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

Expanding the clinical spectrum of hereditary fibrosing poikiloderma with tendon contractures, myopathy and pulmonary fibrosis due to <i>FAM111B </i>mutations

BACKGROUND: Hereditary Fibrosing Poikiloderma (HFP) with tendon contractures, myopathy and pulmonary fibrosis (POIKTMP [MIM 615704]) is a very recently described entity of syndromic inherited poikiloderma. Previously by using whole exome sequencing in five families, we identified the causative gene, FAM111B (NM_198947.3), the function of which is still unknown. Our objective in this study was to better define the specific features of POIKTMP through a larger series of patients. METHODS: Clinical and molecular data of two families and eight independent sporadic cases, including six new cases, were collected. RESULTS: Key features consist of: (i) early-onset poikiloderma, hypotrichosis and hypohidrosis; (ii) multiple contractures, in particular triceps surae muscle contractures; (iii) diffuse progressive muscular weakness; (iv) pulmonary fibrosis in adulthood and (v) other features including exocrine pancreatic insufficiency, liver impairment and growth retardation. Muscle magnetic resonance imaging was informative and showed muscle atrophy and fatty infiltration. Histological examination of skeletal muscle revealed extensive fibroadipose tissue infiltration. Microscopy of the skin showed a scleroderma-like aspect with fibrosis and alterations of the elastic network. FAM111B gene analysis identified five different missense variants (two recurrent mutations were found respectively in three and four independent families). All the mutations were predicted to localize in the trypsin-like cysteine/serine peptidase domain of the protein. We suggest gain-of-function or dominant-negative mutations resulting in FAM111B enzymatic activity changes. CONCLUSIONS: HFP with tendon contractures, myopathy and pulmonary fibrosis, is a multisystemic disorder due to autosomal dominant FAM111B mutations. Future functional studies will help in understanding the specific pathological process of this fibrosing disorder

STAT3 Ubiquitylation and Degradation by Mumps Virus Suppress Cytokine and Oncogene Signaling

Mumps virus is a common infectious agent of humans, causing parotitis, meningitis, encephalitis, and orchitis. Like other paramyxoviruses in the genus Rubulavirus, mumps virus catalyzes the proteasomal degradation of cellular STAT1 protein, a means for escaping antiviral responses initiated by alpha/beta and gamma interferons. We demonstrate that mumps virus also eliminates cellular STAT3, a protein that mediates transcriptional responses to cytokines, growth factors, nonreceptor tyrosine kinases, and a variety of oncogenic stimuli. STAT1 and STAT3 are independently targeted by a single mumps virus protein, called V, that assembles STAT-directed ubiquitylation complexes from cellular components, including STAT1, STAT2, STAT3, DDB1, and Cullin4A. Consequently, mumps virus V protein prevents responses to interleukin-6 and v-Src signals and can induce apoptosis in STAT3-dependent multiple myeloma cells and transformed murine fibroblasts. These findings demonstrate a unique cytokine and oncogene evasion property of mumps virus that provides a molecular basis for its observed oncolytic properties

Model for biological control of canalization and evolvability. In any individual the strength of signaling through Hsp90 target pathways is directly proportional to the level of Hsp90 function (top panel), but the phenotypic effects of changes in signaling strength are often highly nonlinear, creating thresholds (the inflection point, second from top).

<div><p>A simple consequence of steep non-linearity is that sensitivity to all kinds of perturbation and stochastic effects is expected to be highest at the inflection point (second panel from bottom).</p> <p>This simple relationship between sensitivity to variation and the steepness of the signaling-phenotype relationship at the inflection point, the inverse of canalization (bottom panel), suggests why all variation increases in concert for individuals and/or populations near trait thresholds.</p></div

Hsp90 controlled environmental variation specific to previously invariant or canalized traits.

<div><p>Comparison of mean-normalized components of purely-environmental variation (z-axis) across the <i>RI</i> line backgrounds (x-axis).</p> <p>Developmental stability was calculated as the averaged (unsigned) deviations of left and right from the mean, i.e. (L+R)/2, within each individual (<i>V_e within</i>) or on the averaged (unsigned) deviations of each individual (L+R) from their clone means for each <i>RI</i> line genotype (<i>V_e among</i>).</p> <p>There was generally no effect of Hsp90 allele (<i>Sami</i>, blue or <i>P582i</i>, yellow) on the variable traits, and a highly significant effect on either measure of <i>V_e</i> for canalized bristle traits but not wing area, which was highly canalized independent of Hsp90 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000075#pone-0000075-t004" target="_blank">Table 4</a>).</p></div

Hsp90 controlled phenotypic variation of most invariant quantitative traits.

<div><p>(<b>A</b>) Effects of <i>P582i</i> (yellow) and <i>Sami</i> (blue) alleles of Hsp90 in the isogenic <i>Sam</i> background on <i>V_P</i> of mutant and control sets of 450 males across the 9 <i>RI</i> line backgrounds.</p> <p>(<b>B and C</b>) Effects of 3^rd chromosomes carrying null (<i>P582</i>), and dominant-negative (<i>9J1</i>) Hsp90 mutations or wild-type Sam alleles introgressed into the <i>Sam</i> background in mutant and control sets of 225 male or 225 female sibs.</p> <p> <i>TM6B</i> contains the dominant <i>Humeral</i> (<i>Hu</i>) mutation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000075#pone.0000075-FlyBase1" target="_blank">[32]</a>, which increases humeral TH bristle numbers.</p> <p>Therefore, for comparison of TH bristles between TM6B and the other genotypes we used TH-HU, indicating that TH was scored only for the remaining 18 non-humeral TH bristle types.</p> <p>All experiments were conducted under temperature, density and humidity controlled conditions.</p> <p>Environmental effects were further controlled by direct comparisons between flies from the same vial and maternal environments.</p> <p>Coefficients of variation (<i>CV</i> = standard deviation/mean) are shown to enable between-trait comparisons. Statistical tests of the significance of Hsp90 effects on phenotypic variability and <i>P</i>-values are found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000075#pone-0000075-t001" target="_blank">Table 1</a> (for A) and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000075#pone-0000075-t002" target="_blank">Table 2</a> (for B and C).</p></div

Hsp90-buffered variation contributed to predicted selection responses.

<p>Fold-increase in the predicted response to truncation, directional or stabilizing selection of the ‘populations’ of 9 <i>RI</i> line genotypes in the <i>P582i</i> mutant relative to equivalent ‘populations’ of genotypes in the <i>Sami</i> control flies (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000075#pone-0000075-t005" target="_blank">Table 5</a>).</p

Experimental design partitions genetic and purely-environmental components of variation.

<p>Females heterozygous for <i>P582i</i> (<i>Sam1;Sam2;P582i/Sami</i>; left) were crossed to males from each of 9 highly inbred (95% homozygous) <i>RI</i> line backgrounds (different colors) to create matched “clones” of Hsp90 mutant and control male progeny from the same vial and maternal environments and hybrid for <i>Sam</i> and each <i>RI</i> line background.</p