Expression of the rat connexin 39 (rCx39) gene in myoblasts and myotubes in developing and regenerating skeletal muscles: an in situ hybridization study.
ABSTRACT We report a detailed analysis of the expression pattern of the recently identified rat connexin gene, named rat connexin 39 (rCx39), both during embryonic development and in adult life. Qualitative and quantitative reverse transcription/polymerase chain reaction analysis showed intense expression of rCx39 restricted to differentiating skeletal muscles, with a peak of expression detected at 18 days of embryonic life, followed by a rapid decline to undetectable levels within the first week of postnatal life. A combination of the in situ hybridization technique for the detection of rCx39 mRNA and immunohistochemistry for myogenin, a myoblast-specific marker, allowed us to establish that the mRNA for this connexin was expressed in myogenin-positive myoblasts and early myotubes but disappeared in mature myotubes. Moreover, in adult animals, rCx39 mRNA was expressed in myogenic cells involved in skeletal myofiber regeneration following a crush injury. This is the first case of a connexin being mainly expressed in the myogenic cell lineage. The information presented should pave the way to novel molecular approaches in studies on the role of connexin-based gap-junctional communication in skeletal muscle differentiation and regeneration.
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ABSTRACT: Gap junctions are specialized channels composed of several connexins, membrane proteins that mediate electrical and metabolic coupling between cells. Previous data have suggested that changes in the expression of Cx43, the main astrocytic Cx isoform, may be involved in seizure activity in human epileptic tissue. However, Cx43 has never been examined in focal cortical dysplasia (FCD) and in other human refractory epilepsies. We analyzed Cx43 protein localization and Cx43 mRNA levels in surgical specimens of cortex from a cohort of patients with intractable epilepsy vs control nonepileptic tissue. Samples had neuropathologically defined diagnosis of cryptogenic epilepsy or epilepsy secondary to FCD. Cx43 immunoreactivity, which labeled punctate elements, did not reveal distinctive features in cryptogenic epilepsy and FCD type IA and IIA. A peculiar pattern of immunolabeling was instead observed in FCD type IIB, in which large aggregates of Cx43-immunopositive puncta were clustered around subsets of balloon cells and astrocytes. Further characterization revealed that these balloon cells do not express markers of precursor cells, such as CD34. Quantitative real-time reverse transcriptase PCR showed elevated levels of Cx43 transcript in a subgroup (25%) of cryptogenic epilepsy specimens compared to control and FCD ones. Our study points out that a rearrangement of Cx43-positive elements is part of abnormal tissue organization in FCD type IIB, and that cryptogenic epilepsies include forms with increased Cx43 mRNA expression. The data implicate functional consequences of altered Cx43 expression, and therefore of altered gap junctional coupling, in abnormal network properties of subtypes of human refractory epilepsies.Neurology 03/2011; 76(10):895-902. · 8.31 Impact Factor