A null mutation in VAMP1/synaptobrevin is associated with neurological defects and prewean mortality in the lethal-wasting mouse mutant

Abstract

The soluble N-ethylmaleimide sensitive factor attachment receptors are a large family of membrane-associated proteins that are critical for Ca(2+)-mediated synaptic vesicle release. This family includes the VAMP, synaptosomal-associated protein, and syntaxin proteins. In this report, we describe a mutation in vesicle-associated membrane protein 1(VAMP1)/synaptobrevin in the mouse neurological mutant lethal-wasting (lew). The lethal-wasting mutant phenotype is characterized by a general lack of movement and wasting, eventually leading to death before weaning. Mutants are visibly immobile and lay on their side by postnatal day 10 (P10). Before this stage, mutants can be identified by a failure to attempt to right themselves. Affected mice die on average at P15. We used a positional cloning strategy to identify the mutation associated with this neurological phenotype. Lethal wasting had previously been linked to chromosome 6. We further narrowed the genetic disease interval and selected a small number of candidate genes for mutation screening. Genes were evaluated by quantitative reverse transcription-polymerase chain reaction (RT-PCR) to detect differences in their expression levels between control and mutant brain ribonucleic acid (RNA) samples. VAMP1 mRNA was found to be significantly downregulated in the lethal-wasting brain compared to wild-type littermates. Subsequently, a nonsense mutation was identified in the coding region of the gene. This mutation is predicted to truncate approximately half of the protein; however, Western blot analysis showed that no protein is detectable in the mutant. VAMP1 is selectively expressed in the retina and in discrete areas of the brain including the zona incerta and rostral periolivary region, although no gross histological abnormalities were observed in these tissues. Taken together, these data indicate that VAMP1 has a vital role in a subset of central nervous system tissues.

Huntingtin-Interacting Protein 1 Influences Worm and Mouse Presynaptic Function and ProtectsCaenorhabditis elegansNeurons against Mutant Polyglutamine Toxicity

“…Our data are consistent with a role for defective endocytosis as an underlying mechanism in HD (Trushina et al, 2006). Importantly, mouse knock-outs of synaptic and/or htt-interacting proteins such as HIP1 (Ferguson et al, 2000;Metzler et al, 2007;Nystuen et al, 2007) often have neurological phenotypes that may be relevant to HD pathogenesis.…”

Homozygous mutations in VAMP1 cause a presynaptic congenital myasthenic syndrome

“…To further investigate whether a biallelic null mutation in VAMP1 in animal models may cause presynaptic NMJ abnormalities similarly to affected individuals, we re‐examined Vamp1 lew/lew mutant mice that were previously described 11, 12. The endplates were localized along the central regions of the muscle in both control and Vamp1 lew/lew mice (Fig 2).…”

“…These animals, of a model called lethal wasting (carrying a homozygous mutation that causes the truncation of half of the protein), lack movement because of an impaired NMJ transmission and die within 3 weeks of birth 11, 12…”

“…Electrophysiological and morphological analyses of the NMJ in the Vamp1 lew/lew mice were performed as previously reported 11, 12. All experimental protocols were approved by the University of Texas Southwestern Medical Center institutional animal care and use committee.…”

Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins

“…1f-i). Because synaptobrevin-1 had been described originally as one of the SNARE components in IHCs 1 , we first studied exocytosis in IHCs of lethal-wasting mice, which carry a loss-of-function mutation in the synaptobrevin-1 gene 11 . In agreement with the lack of BoNT/D effect described above, we failed to detect any significant differences between IHCs of wild-type and lethal-wasting mice regarding RRP size, sustained exocytosis (approximated as exocytic rate between 20 and 100 ms of depolarization), or Ca 2+ current integrals (Fig.…”