Some peculiar synaptic complexes in the first visual ganglion of the fly,Musca domestica

Summary In the lamina ganglionaris, the first optic ganglion of the fly, the inventory of cell types as well as the patterns of their connections are well known from light microscopic investigations. Even the synaptic contacts are known with relative completeness. However, the structural details visible on electron micrographs are very difficult to interpret in functional terms. This paper concentrates on two aspects: 1) the synaptic complex between a retinula cell axon and four postsynaptic elements, arranged in a constant elongated array (it is suggested that all synapses in which the retinula cell is presynaptic are of this kind), and 2) the gnarl complex in which a presynaptic specialization in one neuron is separated from another neuron by a complicated glial invagination. The participation of glia at postsynaptic sites seems to be quite common in this ganglion. Occasionally it seems that a glia cell is the only postsynaptic partner facing a presynaptic specialization within a neuron.     

Attractive and permissive activities of semaphorin 5A toward dorsal root ganglion axons in higher vertebrate embryos

Elongation of the efferent fibers of dorsal root ganglion (DRG) neurons toward their peripheral targets occurs during development. Attractive or permissive systems may be involved in this elongation. However, the molecular mechanisms that control it are largely unknown. Here we show that class 5 semaphorin Sema5A had attractive/permissive effects on DRG axons. In mouse embryos, Sema5A was expressed in and around the path of DRG efferent fibers, and cell aggregates secreting Sema5A attracted DRG axons in vitro. We also found that ectopic Sema5A expression in the spinal cord attracted DRG axons. Together, these findings suggest that Sema5A functions as an attractant to elongate DRG fibers and contributes to the formation of the early sensory network.     

The unusual suspects: Regulation of retinal calcium channels by somatostatin

Calcium channel family members activate at different membrane potentials which enables tissue specific calcium entry. Pore mutations affecting this voltage dependence are associated with channelopathies. In this review we analyze the link between voltage sensitivity and corresponding kinetic phenotypes of calcium channel activation. Systematic changes in hydrophobicity in the lower third of S6 segments gradually shift the activation curve thereby determining the voltage sensitivity. Homology modeling suggests that hydrophobic residues that are located in all four S6 segments close to the inner channel mouth might form adhesion points stabilizing the closed gate. Simulation studies support a scenario where voltage sensors and the pore are essentially independent structural units. We speculate that evolution designed the voltage sensing machinery as robust "all-or-non" device while the verity of voltage sensitivities of different channel types was accomplished by shaping pore stability.     

TMEM126A is a mitochondrial located mRNA (MLR) protein of the mitochondrial inner membrane

Background

Hereditary optic neuropathies (HONs) are a heterogeneous group of disorders that affect retinal ganglion cells (RGCs) and axons that form the optic nerve. Leber's Hereditary Optic Neuropathy and the autosomal dominant optic atrophy related to OPA1 mutations are the most common forms. Nonsyndromic autosomal recessive optic neuropathies are rare and their existence has been long debated. We recently identified the first gene responsible for these conditions, TMEM126A. This gene is highly expressed in retinal cellular compartments enriched in mitochondria and supposed to encode a mitochondrial transmembrane protein of unknown function.

Methods

A specific polyclonal antibody targeting the TMEM126A protein has been generated. Quantitative fluorescent in situ hybridization, cellular fractionation, mitochondrial membrane association study, mitochondrial sub compartmentalization analysis by both proteolysis assays and transmission electron microscopy, and expression analysis of truncated TMEM126A constructs by immunofluorescence confocal microscopy were carried out.

Results

TMEM126A mRNAs are strongly enriched in the vicinity of mitochondria and encode an inner mitochondrial membrane associated cristae protein. Moreover, the second transmembrane domain of TMEM126A is required for its mitochondrial localization.

Conclusions

TMEM126A is a mitochondrial located mRNA (MLR) that may be translated in the mitochondrial surface and the protein is subsequently imported to the inner membrane. These data constitute the first step toward a better understanding of the mechanism of action of TMEM126A in RGCs and support the importance of mitochondrial dysfunction in the pathogenesis of HON.

General significance

Local translation of nuclearly encoded mitochondrial mRNAs might be a mechanism for rapid onsite supply of mitochondrial membrane proteins.     

Proteome Variations in Pancreatic Stellate Cells upon Stimulation with Proinflammatory Factors

Pancreatic stellate cells are key mediators in chronic pancreatitis and play a central role in the development of pancreatic fibrosis, stromal formation, and progression of pancreatic cancer. This study was aimed at investigating molecular changes at the level of the proteome that are associated with the activation of pancreatic stellate cells by proinflammatory factors, namely TNF-α, FGF2, IL6, and chemokine (C-C motif) ligand 4 (CCL4). They were added individually to cells growing in serum-free medium next to controls in medium supplemented with serum, thus containing a mixture of them all, or in serum-free medium alone. Variations were detected by means of a microarray of 810 antibodies targeting relevant proteins. All tested factors triggered increased proliferation and migration. Further analysis showed that TNF-α is the prime factor responsible for the activation of pancreatic stellate cells. CCL4 is associated with cellular neovascularization, whereas FGF2 and IL6 induction led to better cellular survival and decreased apoptotic activity of the stellate cells. The identified direct effects of individual cytokines on human pancreatic stellate cells provide new insights about their contribution to pancreatic cancer promotion.     

Pou4f2‐GFP knock‐in mouse line: A model for studying retinal ganglion cell development

Pou4f2 acts as a key node in the comprehensive and step‐wise gene regulatory network (GRN) and regulates the development of retinal ganglion cells (RGCs). Accordingly, deletion of Pou4f2 results in RGC axon defects and apoptosis. To investigate the GRN involved in RGC regeneration, we generated a mouse line with a POU4F2‐green fluorescent protein (GFP) fusion protein expressed in RGCs. Co‐localization of POU4F2 and GFP in the retina and brain of Pou4f2‐GFP/+ heterozygote mice was confirmed using immunofluorescence analysis. Compared with those in wild‐type mice, the expression patterns of POU4F2 and POU4F1 and the co‐expression patterns of ISL1 and POU4F2 were unaffected in Pou4f2‐GFP/GFP homozygote mice. Moreover, the quantification of RGCs showed no significant difference between Pou4f2‐GFP/GFP homozygote and wild‐type mice. These results demonstrated that the development of RGCs in Pou4f2‐GFP/GFP homozygote mice was the same as in wild‐type mice. Thus, the present Pou4f2‐GFP knock‐in mouse line is a useful tool for further studies on the differentiation and regeneration of RGCs.