Channel Gating in Kalium Channelrhodopsin Slow Mutants.

Kalium channelrhodopsin 1 from Hyphochytrium catenoides (HcKCR1) is the first discovered natural light-gated ion channel that shows higher selectivity to K+ than to Na+ and therefore is used to silence neurons with light (optogenetics). Replacement of the conserved cysteine residue in the transmembrane helix 3 (Cys110) with alanine or threonine results in a >1,000-fold decrease in the channel closing rate. The phenotype of the corresponding mutants in channelrhodopsin 2 is attributed to breaking of a specific interhelical hydrogen bond (the "DC gate"). Unlike CrChR2 and other ChRs with long distance "DC gates", the HcKCR1 structure does not reveal any hydrogen bonding partners to Cys110, indicating that the mutant phenotype is likely caused by disruption of direct interaction between this residue and the chromophore. In HcKCR1_C110A, fast photochemical conversions corresponding to channel gating were followed by dramatically slower absorption changes. Full recovery of the unphotolyzed state in HcKCR1_C110A was extremely slow with two time constants 5.2 and 70 min. Analysis of the light-minus-dark difference spectra during these slow processes revealed accumulation of at least four spectrally distinct blue light-absorbing photocycle intermediates, L, M1 and M2, and a UV light-absorbing form, typical of bacteriorhodopsin-like channelrhodopsins from cryptophytes. Our results contribute to better understanding of the mechanistic links between the chromophore photochemistry and channel conductance, and provide the basis for using HcKCR1_C110A as an optogenetic tool.

Light-gated channelrhodopsin sparks proton-induced calcium release in guard cells.

Although there has been long-standing recognition that stimuli-induced cytosolic pH alterations coincide with changes in calcium ion (Ca2+) levels, the interdependence between protons (H+) and Ca2+ remains poorly understood. We addressed this topic using the light-gated channelrhodopsin HcKCR2 from the pseudofungus Hyphochytrium catenoides, which operates as a H+ conductive, Ca2+ impermeable ion channel on the plasma membrane of plant cells. Light activation of HcKCR2 in Arabidopsis guard cells evokes a transient cytoplasmic acidification that sparks Ca2+ release from the endoplasmic reticulum. A H+-induced cytosolic Ca2+ signal results in membrane depolarization through the activation of Ca2+-dependent SLAC1/SLAH3 anion channels, which enabled us to remotely control stomatal movement. Our study suggests a H+-induced Ca2+ release mechanism in plant cells and establishes HcKCR2 as a tool to dissect the molecular basis of plant intracellular pH and Ca2+ signaling.

Tumoral cutaneous rhinosporidiosis: Case report and review of literature.

Rhinosporidiosis is a chronic granulomatous disease caused by Rhinosporidium seeberi commonly affecting nasal mucosa, conjunctiva, and urethra. Subcutaneous tumor nodule presentation is rare and often mimics as sarcoma. Such tumoral rhinosporidiosis has been reported rarely. This report describes a 60-year male who presented with a solitary, firm, nontender swelling in posterior aspect of right leg with an ulcer and mimicking clinically as soft tissue sarcoma. Histopathology was diagnostic. Surgical excision was found to be useful.

Structural basis for ion selectivity in potassium-selective channelrhodopsins.

KCR channelrhodopsins (K+-selective light-gated ion channels) have received attention as potential inhibitory optogenetic tools but more broadly pose a fundamental mystery regarding how their K+ selectivity is achieved. Here, we present 2.5-2.7 Å cryo-electron microscopy structures of HcKCR1 and HcKCR2 and of a structure-guided mutant with enhanced K+ selectivity. Structural, electrophysiological, computational, spectroscopic, and biochemical analyses reveal a distinctive mechanism for K+ selectivity; rather than forming the symmetrical filter of canonical K+ channels achieving both selectivity and dehydration, instead, three extracellular-vestibule residues within each monomer form a flexible asymmetric selectivity gate, while a distinct dehydration pathway extends intracellularly. Structural comparisons reveal a retinal-binding pocket that induces retinal rotation (accounting for HcKCR1/HcKCR2 spectral differences), and design of corresponding KCR variants with increased K+ selectivity (KALI-1/KALI-2) provides key advantages for optogenetic inhibition in vitro and in vivo. Thus, discovery of a mechanism for ion-channel K+ selectivity also provides a framework for next-generation optogenetics.

Naso-Bronchial Rhinosporidiosis.

Rhinosporidiosis is a chronic mucocutaneous granulomatous disease caused by Rhinosporidium seeberi, commonly affecting the nose and nasopharynx. Endobronchial involvement is of rare occurrence but can pose challenging problems for diagnosis, surgical excision and anaesthetic management. We report a 40-year-old man with a history of recurrent nasal rhinosporidiosis who presented with unilateral nasal obstruction, cough, shortness of breath and a radiological feature of left lung collapse. Eight years since the last surgery, he presented with a recurrent lesion in the nose with concurrent endobronchial involvement. The patient underwent excision of the nasal and the endobronchial lesion successfully under general anaesthesia without any complication and good symptomatic improvement. The clinical presentation and the management of endobronchial rhinosporidiosis are discussed here. The surgical difficulties faced during the procedure are highlighted.

Nasopharyngeal rhinosporidiosis with intracranial extension masquerading as juvenile angiofibroma: an unusual entity.

Rhinosporidiosis is a chronic fungal inflammatory disease prevalent in India and Sri Lanka. Its manifestations are mostly nasal and extranasal lesions are relatively rare. Occasional atypical presentations of this disease lead to diagnostic dilemma. Herein we report on a case of nasopharyngeal rhinosporidiosis having extensive involvement of paranasal sinuses along with intracranial extension which mimicked radiologically as juvenile nasopharyngeal angiofibroma. To our knowledge, this is the first reported case of rhinosporidiosis having intracranial extension. We discuss the pathology, treatment and briefly review the literature of this rare disease.

Equine rhinosporidiosis in Buenos Aires, Argentina.

Rhinosporidiosis is caused by Rhinosporidium seeberi, a parasitic organism of the family Rhinosporideacea family, class Micomycetozoa. The disease is endemic in India; however, some cases were reported in Europe, Africa, North America, and South America. The aim of the present study is to report three cases of rhinosporidiosis in wild horses in different cities of Buenos Aires province, Argentina. We confirm the presence of R. seeberi in the analyzed samples using histopathological and PCR sequencing techniques.

Rhinosporidiosis-Factors predicting disease recurrence.

BACKGROUND: Rhinosporidiosis is a chronic granulomatous disease of the nose caused by Rhinosporidium seeberi. The disease is largely non-amenable to medical therapy and shows high recurrence rates requiring patients to undergo multiple surgeries often resulting in increased morbidity. OBJECTIVE: To analyse the epidemiological, clinical, histopathological characteristics, treatment and outcome in rhinosporidiosis and to identify factors which predispose to recurrence of the disease. PATIENTS/METHODS: Retrospective analysis of data of all patients with a diagnosis of rhinosporidiosis confirmed by histopathology at a tertiary care hospital from 2015 to 2019. RESULTS: There were 42 patients, 40 males and two females, with a mean age of 37.37 years. Disease showed bilateral involvement in 17 (40.48%) patients. Nineteen (45.24%) patients had more than two sites involved at initial presentation. Most patients had nasal cavity involvement followed by nasopharynx. Among the 28 patients who had a follow-up, 12 showed recurrent disease. However, 21 patients were disease free following a revision excision. Involvement of more than two sites was an independent significant factor for recurrence. On univariate analysis, other factors which showed statistically significant odds of developing recurrence were previous surgery (p = .054), involvement of nasal septum (p = .022), middle turbinate (p = .024), nasopharynx (p = .049) and posterior pharyngeal wall (p = .05). Factors which showed significantly less likelihood of developing a recurrence included patients who had less than 12 months duration from first symptom to intervention (p = .016), involvement of less than two sites (p = .0003) and unilateral disease (p = .019). CONCLUSION: Early intervention in rhinosporidiosis especially when the disease is unilateral and involves less than two sites improves the outcome.

Lacrimal sac rhinosporidiosis.

Rhinosporidiosis is a chronic mucocutaneous granulomatous disease caused by Rhinosporidium seeberi, involving primarily the nose and nasopharynx. Very rarely, the disease can affect the lacrimal sac. Here we report a 35-year-old male patient who had rhinosporidial involvement of the nose 5 years ago, for which he underwent endoscopic nasal surgery. Five years after the excision of the nasal mass, he presented with lacrimal sac involvement. The clinical presentation and the management of lacrimal sac rhinosporidiosis are discussed here.

Rhinosporidium seeberi: Is It a Fungi or Parasite?

Rhinosporidium seeberi (R. seeberi) causes rhinosporidiosis, which is manifested as tumor-like polyps developing primarily in the nostrils and conjunctiva in human and animals. This disease is characterized by the presence of large, round-shaped mature stage and small endospores with resistance to culturing. R. seeberi was first reported in 1900 as a sporozoan parasite, but later classified as a lower fungi, although its morphological similarity with aquatic parasites were also noticed. According to 18S small-subunit ribosomal DNA sequencing, R. seeberi belongs to a group of fish parasite DRIP clade located between the animal and fungal divergence. Histological examination is thus necessary for the definitive diagnosis of rhinosporidiosis, and the first line of treatment is usually total surgical excision and electro-cauterization of the polyp base. Among the drug therapies attempted, remission has been reported in some patients who received only Dapson treatment. This disease is endemic across India, Pakistan and Sri Lanka and occurs sporadically in other parts of The World with a common history of patients bathing in stagnant water. An outbreak in Serbia during 1992-1995 and 5 rhinosporidiosis cases from Turkey have been reported until date. Considering that rhinosporidiosis is associated with exposure to water and the agent belongs to a branch of aquatic parasites, it has been proposed that aquatic animals are the natural hosts and that the mammalian hosts acquire infection by contacting contaminated water. Therefore, there is a need for the investigation of the infection in fish besides mammalian animals as reservoirs as well as to conduct screening of antiparasitic drugs with infected fish or infected cell lines with the nearest phylogenetic relatives of R. seeberi.

Case Report: Rhinosporidiosis Literature Review.

Rhinosporidiosis is caused by Rhinosporidium seeberi, a pathogen currently considered a fungus-like parasite of the eukaryotic group Mesomycetozoea. It is usually a benign condition, with slow growth of polypoid lesions, with involvement of the nose, nasopharynx, or eyes. The clinical characteristics of a painless, friable, polypoid mass, usually unilateral, can guide the diagnosis, but the gold standard for diagnosis is histopathological findings. This article reviews the epidemiology, pathobiology, clinical manifestations, diagnostic strategies, and treatment approach for rhinosporidiosis.

An unexpected host in a soft-tissue lesion of thigh.

Rhinosporidiosis is an enigmatic entity and poses a major health problem in the developing countries of South-East Asia. A soft friable polypoid nasal mass is the most common presentation, while sparse literature is available on extranasal involvement. We describe the case of a 35-year-old female patient who presented with a slow-growing soft-tissue swelling with ulceration over the thigh. On clinical and radiological examination, a provisional diagnosis of soft-tissue neoplasm was made. After resection, histopathological sections showed a closely packed cyst with innumerable endospores. The present case report documents the rare occurrence of an incidentally detected cutaneous rhinosporidiosis causing diagnostic difficulty.

Cluster of Nasal Rhinosporidiosis, Eastern Province, Rwanda.

We report 4 recent cases of nasal rhinosporidiosis in Rwanda. All patients were boys or young men living in the same district (Gatsibo District, Eastern Province), suggesting a reservoir in the area. The recent reemergence of rhinosporidiosis in Rwanda might reflect increased availability of diagnostic services rather than emerging disease.

Three unusual cases of parasites in eye.

A 17-year-old male patient presented with cellulitis and mass in the eye noticed approximately 3 months back. The mass was about 1 cm in size and situated at the limbus. All preoperative routine investigations were normal. Surgical exploration revealed a sub-conjunctival cystic mass near the lateral rectus muscle about 1 cm in diameter; the mass was excised. Gross pathological examination revealed a thin-walled cystic mass. There was a hard nodule in the center. Microscopy revealed a wall of cysticercosis. Scolex was also seen. Surrounding tissue revealed sparse acute and chronic inflammatory cells. The case was confirmed by CDC, Atlanta, and was also included in their departmental presentation as an interesting case. A 60-year-old lady presented with complaints of itching over the forehead and right eye for 5 days. She was prescribed steroid eyedrops and antihistaminics. The itching aggravated with eyedrops along with watering and foreign body sensation. On revisit, the ophthalmologist noticed a worm in the right upper subconjunctival space. The worm was carefully removed in toto and sent to the laboratory for identification. The worm was thin, cylindrical, 8-10 cm long and white in color. After microscopic and gross examination of the worm, it was identified as Dirofilaria spp. CDC (Atlanta) confirmed the diagnosis of Dirofilaria. The patient was treated with antihistaminics and was relieved of symptoms without recurrence. A 45-year-old male patient had a painless mass in the eye for the last 3 months. He had no systemic illness. He gave a history of swimming pool use during that time. The mass was excised and submitted for histopathology. Numerous globular cysts representing thick-walled sporangia containing numerous spores diagnostic of Rhinosporidiosis were seen.

Rhinosporidiosis in horses / Rinosporidiose em equinos

Rhinosporidiosis is a disease caused by Rhinosporidium seeberi, an aquatic protist of the class Mesomycetozoa. It primarily affects the nasal mucosa and transmission is associated with contaminated water contact. This report describes seven cases of rhinosporidiosis in horses in Rio Grande do Sul covering the period of 13 years. The disease predominantly affected Crioulo and thoroughbred horses. No apparent gender predisposition occurs, and age ranged from two to 25 years, with a median of 10 years. The gross aspects were characterized by unilateral (85.7%, 6/7) or bilateral (14.3%, 1/7) polyps. These were soft to friable, whitish to pink, cauliflower-like, with an irregular, sometimes ulcerated surface, measuring 2.5 to 6.0cm in diameter. There was a severe inflammatory infiltrate of the submucosa was observed, associated with moderate proliferation of the epithelium, and numerous rounded structures were identified compatible with sporangia of R. seeberi. Rhinosporidiosis should be included in the differential diagnosis of other conditions affecting the respiratory tract of horses, and it is important to perform histopathology for diagnosis.(AU)

A rinosporidiose é uma doença causada por Rhinosporidium seeberi, protista aquático da classe Mesomycetozoa. Acomete principalmente a mucosa nasal e a transmissão está associada ao contato com água contaminada. Este trabalho descreve sete casos de rinosporidiose em equinos no Rio Grande do Sul em um período de 13 anos. A doença afetou predominantemente cavalos de raça, como Crioulo e Puro Sangue Inglês, sem predisposição sexual evidente e a idade variou de dois a 25 anos, com a mediana de 10 anos. Macroscopicamente foram caracterizadas por pólipos unilaterais (85,7%; 6/7) ou bilaterais (14,3%; 1/7). Os pólipos eram macios a friáveis, esbranquiçados a róseos, com aspecto de couve flor e com superfície irregular, por vezes ulcerada, medindo 2,5 a 6,0cm de diâmetro. Havia infiltrado inflamatório piogranulomatoso acentuado na submucosa associado à moderada proliferação do epitélio e numerosas estruturas arredondadas compatíveis com esporângios de R. seeberi. A rinosporidiose deve ser incluída no diagnóstico diferencial de outras patologias que acometem o trato respiratório de equinos, sendo importante a realização da histopatologia para diagnóstico.(AU)