GRF2 Is Crucial for Cone Photoreceptor Viability and Ribbon Synapse Formation in the Mouse Retina

Using constitutive GRF1/2 knockout mice, we showed previously that GRF2 is a key regulator of nuclear migration in retinal cone photoreceptors. To evaluate the functional relevance of that cellular process for two putative targets of the GEF activity of GRF2 (RAC1 and CDC42), here we compared the structural and functional retinal phenotypes resulting from conditional targeting of RAC1 or CDC42 in the cone photoreceptors of constitutive GRF2KO and GRF2WT mice. We observed that single RAC1 disruption did not cause any obvious morphological or physiological changes in the retinas of GRF2WT mice, and did not modify either the phenotypic alterations previously described in the retinal photoreceptor layer of GRF2KO mice. In contrast, the single ablation of CDC42 in the cone photoreceptors of GRF2WT mice resulted in clear alterations of nuclear movement that, unlike those of the GRF2KO retinas, were not accompanied by electrophysiological defects or slow, progressive cone cell degeneration. On the other hand, the concomitant disruption of GRF2 and CDC42 in the cone photoreceptors resulted, somewhat surprisingly, in a normalized pattern of nuclear positioning/movement, similar to that physiologically observed in GRF2WT mice, along with worsened patterns of electrophysiological responses and faster rates of cell death/disappearance than those previously recorded in single GRF2KO cone cells. Interestingly, the increased rates of cone cell apoptosis/death observed in single GRF2KO and double-knockout GRF2KO/CDC42KO retinas correlated with the electron microscopic detection of significant ultrastructural alterations (flattening) of their retinal ribbon synapses that were not otherwise observed at all in single-knockout CDC42KO retinas. Our observations identify GRF2 and CDC42 (but not RAC1) as key regulators of retinal processes controlling cone photoreceptor nuclear positioning and survival, and support the notion of GRF2 loss-of-function mutations as potential drivers of cone retinal dystrophies.

Critical requirement of SOS1 for tumor development and microenvironment modulation in KRASG12D-driven lung adenocarcinoma

The impact of genetic ablation of SOS1 or SOS2 is evaluated in a murine model of KRASG12D-driven lung adenocarcinoma (LUAD). SOS2 ablation shows some protection during early stages but only SOS1 ablation causes significant, specific long term increase of survival/lifespan of the KRASG12D mice associated to markedly reduced tumor burden and reduced populations of cancer-associated fibroblasts, macrophages and T-lymphocytes in the lung tumor microenvironment (TME). SOS1 ablation also causes specific shrinkage and regression of LUAD tumoral masses and components of the TME in pre-established KRASG12D LUAD tumors. The critical requirement of SOS1 for KRASG12D-driven LUAD is further confirmed by means of intravenous tail injection of KRASG12D tumor cells into SOS1KO/KRASWT mice, or of SOS1-less, KRASG12D tumor cells into wildtype mice. In silico analyses of human lung cancer databases support also the dominant role of SOS1 regarding tumor development and survival in LUAD patients. Our data indicate that SOS1 is critically required for development of KRASG12D-driven LUAD and confirm the validity of this RAS-GEF activator as an actionable therapeutic target in KRAS mutant LUAD.

Critical Requirement of SOS1 for Development of BCR/ABL-Driven Chronic Myelogenous Leukemia

Simple Summary

The p210^BCR/ABL oncoprotein is necessary and sufficient to trigger chronic myelogenous leukemia (CML) in mice. Our prior in vitro studies showing that the ABL-mediated phosphorylation of SOS1 promotes RAC activation and contributes to BCR-ABL leukemogenesis suggested the significant role of SOS1 in the development of CML. To provide direct in vivo experimental evidence of the specific contribution of SOS1 to the development of CML, here, we analyzed the effect of the direct genetic ablation of SOS1 or SOS2 on the genesis of p210^BCR/ABL -driven CML in mice. Our data showed that direct SOS1 genetic ablation causes the significant suppression of all the pathological hallmarks typical of CML, demonstrating that SOS1 deficiency is protective against CML development and identifying this cellular GEF as a relevant, novel therapeutic target for the clinical treatment of this hematological malignancy.

Abstract

We showed previously that the ABL-mediated phosphorylation of SOS1 promotes RAC activation and contributes to BCR-ABL leukemogenesis, suggesting the relevant role of SOS1 in the pathogenesis of CML. To try and obtain direct experimental evidence of the specific mechanistic implication of SOS1 in CML development, here, we combined a murine model of CML driven by a p210^BCR/ABL transgene with our tamoxifen-inducible SOS1/2-KO system in order to investigate the phenotypic impact of the direct genetic ablation of SOS1 or SOS2 on the pathogenesis of CML. Our observations showed that, in contrast to control animals expressing normal levels of SOS1 and SOS2 or to single SOS2-KO mice, p210^BCR/ABL transgenic mice devoid of SOS1 presented significantly extended survival curves and also displayed an almost complete disappearance of the typical hematological alterations and splenomegaly constituting the hallmarks of CML. SOS1 ablation also resulted in a specific reduction in the proliferation and the total number of colony-forming units arising from the population of bone marrow stem/progenitor cells from p210^BCR/ABL transgenic mice. The specific blockade of CML development caused by SOS1 ablation in p210^BCR/ABL mice indicates that SOS1 is critically required for CML pathogenesis and supports the consideration of this cellular GEF as a novel, alternative bona fide therapeutic target for CML treatment in the clinic.

Critical requirement of SOS1 RAS-GEF function for mitochondrial dynamics, metabolism, and redox homeostasis

SOS1 ablation causes specific defective phenotypes in MEFs including increased levels of intracellular ROS. We showed that the mitochondria-targeted antioxidant MitoTEMPO restores normal endogenous ROS levels, suggesting predominant involvement of mitochondria in generation of this defective SOS1-dependent phenotype. The absence of SOS1 caused specific alterations of mitochondrial shape, mass, and dynamics accompanied by higher percentage of dysfunctional mitochondria and lower rates of electron transport in comparison to WT or SOS2-KO counterparts. SOS1-deficient MEFs also exhibited specific alterations of respiratory complexes and their assembly into mitochondrial supercomplexes and consistently reduced rates of respiration, glycolysis, and ATP production, together with distinctive patterns of substrate preference for oxidative energy metabolism and dependence on glucose for survival. RASless cells showed defective respiratory/metabolic phenotypes reminiscent of those of SOS1-deficient MEFs, suggesting that the mitochondrial defects of these cells are mechanistically linked to the absence of SOS1-GEF activity on cellular RAS targets. Our observations provide a direct mechanistic link between SOS1 and control of cellular oxidative stress and suggest that SOS1-mediated RAS activation is required for correct mitochondrial dynamics and function.

Functional Specificity of the Members of the Sos Family of Ras-GEF Activators: Novel Role of Sos2 in Control of Epidermal Stem Cell Homeostasis

Simple Summary

The Sos Ras-GEFs are known to participate in a wide range of skin-related diseases including cutaneous cancers, cardio-facio-cutaneous syndromes, or hirsutism. However, the specific functional roles played by the Sos1 and/or Sos2 family members in specific skin compartments remain largely unknown. This report aimed at precisely characterizing the specific functions played by Sos1 and/or Sos2 in keratinocytes, an essential cellular component of the skin. Our data show that Sos1 and Sos2 make overlapping contributions to both keratinocyte proliferation and survival. However, Sos1 seems to have a preferential involvement in regulating the ERK axis, whereas Sos2 seems to control the signaling output from the PI3K axis. We also uncovered an essential role of Sos2 in the control of the population of epidermal stem cells.

Abstract

Prior reports showed the critical requirement of Sos1 for epithelial carcinogenesis, but the specific functionalities of the homologous Sos1 and Sos2 GEFs in skin homeostasis and tumorigenesis remain unclear. Here, we characterize specific mechanistic roles played by Sos1 or Sos2 in primary mouse keratinocytes (a prevalent skin cell lineage) under different experimental conditions. Functional analyses of actively growing primary keratinocytes of relevant genotypes—WT, Sos1-KO, Sos2-KO, and Sos1/2-DKO—revealed a prevalent role of Sos1 regarding transcriptional regulation and control of RAS activation and mechanistic overlapping of Sos1 and Sos2 regarding cell proliferation and survival, with dominant contribution of Sos1 to the RAS-ERK axis and Sos2 to the RAS-PI3K/AKT axis. Sos1/2-DKO keratinocytes could not grow under 3D culture conditions, but single Sos1-KO and Sos2-KO keratinocytes were able to form pseudoepidermis structures that showed disorganized layer structure, reduced proliferation, and increased apoptosis in comparison with WT 3D cultures. Remarkably, analysis of the skin of both newborn and adult Sos2-KO mice uncovered a significant reduction of the population of stem cells located in hair follicles. These data confirm that Sos1 and Sos2 play specific, cell-autonomous functions in primary keratinocytes and reveal a novel, essential role of Sos2 in control of epidermal stem cell homeostasis.

Ras-GRF2 regulates nestin-positive stem cell density and onset of differentiation during adult neurogenesis in the mouse dentate gyrus

Various parameters of neurogenesis were analyzed in parallel in the two neurogenic areas (the Dentate Gyrus[DG] and the Subventricular Zone[SVZ]/Rostral Migratory Stream[RMS]/Main Olfactory Bulb[MOB] neurogenic system) of adult WT and KO mouse strains for the Ras-GRF1/2 genes (Ras-GRF1-KO, Ras-GRF2-KO, Ras-GRF1/2-DKO). Significantly reduced numbers of doublecortin[DCX]-positive cells were specifically observed in the DG, but not the SVZ/RMS/MOB neurogenic region, of Ras-GRF2-KO and Ras-GRF1/2-DKO mice indicating that this novel Ras-GRF2-dependent phenotype is spatially restricted to a specific neurogenic area. Consistent with a role of CREB as mediator of Ras-GRF2 function in neurogenesis, the density of p-CREB-positive cells was also specifically reduced in all neurogenic regions of Ras-GRF2-KO and DKO mice. Similar levels of early neurogenic proliferation markers (Ki67, BrdU) were observed in all different Ras-GRF genotypes analyzed but significantly elevated levels of nestin-immunolabel, particularly of undifferentiated, highly ramified, A-type nestin-positive neurons were specifically detected in the DG but not the SVZ/RMS/MOB of Ras-GRF2-KO and DKO mice. Together with assays of other neurogenic markers (GFAP, Sox2, Tuj1, NeuN), these observations suggest that the deficit of DCX/p-CREB-positive cells in the DG of Ras-GRF2-depleted mice does not involve impaired neuronal proliferation but rather delayed transition from the stem cell stage to the differentiation stages of the neurogenic process. This model is also supported by functional analyses of DG-derived neurosphere cultures and transcriptional characterization of the neurogenic areas of mice of all relevant Ras-GRF genotypes suggesting that the neurogenic role of Ras-GRF2 is exerted in a cell-autonomous manner through a specific transcriptional program.

RASGRF2 controls nuclear migration in postnatal retinal cone photoreceptors

Detailed immunocytochemical analyses comparing wild-type (WT), GRF1-knockout (KO), GRF2-KO and GRF1/2 double-knockout (DKO) mouse retinas uncovered the specific accumulation of misplaced, 'ectopic' cone photoreceptor nuclei in the photoreceptor segment (PS) area of retinas from GRF2-KO and GRF1/2-DKO, but not of WT or GRF1-KO mice. Localization of ectopic nuclei in the PS area of GRF2-depleted retinas occurred postnatally and peaked between postnatal day (P)11 and P15. Mechanistically, the generation of this phenotype involved disruption of the outer limiting membrane and intrusion into the PS layer by cone nuclei displaying significant perinuclear accumulation of signaling molecules known to participate in nuclear migration and cytoskeletal reorganization, such as PAR3, PAR6 and activated, phosphorylated forms of PAK, MLC2 and VASP. Electroretinographic recordings showed specific impairment of cone-mediated retinal function in GRF2-KO and GRF1/2-DKO retinas compared with WT controls. These data identify defective cone nuclear migration as a novel phenotype in mouse retinas lacking GRF2 and support a crucial role of GRF2 in control of the nuclear migration processes required for proper postnatal development and function of retinal cone photoreceptors.

Transcriptional profiling reveals functional links between RasGrf1 and Pttg1 in pancreatic beta cells

BACKGROUND

Our prior characterization of RasGrf1 deficient mice uncovered significant defects in pancreatic islet count and size as well as beta cell development and signaling function, raising question about the mechanisms linking RasGrf1 to the generation of those "pancreatic" phenotypes.

RESULTS

Here, we compared the transcriptional profile of highly purified pancreatic islets from RasGrf1 KO mice to that of WT control animals using commercial oligonucleotide microarrays. RasGrf1 elimination resulted in differential gene expression of numerous components of MAPK- and Calcium-signaling pathways, suggesting a relevant contribution of this GEF to modulation of cellular signaling in the cell lineages integrating the pancreatic islets. Whereas the overall transcriptional profile of pancreatic islets was highly specific in comparison to other organs of the same KO mice, a significant specific repression of Pttg1 was a common transcriptional alteration shared with other tissues of neuroectodermal origin. This observation, together with the remarkable pancreatic phenotypic similarities between RasGrf1 KO and Pttg1 KO mice suggested the possibility of proximal functional regulatory links between RasGrf1 and Pttg1 in pancreatic cell lineages expressing these proteins.Analysis of the mPttg1 promoter region identified specific recognition sites for numerous transcription factors which were also found to be differentially expressed in RasGrf1 KO pancreatic islets and are known to be relevant for Ras-ERK signaling as well as beta cell function. Reporter luciferase assays in BT3 insulinoma cells demonstrated the ability of RasGrf1 to modulate mPttg1 promoter activity through ERK-mediated signals. Analysis of the phenotypic interplay between RasGrf1 and Pttg1 in double knockout RasGrf1/Pttg1 mice showed that combined elimination of the two loci resulted in dramatically reduced values of islet and beta cell count and glucose homeostasis function which neared those measured in single Pttg1 KO mice and were significantly lower than those observed in individual RasGrf1 KO mice.

CONCLUSIONS

The specific transcriptional profile and signaling behavior of RasgGrf1 KO pancreatic islets, together with the dominance of Pttg1 over RasGrf1 with regards to the generation of these phenotypes in mouse pancreas, suggest that RasGrf1 is an important upstream component of signal transduction pathways regulating Pttg1 expression and controlling beta cell development and physiological responses.

C3G transgenic mouse models with specific expression in platelets reveal a new role for C3G in platelet clotting through its GEF activity

We have generated mouse transgenic lineages for C3G (tgC3G) and C3GΔCat (tgC3GΔCat, C3G mutant lacking the GEF domain), where the transgenes are expressed under the control of the megakaryocyte and platelet specific PF4 (platelet factor 4) gene promoter. Transgenic platelet activity has been analyzed through in vivo and in vitro approaches, including bleeding time, aggregation assays and flow cytometry. Both transgenes are expressed (RNA and protein) in purified platelets and megakaryocytes and do not modify the number of platelets in peripheral blood. Transgenic C3G animals showed bleeding times significantly shorter than control animals, while tgC3GΔCat mice presented a remarkable bleeding diathesis as compared to their control siblings. Accordingly, platelets from tgC3G mice showed stronger activation in response to platelet agonists such as thrombin, PMA, ADP or collagen than control platelets, while those from tgC3GΔCat animals had a lower response. In addition, we present data indicating that C3G is a mediator in the PKC pathway leading to Rap1 activation. Remarkably, a significant percentage of tgC3G mice presented a higher level of neutrophils than their control siblings. These results indicate that C3G plays an important role in platelet clotting through a mechanism involving its GEF activity and suggest that it might be also involved in neutrophil development.

Kinetics of antibodies in sera, saliva, and urine samples from adult patients with primary or secondary dengue 3 virus infections

OBJECTIVES

The kinetics of three serological markers (IgM, IgA, and IgG) in serum, saliva, and urine samples from adult patients with primary or secondary dengue infection were studied.

DESIGN

Serum, saliva, and urine samples were collected from 22 patients with clinical and confirmed dengue 3 virus infection during the outbreak in Havana City in 2001. They were tested by capture IgM (MAC-ELISA), IgA (AAC-ELISA), and IgE (EAC-ELISA) and IgG ELISA inhibition method (EIM) to detect specific dengue antibodies.

RESULTS

Similar kinetics were observed in IgM, IgA, and IgG antibodies in saliva and IgA and IgG in urine samples from secondary cases compared with kinetics in serum samples, although the values were lower. No IgG antibody was detected in saliva and urine samples in primary cases and IgM antibody was not detected in urine samples from either primary or secondary infection. All secondary cases were positive for IgG in saliva and urine samples at day 7. The kinetics of specific IgE antibodies in primary and secondary cases were different.

CONCLUSIONS

The kinetics of three serological markers (IgM, IgA, and IgG) in serum, saliva, and urine samples from adult patients with primary or secondary dengue 3 virus infection were studied for the first time, showing its behavior and usefulness in dengue virus diagnosis. The specific IgE could play a role as a serological marker in secondary infections.

Serological markers during dengue 3 primary and secondary infections

BACKGROUND

The detection of the IgM antibody for the dengue virus in serum by ELISA has become one of the most important and useful methods for diagnosis of dengue using a single acute-phase serum sample. Currently, this system is an invaluable tool for the surveillance of dengue fever (DF) and dengue hemorrhagic fever (DHF). The usefulness of other serological markers such as IgA and IgE have been less studied.

OBJECTIVE

To study the IgM, IgA and IgE specific antibody response in dengue 3 infected patients with different clinical picture and type of infection.

STUDY DESIGN

One hundred and twenty-seven serum samples collected on days 5-7 at the onset of fever from clinically and serologically confirmed dengue cases were studied. Forty-two were classified as primary dengue fever cases, 48 as secondary dengue fever cases and 37 as secondary dengue hemorrhagic fever cases. All samples were tested by capture ELISA in order to detect dengue IgM, IgA and IgE antibodies.

RESULTS AND CONCLUSIONS

In this study, significant differences were observed in the IgM, IgA and IgE response between the study groups. High IgA and IgE OD ratios in secondary dengue cases were found. The usefulness of serotype specific IgM antibody detection is also analyzed and discussed. A priority for future dengue research in terms of protection, recovery of infection and immunopathogenesis is to elucidate the role of these immunoglobulins. The cross reactivity response to IgM between dengue virus serotypes in primary and secondary cases should also be more studied.

Patch migration: a serious late complication of thoracotomy lead systems

Thoracotomy patch leads used for implantable cardioverter defibrillators (ICDs) are generally safe and effective. We describe two patients in whom a late complication of patch lead migration occurred years after the original implants, causing a bronchopleural fistula in one and lingular lobe collapse in the other patient. We conclude that patch migration is a late but possible complication of extrapericardial ICD leads, and should be suspected in patients who present with hemoptysis, atypical pneumonia, or lung collapse after the initial ICD surgery.

[Cardiac insufficiency and B-blockers]

This article summarise our experience with the Beta-Blocker in the management of congestive heart failure, which did not respond to the usual medical treatment.

Luteinized ovarian cysts in Mediterranean striped dolphins

The morbillivirus epizootic during 1990 to 1992 in Mediterranean striped dolphins (Stenella coeruleoalba) off the Mediterranean coast of Spain diminished these populations directly through mortalities, and indirectly through loss of normal fecundity. High levels of polychlorinated biphenyls (PCB's) also were detected in stranded animals. In addition to high numbers of abortions during the epidemic, unusual cystic structures were noted in the ovaries of several morbillivirus-infected dolphins with high PCB levels. These structures were identified as multiple luteinized cysts from their gross and histomorphologic characteristics. No morbillivirus antigens were detected in the lesions by immunohistochemistry. Because luteinized cysts occur when ovulation is impeded, either an effect of morbillivirus or PCB's on hypothalamic/pituitary function or an effect of PCB's on ovarian responsiveness are proposed as pathogenic mechanisms. These cysts may impede population recovery from the epidemic if similar cysts occurred on surviving dolphins.

Atrial fibrillation: a delayed presentation of traumatic tricuspid valve incompetence

Isolated tricuspid valve incompetence resulting from blunt thoracic injury is rare. The diagnosis may be challenging. Subsequent clinical course may be variable. Early surgical intervention rather than medical therapy has been suggested in selected cases. We report a case of blunt chest trauma causing delayed chronic tricuspid regurgitation manifesting primarily as atrial fibrillation many years after the initial blunt chest trauma. Replacement of tricuspid valve restored normal sinus rhythm.

Trace elements in striped dolphins (Stenella coeruleoalba) from the western Mediterranean

Tissues obtained from Stenella coeruleoalba stranded along the Spanish and Italian Mediterranean coasts from 1987 to 1994 were analysed for cadmium (Cd), copper (Cu), mercury (Hg), selenium (Se) and zinc (Zn). The age, length and weight of the dolphins were recorded. Hg levels were also assayed in skin biopsies from dolphins of the same species in the waters off northeastern Spain and in the Tyrrhenian and Ligurian Seas. Levels of all elements differed in muscle of stranded dolphins from the two areas. Hg was higher in tissues from animals stranded on the Italian coasts and in skin biopsies obtained in the Tyrrhenian and Ligurian Seas, than in the respective Spanish samples. This is probably related to Hg pollution from the natural weathering of cinnabar ores in central Italy. Se and Cd levels had similar accumulation patterns to those of Hg. Accumulation of Hg and Se is explained by the existence of a detoxification pathway involving both elements, however the reason for the similar Cd trend is unclear. Geographical differences in the accumulation pattern of these elements may reflect the existence of two different populations of Stenella coeruleoalba in the western Mediterranean.

Patterns of growth and physical maturity in the western Mediterranean striped dolphin, Stenella coeruleoalba (Cetacea: Odontoceti)

The growth and physical maturation of striped dolphins (Stenella coeruleoalba) of the northern section of the western Mediterranean Sea were studied. Fitted Gompertz growth curves indicate that females grow faster than males when they are young, but their growth ceases and the asymptotic length is attained earlier than in males. Asymptotic length was greater in males (200 cm) than in females (194 cm). Males reached vertebral physical maturity at 15–20 years old and females earlier, at 13–18 years old. Cranial maturity was apparently achieved at similar ages and body lengths. The radius and ulna, however, completed their ossification much earlier, again showing sexual dimorphism, with females maturing at a younger age (5–6 years) and smaller body length (160–175 cm) than males (8–9 years and 170–181 cm). Age-related parameters of physical maturation and growth determined for this population were similar to those estimated for the striped dolphins inhabiting Japanese waters, while length-related parameters differed markedly between the two conspecific populations. It is concluded that the only age- or length-related parameter associated with body growth or ossification of the skeleton that is liable to be affected by density-dependent forces is the body growth rate or, as a consequence, the age at attainment of sexual maturity.

Flipper development in the Mediterranean striped dolphin (Stenella coeruleoalba)

BACKGROUND

Studies of population biology are scarce in Mediterranean striped dolphins (Stenella coeruleoalba) mostly because of the lack of samples. Until now, studies of physical maturity, growth, and development of the flipper bones were not available for this species in the Mediterranean.

METHODS

The osteological features and metric characters of the pectoral limbs of Mediterranean striped dolphins were analyzed with radiological techniques. Measurements were made directly on the radiographic films.

RESULTS AND CONCLUSIONS

We found five carpal bones arranged in a proximal row of three and a distal row of two, although one or two additional osseous elements were occasionally observed. The phalangeal formula (excluding metacarpals) was established as 1-2:8-9-10:6-5-7:3-2:1-2. In metacarpals, epiphyseal ossification centers matured at the same time at both ends. As a general rule, the ossification of the epiphyses in the flipper bones showed a decreasing gradient in the proximodistal direction, confirming the pattern previously described in other species. Phalangeal epiphyses were not useful as indicators of skeletal maturity, and grading epiphyseal maturation of the distal radius and ulna is proposed as the more straight-forward and precise method for assessing bone maturation. In females, maturity of the flipper was achieved between 5 and 6 years of age and 160-175 cm of body length, whereas this maturation occurred between 8 and 9 years of age and 170-181 cm in length in males. Prediction of gender through examination of flipper structure was not feasible.

Pathology of morbillivirus infection in striped dolphins (Stenella coeruleoalba) from Valencia and Murcia, Spain

During the summer and fall of 1990 hundreds of striped dolphins (Stenella coeruleoalba) died in the Spanish Mediterranean as a result of morbillivirus infection. A pathological investigation was carried out on dolphins from Valencia and Murcia which were among the first to die in the epizootic. The dolphins were in poor body condition and pneumonia was the main necropsy finding. Microscopic lung lesions characterized by necrosis of bronchial and bronchiolar epithelium and infiltration of alveoli with macrophages, lymphocytes, neutrophils and multinucleated syncytia were seen in most dolphins. Cytoplasmic and nuclear eosinophilic viral inclusions were present in bronchial and bronchiolar epithelium and in syncytia. Focal granulomatous inflammation associated with nematodes was also present. Brain lesions included diffuse degeneration and necrosis of neurons, microgliosis, perivascular cuffing, formation of syncytia and focal demyelination. Cytoplasmic and nuclear eosinophilic inclusions were present in neurons and glial cells. There was severe lymphoid necrosis and depletion of spleen and lymph nodes and syncytia also occurred in lymph nodes. Biliary and transitional epithelium contained nuclear and cytoplasmic eosinophilic inclusions. Immunoperoxidase staining using monoclonal antibodies to phocine distemper virus confirmed the presence of morbillivirus antigens in lung and brain. The distribution and severity of lesions in striped dolphins are similar to those of distemper in seals, harbor porpoises and terrestrial mammals. The formation of syncytia in the lung and brain may be a useful pathological indicator of morbillivirus infection and may be used in the investigation of pinniped and cetacean strandings in North America.