Gap Junction Gene Expression In The Developing Nervous System

Gap junctions provide for the transfer of low molecular weight molecules and ions between cytoplasms of adjacent cells. Connexins exist as a multigene family with one or more members found in almost all adult tissues. In the central nervous system, gap junctions have been detected in a variety of cell types including neurons, astrocytes and oligodendrocytes. Gap junctions have been detected in the developing brain in a spacial and temporal pattern. This study examines gap junction expression and cellular specificity during development of the rodent central nervous system. To investigate the role of gap junctions during development, a model of neural development is examined with respect to its connexin expression.;In the developing rodent brain, connexin32 and connexin43 were detected by Northern blot analysis. Connexin43 mRNA was detected pre- and postnatally, whereas connexin32 mRNA was differentially expressed, being first detectable at postnatal day 10 in hindbrain and day 15 in forebrain. Western blot analysis demonstrated the presence of connexin protein during postnatal development of the rodent brain. To examine connexin expression in greater detail, in situ hybridization studies were performed. Connexin43 mRNA was found in the leptomeninges and astrocytes. Oligodendrocytes and select populations of neurons were shown to express connexin32 mRNA. Cultured astrocytes express cx43 confirming the in vivo findings. Initially, in culture, neurons express connexin26 protein which becomes less abundant with time. Neurons cultured for extended periods of time express cx32.;The embryonal carcinoma cell line, P19, differentiates into neurons and astrocytes following treatment with retinoic acid. Undifferentiated P19 cells express connexin26 and 43. The mRNA level of these two connexins do not change when P19 cells were exposed to retinoic acid. Connexin43 protein, however, is significantly reduced after exposure to retinoic acid. During differentiation, the neurons expressed connexin26 and astroctyes expressed connexin43.;These investigations have determined that gap junctions are differentially expressed during development of the central nervous system. Astrocytes express connexin43 whereas neurons and oligodendrocytes express connexin32. Connexin26 is present in immature neurons in culture. The studies on P19 cells further support the presence of connexin26 in neurons and represents a model of neural differentiation that modulates connexin expression

Ranibizumab for idiopathic epiretinal membranes: A retrospective case series

AbstractPurposeTo study the effect of intravitreal ranibizumab on idiopathic epiretinal membranes (ERMs).MethodsA retrospective cohort study on a consecutive series of ranibizumab intravitreal injections for epiretinal membranes was performed. Four cases were identified by reviewing a claims database linked to electronic medical records. All patients received a total of three 0.05mg/0.05ml ranibizumab intravitreal injections at a monthly interval. The primary outcome measure was the final best-corrected visual acuity (BCVA) at the end of the injection series, and the final central macular thickness (CMT).ResultsAll four patients completed 3months follow-up after the last ranibizumab injection. The mean baseline CMT was 509microns (SD=111). A trend was noticed for reduction in CMT (Δ=41microns) P=0.08. Three patients improved by one line in their BCVA. The remaining patient maintained the same BCVA. No complications were noted.ConclusionIn this study, intravitreal injection of ranibizumab marginally reduced retinal thickness in four patients with minimal improvement in visual acuity. No safety concerns were noticed. Further basic science and clinical studies may be warranted to assess the role of vascular endothelial growth factor and the effect of ranibizumab on idiopathic epiretinal membranes

Theoretical investigation of a genetic switch for metabolic adaptation

Membrane transporters carry key metabolites across the cell membrane and, from a resource standpoint, are hypothesized to be produced when necessary. The expression of membrane transporters in metabolic pathways is often upregulated by the transporter substrate. In E. coli, such systems include for example the lacY, araFGH, and xylFGH genes, which encode for lactose, arabinose, and xylose transporters, respectively. As a case study of a minimal system, we build a generalizable physical model of the xapABR genetic circuit, which features a regulatory feedback loop via membrane transport (positive feedback) and enzymatic degradation (negative feedback) of an inducer. Dynamical systems analysis and stochastic simulations show that the membrane transport makes the model system bistable in certain parameter regimes. Thus, it serves as a genetic “on-off” switch, enabling the cell to only produce a set of metabolic enzymes when the corresponding metabolite is present in large amounts. We find that the negative feedback from the degradation enzyme does not significantly disturb the positive feedback from the membrane transporter. We investigate hysteresis in the switching and discuss the role of cooperativity and multiple binding sites in the model circuit. Fundamentally, this work explores how a stable genetic switch for a set of enzymes is obtained from transcriptional auto-activation of a membrane transporter through its substrate

Microtesla MRI of the human brain combined with MEG

One of the challenges in functional brain imaging is integration of complementary imaging modalities, such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). MEG, which uses highly sensitive superconducting quantum interference devices (SQUIDs) to directly measure magnetic fields of neuronal currents, cannot be combined with conventional high-field MRI in a single instrument. Indirect matching of MEG and MRI data leads to significant co-registration errors. A recently proposed imaging method - SQUID-based microtesla MRI - can be naturally combined with MEG in the same system to directly provide structural maps for MEG-localized sources. It enables easy and accurate integration of MEG and MRI/fMRI, because microtesla MR images can be precisely matched to structural images provided by high-field MRI and other techniques. Here we report the first images of the human brain by microtesla MRI, together with auditory MEG (functional) data, recorded using the same seven-channel SQUID system during the same imaging session. The images were acquired at 46 microtesla measurement field with pre-polarization at 30 mT. We also estimated transverse relaxation times for different tissues at microtesla fields. Our results demonstrate feasibility and potential of human brain imaging by microtesla MRI. They also show that two new types of imaging equipment - low-cost systems for anatomical MRI of the human brain at microtesla fields, and more advanced instruments for combined functional (MEG) and structural (microtesla MRI) brain imaging - are practical.Comment: 8 pages, 5 figures - accepted by JM