Loss of cortical and thalamic neuronal tenascin-C expression in a transgenic mouse expressing exon 1 of the human Huntington disease gene.

A transgenic mouse containing the first exon of the human Huntington's disease (HD) gene has revealed a variety of behavioral and pathophysiological anomalies reminiscent of certain aspects of human Huntington's disease (HD). The present study has found that expression of the extracellular matrix glycoprotein tenascin-C appears to be unaffected in astroglial cells in wild-type and R6/2 transgenic mice that express the mutant huntingtin protein but that it is conspicuously absent in two neuronal populations within the cerebral cortex and thalamus of the R6/2 mice. Loss of tenascin-C expression begins between the fourth and eighth postnatal weeks, coincidental with the onset of abnormal behavioral phenotype and the appearance of intranuclear inclusion bodies and neuropil aggregates. By 12 weeks, R6/2 mice exhibit a complete absence of tenascin-C neuronal immunolabeling, a disappearance of cRNA probe-positive neurons across discrete cytoarchitectonic regions of the dorsal thalamus (e.g., the ventromedial, parafascicular, lateral posterior, and posterior thalamic groups) and frontal cortex, and an accompanying thalamic astrogliosis. The loss of neuronal tenascin-C expression includes structures that are known to send converging excitatory axonal projections to the caudate-putamen, the structure that is most at risk for neurodegeneration in HD. Altered neuronal expression of tenascin-C in R6/2 mice implicates altered transcriptional activities of the mutant huntingtin protein. The abnormal biochemistry and possibly abnormal activity of thalamostriate and corticostriate projection neurons may also affect abnormal neuronal activities in their primary connectional target, the neostriatum, which is severely compromised in HD.

Vacuolar processing enzyme is self-catalytically activated by sequential removal of the C-terminal and N-terminal propeptides.

A vacuolar processing enzyme (VPE) responsible for maturation of various vacuolar proteins is synthesized as an inactive precursor. To clarify how to convert the VPE precursor into the active enzyme, we expressed point mutated VPE precursors of castor bean in the pep4 strain of Saccharomyces cerevisiae. A VPE with a substitution of the active site Cys with Gly showed no ability to convert itself into the mature form, although a wild VPE had the ability. The mutated VPE was converted by the action of the VPE that had been purified from castor bean. Substitution of the conserved Asp-Asp at the putative cleavage site of the C-terminal propeptide with Gly-Gly abolished both the conversion into the mature form and the activation of the mutated VPE. In vitro assay with synthetic peptides demonstrated that a VPE exhibited activity towards Asp residues and that a VPE cleaved an Asp-Gln bond to remove the N-terminal propeptide. Taken together, the results indicate that the VPE is self-catalytically maturated to be converted into the active enzyme by removal of the C-terminal propeptide and subsequent removal of the N-terminal one.

Vacuolar processing enzyme of soybean that converts proproteins to the corresponding mature forms.

A vacuolar processing enzyme was detected in soybean protein bodies. A 39-kDa immunoreactive polypeptide obtained by chromatography on a hydroxyapatite column processed both a decapeptide substrate and proproteins. A cDNA was isolated for a 55-kDa protein with 71% identity to the castor bean vacuolar processing enzyme.