Biology subjects

Hajnal, A.

Publications and source records attributed to Hajnal, A..

15 recordsLinked to original sources

bioRxiv2026

Conserved role of EGFR signaling in apoptotic cell recognition and processing across different phagocytes

Efferocytosis is an essential process that clears dying cells from tissues and prevents inflammation. However, the mechanisms by which apoptotic cells recruit and activate phagocytes remain poorly understood. Here, we show that EGFR signaling is both necessary and sufficient for efficient efferocytosis in two diverse phagocytes: the gonadal sheath cells of C. elegans and the zebrafish microglia. In C. elegans, loss of LET-23 EGFR or its downstream effector MPK-1 ERK in the sheath cells impairs the recognition and degradation of apoptotic germ cells. Germ cells undergoing apoptosis secrete the EGF ligand LIN-3, which promotes their recognition and engulfment. Overexpression of EGF in non-apoptotic germ cells is sufficient to trigger their engulfment, indicating that EGF can function as an engulfment signal independently of apoptotic cell death. In zebrafish larvae, pharmacological inhibition of EGFR signaling reduces microglial motility, recognition of apoptotic neurons, and corpse clearance in the optic tectum. Similar to C. elegans, an ectopic source of EGF serves as an attractive cue that promotes microglial recruitment. Our findings suggest that EGFR signaling controls an evolutionarily conserved efferocytosis module that coordinates the recognition and processing of apoptotic corpses in different types of phagocytes.

cell biology↗

bioRxiv2024

SUMO's intrinsically disordered N-terminus is an intramolecular inhibitor of SUMO - SIM interactions

Ubiquitin-related proteins of the SUMO family are reversibly attached to thousands of proteins in eukaryotic cells. Many SUMO substrates, effectors and enzymes carry short motifs (SIMs) that mediate low affinity interactions with SUMO proteins. How specificity is achieved in target selection, SUMO paralogue choice and SUMO-dependent interactions is largely unknown. A unique but poorly understood feature of SUMO proteins is their intrinsically disordered N-terminus. We reveal a function for N-termini of human, C. elegans, and yeast SUMO proteins as intramolecular inhibitors of SUMO- SIM interactions. Mutational analyses, NMR spectroscopy, and Molecular Dynamics simulations indicate that SUMOs N-terminus can inhibit SIM binding by fast and fuzzy interactions with SUMO s core. Deletion of the C. elegans SUMO1 N-terminus leads to p53-dependent apoptosis during germline development, indicating an important role in DNA damage repair. Our findings reveal a mechanism of disorder-based autoinhibition that contributes to the specificity of SUMOylation and SUMO-dependent interactions.

biochemistry↗

bioRxiv2023

Nutritional vitamin B12 regulates RAS/MAPK-mediated cell fate decisions through the one-carbon metabolism

Vitamin B12 is an essential nutritional co-factor for the folate and methionine cycles, which together constitute the one-carbon metabolism. Here, we show that dietary uptake of vitamin B12 modulates cell fate decisions controlled by the conserved RAS/MAPK signaling pathway in C. elegans. A bacterial diet rich in vitamin B12 increases vulval induction, germ cell apoptosis and oocyte differentiation. These effects are mediated by different one-carbon metabolites in a tissue-specific manner. Vitamin B12 enhances via the choline/phosphatidylcholine metabolism vulval induction by down-regulating fat biosynthesis genes and increasing H3K4 tri-methylation, which results in increased expression of RAS/MAPK target genes. Furthermore, the nucleotide metabolism and H3K4 tri-methylation positively regulate germ cell apoptosis and oocyte production. Using mammalian cells carrying different activated KRAS and BRAF alleles, we show that the effects of methionine on RAS/MAPK-regulated phenotype are conserved in mammals. Our findings suggest that the vitamin B12-dependent one-carbon metabolism is a limiting factor for diverse RAS/MAPK-induced cellular responses.

developmental biology↗

bioRxiv2023

Actomyosin-mediated apical constriction promotes physiological germ cell death in C. elegans

Germ cell apoptosis in C. elegans hermaphrodites is a physiological process eliminating around 60% of all cells in meiotic prophase to maintain tissue homeostasis. In contrast to programmed cell death in the C. elegans soma, the selection of germ cells undergoing apoptosis is stochastic. By live-tracking individual germ cells at the pachytene stage, we found that germ cells smaller than their neighbors are selectively eliminated through apoptosis before differentiating into oocytes. Thus, cell size is a strong predictor of physiological germ cell death. The RAS/MAPK and ECT/RHO/ROCK pathways together regulate germ cell size by controlling actomyosin constriction at the apical rachis bridges, which are cellular openings connecting the syncytial germ cells to a shared cytoplasmic core. Enhancing apical constriction reduces germ cell size and increases the rate of cell death while inhibiting the actomyosin network in the germ cells prevents their death. We propose that actomyosin contractility at the rachis bridges of the syncytial germ cells amplifies intrinsic disparities in cell size. Through this mechanism, animals can adapt the rate of germ cell death and differentiation to changing environmental conditions.

developmental biology↗

bioRxiv2021

Tissue-specific inhibition of protein sumoylation uncovers diverse SUMO functions during C. elegans vulval development

The sumoylation (SUMO) pathway is involved in a variety of processes during C. elegans development, such as gonadal and vulval fate specification, cell cycle progression and maintenance of chromosome structure. The ubiquitous expression of the sumoylation machinery and its involvement in many essential processes has made it difficult to dissect the tissue-specific roles of protein sumoylation and identify the specific target proteins. To overcome these challenges, we have established tools to block protein sumoylation and degrade sumoylated target proteins in a tissue-specific and temporally controlled manner. We employed the auxin-inducible protein degradation system (AID) to down-regulate AID-tagged SUMO E3 ligase GEI-17 or the SUMO ortholog SMO-1, either in the vulval precursor cells (VPCs) or in the gonadal anchor cell (AC). Tissue-specific inhibition of GEI-17 and SMO-1 revealed diverse roles of the SUMO pathway during vulval development, such as AC positioning, basement membrane (BM) breaching, vulval cell fate specification and epithelial morphogenesis. Inhibition of sumoylation in the VPCs resulted in an abnormal shape of the vulval toroids and ectopic cell fusions. Sumoylation of the ETS transcription factor LIN-1 at K169 mediates a subset of these SUMO functions, especially the proper contraction of the ventral vulA toroids. Thus, the SUMO pathway plays diverse roles throughout vulval development.

developmental biology↗

bioRxiv2021

Reciprocal EGFR signaling in the Anchor Cell ensures precise inter-organ connection during C. elegans vulval morphogenesis

During C. elegans vulval development, the uterine anchor cell (AC) first secretes an epidermal growth factor (EGF) to specify the vulval cell fates and then invades into the underlying vulval epithelium. Thereby, the AC establishes direct contact with the invaginating 1{degrees} vulF cells and attaches the developing uterus to the vulva. The signals involved and the exact sequence of events joining these two organs are not fully understood. Using a conditional let-23 egf receptor (EGFR) allele along with novel microfluidic short- and long-term imaging methods, we discovered a specific function of the EGFR in the AC during vulval lumen morphogenesis. Tissue-specific inactivation of let-23 in the AC resulted in imprecise alignment of the AC with the 1{degrees} vulval cells, delayed AC invasion and disorganized adherens junctions at the newly forming contact site between the AC and the dorsal vulF toroid. We propose that EGFR signaling, activated by a reciprocal EGF cue from the 1{degrees} vulval cells, positions the AC at the vulval midline, guides it during invasion and assembles a cytoskeletal scaffold organizing the adherens junctions that connect the developing uterus to the dorsal vulF toroid. EGFR signaling in the AC thus ensures the precise alignment of the two developing organs.

developmental biology↗

bioRxiv2021

A DNA Replication-Independent Function of the pre-Replication Complex during Cell Invasion in C. elegans

Cell invasion is an initiating event during tumor cell metastasis and an essential process during development. A screen of C. elegans orthologs of genes over-expressed in invasive human melanoma cells has identified several components of the conserved DNA pre-replication complex (pre-RC) as positive regulators of anchor cell (AC) invasion. The pre-RC functions cell-autonomously in the G1-arrested AC to promote invasion, independently of its role in licensing DNA replication origins in proliferating cells. While the helicase activity of the pre-RC is necessary for AC invasion, the downstream acting DNA replication initiation factors are not required. The pre-RC promotes the invasive fate by regulating the expression of extracellular matrix genes and components of the PI3K signaling pathway. Increasing PI3K pathway activity partially suppressed the AC invasion defects caused by pre-RC depletion, suggesting that the PI3K pathway is one critical pre-RC target. We propose that the pre-RC acts in the non-proliferating AC as a transcriptional regulator that facilitates the switch to an invasive phenotype.

cell biology↗

bioRxiv2021

The vagus nerve is critical for regulation of hypothalamic-pituitary-adrenal axis responses to acute stress

The hypothalamic pituitary adrenal (HPA) axis is a critical regulator of physiologic and psychological responses to acute and chronic stressors. HPA axis function is control by numerous feedback inhibitory mechanisms, disruptions of which can lead to various psychiatric conditions, such as depression, posttraumatic stress disorder, and schizophrenia. Vagus nerve stimulation has been shown to be efficacious in the treatment of in these various mental health issues potentially via modulation of HPA axis function, but the mechanisms by which the vagus nerve may regulate HPA function has not been fully elucidated. In the present studies, we sought to test the hypothesis that the vagus nerve is a critical regulator of HPA function. Neuroendocrine function and neurocircuit changes in corticotropin releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) were examined following acute stress after subdiaphragmatic left vagotomy (VX) in adult male Sprague-Dawley rats. We found that VX mimics HPA activation seen in sham surgery animals exposed to acute restraint stress, particularly increased plasma corticosterone levels, elevated PVN CRF mRNA, and increased action potential firing of putative CRF neurons in PVN brain slices. Furthermore, VX animals exposed to acute restraint stress showed increased elevations of plasma corticosterone and PVN CRF mRNA which may be due to lack of compensatory PVN GABAergic signaling in response to acute stress. Both Sham/Stress and VX/no stress conditions increased action potential firing in putative PVN CRF neurons, but this effect was not seen in the VX/stress condition, suggesting that not all forms of stress compensation are lost following VX. Overall, these findings suggest that the vagus nerve may play a critical role in regulating HPA axis function via modulation of local PVN neurocircuit activity.

neuroscience↗

bioRxiv2021

Microfluidic-based imaging of complete C. elegans larval development

Several microfluidic-based methods for long-term C. elegans imaging have been introduced in recent years, allowing real-time observation of previously inaccessible processes. The existing methods either permit imaging across multiple larval stages without maintaining a stable worm orientation, or allow for very good immobilization but are only suitable for shorter experiments. Here, we present a novel microfluidic imaging method, which allows parallel live-imaging across multiple larval stages, while delivering excellent immobilization and maintaining worm orientation and identity over time. This is achieved by employing an array of microfluidic trap channels carefully tuned to maintain worms in a stable orientation, while allowing growth and molting to occur. Immobilization is supported by an active hydraulic valve, which presses worms onto the cover glass during image acquisition, with the animals remaining free for most of an experiment. Excellent quality images can be acquired of multiple worms in parallel, with little impact of the imaging method on worm viability or developmental timing. The capabilities of this methodology are demonstrated by observing the hypodermal seam cell divisions and, for the first time, the entire process of vulval development from induction to the end of morphogenesis. Moreover, we demonstrate RNAi on-chip, which allows for perturbation of dynamic developmental processes, such as basement membrane breaching during anchor cell invasion.

developmental biology↗

bioRxiv2020

Consumption of a high energy density diet triggers microbiota dysbiosis, hepatic lipidosis, and microglia activation in the nucleus of the solitary tract in rats.

Obesity is a multifactorial chronic inflammatory disease. Consumption of high energy density (ED) diets is associated with hyperphagia, increased body weight and body fat accumulation, and obesity. Our lab has previously shown that short-term (4 weeks) consumption of a high ED diet triggers gut microbiota dysbiosis, gut inflammation, and reorganization of the gut-brain vagal communication. The aim of the current study was to investigate the effect of long-term (6 months) consumption of high ED diet on body composition, gut microbiome, hepatocellular lipidosis, microglia activation in the Nucleus of the Solitary Tract, and the development of systemic inflammation. Male Sprague-Dawley rats were fed a low ED diet (5% fat) for two weeks and then switched to a high ED (45% fat) diet for 26 weeks. Twenty-four hour food intake, body weight, and body composition were measured twice a week. Blood serum and fecal samples were collected at baseline, and 1, 4, 8, and 26 weeks after introduction of the high ED diet. Serum samples were used to measure insulin, leptin, and inflammatory cytokines using Enzyme-linked Immunosorbent Assay. Fecal samples were used for 16S rRNA genome sequencing. High ED diet induced microbiota dysbiosis within a week of introducing the diet. In addition, there was significant microglia activation in the intermediate NTS and marked hepatic lipidosis after four weeks of high ED diet. We further observed changes in the serum cytokine profile after 26 weeks of high ED feeding. These data suggest that microbiota dysbiosis is the first response of the organism to high ED diets and this, in turn, detrimentally affects liver fat accumulation, microglia activation in the brain, and circulating levels of inflammatory markers.

physiology↗

bioRxiv2019

The C. elegans homolog of the Evi1 proto-oncogene, egl-43, coordinates G1 cell cycle arrest with pro-invasive gene expression during anchor cell invasion

Cell invasion allows cells to migrate across compartment boundaries formed by basement membranes. Aberrant cell invasion is a first step during the formation of metastases by malignant cancer cells.\n\nAnchor cell (AC) invasion in C. elegans is an excellent in vivo model to study the regulation of cell invasion during development. Here, we have examined the function of egl-43, the homolog of the human Evi1 proto-oncogene (also called MECOM), in the invading AC. egl-43 plays a dual role in this process, firstly by imposing a G1 cell cycle arrest to prevent AC proliferation, and secondly, by activating pro-invasive gene expression. We have identified the AP-1 transcription factor fos-1 and the Notch homolog lin-12 as critical egl-43 targets. A positive feedback loop between fos-1 and egl-43 induces pro-invasive gene expression in the AC, while repression of lin-12 Notch expression by egl-43 ensures the G1 cell cycle arrest necessary for invasion. Reducing lin-12 levels in egl-43 depleted animals restored the G1 arrest, while hyperactivation of lin-12 signaling in the differentiated AC was sufficient to induce proliferation.\n\nTaken together, our data have identified egl-43 Evi1 as a critical factor coordinating cell invasion with cell cycle arrest.\n\nAuthor summaryCells invasion is a fundamental biological process that allows cells to cross compartment boundaries and migrate to new locations. Aberrant cell invasion is a first step during the formation of metastases by malignant cancer cells.\n\nWe have investigated how a specialized cell in the Nematode C. elegans, the so-called anchor cell, can invade into an adjacent epithelium. Our work has identified an oncogenic transcription factor that controls the expression of specific target genes necessary for cell invasion, and at the same time inhibits the proliferation of the invading anchor cell.\n\nThese findings shed light on the mechanisms, by which cells decide whether to proliferate or invade.

developmental biology↗

bioRxiv2019

The CHORD protein CHP-1 regulates EGF receptor trafficking and signaling in C. elegans and human cells

The intracellular trafficking of growth factor receptors determines the activity of their downstream signaling pathways. The putative co-chaperone CHP-1 acts as a regulator of EGFR trafficking during C.elegans vulval development. Loss of chp-1 causes the retention of the EGFR in the ER and decreased MAPK signaling. CHP-1 functions specifically, as the localization of other receptors is unaltered in chp-1(lf) mutants, and inhibiting other co-chaperones does not affect EGFR localization. The role of CHP-1 during EGFR trafficking is conserved in humans. Analogous to C.elegans, the response of CHP-1-deficient human cells to EGF stimulation is attenuated, the EGFR accumulates in the ER and ERK2 activity is decreased. Although CHP-1 has been proposed to act as a co-chaperone for HSP90, our data indicate an HSP90-independent function of CHP-1. The identification of CHP-1 as a regulator of EGFR trafficking opens the possibility to identify small molecule chaperone inhibitors targeting the EGFR pathway with increased selectivity.

cell biology↗

bioRxiv2019

Epidermal Growth Factor signaling acts directly and through a sedation neuron to depolarizes a sleep-active neuron following cellular stress

Sleep is induced by sleep-active neurons that depolarize at sleep onset to inhibit wake circuits. Sleep-active neurons are under the control of homeostatic and allostatic mechanisms that determine sleep need. However, little is known about the molecular and circuit mechanisms that translate sleep need into the depolarization of sleep-active neurons. During many conditions in C. elegans sleep induction requires a sleep-active neuron called RIS. Here, we defined the transcriptome of RIS to discover that genes of the Epidermal Growth Factor Receptor (EGFR) signaling pathway are expressed in RIS. With cellular stress, EGFR activates RIS, and RIS induces sleep. Activation of EGFR signaling in the ALA neuron has previously been suggested to promote sleep independently of RIS. Unexpectedly, we found that ALA activation promotes RIS depolarization. Our results suggest that ALA is a sedating neuron with two separable functions. (1) It inhibits specific wakefulness behaviors independently of RIS, (2) and it activates RIS to induce sleep. Whereas ALA plays a strong role in surviving cellular stress, surprisingly, RIS does not. In summary, EGFR signaling can induce sleep-active neuron depolarization by an indirect mechanism through activation of the sedating ALA neuron that acts upstream of the sleep-active RIS neuron as well as through a direct mechanism using EGFR signaling in RIS. Sedation rather than sleep appears to be important for increasing survival following cellular stress, suggesting that sedation and sleep play different roles in restoring health.\n\nHighlights- The transcriptome of the sleep-active RIS neuron reveals the presence of the EGFR signaling machinery\n- EGFR activates RIS directly upon cellular stress to induce sleep bouts\n- In parallel, EGFR activates RIS indirectly through the sedating ALA neuron\n- Sedation rather than sleep bouts support survival following cellular stress

neuroscience↗

bioRxiv2019

Neural Coding of Gustatory Information in the Nucleus of the Solitary Tract in Lean and Obese Awake Freely-licking Rats

Taste perception changes with obesity but the underlying neural changes remain poorly understood. To address this issue, we recorded taste responses from single cells in the nucleus tractus solitarius (NTS, the fist central synapse in the gustatory circuit) in awake, diet-induced obese [(DIO; [≥]8wks on a high-energy diet (HED)] and lean rats. Rats were implanted with a bundle of microelectrodes in the NTS and allowed to recover. Water-deprived rats were allowed to freely lick various tastants in an experimental chamber. Taste stimuli included an array of sapid stimuli dissolved in artificial saliva (AS). Each taste trial consisted of 5 consecutive licks followed by 5 AS licks presented on a VR5 schedule. Results showed that taste responses in NTS cells in DIO rats (n=49) were smaller in magnitude, shorter in duration and longer in latency that those in lean rats (n=74). However, there were proportionately more taste-responsive cells in DIO than in lean rats. Lick coherence in DIO rats was significantly lower than in lean rats, both in taste-responsive and lick-related cells (n=172 in lean; n=65 in DIO). Analyses of temporal coding showed that taste cells in DIO rats conveyed less information about taste quality than cells in lean rats. Collectively, results suggest that a HED produces blunted, but more prevalent, responses to taste in the NTS and a weakened association of taste responses with ingestive behavior. These neural adaptations may represent both negative effects and compensatory mechanisms of a HED that may underlie deficits in taste-related behavior associated with obesity.

neuroscience↗

bioRxiv2017

Genetical genomics reveals Ras/MAPK modifier loci

The oncogenic Ras/MAPK pathway is evolutionary conserved across metazoans and is essential for many cellular functions. Mutant screens in the model nematode Caenorhabditis elegans have been invaluable for elucidating Ras/MAPK pathway characteristics and identification of the genes involved. Almost all of these screens have been conducted in a single genetic background. However, phenotypic traits of induced mutations can vary widely depending on the genetic background. At the moment, we lack insight into how different genetic backgrounds modulate Ras/MAPK-signaling and which genetic modifiers are involved.\n\nWe previously introduced a gain-of-function mutation in the Ras/MAPK pathway gene let-60 in over 200 recombinant inbred lines (mutant introgressed RILs: miRILs) and detected genetic modifiers affecting this pathway by studying variation in vulval development. In the present study, we investigate how gene expression regulation is affected by the let-60 gain-of-function mutation and the genetic background by mapping eQTL using 33 miRILs. We found that the majority ([~]73%) of the 1516 detected cis-eQTL are not specific for the let-60 mutation, whereas most ([~]76%) of the 898 detected trans-eQTL are associated with the let-60 mutation. We detected 6 eQTL trans-bands that were specific for the interaction between the genetic background and the mutation. One of these eQTL hotspots co-localizes with the previously identified polymorphic Ras/MAPK modifier amx-2. Comparing gene expression profiles between transgenic lines expressing either the N2 or the CB4856 alleles of amx-2 showed the involvement of amx-2 in 79% of the trans-eQTLs for genes mapping to this trans-band.\n\nTogether, our results have revealed hidden loci affecting Ras/MAPK signaling using sensitized backgrounds in C. elegans. These loci harbor putative polymorphic modifier genes that would not have been detected using mutant screens in single genetic backgrounds.

genetics↗