Prahlad V (2020) J Neurogenet "The discovery and consequences of the central role of the nervous system in the control of protein homeostasis."

Prahlad V

[J Neurogenet, 2020]

Organisms function despite wide fluctuations in their environment through the maintenance of homeostasis. At the cellular level, the maintenance of proteins as functional entities at target expression levels is called protein homeostasis (or proteostasis). Cells implement proteostasis through universal and conserved quality control mechanisms that surveil and monitor protein conformation. Recent studies that exploit the powerful ability to genetically manipulate specific neurons in <i>C. elegans</i> have shown that cells within this metazoan lose their autonomy over this fundamental survival mechanism. These studies have uncovered novel roles for the nervous system in controlling how and when cells activate their protein quality control mechanisms. Here we discuss the conceptual underpinnings, experimental evidence and the possible consequences of such a control mechanism. <b>PRELUDE:</b> Whether the detailed examination of parts of the nervous system and their selective perturbation is sufficient to reconstruct how the brain generates behavior, mental disease, music and religion remains an open question. Yet, Sydney Brenner's development of <i>C. elegans</i> as an experimental organism and his faith in the bold reductionist approach that 'the understanding of wild-type behavior comes best after the discovery and analysis of mutations that alter it', has led to discoveries of unexpected roles for neurons in the biology of organisms.

Prahlad V et al. (2003) Science "Roles for mating and environment in C. elegans sex determination."

Goodwin EB, Prahlad V, Pilgrim D

[Science, 2003]

In Caenorhabditis elegans the two sexes, hermaphrodites and males, are thought to be irreversibly determined at fertilization by the ratio of X chromosomes to sets of autosomes: XX embryos develop as hermaphrodites and XO embryos as males. We show instead that both sex and genotype of C. elegans can be altered postembryonically and that this. exibility requires sexual reproduction. When grown in specific bacterial metabolites, some XX larvae generated by mating males and hermaphrodites develop as males and lose one X chromosome. However, XX larvae produced by hermaphrodite self-fertilization show no such changes. We propose that sexual reproduction increases developmental. exibility of progeny, allowing for better adaptation to changing environments.

Prahlad V et al. (2008) Science "Regulation of the cellular heat shock response in Caenorhabditis elegans by thermosensory neurons."

Morimoto RI, Cornelius T, Prahlad V

[Science, 2008]

Temperature pervasively affects all cellular processes. In response to a rapid increase in temperature, all cells undergo a heat shock response, an ancient and highly conserved program of stress-inducible gene expression, to reestablish cellular homeostasis. In isolated cells, the heat shock response is initiated by the presence of misfolded proteins and therefore thought to be cell-autonomous. In contrast, we show that within the metazoan Caenorhabditis elegans, the heat shock response of somatic cells is not cell-autonomous but rather depends on the thermosensory neuron, AFD, which senses ambient temperature and regulates temperature-dependent behavior. We propose a model whereby this loss of cell autonomy serves to integrate behavioral, metabolic, and stress-related responses to establish an organismal response to environmental change.

Prahlad, V. et al. (2017) International Worm Meeting "Serotonergic control of the conserved heat shock factor transcription factor (HSF-1)."

Prahlad, V., Ooi, Felicia

[International Worm Meeting, 2017]

One of the recent developments in the study of protein homeostasis is the discovery that in a metazoan such as Caenorhabditis elegans, the cellular response to protein misfolding is not autonomously controlled by individual cells, but instead is under the regulation of the animals' nervous system. However, the functional significance of such regulation remains to be shown. We have previously shown that serotonergic signaling in C. elegans can activate HSF1-dependent hsp70 expression through cell non-autonomous mechanisms. Serotonin (5-hydroxytryptamine, 5-HT) plays a central role in the neuronal mechanisms of learning and memory that allows organisms to synthesize information from their surroundings to predict danger. We find that olfactory learning in C. elegans mediated by the serotonergic system not only enhances avoidance behaviors to potential threats, but also induces neuronal and non-neuronal cells throughout the organism to increase expression of their molecular chaperones if they subsequently encounter this threat. Specifically, neurosensory training potentiates HSF-1 activity in anticipation of the actual encounter with the stressor, while not in itself, resulting in chaperone expression. Molecular chaperones are subsequently expressed if and when animals encounter the actual stressor. Our data show that serotenergic control of HSF-1 equips C. elegans to better survive environmental dangers by pre-emptively and specifically enhancing cellular homeostasis using the neuronal circuitry underlying memory and learning. We will discuss the mechanisms by which neuronal 5-HT and learning potentiate HSF-1 to enhance chaperone expression.

Prahlad V et al. (2009) Trends Cell Biol "Integrating the stress response: lessons for neurodegenerative diseases from C. elegans."

Morimoto RI, Prahlad V

[Trends Cell Biol, 2009]

All cells possess surveillance and homeostatic mechanisms to adjust protein biogenesis to the demands of growth, differentiation, ageing and environmental stress. However, under certain circumstances, these mechanisms fail to adequately respond to proteotoxic imbalances and result in the accumulation of misfolded proteins. In humans, this can lead to neurodegeneration and other protein conformational diseases. To protect itself, the cell employs highly conserved stress responses and chaperone networks to maintain protein-folding homeostasis (proteostasis). Although the regulation of stress responses, such as the heat-shock response, and of proteostasis have been widely considered to be cell autonomous, recent studies using Caenorhabditis elegans have shown that these processes are regulated by neuronal signaling and endocrine pathways and integrated into other functions of the organism. The hierarchical control of the cellular proteostasis machinery affords insight into the organization of stress regulatory networks in multicellular organisms and offers novel targets for the treatment of human protein conformational diseases.

Prahlad V et al. (2011) Proc Natl Acad Sci U S A "Neuronal circuitry regulates the response of Caenorhabditis elegans to misfolded proteins."

Prahlad V, Morimoto RI

[Proc Natl Acad Sci U S A, 2011]

The consequence of chronic protein misfolding is the basis of many human diseases. To combat the deleterious effects of accumulated protein damage, all cells possess robust quality-control systems, specifically molecular chaperones and clearance machineries, that sense and respond to protein misfolding. However, for many protein conformational diseases, it is unclear why this quality-control system does not efficiently counter protein aggregation. Previous findings that the heat shock response in Caenorhabditis elegans is regulated by thermosensory neurons led us to consider whether neuronal activity could also be responsible for the inadequate response of an organism to chronic protein misfolding. Here we show, in animals expressing polyglutamine expansion proteins and mutant SOD-1(G93A) in intestinal or muscle cells, that the nervous system does indeed control the cellular response to misfolded proteins. Whereas polyglutamine expansion-expressing animals with WT thermosensory neurons readily express protein aggregates, leading to cellular dysfunction without concomitant up-regulation of molecular chaperones, modulation of the nervous system results in chaperone up-regulation that suppresses aggregation and toxicity. The neuronal signal is transmitted through calcium-activated dense core vesicle neurosecretion. Cell-nonautonomous control of chaperone expression by the thermosensory neurons allows C. elegans to respond differently to acute stress such as heat shock, and chronic stress caused by the expression of misfolded proteins, suggesting that neuronal signaling determines the course of cellular proteotoxicity.

Alcedo J et al. (2020) J Neurogenet "Neuromodulators: an essential part of survival."

Prahlad V, Alcedo J

[J Neurogenet, 2020]

The coordination between the animal's external environment and internal state requires constant modulation by chemicals known as neuromodulators. Neuromodulators, such as biogenic amines, neuropeptides and cytokines, promote organismal homeostasis. Over the past several decades, <i>Caenorhabditis</i><i>elegans</i> has grown into a powerful model organism that allows the elucidation of the mechanisms of action of neuromodulators that are conserved across species. In this perspective, we highlight a collection of articles in this issue that describe how neuromodulators optimize <i>C. elegans</i> survival.

Ooi FK et al. (2017) Sci Signal "Olfactory experience primes the heat shock transcription factor HSF-1 to enhance the expression of molecular chaperones in C. elegans."

Prahlad V, Ooi FK

[Sci Signal, 2017]

Learning, a process by which animals modify their behavior as a result of experience, enables organisms to synthesize information from their surroundings to acquire resources and avoid danger. We showed that a previous encounter with only the odor of pathogenic bacteria prepared Caenorhabditis elegans to survive exposure to the pathogen by increasing the heat shock factor 1 (HSF-1)-dependent expression of genes encoding molecular chaperones. Experience-mediated enhancement of chaperone gene expression required serotonin, which primed HSF-1 to enhance the expression of molecular chaperone genes by promoting its localization to RNA polymerase II-enriched nuclear loci, even before transcription occurred. However, HSF-1-dependent chaperone gene expression was stimulated only if and when animals encountered the pathogen. Thus, learning equips C. elegans to better survive environmental dangers by preemptively and specifically initiating transcriptional mechanisms throughout the whole organism that prepare the animal to respond rapidly to proteotoxic agents. These studies provide one plausible basis for the protective role of environmental enrichment in disease.

Das S et al. (2021) Mol Cell "Gene bookmarking by the heat shock transcription factor programs the insulin-like signaling pathway."

Das S, Min S, Prahlad V

[Mol Cell, 2021]

Maternal stress can have long-lasting epigenetic effects on offspring. To examine how epigenetic changes are triggered by stress, we examined the effects of activating the universal stress-responsive heat shock transcription factor HSF-1 in the germline of Caenorhabditis elegans. We show that, when activated in germ cells, HSF-1 recruits MET-2, the putative histone 3 lysine 9 (H3K9) methyltransferase responsible for repressive H3K9me2 (H3K9 dimethyl) marks in chromatin, and negatively bookmarks the insulin receptor daf-2 and other HSF-1 target genes. Increased H3K9me2 at these genes persists in adult progeny and shifts their stress response strategy away from inducible chaperone expression as a mechanism to survive stress and instead rely on decreased insulin/insulin growth factor (IGF-1)-like signaling (IIS). Depending on the duration of maternal heat stress exposure, this epigenetic memory is inherited by the next generation. Thus, paradoxically, HSF-1 recruits the germline machinery normally responsible for erasing transcriptional memory but, instead, establishes a heritable epigenetic memory of prior stress exposure.

Smith BS et al. (1990) Cryobiology "Cryopreservation of the entomogenous nematode parasite Steinernema feltiae (= Neoaplectana carpocapsae)."

Hodgson-Smith A, Popiel I, James ER, Smith BS, Minter DM

[Cryobiology, 1990]

Cryopreservation studies were conducted with the J1 juvenile and third stage infective juvenile (IJ) larval stages of the entomogenous parasitic nematode Steinernema feltiae (=Neoaplectana carpocapsae). The main parameters evaluated were (i) tolerance of the organisms to the cryoprotectants methanol, ethanediol, glycerol, and dimethyl sulfoxide; (ii) the incubation temperature and exposure period in cryoprotectant; and (iii) slow cooling (circa 1C min-1) vs rapid cooling (circa 5,100C min-1). The J1 stage was sensitive to all cryoprotectants at >20% (v/v). This sensitivity increased at 22 and 37C. Exsheathed IJ stage organisms tolerated exposure to 50% (v/v) ethanediol or Me2SO and 60% (v/v) methanol or glycerol. A proportion (3.4%) of J1s preincubated in 20% (v/v) methanol for 10 min at 0C survived slow cooling to -35C followed by plunge into liquid nitrogen. Preincubation in 60% (v/v) Me2SO for 45 sec at 0C followed by rapid cooling yielded a higher proportion (12.3%0 of surviving J1s. The infective IJ stage only survived rapid cooling. Preincubation for 20 min at 0C in either 60% (v/v) methanol or 45% glycerol, followed by rapid cooling at 5,100C min-1, yielded 30-34% viable IJs following thawing. These larvae were capable of further growth and development in vitro. The results suggest that the organisms are vitrified during the rapid cooling step. For routine maintenance of strains of S. feltiae and related