Duplicate sfrp1 genes in zebrafish: sfrp1a is dynamically expressed in the developing central nervous system, gut and lateral line

The secreted frizzled-related proteins (Sfrp) are a family of soluble proteins with diverse biological functions having the capacity to bind Wnt ligands, to modulate Wnt signalling, and to signal directly via the Wnt receptor, Frizzled. In an enhancer trap screen for embryonic expression in zebrafish we identified an sfrp1 gene. Previous studies suggest an important role for sfrp1 in eye development, however, no data have been reported using the zebrafish model. In this paper, we describe duplicate sfrp1 genes in zebrafish and present a detailed analysis of the expression profile of both genes. Whole mount in situ hybridisation analyses of sfrp1a during embryonic and larval development revealed a dynamic expression profile, including: the central nervous system, where sfrp1a was regionally expressed throughout the brain and developing eye; the posterior gut, from the time of endodermal cell condensation; the lateral line, where sfrp1a was expressed in the migrating primordia and interneuromast cells that give rise to the sensory organs. Other sites included the blastoderm, segmenting mesoderm, olfactory placode, developing ear, pronephros and fin-bud. We have also analysed sfrp1b expression during embryonic development. Surprisingly this gene exhibited a divergent expression profile being limited to the yolk syncytium under the elongating tail-bud, which later covered the distal yolk extension, and transiently in the tail-bud mesenchyme. Overall, our studies provide a basis for future analyses of these developmentally important factors using the zebrafish model.     

The Legs at odd angles (Loa) Mutation in Cytoplasmic Dynein Ameliorates Mitochondrial Function in SOD1G93A Mouse Model for Motor Neuron Disease

Amyotrophic lateral sclerosis (ALS) is a debilitating and fatal late-onset neurodegenerative disease. Familial cases of ALS (FALS) constitute ∼10% of all ALS cases, and mutant superoxide dismutase 1 (SOD1) is found in 15–20% of FALS. SOD1 mutations confer a toxic gain of unknown function to the protein that specifically targets the motor neurons in the cortex and the spinal cord. We have previously shown that the autosomal dominant Legs at odd angles (Loa) mutation in cytoplasmic dynein heavy chain (Dync1h1) delays disease onset and extends the life span of transgenic mice harboring human mutant SOD1^G93A. In this study we provide evidence that despite the lack of direct interactions between mutant SOD1 and either mutant or wild-type cytoplasmic dynein, the Loa mutation confers significant reductions in the amount of mutant SOD1 protein in the mitochondrial matrix. Moreover, we show that the Loa mutation ameliorates defects in mitochondrial respiration and membrane potential observed in SOD1^G93A motor neuron mitochondria. These data suggest that the Loa mutation reduces the vulnerability of mitochondria to the toxic effects of mutant SOD1, leading to improved mitochondrial function in SOD1^G93A motor neurons.     

Interaction with Polyglutamine Aggregates Reveals a Q/N-rich Domain in TDP-43

The identification of pathologic TDP-43 aggregates in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration, followed by the discovery of dominantly inherited point mutations in TDP-43 in familial ALS, have been critical insights into the mechanism of these untreatable neurodegenerative diseases. However, the biochemical basis of TDP-43 aggregation and the mechanism of how mutations in TDP-43 lead to disease remain enigmatic. In efforts to understand how TDP-43 alters its cellular localization in response to proteotoxic stress, we found that TDP-43 is sequestered into polyglutamine aggregates. Furthermore, we found that binding to polyglutamine aggregates requires a previously uncharacterized glutamine/asparagine (Q/N)-rich region in the C-terminal domain of TDP-43. Sequestration into polyglutamine aggregates causes TDP-43 to be cleared from the nucleus and become detergent-insoluble. Finally, we observed that sequestration into polyglutamine aggregates led to loss of TDP-43-mediated splicing in the nucleus and that polyglutamine toxicity could be partially rescued by increasing expression of TDP-43. These data indicate pathologic sequestration into polyglutamine aggregates, and loss of nuclear TDP-43 function may play an unexpected role in polyglutamine disease pathogenesis. Furthermore, as Q/N domains have a strong tendency to self-aggregate and in some cases can function as prions, the identification of a Q/N domain in TDP-43 has important implications for the mechanism of pathologic aggregation of TDP-43 in ALS and other neurodegenerative diseases.     

Prey-capture in the African clawed toad (Xenopus laevis): comparison of turning to visual and lateral line stimuli

Separately delivered visual and lateral line stimuli elicit similar but not identical orientation and approach by intact, sighted Xenopus. Response frequencies for visual stimuli declined sharply for distant or caudal stimuli while those for lateral line stimuli changed little. Turn angles correlated highly with stimulus angles but were smaller on average, so regression slopes were less than one. Regression slopes were smaller for visual than for lateral line stimuli, but this apparent difference was due to different distributions of stimulus distance interacting with the toad’s rotation center. Errors in final headings, most often under-rotations, did not differ by modality. Frequencies of lunges and arm capture movements were higher for visual stimuli both overall and especially for rostral proximal stimuli. The results demonstrate accurate orientation by sighted Xenopus to visual and lateral line stimuli; they are consistent with expectations based on in-register tectal maps. Orientation to lateral line stimuli is similar to previous results with blinded animals, revealing no heightened acuity in the latter. Modality differences indicate that the lateral line system is better for omnidirectional orientation and approach to distant stimuli whereas the visual system is more attuned to nearby rostral stimuli and more apt to mediate strikes.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Neuropeptide binding reflects convergent and divergent evolution in species-typical group sizes

Neuroendocrine factors that produce species differences in aggregation behavior ("sociality") are largely unknown, although relevant studies should yield important insights into mechanisms of affiliation and social evolution. We here focused on five species in the avian family Estrildidae that differ selectively in their species-typical group sizes (all species are monogamous and occupy similar habitats). These include two highly gregarious species that independently evolved coloniality; two territorial species that independently evolved territoriality; and an intermediate, modestly gregarious species that is a sympatric congener of one of the territorial species. Using males and females of each species, we examined binding sites for (125)I-vasoactive intestinal polypeptide (VIP), (125)I-sauvagine (SG; a ligand for corticotropin releasing factor, CRF, receptors) and a linear (125)I-V(1a) vasopressin antagonist (to localize receptors for vasotocin, VT). VIP, CRF and VT are neuropeptides that influence stress, anxiety and/or various social behaviors. For numerous areas (particularly within the septal complex), binding densities in the territorial species differed significantly from binding in the more gregarious species, and in most of these cases, binding densities for the moderately gregarious species were either comparable to the two colonial species or were intermediate to the territorial and colonial species. Such patterns were observed for (125)I-VIP binding in the medial bed nucleus of the stria terminalis, medial septum, septohippocampal septum, and subpallial zones of the lateral septum; for (125)I-SG binding in the infundibular hypothalamus, and lateral and medial divisions of the ventromedial hypothalamus; and for the linear (125)I-V(1a) antagonist in the medial septum, and the pallial and subpallial zones of the caudal lateral septum. With the exception of (125)I-SG binding in the infundibular hypothalamus, binding densitites are positively related to sociality.     

Food competition and social experience effects on V1a receptor binding in the forebrain of male Long-Evans hooded rats

The present study investigated the effect of social status in Long-Evans hooded rats established during food competition on V(1a) vasopressin receptor (V(1a)R) binding in the lateral septum (LS), medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), anterior hypothalamus (AH), and central/basolateral amygdala (CeB). Serum concentration of testosterone (T) and corticosterone (CORT) was also measured. In Experiment 1, thirty-two lever-trained weight-matched rat pairs were placed in operant chambers where a single bar press provided access to milk reinforcement. A dominant-subordinate relationship, determined by the duration of drinking, was evident in 88% of the pairs. Sixteen rats were lever-trained but did not interact and served as no-treatment (NT) controls. In the LS, V(1a)R binding in the subordinate (SUB) group was significantly higher than in the dominant (DOM) group. V(1a)R binding was significantly higher in the LS, BNST, CeB, and AH in the NT group than in the other groups. The levels of CORT and T were not affected significantly by group membership. Experiment 2 investigated whether the binding effect in the LS was related to differences in fluid consumption. The results did not indicate a significant effect of fluid consumption. In the rat, V(1a)R binding in several forebrain areas seems to be affected by brief periods of social interactions, and, in the LS, it also appears to be related to dominance status.     

Roles of Ataxin-2 in Pathological Cascades Mediated by TAR DNA-binding Protein 43 (TDP-43) and Fused in Sarcoma (FUS)

The RNA-binding proteins TDP-43 and Fused in Sarcoma (FUS) play central roles in neurodegeneration associated with amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Both proteins are components of messenger ribonucleoprotein (mRNP) granules and show cytoplasmic mislocalization in affected tissues. Recently, ataxin-2 was identified as a potent modifier of TDP-43 toxicity in an RNA-dependent manner. This study investigated to clarify how ataxin-2 modifies the TDP-43 and FUS pathological pathway. The expression of cytoplasmic TDP-43, the 35-kDa C-terminal fragment (TDP-p35f), and mutant FUS recruited ataxin-2 to mRNP granules, whereas increased ataxin-2 inhibited the mRNP granule formation of the 35-kDa C-terminal fragment and mutant FUS. A subcellular compartment analysis showed that the overexpressed ataxin-2 increased the cytoplasmic concentrations of both proteins, whereas it decreased their nuclear distributions. These data indicate that increased ataxin-2 impairs the assembly of TDP-43 and FUS into mRNP granules, leading to an aberrant distribution of RNA-binding proteins. Consequently, these sequences may exacerbate the impairment of the RNA-quality control system mediated by amyotrophic lateral sclerosis/frontotemporal lobar degeneration-associated RNA-binding proteins, which forms the core of the degenerative cascade.     

Corruption and Spread of Pathogenic Proteins in Neurodegenerative Diseases

With advancing age, the brain becomes increasingly susceptible to neurodegenerative diseases, most of which are characterized by the misfolding and errant aggregation of certain proteins. The induction of aggregation involves a crystallization-like seeding mechanism by which a specific protein is structurally corrupted by its misfolded conformer. The latest research indicates that, once formed, proteopathic seeds can spread from one locale to another via cellular uptake, transport, and release. Impeding this process could represent a unified therapeutic strategy for slowing the progression of a wide range of currently intractable disorders.