Identification of Components of the Hippo Pathway in Hydra and Potential Role of YAP in Cell Division and Differentiation

The Hippo signaling pathway has been shown to be involved in regulating cellular identity, cell/tissue size maintenance and mechanotransduction. The Hippo pathway consists of a kinase cascade which determines the nucleo-cytoplasmic localization of YAP in the cell. YAP is the effector protein in the Hippo pathway, which acts as a transcriptional cofactor for TEAD. Phosphorylation of YAP upon activation of the Hippo pathway prevents it from entering the nucleus and abrogates its function in the transcription of the target genes. In Cnidaria, the information on the regulatory roles of the Hippo pathway is virtually lacking. Here, we report the existence of a complete set of Hippo pathway core components in Hydra for the first time. By studying their phylogeny and domain organization, we report evolutionary conservation of the components of the Hippo pathway. Protein modelling suggested the conservation of YAP-TEAD interaction in Hydra. Further, we characterized the expression pattern of the homologs of yap, hippo, mob and sav in Hydra using whole-mount RNA in situ hybridization and report their possible role in stem cell maintenance. Immunofluorescence assay revealed that Hvul_YAP expressing cells occur in clusters in the body column and are excluded in the terminally differentiated regions. Actively proliferating cells marked by Ki67 exhibit YAP colocalization in their nuclei. Strikingly, a subset of these colocalized cells is actively recruited to the newly developing bud. Disruption of the YAP-TEAD interaction increased the budding rate indicating a critical role of YAP in regulating cell proliferation in Hydra. Collectively, we posit that the Hippo pathway is an essential signaling system in Hydra; its components are ubiquitously expressed in the Hydra body column and play a crucial role in Hydra tissue homeostasis.

Spatially-resolved nanometer-scale measurement of cartilage extracellular matrix mobility

OBJECTIVE

Tissues have complex structures, comprised of solid and fluid phases. Improved understanding of interactions between joint fluid and extracellular matrix (ECM) is required in models of cartilage mechanics. X-ray photon correlation spectroscopy (XPCS) directly measures nanometer-scale dynamics and can provide insight into biofluid-biosolid interactions in cartilage. This study applies XPCS to evaluate dynamic interactions between intact cartilage and biofluids.

DESIGN

Cartilage biopsies were collected from bovine femoral condyles. During XPCS measurements, cartilage samples were exposed to different fluids: deionized water, PBS, synovial fluid, or sonicated synovial fluid. ECM-biofluid interactions were also assessed at different length scales and different depths from the cartilage surface.

RESULTS

Using XPCS, cartilage ECM mobility was detected at length scales from 50 to 207 nm. As length scale decreased, time scale for autocorrelation decay decreased, suggesting smaller ECM components are more mobile. ECM dynamics were slowed by dehydrating the sample, demonstrating XPCS assesses matrix mobility in hydrated environments. At all length scales, the matrix was more mobile in deionized water and slowest in synovial fluid. Using the 207 nm length scale assessment, ECM dynamics in synovial fluid were fastest at the cartilage surface and progressively slowed as depth into the sample increased, demonstrating XPCS can assess spatial distribution of ECM dynamics. Finally, ECM mobility increased for degraded synovial fluid.

CONCLUSIONS

This study demonstrates the potential of XPCS to provide unique insights into nanometer-scale cartilage ECM mobility in a spatially resolved manner and illustrates the importance of biosolid-biofluid interactions in dictating ECM dynamics.

Differential tissue stiffness of body column facilitates locomotion of Hydra on solid substrates

The bell-shaped members of the Cnidaria typically move around by swimming, whereas the Hydra polyp can perform locomotion on solid substrates in an aquatic environment. To address the biomechanics of locomotion on rigid substrates, we studied the 'somersaulting' locomotion in Hydra We applied atomic force microscopy to measure the local mechanical properties of Hydra's body column and identified the existence of differential Young's modulus between the shoulder region versus rest of the body column at 3:1 ratio. We show that somersaulting primarily depends on differential tissue stiffness of the body column and is explained by computational models that accurately recapitulate the mechanics involved in this process. We demonstrate that perturbation of the observed stiffness variation in the body column by modulating the extracellular matrix polymerization impairs the 'somersault' movement. These results provide a mechanistic basis for the evolutionary significance of differential extracellular matrix properties and tissue stiffness.

Cellular and Molecular Mechanisms of Hydra Regeneration

Regeneration of lost body parts is essential to regain the fitness of the organism for successful living. In the animal kingdom, organisms from different clades exhibit varied regeneration abilities. Hydra is one of the few organisms that possess tremendous regeneration potential, capable of regenerating complete organism from small tissue fragments or even from dissociated cells. This peculiar property has made this genus one of the most invaluable model organisms for understanding the process of regeneration. Multiple studies in Hydra led to the current understanding of gross morphological changes, basic cellular dynamics, and the role of molecular signalling such as the Wnt signalling pathway. However, cell-to-cell communication by cell adhesion, role of extracellular components such as extracellular matrix (ECM), and nature of cell types that contribute to the regeneration process need to be explored in depth. Additionally, roles of developmental signalling pathways need to be elucidated to enable more comprehensive understanding of regeneration in Hydra. Further research on cross communication among extracellular, cellular, and molecular signalling in Hydra will advance the field of regeneration biology. Here, we present a review of the existing literature on Hydra regeneration biology and outline the future perspectives.

Recurrent acute renal failure

While acute renal failure secondary to intravascular hemolysis is well described in hemolytic anemias, recurrent acute renal failure as the presenting manifestation of a hemolytic anemia is rare. We report a patient with recurrent acute renal failure who was found to have paroxysmal nocturnal hemoglobinuria (PNH), on evaluation.

Mycobacterium fortuitumBacteraemia in an Immunocompromised Patient

A case of Mycobacterium fortuitum bacteraemia in an immunocompromised patient confirmed by four positive serial blood cultures is reported here. The patient was a known case of acute lymphoblastic leukemia (ALL) on intensive chemotherapy. The source of bacteraemia was most probably a peripherally inserted vascular catheter. After initiation, of treatment with amikacin to which the strain was sensitive and clarithromycin and removal of the central line the patient's fever defervesced and repeat blood cultures were negative. This is the first time we have encountered an immunocompromised patient with M. fortuitum septicaemia in our hospital. The possibility of an infection with rapidly growing mycobacteria is important to consider when conventional organisms are not isolated in culture especially in the context of patients with malignancy.

Angiographic analysis and results of endovascular therapy of aneurysm of vein of Galen

Angioarchitecture of the aneurysmal malformation of the vein of Galen in 9 patients is analysed. An arterial maze arborised directly into the vein of Galen in 6 patients. Direct fistulous communication from one or two pedicles was noted in three children. Unilateral choroidal arterial contribution via an eccentric cul-de-sac in two infants suggested embryonic involvement of the ipsilateral internal cerebral vein along with the median prosencephalic vein of Markowski. Unusually, a sylvian branch of the middle cerebral artery drained directly into the basal vein of Rosenthal which in turn communicated to the aneurysm of vein of Galen in another patient. Two adult patients had curvilinear rim calcification of the venous sac with rapid circulation. All but two showed venous sinus anomalies. Two children had prior shunt surgery at the referring hospitals. The pathophysiology of hydrocephalus and the possible consequences of shunt, question the need for CSF diversion as a routine in these patients. Percutaneous trans-arterial embolotherapy, in five patients achieved complete obliteration of the malformation in four patients and partial reduction of flow in another. While transvenous/trans-torcular approach is reserved for selected patients and direct surgery carries high morbidity, this report emphasises the efficacy of trans-arterial embolotherapy.

Modified crossover and guidewire loop technique for double-balloon angioplasty of the aortic bifurcation

A modified form of crossover railroad technique is described for iliac and aortic bifurcation obstructions in which the iliac occlusion is crossed from the opposite side by a guidewire which is brought out through the ipsilateral puncture site. After forming a loop in the abdominal aorta, dilatation with two balloons is performed. This procedure was successfully performed in 2 patients having iliac artery occlusions and aortic bifurcation obstruction.

Multiple pulmonary-artery aneurysms due to mucoid vasculopathy--angiographic and histological observations

Multiple peripheral pulmonary artery aneurysms were diagnosed by computed tomography and confirmed angiographically in a 7-year-old boy. On histological examination unusual mucoid vasculopathic changes were noted in the pulmonary artery aneurysms and pulmonary vasculature as a part of systemic vascular involvement. This case demonstrates a new association between mucoid vasculopathic changes and pulmonary aneurysms. Mucoid vasculopathy could represent one more disorder having a causative role in the etiology of intrapulmonary arterial aneurysms.

Total occlusion of iliac arteries: results of balloon angioplasty

Fifty-six occluded iliac arteries (mean length 6.1 cm; range 1-17 cm) in 50 patients were treated by percutaneous transluminal angioplasty (PTA) or laser-assisted PTA (bilateral lesions in 6 patients). Twenty-seven patients (54%) were at high risk for surgery. Patients were followed for a maximum period of 72 months (mean 23.12 months; median 20 months). The initial success rate was 78.57% for arteries and 82% for patients. Laser-assisted PTA was attempted in 11 occluded arteries (19.64%) and was successful in 4 arteries (7.14%). Conventional PTA was successful in 71.4% of arteries including all 7 arteries for which laser-assisted PTA failed (76% of patients). PTA was unsuccessful in 12 arteries (21.43%). Urokinase was used before PTA in 1 artery. The effect of PTA was evident clinically by relief of rest pain (66.66%), healing of ulcer (57%), increased claudication distance or no claudication (79%) in limbs, and objectively, by improvement in ankle/arm index (AAI) (an increase of 0.16 to 0.91) and increased exercise tolerance. Continuous improvement in AAI was observed after PTA on follow-up in 9 limbs. One patient died during follow-up. On follow-up, 3 arteries were occluded, 6 showed evidence of stenosis, and 1 showed fusiform dilatation at the PTA site. The long-term results using the life-table method determined a 76% primary patency rate and 81% secondary patency rate for 72 months. The overall patency including failures was 63%. Age of the patients (p = 0.0169) and hypertension (p = 0.0015) significantly affected the long-term patency of the artery but not the initial success. The major complications were arterial rupture in a repeat procedure in 1 artery, axillary artery thrombosis in 1, and distal thromboembolic occlusion during PTA in 4. The long-term patency rates suggest that PTA of totally occluded iliac arteries is a safe and effective procedure and provides a long-term benefit.

Arteriovenous aneurysm of the occipital artery

We report an unique case of a giant aneurysm of the occipital artery, with a venous connection to the transverse sinus via an emissary vein. Because of this connection, the term arteriovenous aneurysm is used.

Obstruction of the infrarenal portion of the abdominal aorta: results of treatment with balloon angioplasty

Our experience in the treatment of stenoses of the infrarenal portion of the abdominal aorta with balloon angioplasty in 27 patients is reported. Clinical findings were lower limb claudication (all patients), impotence (eight patients), and blue-toe syndrome (two patients). The underlying disease was atherosclerosis in 24 patients and nonspecific aortoarteritis in three patients. Dilatation was successful in all patients. Embolic occlusions of the left common iliac artery (one patient) and left superficial femoral artery (one patient) were the only major complications. Claudication in the affected limb continued in the first patient; the second died when diagnostic angiography, performed 3 months after angioplasty, caused a severe atheroembolus. Of the other 25 patients, nine of the 10 followed up for 13-48 months and all seven followed up for 3-8 months were free of symptoms. Six of eight patients with sexual dysfunction had normal function after angioplasty. Seven patients still awaited follow-up and one was lost to follow-up. Our experience suggests that balloon angioplasty is an effective treatment of stenoses of the infrarenal portion of the abdominal aorta.

Corpus callosum lipoma with frontal encephalocele

Computed tomographic and plain X-ray observations in a patient with corpus callosum lipoma associated with frontal encephalocele are reported. The rarity of the lesion and the specific diagnostic criteria on CT are emphasised.

Percutaneous transluminal angioplasty in nonspecific aortoarteritis (Takayasu's disease): experience of 16 cases

Sixteen patients with aortoarteritis underwent percutaneous transluminal angioplasty for dilatation of 19 stenotic arteries. Sites included renal arteries (9), subclavian arteries (5), innominate artery (1), abdominal aorta (2), and descending thoracic aorta (2). Angiographic success was obtained in 14 lesions (74%) and partial success in 1 stenosis. The procedure was unsuccessful in 3 renal and 1 subclavian stenoses (21%). There were three complications. Clinically, there was cure of hypertension in three patients and improvement in six patients who had hypertension. Relief of claudication or return of pulsations was observed in seven patients. There was no evidence of any recurrence in the follow-up period (2-33 months). We conclude that percutaneous transluminal angioplasty is a safe and effective procedure for treating symptomatic stenotic lesions in aortoarteritis.

Left cervical arch and associated abnormalities

Cervical aortic arch is a rare congenital anomaly. Occasionally it is associated with other cardiac and aortic abnormalities. This paper describes the association of a left cervical aortic arch with a fusiform aneurysm of the arch in one patient and with multiple coarctations in another.

Thrombosis of multiple aneurysms of a lateral lenticulostriate artery. An angiographic follow-up

The authors report the radiological features of a patient, believed to be unique in the literature, of multiple aneurysms of the lateral-most lenticulostriate artery in a normotensive, non-diabetic, young, female patient who presented with left basal ganglionic hematoma and showed spontaneous obliteration of these aneurysms, on follow-up angiography.