Vesicular glutamate transporter 3 expression identifies glutamatergic amacrine cells in the rodent retina.
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Synaptic transmission from glutamatergic neurons requires vesicular glutamate transporters (VGLUTs) to concentrate cytosolic glutamate in synaptic vesicles. In retina, glutamatergic photoreceptors and bipolar cells exclusively express the VGLUT1 isoform, whereas ganglion cells express VGLUT2. Surprisingly, the recently identified VGLUT3 isoform was found in presumed amacrine cells, generally considered to be inhibitory interneurons. To investigate the synaptic machinery and conceivable secondary neurotransmitter composition of VGLUT3 cells, and to determine a potential functional role, we further investigated these putative glutamatergic amacrine cells in adult and developing rodent retina. Reverse transcriptase-PCR substantiated VGLUT3 expression in mouse retina. VGLUT3 cells did not immunostain for ganglion or bipolar cell markers, providing evidence that they are amacrine cells. VGLUT3 colocalized with synaptic vesicle markers, and electron microscopy showed that VGLUT3 immunostained synaptic vesicles. VGLUT3 cells were not immunoreactive for amacrine cell markers gamma-aminobutyric acid, choline acetyltransferase, calretinin, or tyrosine hydroxylase, although they immunostain for glycine. VGLUT3 processes made synaptic contact with ganglion cell dendrites, suggesting input onto these cells. VGLUT3 immunostaining was closely associated with the metabotropic glutamate receptor 4, which is consistent with glutamatergic synaptic exocytosis by these cells. In the maturing mouse retina, Western blots showed VGLUT3 expression at postnatal day 7/8 (P7/8). VGLUT3 immunostaining in retinal sections was first observed at P8, achieving an adult pattern at P12. Thus, VGLUT3 function commences around the same time as VGLUT1-mediated glutamatergic transmission from bipolar cells. Furthermore, a subset of VGLUT3 cells expressed the circadian clock gene period 1, implicating VGLUT3 cells as part of the light-entrainable retina-based circadian system. (+info)
Autogenous modulation of the Bacillus subtilis sacB-levB-yveA levansucrase operon by the levB transcript.
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Silencing of levB, the second structural gene of the tricistronic levansucrase operon encoding the endolevanase LevB, decreases the level of levansucrase expression in Bacillus subtilis. Conversely, independent expression of levB greatly stimulates operon expression. This autogenous effect is mediated by the levB transcript, which carries an internal sequence (5'-AAAGCAGGCAA-3') involved in the enhancing effect. In vitro, the levB transcript displays an affinity for the N-terminal fragment of SacY (K(D) 0.2 microM), the regulatory protein that prevents transcription termination of the levansucrase operon. This positive-feedback loop leads to an increase in the operon expression when B. subtilis is growing in the presence of high sucrose concentrations. Under these conditions, extracellular levan synthesized by the fructosyl polymerase activity of levansucrase can be degraded mainly into levanbiose by the action of LevB. Levanbiose is neither taken up nor metabolized by the bacteria. This work modifies the present view of the status of levansucrase in B. subtilis physiology. (+info)
Molecular physiology of vesicular glutamate transporters in the digestive system.
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Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system (CNS). Packaging and storage of glutamate into glutamatergic neuronal vesicles require ATP-dependent vesicular glutamate uptake systems, which utilize the electrochemical proton gradient as a driving force. Three vesicular glutamate transporters (VGLUT1-3) have been recently identified from neuronal tissue where they play a key role to maintain the vesicular glutamate level. Recently, it has been demonstrated that glutamate signaling is also functional in peripheral neuronal and non-neuronal tissues, and occurs in sites of pituitary, adrenal, pineal glands, bone, GI tract, pancreas, skin, and testis. The glutamate receptors and VGLUTs in digestive system have been found in both neuronal and endocrinal cells. The glutamate signaling in the digestive system may have significant relevance to diabetes and GI tract motility disorders. This review will focus on the most recent update of molecular physiology of digestive VGLUTs. (+info)
Recombinant hepatitis B surface antigen and anionic phospholipids share a binding region in the fifth domain of beta2-glycoprotein I (apolipoprotein H).
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