Normal and expanded Huntington's disease gene alleles produce distinguishable proteins due to translation across the CAG repeat.

BACKGROUND: An expanded CAG trinucleotide repeat is the genetic trigger of neuronal degeneration in Huntington's disease (HD), but its mode of action has yet to be discovered. The sequence of the HD gene places the CAG repeat near the 5' end in a region where it may be translated as a variable polyglutamine segment in the protein product, huntingtin. MATERIALS AND METHODS: Antisera directed at amino acid stretches predicted by the DNA sequence upstream and downstream of the CAG repeat were used in Western blot and immunohistochemical analyses to examine huntingtin expression from the normal and the HD allele in lymphoblastoid cells and postmortem brain tissue. RESULTS: CAG repeat segments of both normal and expanded HD alleles are indeed translated, as part of a discrete approximately 350-kD protein that is found primarily in the cytosol. The difference in the length of the N-terminal polyglutamine segment is sufficient to distinguish normal and HD huntingtin in a Western blot assay. CONCLUSIONS: The HD mutation does not eliminate expression of the HD gene but instead produces an altered protein with an expanded polyglutamine stretch near the N terminus. Thus, HD pathogenesis is probably triggered by an effect at the level of huntingtin protein.     

Magic roundabout, a tumor endothelial marker: expression and signaling

Molecular signals that guide blood vessels to specific paths are not fully deciphered, but are thought to be similar to signals that mediate neuronal guidance. These cues are not only critical for normal blood vessel development, but may also play a major role in tumor angiogenesis. In this study, we have demonstrated the tumor endothelial specific expression of a Robo family member, magic roundabout (MRB), functionally characterized its role in endothelial cell migration and defined a signaling pathway that might mediate this function. We show that MRB is differentially over-expressed in tumor endothelial cells versus normal adult endothelial cells in numerous solid tumors. Moreover, over-expression of MRB in endothelial cells activates MRB in a ligand-independent fashion, and activation of MRB via Slit2, a putative ligand, results in inhibition of VEGF and FGF induced migration. We also demonstrate that MRB induced inhibition of endothelial migration is partially mediated by the Ras-Raf-Mek-Erk signaling pathway. We therefore hypothesize that expression of MRB is involved in regulating the migration of endothelial cells during tumor angiogenesis.     

Synteny conservation of the Huntington's disease gene and surrounding loci on mouse Chromosome 5

The mouse homologs of the Huntington's disease (HD) gene and 17 other human Chromosome (Chr) 4 loci (including six previously unmapped) were localized by use of an interspecific cross. All loci mapped in a continuous linkage group on mouse Chr 5, distal to En2 and Il6, whose human counterparts are located on Chr y. The relative order of the loci on human Chr 4 and mouse Chr 5 was maintained, except for a break between D5H4S115E and Idua/rd, with relocation of the latter to the opposite end of the map. The mouse HD homolog (Hdh) mapped within a cluster of seven genes that were completely linked in our data set. In human these loci span a1.8 Mb stretch of human 4p 16.3 that has been entirely cloned. To date, there is no phenotypic correspondence between human and mouse mutations mapping to this region of synteny conservation.     

Inactivation of the Huntington's disease gene (Hdh) impairs anterior streak formation and early patterning of the mouse embryo

Background

Delta, Notch, and Scabrous often function together to make different cell types and refine tissue patterns during Drosophila development. Delta is known as the ligand that triggers Notch receptor activity. Scabrous is known to bind Notch and promote Notch activity in response to Delta. It is not known if Scabrous binds Delta or Delta has activity other than its activity as a ligand of Notch. It is very difficult to clearly determine this binding or activity in vivo as all Notch, Delta, and Scabrous activities are required simultaneously or successively in an inter-dependent manner.

Results

Using Drosophila cultured cells we show that the full length Delta promotes accumulation of Daughterless protein, fringe RNA, and pangolin RNA in the absence of Scabrous or Notch. Scabrous binds Delta and suppresses this activity even though it increases the level of the Delta intracellular domain. We also show that Scabrous can promote Notch receptor activity, in the absence of Delta.

Conclusion

Delta has activity that is independent of its activity as a ligand of Notch. Scabrous suppresses this Delta activity. Scabrous also promotes Notch activity that is dependent on Delta's ligand activity. Thus, Notch, Delta, and Scabrous might function in complex combinatorial or mutually exclusive interactions during development. The data reported here will be of significant help in understanding these interactions in vivo.     

Inactivation of the Huntington's disease gene (Hdh) impairs anterior streak formation and early patterning of the mouse embryo

Background  

Huntingtin, the HD gene encoded protein mutated by polyglutamine expansion in Huntington's disease, is required in extraembryonic tissues for proper gastrulation, implicating its activities in nutrition or patterning of the developing embryo. To test these possibilities, we have used whole mount in situ hybridization to examine embryonic patterning and morphogenesis in homozygous Hdh ^ex4/5huntingtin deficient embryos.