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A. M. Nystuen, A. J. Sachs, J. K. Schwendinger, A. W. Yang, N. B. Haider; Lack of Vamp1/synaptobrevin in the Lethal Wasting Mouse Mutant Causes Eyelid Apraxia and Synaptic Dysfunction. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2974.
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The SNAREs are a large family of membrane associated proteins that are critical for Ca2+ mediated synaptic vesicle release. This family includes the VAMP, SNAP-25 and syntaxin proteins. Vamp1 and Vamp2 are expressed in the retina and CNS. The roles of VAMPs in the retina are currently unknown. In this report, we describe a mutation in Vamp1 in the lethal wasting mouse mutant and its effects on the retina.
We used a positional candidate approach to identify the disease causing mutation in the lethal wasting mouse mutant. RT-PCR was used to identify specific alternative Vamp1 transcripts in tissues including retina and brain. Immunohistochemistry was used to identify tissues and cell types that express Vamp1, and determine the effect of the lethal wasting mutation on the topography of the retina, while electron microscopy was used to determine if synaptic vesicles abnormalities were present in the mutant. Quantitative RT-PCR was used to determine if the expression levels of other SNARE proteins were altered in the mutant.
We identified a single base change that results in a null mutation in Vamp1/synaptobrevin that is associated with the mouse neurological mutant lethal wasting. The lethal wasting mutant phenotype is characterized by a general lack of purposeful movement and wasting, eventually leading to death prior to weaning. Mutant mice appear to have difficulty opening their eyes, which may be a result of Vamp1 expression in the midbrain. VAMP1 is expressed in a subset of large neurons in the ganglion cell layer of the retina, no expression of the protein is observed in the mutant. Synaptic abnormalities were identified by electron microscopy.
The SNARE complex is well studied; however, most of these studies have focused on Vamp2. A knockout mutation of Vamp2 is available; however, this mutant is dead upon birth, while the Vamp1lew mutant mouse survives significantly longer. Thus, the Vamp1lew mutant gives us a unique resource to study SNARE function in the retina.
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