candidate loci in a cohort of children to test the hypothesis that the development and dermoscopic type of naevi are modulated by genetic variants.

METHODS

Buccal DNAs were obtained from a cohort of 353 fifth graders (mean age 10·4 years). Polymorphisms were chosen based on a known or anticipated role in naevi and melanoma. Associations between single-nucleotide polymorphisms (SNPs) and baseline naevus count were determined by multivariate regression adjusting for sex, race/ethnicity and sun sensitivity. Dermoscopic images were available for 853 naevi from 290 children. Associations between SNPs and dermoscopic patterns were determined by polytomous regression.

RESULTS

Four SNPs were significantly associated with increasing (IRF4) or decreasing (PARP1, CDK6 and PLA2G6) naevus count in multivariate shrinkage analyses with all SNPs included in the model; IRF4 rs12203952 showed the strongest association with log naevus count (relative risk 1·56, P < 0·001). Using homogeneous naevi as the reference, IRF4 rs12203952 and four other SNPs in TERT, CDKN1B, MTAP and PARP1 were associated with either globular or reticular dermoscopic patterns (P < 0·05).

CONCLUSIONS

Our results provide evidence that subsets of naevi defined by dermoscopic patterns differ in their associations with germline genotypes and support the hypothesis that dermoscopically defined subsets of naevi are biologically distinct. These results require confirmation in larger cohorts. If confirmed, these findings will improve the current knowledge of naevogenesis and assist in the identification of individuals with high-risk phenotypes.

Melanocytic naevi with globular and reticular dermoscopic patterns display distinct BRAF V600E expression profiles and histopathological patterns

BACKGROUND

BRAF (v-raf murine sarcoma viral oncogene homologue B) V600E mutations have been detected with high frequency in melanocytic naevi. Few studies have stratified analyses by naevus dermoscopic pattern.

OBJECTIVES

To determine the frequency of BRAF V600E expression and histopathological pattern in acquired melanocytic naevi distinguished by a globular vs. reticular dermoscopic pattern.

METHODS

We retrospectively identified histologically proven melanocytic naevi with banal reticular or globular dermoscopic patterns and evaluated BRAF V600E expression using immunohistochemistry.

RESULTS

BRAF V600E expression was detected in 11 of 12 globular naevi vs. four of 13 reticular naevi (91·7% vs. 30·1%, P = 0·004). A predominantly dermal growth pattern (P < 0·001) and the presence of large junctional nests (P = 0·017) were each associated with a globular dermoscopic pattern. The presence of either a predominantly dermal growth pattern or large junctional nests was found in 13 of 15 naevi positive for BRAF V600E and in two of 10 naevi negative for BRAF V600E (86·7% vs. 20%, P = 0·002).

CONCLUSIONS

The frequency of BRAF V600E mutations differs in naevi distinguished by unique dermoscopic structures and microanatomical growth patterns. Globular naevi, which most often histologically correspond to a predominantly dermal growth pattern and/or the presence of large junctional nests, are significantly more likely to express BRAF V600E than reticular naevi. These preliminary results require validation, but may directly inform future studies of naevogenesis and melanoma genesis.

Taxane associated subacute cutaneous lupus erythematosus

Numerous medications have been associated with the development of subacute cutaneous lupus erythematosus. A mechanism explaining how unrelated drug classes can lead to subacute cutaneous lupus erythematosus has remained elusive, suggesting that there may be multiple etiologic pathways. Taxanes (docetaxel, paclitaxel, and cabazitaxel) inhibit cell mitosis through microtubule stabilization and their use has uncommonly been associated with subacute cutaneous lupus erythematosus. Recently the antigen recognized by anti-Ro/SS-A antibody (Ro52) has been localized to the cytoplasmic microtubule network. A case report of docetaxel exacerbated subacute cutaneous lupus erythematosus is presented and literature review performed, revealing 11 additional cases of taxane associated subacute cutaneous lupus erythematosus. Taxanes are proposed to exacerbate or induce subacute cutaneous lupus erythematosus in immunogenetically predisposed patients by stabilizing microtubules and affecting Ro/SS-A antigen (Ro52) expression. This may be an under recognized adverse drug reaction because taxanes are used for a defined period and the cutaneous eruption tends to spontaneously improve. Studies analyzing how particular drug classes affect Ro/SS-A antigen expression may be useful in identifying mechanisms of action in drug-induced subacute cutaneous lupus erythematosus.

Rapid Determination of Rice Cultivar Responses to the Sheath Blight Pathogen Rhizoctonia solani Using a Micro-Chamber Screening Method

An accurate greenhouse screening method has not been developed previously to identify host response to sheath blight disease caused by Rhizoctonia solani Kühn that causes significant economic losses in rice yield worldwide. The unavailability of a robust screening system in the greenhouse has made it difficult to quantify disease reactions to R. solani, and has hampered studies on the genetics of resistance and plant breeding efforts to improve resistance. In an effort to develop a standardized laboratory micro-chamber screening method to quantify resistance to R. solani in rice, five rice cultivars, representing a wide range of observed disease reactions under field conditions, were examined in a blind inoculation test at three locations (Arkansas, Texas, and Colombia). Rice seedlings were inoculated at the three- to four-leaf stage with potato dextrose agar plugs containing mycelium and then covered with a 2- or 3-liter transparent plastic bottle for maintaining high humidity after inoculation. Two cultivars, Jasmine 85 and Lemont, that consistently have shown the highest and lowest levels of resistance, respectively, in previous field and greenhouse studies, were used as standards. Concurrent field experiments in Arkansas and Texas also were performed to compare the greenhouse disease ratings with those observed under field conditions. Overall, the relative disease ratings of the seven test cultivars were consistent between test locations and with field evaluations. Thus, the micro-chamber screening method can be used as an effective approach to accurately quantify resistance to the sheath blight pathogen under controlled greenhouse conditions and should help expedite the selection process to improve resistance to this important pathogen.

Molecular markers linked to the blast resistance gene Pi-z in rice for use in marker-assisted selection

Rice blast, caused by the fungal pathogen Pyricularia grisea, is a serious disease affecting rice-growing regions around the world. Current methods for identification of blast-resistant germplasm and progeny typically utilize phenotypic screening. However, phenotypic screens are influenced by environmental conditions and the presence of one resistance gene can sometimes phenotypically mask other genes conferring resistance to the same blast race. Pi-z is a dominant gene located on the short arm of chromosome 6 that confers complete resistance to five races of blast. Using sequence data found in public databases and degenerate primer pairs based on the P-loop, nucleotide binding sites and kinase domain motifs of previously cloned resistance genes, we have developed PCR-based DNA markers that cosegregate with the gene. These markers are polymorphic in a wide range of germplasm, including the narrow crosses characteristic of applied rice-breeding programs. They can now be used as a low cost, high-throughput alternative to conventional phenotypic screening for direct detection of blast resistance genes, allowing rapid introgression of genes into susceptible varieties as well as the incorporation of multiple genes into individual lines for more-durable blast resistance.

The influence of silicon on components of resistance to blast in susceptible, partially resistant, and resistant cultivars of rice

ABSTRACT The application of silicon (Si) fertilizers reduces the severity of blast, caused by Magnaporthe grisea, in irrigated and upland rice; however, little research has been conducted to examine the epidemiological and etiological components of this reduction. Four cultivars of rice with differential susceptibilities to race IB-49 of M. grisea were fertilized with three rates of a calcium silicate fertilizer and inoculated with the pathogen to test the effects of Si on the following components of resistance to blast: incubation period, latent period, infection efficiency, lesion size, rate of lesion expansion, sporulation per lesion, and diseased leaf area. For each cultivar, the incubation period was lengthened by increased rates of Si, and the numbers of sporulating lesions, lesion size, rate of lesion expansion, diseased leaf area, and number of spores per lesion were reduced. Lesion size and sporulation per lesion were lowered by 30 to 45%, and the number of sporulating lesions per leaf and diseased leaf area were significantly reduced at the highest rate of Si. The net effect of Si on these components of resistance is an overall reduction in the production of conidia on plants infected with M. grisea, thereby slowing the epidemic rate of blast.

Import of proteins into the trypanosome nucleus and their distribution at karyokinesis

In all eukaryotic organisms proteins are targeted to the nucleus via a receptor-mediated mechanism that requires a specific nuclear localization sequence (NLS) in the protein. Little is known about this process in trypanosomatid protozoa that are considered amongst the earliest divergent eukaryotes. We have used the green fluorescent protein (gfp) and beta-galactosidase reporters to identify the NLS of two trypanosomal proteins, namely the Trypanosoma brucei La protein homologue and histone H2B of T. cruzi. A monopartite NLS was demonstrated at the C terminus of the La protein, whereas a bipartite NLS was identified within the first 40 amino acids of histone H2B. Treatment of live trypanosomes with poisons of ATP synthesis resulted in exit of the La NLS-gfp fusion from the nucleus. Interestingly, this fusion protein accumulated at several discrete sites in the cytoplasm, rather than equilibrating between the nucleus and the cytoplasm. When ATP levels returned to normal, the protein reentered the nucleus, demonstrating that the process was energy dependent. Finally, using fusion proteins that localize to the nucleoplasm or the nucleolus, we identified a subpopulation of mitotic cells in which the chromosomes have segregated but the daughter nuclei remain connected by a thin thread-like structure. We propose that cells containing this structure represent a late stage in nuclear division that can be placed after chromosome segregation, but before completion of karyokinesis.

Comparative Slow-Blasting in Rice Grown Under Upland and Flooded Blast Nursery Culture

Evaluation of rice for resistance to rice blast disease caused by Pyricularia grisea usually is conducted in upland (nonflooded) disease nurseries, although all commercial U.S. rice is produced under flood irrigation. Upland rice is more susceptible to leaf blast than is flooded rice, and the magnitude of this differential susceptibility can vary among cultivars. This 2-year study was undertaken to determine (i) the relationship between rates of disease development (slow-blasting) in upland and flooded rice and (ii) the value to a rice breeding program of establishing a flooded blast nursery, a facility far more difficult to manage than an upland nursery. Among 200 rice lines compared for leaf blast susceptibility under upland and flooded cultures, only 7 were rated as slightly more resistant under upland culture and 136 rated more resistant under flooded culture. Disease ratings under upland and flooded cultures were highly correlated (R = 0.819). Among 14 preselected cultivars over 2 years, disease development curves under upland and flooded cultures were highly correlated (R = 0.990). The cultivars with intermediate susceptibility under upland culture appeared to benefit most from flooded culture. Upland culture provided more opportunities to assess slow-blasting than did flooded culture, since many lines that produced susceptible-type lesions in upland culture failed to do so under flooded culture. It was concluded that adequate information on comparative leaf blast resistance among rice lines was attainable from upland blast nurseries and that routine evaluation of rice breeding lines for blast resistance in flooded nurseries was not necessary.

Physical and transcriptional analysis of the Trypanosoma brucei genome reveals a typical eukaryotic arrangement with close interspersionof RNA polymerase II- and III-transcribed genes

To further our understanding of the structural and functional organization of the Trypanosoma brucei genome, we have searched for and analyzed sites in the genome where Pol II transcription units meet Pol III genes. Physical and transcriptional maps of cosmid clones spanning the Pol III-transcribed U2 small nuclear RNA (snRNA) and U3 snRNA/7SL RNA gene loci demonstrated that single-copy Pol II genes are closely associated with Pol III-transcribed genes, being separated from each other by 0.6-3 kb. At the U3/7SL transcriptional domain, two Pol II transcription units converged from either side of the chromosome towards the Pol III genes, suggesting that at least for the chromosome containing the U3 snRNA and 7SL RNA genes, there exist two distinct initiation sites for Pol II. Furthermore, in all cases the Pol III genes hallmark the end of Pol II transcription units, suggesting perhaps a functional role for this genetic arrangement. Lastly, we asked whether the environment within a Pol III transcriptional domain allowed expression of pre-mRNA. To test this we inserted a CAT gene cassette, seemingly promoterless but endowed with pre-mRNA processing signals, in the chromosome between the U3 snRNA and 7SL RNA genes. Interestingly, abundant CAT mRNA was produced suggesting that the Pol III genes in the immediate vicinity did not prevent access of presumably Pol II to the CAT gene cassette. We propose that either CAT mRNA is synthesized by Pol II run-through transcription or by Pol II initiationupstream from the CAT gene.

Characterization of quantitative trait loci (QTLs) in cultivated rice contributing to field resistance to sheath blight (Rhizoctonia solani)

Sheath blight, caused by Rhizoctonia solani, is one of the most important diseases of rice. Despite extensive searches of the rice germ plasm, the major gene(s) which give complete resistance to the fungus have not been identified. However, there is much variation in quantitatively inherited resistance to R. solani, and this type of resistance can offer adequate protection against the pathogen under field conditions. Using 255 F4 bulked populations from a cross between the susceptible variety 'Lemont' and the resistant variety 'Teqing', 2 years of field disease evaluation and 113 well-distributed RFLP markers, we identified six quantitative trait loci (QTLs) contributing to resistance to R. solani. These QTLs are located on 6 of the 12 rice chromosomes and collectively explain approximately 60% of the genotypic variation or 47% of the phenotypic variation in the 'Lemont'x'Teqing' cross. One of these resistance QTLs (QSbr4a), which accounted for 6% of the genotypic variation in resistance to R. solani, appeared to be independent of associated morphological traits. The remaining five putative resistance loci (QSbr2a, QSbr3a, QSbr8a, QSbr9a and QSbr12a) all mapped to chromosomal regions also associated with increased plant height, three of which were also associated with QTLs causing later heading. This was consistent with the observation that heading date and plant height accounted for 47% of the genotypic variation in resistance to R. solani in this population. There were also weak associations between resistance to R. solani and leaf width, which were likely due to linkage with a QTL for this trait rather than to a physiological relationship.

A novel approach to protein-protein interaction: complex formation between the p53 tumor suppressor and the HIV Tat proteins

By using a novel genetic approach, based on the properties of lambda cl repressor, we demonstrate that the HIV-1 Tat protein specifically interacts with the human p53 protein via the p53 O2 dimerization domain. By random and site-specific mutagenesis, we also identify the residues in Tat and O2 peptides which are involved in this interaction. Two alternative biological consequences are expected to result from Tat-p53 interaction: (i) Tat-O2 interaction inactivates p53 regulation function, thus producing cell transformation; (ii) Tat-O2 interaction favours the formation of p53 dimers, thus leading the cell towards apoptosis.