An evaluation of Hsp90 as a mediator of cortical patterning in Tetrahymena

Silencing of heat shock protein 90 (hsp90): Effect on development and infectivity of Ichthyophthirius multifiliis

BACKGROUND

Recently, an increasing number of ichthyophthiriasis outbreaks has been reported, leading to high economic losses in fisheries and aquaculture. Although several strategies, including chemotherapeutics and immunoprophylaxis, have been implemented to control the parasite, no effective method is available. Hence, it is crucial to discover novel drug targets and vaccine candidates against Ichthyophthirius multifiliis. For this reason, understanding the parasite stage biology, host-pathogen interactions, molecular factors, regulation of major aspects during the invasion, and signaling pathways of the parasite can promote further prospects for disease management. Unfortunately, functional studies have been hampered in this ciliate due to the lack of robust methods for efficient nucleic acid delivery and genetic manipulation. In the current study, we used antisense technology to investigate the effects of targeted gene knockdown on the development and infectivity of I. multifiliis. Antisense oligonucleotides (ASOs) and their gold nanoconjugates were used to silence the heat shock protein 90 (hsp90) of I. multifiliis. Parasite stages were monitored for motility and development. In addition, the ability of the treated parasites to infect fish and cause disease was evaluated.

RESULTS

We demonstrated that ASOs were rapidly internalized by I. multifiliis and distributed diffusely throughout the cytosol. Knocking down of I. multifiliis hsp90 dramatically limited the growth and development of the parasite. In vivo exposure of common carp (Cyprinus carpio) showed reduced infectivity of ASO-treated theronts compared with the control group. No mortalities were recorded in the fish groups exposed to theronts pre-treated with ASOs compared with the 100% mortality observed in the non-treated control fish.

CONCLUSION

This study presents a gene regulation approach for investigating gene function in I. multifiliis in vitro. In addition, we provide genetic evidence for the crucial role of hsp90 in the growth and development of the parasite, suggesting hsp90 as a novel therapeutic target for successful disease management. Further, this study introduces a useful tool and provides a significant contribution to the assessing and understanding of gene function in I. multifiliis.

Stress response gene family expansions correlate with invasive potential in teleost fish

The bluegill sunfish Lepomis macrochirus and the closely related redear sunfish Lepomis microlophus have important ecological and recreational value and are widely used for research and aquaculture. While both species have been introduced outside of their native ranges, only the bluegill is considered invasive. Here, we report de novo transcriptome assemblies for these fish as a resource for sunfish biology. Comparative analyses of the transcriptomes revealed an unexpected, bluegill-specific expansion in the HSP70 and HSP90 molecular chaperone gene families. These expansions were not unique to the bluegill as expansions in HSP70s and HSP90s were identified in the genomes of other teleost fish using the NCBI RefSeq database. To determine whether gene family expansions are specific for thermal stress responses, GST and SOD gene families that are associated with oxidative stress responses were also analyzed. Species-specific expansions were also observed for these gene families in distinct fish species. Validating our approach, previously described expansions in the MHC gene family were also identified. Intriguingly, the number of HSP70 paralogs was positively correlated with thermotolerance range for each species, suggesting that these expansions can impact organismal physiology. Furthermore, fish that are considered invasive contained a higher average number of HSP70 paralogs than non-invasive fish. Invasive fish also had higher average numbers of HSP90, MHC and GST paralogs, but not SOD paralogs. Taken together, we propose that expansions in key cellular stress response gene families represent novel genetic signatures that correlate with invasive potential.

Proteins of the Ciliated Protozoan Parasite Ichthyophthirius multifiliis Identified in Common Carp Skin Mucus

The skin mucus is the fish primary defense barrier protecting from infections via the skin epidermis. In a previous study, we have investigated the proteome of common carp (Cyprinus carpio) skin mucus at two different time points (1 and 9 days) post-exposure to Ichthyophthirius multifiliis. Applying a nano-LC ESI MS/MS technique, we have earlier revealed that the abundance of 44 skin mucus proteins has been differentially regulated including proteins associated with host immune responses and wound healing. Herein, in skin mucus samples, we identified six proteins of I. multifiliis associated with the skin mucus in common carp. Alpha and beta tubulins were detected in addition to the elongation factor alpha, 26S proteasome regulatory subunit, 26S protease regulatory subunit 6B, and heat shock protein 90. The identified proteins are likely involved in motility, virulence, and general stress during parasite growth and development after parasite attachment and invasion. Two KEGG pathways, phagosome and proteasome, were identified among these parasite proteins, mirroring the proteolytic and phagocytic activities of this parasite during host invasion, growth, and development, which represent a plausible host invasion strategy of this parasite. The results obtained from this study can support revealing molecular aspects of the interplay between carp and I. multifiliis and may help us understand the I. multifiliis invasion strategy at the skin mucus barrier. The data may advance the development of novel drugs, vaccines, and diagnostics suitable for the management and prevention of ichthyophthiriosis in fish.

Assessing the utility of Hsp90 gene for inferring evolutionary relationships within the ciliate subclass Hypotricha (Protista, Ciliophora)

BACKGROUND

Although phylogenomic analyses are increasingly used to reveal evolutionary relationships among ciliates, relatively few nuclear protein-coding gene markers have been tested for their suitability as candidates for inferring phylogenies within this group. In this study, we investigate the utility of the heat-shock protein 90 gene (Hsp90) as a marker for inferring phylogenetic relationships among hypotrich ciliates.

RESULTS

A total of 87 novel Hsp90 gene sequences of 10 hypotrich species were generated. Of these, 85 were distinct sequences. Phylogenetic analyses based on these data showed that: (1) the Hsp90 gene amino acid trees are comparable to the small subunit rDNA tree for recovering phylogenetic relationships at the rank of class, but lack sufficient phylogenetic signal for inferring evolutionary relationships at the genus level; (2) Hsp90 gene paralogs are recent and therefore unlikely to pose a significant problem for recovering hypotrich clades; (3) definitions of some hypotrich orders and families need to be revised as their monophylies are not supported by various gene markers; (4) The order Sporadotrichida is paraphyletic, but the monophyly of the "core" Urostylida is supported; (5) both the subfamily Oxytrichinae and the genus Urosoma seem to be non-monophyletic, but monophyly of Urosoma is not rejected by AU tests.

CONCLUSIONS

Our results for the first time demonstrate that the Hsp90 gene is comparable to SSU rDNA for recovering phylogenetic relationships at the rank of class, and its paralogs are unlikely to pose a significant problem for recovering hypotrich clades. This study shows the value of careful gene marker selection for phylogenomic analyses of ciliates.

The Hsp90 capacitor, developmental remodeling, and evolution: the robustness of gene networks and the curious evolvability of metamorphosis

Genetic capacitors moderate expression of heritable variation and provide a novel mechanism for rapid evolution. The prototypic genetic capacitor, Hsp90, interfaces stress responses, developmental networks, trait thresholds and expression of wide-ranging morphological changes in Drosophila and other organisms. The Hsp90 capacitor hypothesis, that stress-sensitive storage and release of genetic variation through Hsp90 facilitates adaptive evolution in unpredictable environments, has been challenged by the belief that Hsp90-buffered variation is unconditionally deleterious. Here we review recent results supporting the Hsp90 capacitor hypothesis, highlighting the heritability, selectability, and potential evolvability of Hsp90-buffered traits. Despite a surprising bias toward morphological novelty and typically invariable quantitative traits, Hsp90-buffered changes are remarkably modular, and can be selected to high frequency independent of the expected negative side-effects or obvious correlated changes in other, unselected traits. Recent dissection of cryptic signal transduction variation involved in one Hsp90-buffered trait reveals potentially dozens of normally silent polymorphisms embedded in cell cycle, differentiation and growth control networks. Reduced function of Hsp90 substrates during environmental stress would destabilize robust developmental processes, relieve developmental constraints and plausibly enables genetic network remodeling by abundant cryptic alleles. We speculate that morphological transitions controlled by Hsp90 may fuel the incredible evolutionary lability of metazoan life-cycles.

Control of canalization and evolvability by Hsp90

Partial reduction of Hsp90 increases expression of morphological novelty in qualitative traits of Drosophila and Arabidopsis, but the extent to which the Hsp90 chaperone also controls smaller and more likely adaptive changes in natural quantitative traits has been unclear. To determine the effect of Hsp90 on quantitative trait variability we deconstructed genetic, stochastic and environmental components of variation in Drosophila wing and bristle traits of genetically matched flies, differing only by Hsp90 loss-of-function or wild-type alleles. Unexpectedly, Hsp90 buffering was remarkably specific to certain normally invariant and highly discrete quantitative traits. Like the qualitative trait phenotypes controlled by Hsp90, highly discrete quantitative traits such as scutellor and thoracic bristle number are threshold traits. When tested across genotypes sampled from a wild population or in laboratory strains, the sensitivity of these traits to many types of variation was coordinately controlled, while continuously variable bristle types and wing size, and critically invariant left-right wing asymmetry, remained relatively unaffected. Although increased environmental variation and developmental noise would impede many types of selection response, in replicate populations in which Hsp90 was specifically impaired, heritability and ‘extrinsic evolvability’, the expected response to selection, were also markedly increased. However, despite the overall buffering effect of Hsp90 on variation in populations, for any particular individual or genotype in which Hsp90 was impaired, the size and direction of its effects were unpredictable. The trait and genetic-background dependence of Hsp90 effects and its remarkable bias toward invariant or canalized traits support the idea that traits evolve independent and trait-specific mechanisms of canalization and evolvability through their evolution of non-linearity and thresholds. Highly non-linear responses would buffer variation in Hsp90-dependent signaling over a wide range, while over a narrow range of signaling near trait thresholds become more variable with increasing probability of triggering all-or-none developmental responses.

Modularity and intrinsic evolvability of Hsp90-buffered change

Hsp90 controls dramatic phenotypic transitions in a wide array of morphological features of many organisms. The genetic-background dependence of specific abnormalities and their response to laboratory selection suggested Hsp90 could be an ‘evolutionary capacitor’, allowing developmental variation to accumulate as neutral alleles under normal conditions and manifest selectable morphological differences during environmental stress. The relevance of Hsp90-buffered variation for evolution has been most often challenged by the idea that large morphological changes controlled by Hsp90 are unconditionally deleterious. To address this issue, we tested an Hsp90-buffered abnormality in Drosophila for unselected pleiotropic effects and correlated fitness costs. Up to 120-fold differences in penetrance among six highly related selection lines, started from an initially small number of flies and rapidly selected for and against a deformed eye trait (dfe), did not translate into measurable differences in any of several tests of viability, lifespan or competitive fitness. Nor were 17 dfe Quantitative Trait Loci (QTL) associated with fitness effects in over 1,400 recombinant lines. Our ability to detect measurable effects of inbreeding, media environment and the white mutation in the selection line backgrounds independent of dfe penetrance suggests that, within the limitations of laboratory tests of fitness, this large morphological change controlled by Hsp90 was selectable independent of strong, correlated and unconditionally deleterious effects—abundant, polygenic variation hidden by Hsp90 allows potentially deleterious alleles to be readily replaced during selection by less deleterious alleles with similar phenotypic effects. Hsp90 links environmental stress with the expression of developmental variation controlling unprecedented morphological plasticity. As outlined here and in the companion paper of this issue, the complex genetic architecture of Hsp90-buffered variation supports a remarkable modularity of Hsp90 effects on quantitative and qualitative phenotypes, consistent with the ‘Hsp90 capacitor hypothesis’ and standard quantitative genetic models of threshold traits.

Identification of the pentapeptide constituting a dominant epitope common to all eukaryotic heat shock protein 90 molecular chaperones

We previously reported that, in human heat shock protein (Hsp) 90 (hHsp90), there are 4 highly immunogenic sites, designated sites Ia, Ib, Ic, and II. This study was performed to further characterize their epitopes and to identify the epitope that is potentially common to all members of the Hsp90 family. Panning of a bacterial library carrying randomized dodecapeptides revealed that Glu251-Ser-X-Asp254 constituted site Ia and Pro295-Ile-Trp-Thr-Arg299, site Ic. Site II (Asp701-Pro717) was composed of several epitopes. When 19 anti-hHsp90 monoclonal antibodies (mAbs) were subjected to immunoblotting against recombinant forms of 7 Hsp90-family members, 2 mAbs (K41110 and K41116C) that recognized site Ic bound to yeast Hsp90 with affinity identical to that for hHsp90, and 1 mAb (K3729) that recognized Glu222-Ala23, of hHsp90beta could bind to human 94-kDa glucose-regulated protein (Grp94), an endoplasmic reticulum paralog of Hsp90. Among the 5 amino acids constituting site Ic, Trp297 and Pro295 were essential for recognition by all anti-site-Ic mAbs, and Arg299 was important for most of them. The necessity of Ile296, Thr298, and Arg299, which are replaced by Leu, Met/Leu, and Lys, respectively, in some eukaryotic Hsp90, was dependent on the mAbs, and K41110 and K41116C could react with Hsp90s carrying these substitutions. From these data taken together, we propose that the pentapeptide Pro295-Ile-Trp-Thr-Arg299 of hHsp90 functions as an immunodominant epitope common to all eukaryotic Hsp90.

The Epiplasm Gene EPC1 Influences Cell Shape and Cortical Pattern in Tetrahymena thermophila1

The cortical protein Epc1p is the most abundant protein in the membrane skeleton, or epiplasm, of Tetrahymena thermophila. A partial sequence of the EPC1 gene was obtained and used to obtain a knockout construct that was successful in transforming Tetrahymena thermophila cells. The results support the conclusion that Epc1p influences cell shape and the fidelity of cortical development. It was further observed that this protein is transferred from plus to minus cells during conjugation, and that the imported protein is assembled into the epiplasm of the recipient cell in a discreet series of steps.

Between genotype and phenotype: protein chaperones and evolvability

Protein chaperones direct the folding of polypeptides into functional proteins, facilitate developmental signalling and, as heat-shock proteins (HSPs), can be indispensable for survival in unpredictable environments. Recent work shows that the main HSP chaperone families also buffer phenotypic variation. Chaperones can do this either directly through masking the phenotypic effects of mutant polypeptides by allowing their correct folding, or indirectly through buffering the expression of morphogenic variation in threshold traits by regulating signal transduction. Environmentally sensitive chaperone functions in protein folding and signal transduction have different potential consequences for the evolution of populations and lineages under selection in changing environments.