Amplification of neurotoxic HTTex1 assemblies in human neurons

Huntington's disease (HD) is a genetically inherited neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) repeat in the exon-1 of huntingtin protein (HTT). The expanded polyQ enhances the amyloidogenic propensity of HTT exon 1 (HTTex1), which forms a heterogeneous mixture of assemblies with a broad neurotoxicity spectrum. While predominantly intracellular, monomeric and aggregated mutant HTT species are also present in the cerebrospinal fluids of HD patients, however, their biological properties are not well understood. To explore the role of extracellular mutant HTT in aggregation and toxicity, we investigated the uptake and amplification of recombinant HTTex1 assemblies in cell culture models. We find that small HTTex1 fibrils preferentially enter human neurons and trigger the amplification of neurotoxic assemblies; astrocytes or epithelial cells are not permissive. The amplification of HTTex1 in neurons depletes endogenous HTT protein with non-pathogenic polyQ repeat, activates apoptotic caspase-3 pathway and induces nuclear fragmentation. Using a panel of novel monoclonal antibodies and genetic mutation, we identified epitopes within the N-terminal 17 amino acids and proline-rich domain of HTTex1 to be critical in neural uptake and amplification. Synaptosome preparations from the brain homogenates of HD mice also contain mutant HTT species, which enter neurons and behave similar to small recombinant HTTex1 fibrils. These studies suggest that amyloidogenic extracellular mutant HTTex1 assemblies may preferentially enter neurons, propagate and promote neurodegeneration.

Comparative life histories of fishes in the subgenus Limia (Pisces: Poeciliidae)

This study presents life-history descriptions for 12 species in the subgenus Limia, which are endemic to the Greater Antilles. All species in this study lack evidence of superfoetation, producing a single brood of offspring before developing subsequent broods. Interbrood intervals (number of days between parturition events) are also consistent with intervals of species that lack superfoetation. Maternal provisioning, characterized by matrotrophy index, is <1.0 for all species of Limia. This is consistent with species that provide little or no maternal provisioning to developing embryos after ovum fertilization (lecithotrophic). Four species exhibit potentially bi-modal size distributions of mature males. Work on other poeciliids suggests that such bimodal distributions can be caused by genetic polymorphisms in some species. Principle component analyses revealed an axis of interspecific variation in life histories that separated species with small size at maturity and the production of many, small offspring from those with large size at maturity and that produce few, large offspring. This pattern of life-history diversity occurs in many other groups of organisms.

Protease sequences from HIV-1 group M subtypes A-H reveal distinct amino acid mutation patterns associated with protease resistance in protease inhibitor-naive individuals worldwide. HIV Variant Working Group

BACKGROUND

Although numerous mutations that confer resistance to protease inhibitors (PRI) have been mapped for HIV-1 subtype B, little is known about such substitutions for the non-B viruses, which globally cause the most infections.

OBJECTIVES

To determine the prevalence of PRI-associated mutations in PRI-naive individuals worldwide.

DESIGN

Using the polymerase chain reaction, protease sequences were amplified from 301 individuals infected with HIV-1 subtypes A (79), B (95), B' (19), C (12), D (26), A/E (23), F (26), A/G (11), and H (3) and unclassifiable HIV-1 (7). Amplified DNA was directly sequenced and translated to amino acids to analyze PRI-associated major and accessory mutations.

RESULTS

Of the 301 sequences, 85% contained at least one codon change giving substitution at 10, 20, 30, 36, 46, 63, 71, 77, or 82 associated with PRI resistance; the frequency of these substitutions was higher among non-B (91%) than B (75%) viruses (P < 0.0005). Of these, 25% carried dual and triple substitutions. Two major drug resistance-conferring mutations, either 20M or 30N, were identified in only three specimens, whereas drug resistance accessory mutations were found in 252 isolates. These mutations gave distinct prevalence patterns for subtype B, 63P (62%) > 77I (19%) > 10I/V/R (6%) = 361 (6%) = 71T/V (6%) > 20R (2%), and non-B strains, 36I (83%) > 63P (17%) > 10I/V/R (13%) > 20R (10%) > 77I (2%), which differed statistically at positions 20, 36, 63, 71, and 77.

CONCLUSIONS

The high prevalence of PRI-associated substitutions represent natural polymorphisms occurring in PRI-naive patients infected with HIV-1 strains of subtypes A-H. The significance of distinct mutation patterns identified for subtype B and non-B strains warrants further clinical evaluation. A global HIV-1 protease database is fundamental for the investigation of novel PRI.