Mutations and polymorphisms of the skeletal muscle α‐actin gene (ACTA1)

The ACTA1 gene encodes skeletal muscle α‐actin, which is the predominant actin isoform in the sarcomeric thin filaments of adult skeletal muscle, and essential, along with myosin, for muscle contraction. ACTA1 disease‐causing mutations were first described in 1999, when a total of 15 mutations were known. In this article we describe 177 different disease‐causing ACTA1 mutations, including 85 that have not been described before. ACTA1 mutations result in five overlapping congenital myopathies: nemaline myopathy; intranuclear rod myopathy; actin filament aggregate myopathy; congenital fiber type disproportion; and myopathy with core‐like areas. Mixtures of these histopathological phenotypes may be seen in a single biopsy from one patient. Irrespective of the histopathology, the disease is frequently clinically severe, with many patients dying within the first year of life. Most mutations are dominant and most patients have de novo mutations not present in the peripheral blood DNA of either parent. Only 10% of mutations are recessive and they are genetic or functional null mutations. To aid molecular diagnosis and establishing genotype–phenotype correlations, we have developed a locus‐specific database for ACTA1 variations ( http://waimr.uwa.edu.au ). Hum Mutat 30:1–11, 2009. © 2009 Wiley‐Liss, Inc.     

Opportunities for the replacement of animals in the study of nausea and vomiting

Nausea and vomiting are among the most common symptoms encountered in medicine as either symptoms of disease or side effects of treatments. Developing novel anti-emetics and identifying emetic liability in novel chemical entities rely on models that can recreate the complexity of these multi-system reflexes. Animal models (especially the ferret and dog) are the current gold standard; however, the selection of appropriate models is still a matter of debate, especially when studying the subjective human sensation of nausea. Furthermore, these studies are associated with animal suffering. Here, following a recent workshop held to review the utility of animal models in nausea and vomiting research, we discuss the limitations of some of the current models in the context of basic research, anti-emetic development and emetic liability detection. We provide suggestions for how these limitations may be overcome using non-animal alternatives, including greater use of human volunteers, in silico and in vitro techniques and lower organisms.     

Hypothalamic hamartomas associated with epilepsy: ultrastructural features

Hypothalamic hamartomas (HHs) are associated with a catastrophic form of childhood epilepsy and are intrinsically epileptogenic for the gelastic seizures that are peculiar to this disorder. The cellular mechanisms of seizure generation within HH tissue are unknown. Hypothalamic hamartoma tissue consists of well-differentiated neurons interspersed with glial cells. Based on intrinsic electrophysiologic properties, we hypothesized that small and large HH neurons would have different ultrastructural features. Surgically resected HH tissue samples from 7 patients with refractory epilepsy were studied using electron microscopy. Models of neurons were made from reconstruction of serial sections. Nissl body density, polyribosome density, glycogen density, and the ratio of nuclear area to cytoplasmic area differed significantly between small and large neurons. Abundant small neurons were found in clusters and elaborated terminals that made symmetric, putatively inhibitory, synapses. Symmetric synapses were found predominantly on the soma and proximal dendrites of large projection-like neurons, whereas asymmetric, putatively excitatory, synapses were found primarily on distal dendrites. All samples showed unusual dendritic varicosities. The presence of these morphologically and functionally distinct neurons, the large number of nerve fibers in the neuropil, and the presence of inhibitory and excitatory synapses suggest that HH tissue has the necessary substrate to generate seizures.     

Reconciling the roles of FAK in osteoblast differentiation, osteoclast remodeling, and bone regeneration

Integrins link the inside of a cell with its outside environment and in doing so regulate a wide variety of cell behaviors. Integrins are well known for their roles in angiogenesis and cell migration but their functions in bone formation are less clear. The majority of integrin signaling proceeds through focal adhesion kinase (FAK), an essential component of the focal adhesion complex. We generated transgenic mice in which FAK was deleted in osteoblasts and uncovered a previously unknown role in osteoblast differentiation associated with bone healing. FAK mutant cells migrated to the site of skeletal injury and angiogenesis was unaffected yet the transgenic mice still exhibited numerous defects in reparative bone formation. Osteoblast differentiation itself was unperturbed by the loss of FAK, whereas the attachment of osteoclasts to the bone matrix was disrupted in vivo. We postulate that defective bi-directional integrin signaling affects the organization of the collagen matrix. Finally, we present a compensatory candidate molecule, Pyk2, which localized to the focal adhesions in osteoblasts that were lacking FAK.     

Vascular amyloidosis causing spontaneous mediastinal haemorrhage with haemothorax.

Bleeding diathesis is a recognised complication of amyloid disease. Localised and generalised bleeding manifestations are usually associated with intravascular coagulopathy related to isolated or multiple coagulation factor deficiencies. Recently, there have been reports of haemorrhage due to amyloid deposition in blood vessel walls and in the perivascular region leading to increased fragility and poor haemostasis. We report a case of spontaneous mediastinal haemorrhage due to amyloid involvement of vascular tissue in the absence of coagulopathy.     

Focal adhesion kinase is required for CXCL12-induced chemotactic and pro-adhesive responses in hematopoietic precursor cells.

Hematopoietic stem/progenitor cells (HSC/P) reside in the bone marrow in distinct anatomic locations (niches) to receive growth, survival and differentiation signals. HSC/P localization and migration between niches depend on cell-cell and cell-matrix interactions, which result from the cooperation of cytokines, chemokines and adhesion molecules. The CXCL12-CXCR4 pathway, in particular, is essential for myelopoiesis and B lymphopoiesis but the molecular mechanisms of CXCL12 action remain unclear. We previously noted a strong correlation between prolonged CXCL12-mediated focal adhesion kinase (FAK) phosphorylation and sustained pro-adhesive responses in progenitor B cells, but not in mature B cells. Although FAK has been well studied in adherent fibroblasts, its function in hematopoietic cells is not defined. We used two independent approaches to reduce FAK expression in (human and mouse) progenitor cells. RNA interference (RNAi)-mediated FAK silencing abolished CXCL12-induced responses in human pro-B leukemia, REH cells. FAK-deficient REH cells also demonstrated reduced CXCL12-induced activation of the GTPase Rap1, suggesting the importance of FAK in CXCL12-mediated integrin activation. Moreover, in FAK(flox/flox) hematopoietic precursor cells, Cre-mediated FAK deletion resulted in impaired CXCL12-induced chemotaxis. These studies suggest that FAK may function as a key intermediary in signaling pathways controlling hematopoietic cell lodgment and lineage development.