worldwide, resulting in up to 300,000 deaths per year (1, 2) . No efficacious vaccine is 85 available for human schistosomiasis, and the control and treatment of the disease rely almost 86 exclusively on praziquantel (PZQ), the only effective drug against schistosome species. 87
Despite its efficacy, PZQ does not kill juvenile parasites, allowing reinfection (3) , and there is 88 a constant concern with the appearance of PZQ-resistant strains of Schistosoma (4) (5) (6) . Thus, 89
there is an urgent need to search for promising protein targets to develop new drugs. 90
Transcription factors and chromatin modifiers play primary roles in the programming 91 and reprogramming of cellular states during development and differentiation, as well as in 92 maintaining the correct cellular transcriptional profile (7) . Indeed, a plethora of 93 groundbreaking studies has demonstrated the importance of posttranslational modifications of 94 histones for transcription control and normal cell development. Therefore, the deregulation of 95 epigenetic control is a common feature of a number of diseases, including cancer (7) . 96
The complexity of schistosome development and differentiation implies tight control 97 of gene expression at all stages of the life cycle and that epigenetic mechanisms are likely to 98
play key roles in these processes. In recent years, targeting the Schistosoma mansoni 99 epigenome has emerged as a new and promising strategy to control schistosomiasis. The 100 study of histone acetylation in S. mansoni biology and the effect of inhibitors of histone 101 deacetylases (HDACs and SIRTs) or histone acetyltransferases (HATs) on parasite 102 development and survival have demonstrated the importance of these enzymes as potential 103 therapeutic targets (8) (9) (10) (11) (12) . 104
Unlike histone lysine acetylation, which is generally coupled to gene activation, 105 histone lysine methylation can have different biological associations depending on the 106 position of the lysine residue and the degree of methylation (13) . Patterns of specific lysine 107 methyl modifications are achieved by a precise lysine methylation system, consisting of 108 proteins that add, remove and recognize the specific lysine methyl marks. Importantly, 109 histone lysine methylation (14) (15) (16) and demethylation (17) have been recently demonstrated 110 to be potential drug targets against S. mansoni. 111
Lysine-specific demethylase 1 (LSD1) was the first protein reported to exhibit histone 112 demethylase activity and has since been shown to have multiple essential roles in metazoan 113 biology (18) . LSD1 enzymes are characterized by the presence of an amine oxidase (AO)-like 114 domain, which is dependent on its cofactor flavin-adenine dinucleotide (FAD), a SWIRM 115 domain, which is unique to chromatin-associated proteins (19) and an additional coiled-coil 116 TOWER domain (20) . LSD1 is a component of the CoREST transcriptional corepressor 117 complex that also contains CoREST, CtBP, HDAC1 and HDAC2. As part of this complex, 118 LSD1 demethylates mono-methyl and di-methyl histone H3 at Lys4 (H3K4me1/2), but not 119
H3K4me3 (21) . In addition, when recruited by androgen or estrogen receptor, LSD1 functions 120 as a H3K9 demethylase. Given the high level of expression and enzymatic activity of LSD1 in 121 many types of tumors, there has been significant recent interest in the development of 122 pharmacological inhibitors (22) . 123
In our continuing effort to study the biology and therapeutic potential of epigenetic 124 regulators in S. mansoni, we have found schistosome LSD1 (SmLSD1, Sm_150560) as a 125 potential drug target (this paper). During the course of our investigation, a recent publication 126 (17) described the repurposing of some anthracyclines as anti-Schistosoma agents, suggesting 127 by in silico docking SmLSD1 as a putative target without any evidence of enzyme inhibition. 128
In the present work we show the SmLSD1-inhibitory activity of a novel synthetic 129 LSD1 inhibitor MC3935 (100-fold more potent than the canonical human LSD1 inhibitor 130 tranylcypromine, TCP). In addition, we show that the LSD1 inhibitor MC3935 was able to 131 kill both adult worms and schistosomula in vitro. Importantly, silencing of SmLSD1 by 132 dsRNAi partially recapitulated MC3935-treatment phenotypes in adult worms. Our RNA-seq 133 analysis revealed a large-scale transcriptional deregulation in parasites that were treated with 134 sublethal doses of MC3935, which could be the primary cause of the ultrastructure defects 135 and death of S. mansoni. Together, these findings elucidate the biological relevance of histone 136 lysine methylation in S. mansoni and provide insights into the therapeutic potential of 137 SmLSD1 to control schistosomiasis. 138
Multiple-sequence alignment of the full-length proteins was performed using mansoni (Smp_150560) LSD1 protein sequences, as previously published (23) . Pairwise 151 comparisons to the reference followed by calculation of the maximum distance matrix 152 resulted in an unrooted phylogenetic tree, which was visualized using Tree of Life v1.0 (24) . 153
Compound MC3935 ( Supplementary Fig S1A) 
To a solution of 3 (125 mg, 0.332 mmol, 1 eq.) in dry THF (9 mL) was added 4N HCl 194 in dioxane (5.4 mL, 21.6 mmol, 65 eq.) while cooling at 0 °C. Then, the resulting suspension 195 
Compound 1 (MC3935) was screened for inhibition against human recombinant 216 LSD1. The in vitro assay was based on the oxidative demethylation of the monomethylated 217 histone peptide H3K4N(CH3) via a FAD/FADH2 mediated reduction of O2 to H2O2. The 218 remaining LSD1 activity was monitored via the detection of the amount of H2O2 formed. This 219 was done by horseradish peroxidase (HRP), which reduces H2O2 to H2O using Amplex Red 2 220
as the electron donor. The resulting product, resorufin, was highly fluorescent at 590 nm. The 221
inhibition assay was performed as described previously (26) . The compound was 222 preincubated at different concentrations with LSD1 for 15 min at room temperature in the 223 presence of HRP-Amplex Red. The substrate was then added, and the fluorescence was 224 measured for 30 min. 225
The amino acid sequence of SmLSD1 was retrieved from Unipro (27) The saved alignment file was used to generate a homology model of SmLSD1 based on the 232 cocrystal structure of hLSD1 with MC2580 (PDB ID 2XAS) (26) using MODELLER 9.11 233 (28) . 234
Similar to the observed adduct of the analogous tranylcypromine derivative MC2584 236 with FAD (PDB ID 2XAQ (29)), an N5 adduct of MC3935 with FAD was generated in MOE 237 using only the flavin ring of FAD. The generated adduct was then cured using LigPrep 238 (Schrödinger Release 2018-1): protonation states were assigned at pH 7±1 using Epik, 239 tautomeric forms, as well as possible conformers were generated, and energy minimized using 240 the OPLS03 force field. As a result, 25 low-energy conformers were generated using the 241 bioactive search module implemented in Schrödinger. 242
The generated homology model of SmLSD1 was prepared with Schrödinger's Protein 244
Preparation Wizard (Schrödinger Release 2018-1); where hydrogen atoms were added and the 245 hydrogen bond network was optimized. The protonation states at pH 7.0 were predicted using 246 the PROPKA tool in Schrödinger, and the structure was subsequently subjected to a restrained 247 energy minimization using the OPLS03 force field (RMSD of the atom displacement for 248 terminating the minimization was 0.3 Å). 249
The receptor grid preparation for the docking procedure was carried out by assigning 
An inverted stereomicroscope (Leica M80) was used to evaluate the physiology and 279 behavior of the parasites. Parasites were observed every 24 h, and representative images and 280 videos were acquired. Schistosomula motility, light opacity, and membrane integrity were 281 evaluated. Adult worm motility, pairing state, adherence to dish surface, and egg laying were 282 monitored and determined. The viability was determined using the CellTiter-Glo Luminescent 283
Cell Viability Assay (Promega) (32) . Total cell lysates from one thousand schistosomula or 284 10 adult worms (paired or unpaired) were submitted to an ATP dosage. Eggs laid on the 285 plates were quantified daily. 286
After treatment, the total RNA was extracted using a RiboPure kit (Ambion) followed Real-Time PCR System (Applied Biosystems) was used. The results were analyzed by the 298 comparative Ct method, and the statistical significance was calculated with the student t-test. 299
Nuclear protein extracts from schistosomula or adult worms were prepared as 301 previously described (31) . From each sample, 10 µg of each extract was loaded on 7-12% 302 precast SDS-polyacrylamide gels (Bio-Rad). After transference, membranes were blocked 303
with Tris-buffered saline (TBS) containing 0.1% Tween 20 and 2% bovine serum albumin 304 (TBST/2% BSA) and then probed overnight with specific antibodies in TBS/2% BSA. 305
Membranes were washed with TBST and incubated for 1 h in TBST/2% BSA with secondary 306 antibody (Immunopure goat anti-mouse # 31430, Thermo Scientific, and peroxidase-labeled 307 affinity anti-rabbit # 04-15-06, KPL). After washing the membranes in TBST, the bands were 308 visualized and images were recorded with the Amersham Imaging System (GE Healthcare), 309
and quantified with ImageJ software (NIH). Histone monoclonal antibodies used were anti-310 H3K4me1 (#5326, Cell Signaling), anti-H3K4me2 (#9725, Cell Signaling) and anti-311
H3K4me3 (#9727, Cell Signaling), following the manufacturer's instructions. For all 312 antibodies, a 1:1000 dilution was used. For normalization of the signals across the samples, 313
anti-histone H3 antibody (#14269, Cell Signaling) was used. 314
The activity of caspase 3/7 was measured using the Caspase-Glo 3/7 assay kit 316 (Promega) following the instructions. Cell lysates from schistosomula were obtained from 317 2,000 parasites cultivated in a 24-well plate with complete medium (as described above) and 318 treated with MC3935 25 µM or vehicle (DMSO 0.25%). The luminescence was measured in a 319 white-walled 96-well plate in a Wallac Victor2 1420 multilabel counter (PerkinElmer). 320
Detection of DNA strand breaks in MC3935-treated schistosomula was performed 322 using the In situ Cell Death Detection kit (Roche), as previously described (33) . 323
Schistosomula were fixed after 72 h treatment with MC3935 or DMSO. Parasites were 324 mounted in a superfrost glass slide using Prolong with DAPI (Invitrogen) for nuclear 325 visualization. Images were taken on a Zeiss Axio Observer Z1 (Zeiss) inverted microscope 326 equipped with a 40X objective lens and an AxioCam MRm camera in ApoTome mode. 327
For the confocal microscopy analysis, the adult worms were fixed and stained as 329 previously described (34) . Confocal scanning laser microscopy was performed on a Zeiss 330 LSM 800 microscope equipped with a 488-nm HE/Ne laser and a 470-nm long-pass filter but 331 without the reflection mode. Thin-sections (60 nm) were collected on copper grids and stained for 30 minutes in 5% 347 aqueous uranyl acetate and for 5 minutes in lead citrate. 348
The coding sequence of lysine-specific histone demethylase 1 (SmLSD1) (GenBank 350 accession #: XM_018797592.1) was amplified by PCR using the oligonucleotides 351 
The GFP gene was used as a nonrelated dsRNA control and was amplified from pEGFP-N3 366 with the oligonucleotides: GFP_F_woT7 (5' -AGCAGAGCTGGTTTAGTGAACC -3') 367
with GFP_R_woT7 (5' -TTATGATCTAGAGTCGCGGCCG -3'). This amplicon was used 368 in a nested PCR with the oligonucleotides containing a T7 tail: GFP_F_wT7 (5' -369
GFP_R_wT7 (5' -371
Double-stranded RNA (dsRNA) was synthesized from templates of amplified PCR with 373 oligonucleotides containing the T7 tail. The dsRNA was delivered by soaking the parasite 374 couples in media containing 30 µg/mL of the desired dsRNA, and everyday, 70% of the 375 medium was changed to a fresh medium also containing 30 µg/mL of dsRNA. At the end of 376 the 2 nd , 4 th , and 7 th days of incubation, parasites were collected, washed twice in PBS and 
The general outline of the bioinformatics pipeline used for the analysis of the RNA-391 Seq data is completely described in Pereira et al. (36) , including the three different statistical 392 approaches that were used to obtain lists of differentially expressed genes, and considering as 393 the final set only those genes that were listed at the intersection of the three sets. We used the 394 same versions of genome and transcriptome annotation, including the use of a metagenes 395 transcriptome to deal with isoforms, as previously described (36) . All software parameters 396 were as described (36) 
Schistosoma mansoni lysine specific-demethylase 1 402
The Schistosoma mansoni LSD1 (SmLSD1) contains all three canonical structural, 403 and functional domains (SWIRM, amino-oxidase-like and TOWER domains) (Fig 1A) found 404 in the LSD1 protein family. We examined in detail the protein alignment between SmLSD1 405 and human LSD1 (hLSD1) (Supplementary Fig S2) , particularly since the latter is a well-406 defined drug target (18) and carried out a limited phylogenetic study including further 407 orthologs. In this regard, our phylogenetic tree revealed that the SmLSD1 protein was closer 408 to human LSD1 than to plant or nematode LSD1 (Fig 1B) . It is worth noting that among the worms were recovered by perfusion of infected hamsters (Fig 2A) . We screened a series of 423 Fig S3B) . Interestingly, TCP showed 428 the least toxic activity, whereas MC3935 was the most potent compound ( Supplementary Fig  429   S3A and B). Therefore, MC3935 was chosen for all further analyses in this study. We showed 430 that MC3935 was able to inhibit the catalytic activity of the recombinant human LSD1 protein 431 ( Supplementary Fig S1B) , revealing a 1,000 fold higher inhibitory activity than TCP, proving 432 it as a bona fide LSD1 inhibitor. The toxic effect of MC3935 on schistosomula or adult worm 433 pairs was further confirmed (Fig 2 B and C and Supplementary Fig S3C) . A significant loss of 434 viability at 10 µM and a complete loss of viability (what we judged death) at 25 µM MC3935 435 was observed in schistosomula or adult worms after cultivation for 72 or 96 h, respectively 436 ( Supplementary Fig S3C) . These results were confirmed with videos (Supplementary videos 437 S1-S4), which showed nearly 100% of the schistosomula had a complete lack of motility, 438 high granularity and altered body shape (supplementary video S2) when compared to healthy 439 schistosomula that were treated with DMSO only (supplementary video S1). MC3935-440 treated-adult worms also showed significant alterations when compared to the control (Fig 2D  441 and Supplementary video S3), which included unpairing, lack of adherence, extremely low 442 motility, vitellaria involution and no egg laying (Fig 2D and supplementary video S4) . In 443 order to evaluate whether the lack of eggs (Fig 2D; Egg laying) was exclusively due to the 444 separation of the worms (Fig 2D; Pairing) , we performed an additional experiment in which 445 only adult worms that were kept coupled were maintained in culture, followed by egg 446
counting. Worm pairs that were not treated, or treated with DMSO laid a significant number 447 of eggs, while worm pairs that received the treatment of MC3935 laid no eggs whatsoever 448 ( Supplementary Fig S4A and B) . 449 with the hLSD1 counterpart ( Fig 3B) . 485
We next performed western blot analysis and showed that schistosomula or adult 486 worms treated with MC3935 displayed higher band intensities of H3K4me1 or H3K4me2 487 marks when compared to the DMSO controls (Fig 3C) , confirming the inhibition of SmLSD1 488 demethylase activity. Of note, the increase in H3K4me1 or H3K4me2 methylation was not 489 due to the downregulation of SmLSD1 transcription (Supplementary Fig S5, 
A and B). Together, these data confirm that MC3935 inhibited SmLSD1 demethylase activity. 491 Importantly, MC3935 treatments did not alter the H3K4me3 mark in schistosomula or adult 492 worms (Supplementary Fig S5, western blots in A and B) , pointing to a selective inhibition of 493 LSD1-specific histone marks. 494 
The treatment of schistosomula with MC3935 significantly induced apoptosis, as 511 detected by the 8-fold increase in the activities of caspases 3 and 7 (Fig 4A) . In addition, the 512 TUNEL assay indicated extensive double-strand DNA breaks (Fig 4B) , as revealed by the 513 green staining of the whole body of the worm treated with the inhibitor. Worms treated with 514 DMSO showed no apoptotic activity, whatsoever (Fig 4A and B) . These results are in 515 agreement with our data from the ATP viability assay (Fig 2B, Supplementary Fig S3C) and 516 our observations taken from the optical microscope (Supplementary videos S1 and S2). 517 The results from our scanning electron microscopy clearly showed that inhibition of 527 SmLSD1 by MC3935 induced severe erosions and fissures in the tegument of schistosomula 528 (Fig 5B and D) . Worms treated with DMSO revealed the typical healthy status of 529 schistosomula (panel A), showing preserved tegumental spines (panel C). These images 530 corroborate our conclusions that the MC3935 treatment led to schistosomula death. In this 531 respect, it is reasonable to assume that the survival of these worms (note in panels B and D 532 the depth of tegumental damage) could not be rescued even by the eventual withdrawal of the 533 inhibitor. 534 
Transmission electron microscopy of DMSO-treated schistosomula revealed preserved 543 ultrastructures in the worms (Fig 6, panels A, 
Analysis of the adult male tegument and its oral sucker by scanning electron 580 microscopy showed significant alterations upon MC3935 treatment (Fig 7, right panels) , 581 when compared to the control worms (Fig 7, left panels) . A detailed inspection of the SEM 582 images revealed extensive damage in the dorsal tegument of the male worms that were treated 583 with the LSD1 inhibitor, with the presence of a large number of blisters (Fig 7B and D,  584 yellow arrowheads), as well as fissures and holes in the tubercles (Fig 7B and D, yellow  585 arrows). Blisters and fissures were also seen in the male oral sucker (Fig 7F, yellow arrows,  586 and arrowheads). Confocal laser scanning microscopy (CLSM) showed important alterations 587 of the sexual organs of MC3935-treated male or female parasites (Fig 7H and J) . It is worth 588 noting the deleterious effect of the LSD1 inhibitor in the involution of the ovary, leading to a 589 reduced number of mature or immature oocytes (Fig 7, compare panels G and H) . The 590
inhibitor also generated severe disorganization of the testicular lobes, culminating in a 591 significantly reduced number of spermatocytes (Fig 7, 
We performed RNA sequencing (RNA-Seq) analysis to evaluate the effect of LSD1 inhibition on global gene transcription in S. mansoni. Unsupervised hierarchical clustering analysis of RNA-seq data depicted the changes in global gene expression profile in males, females, or schistosomula upon treatment with MC3935 (Fig 8) . Interestingly, inhibition of SmLSD1 significantly modulated 3608 transcribed genes in male, female or schistosomula, with 1964 being downregulated, and 1644 being upregulated (Fig 8A) . The highest modulation of gene expression was observed in male worms, for either up-or downregulation . Importantly, when we analyzed commonly regulated genes in male, female, or schistosomula, we found 220 and 50 genes down-or upregulated, respectively (Fig 8A) . The complete lists of significantly upregulated genes in each female, male or schistosomula (Tables S1-S3), downregulated genes in each females, males or schistosomula (Tables S4-S6) , down-or upregulated genes in common between females and males (Tables S7 and S8 , respectively) are presented in the supporting information. It is noteworthy that in schistosomula, a smaller number of consensus of differentially expressed genes (DEGs) was detected when compared with adult worms (Fig. 8A) .
A clear profile of the differential gene expression between control and MC3935treated parasites is depicted in the heatmap (Fig. 8B) , which confirmed that the treatment led to a significant change in the regulation of genes in females, males and schistosomula, with many genes being either up- (Fig. 8B , red) or downregulated (Fig. 8B, blue) . A closer look at the twenty most differentially expressed genes in females, males or schistosomula revealed that inhibition of SmLSD1 by MC3935 changed the levels of expression of genes belonging to different critical biological processes, including protein and lipid degradation, RNA processing, calcium and sodium homeostasis, antioxidants and transcription factors (Tables S9-S11). Within this list, genes encoding proteases stood out as being downregulated in MC3935-treated schistosomula, males and females as compared to DMSO-treated parasites (Tables S9-S11, shaded in green). Genes encoding protease inhibitors were upregulated in females and males (Tables S9 and S10, shaded in dark green).
Importantly, genes of the digestive system of S. mansoni were found down-or upregulated (Tables S9-S11, shaded in green with *).
Genes encoding kinases and phosphatases were upregulated in treated females and males (Tables S9 and S10, shaded pink and yellow, respectively). Overall, the analysis of the twenty most differentially expressed genes in treated males revealed a more heterogeneous gene expression profile (Table S10 ). Of note, in MC3935-treated schistosomula, a significant number of genes encoding proteins involved in RNA metabolism were upregulated (Table   S11 , shaded in blue). Downregulated genes encoding proteases stood out in treated schistosomula (Table S11, shaded in green).
We conducted dsRNAi experiments in adult worm pairs and were able to achieve 70% silencing of SmLSD1 transcription at day 7 ( Supplementary Fig S6A and B) . Western blot analysis of protein extracts from silenced adult worm pairs revealed a 2-fold inhibition of SmLSD1 demethylase activity (Supplementary Fig S6C) . By monitoring the behavior of the worms on a daily basis, we clearly observed progressive harm in whole-worm physiology during SmLSD1 silencing, which culminated in significant unpairing of male and female worms, a decrease of nearly 50% in the number of laid eggs, low motility and compromised surface adherence by the oral sucker of male worms ( Supplementary Fig S6D -F) . Silencing of SmLSD1 promoted damage to the oral sucker of male worms (Supplementary Fig S6G) .
Of note, the silencing of the parasites with the control dsRNAi showed no decrease in SmLSD1 gene expression or activity and no deleterious effects in the worms ( Supplementary   Fig S6, dsGFP) 
Lysine-specific demethylase 1 (LSD1) is an epigenetic enzyme that oxidatively cleaves methyl groups from mono and dimethyl Lysine 4 of histone H3 (H3K4me1/2) and can contribute to gene silencing (38) (39) (40) (41) . Since its discovery, LSD1 histone demethylase activity has been investigated as a pharmacologic target for cancer and other diseases. As part of a continuing effort of several different investigators to identify epigenetic modifications as therapeutic targets to control schistosomiasis, a recent paper published during our study also identified S. mansoni LSD1 (SmLSD1) as an additional promising drug candidate (17) . In the present study, we provide evidence that SmLSD1 plays important biological roles in the physiology of S. mansoni and that inhibition of SmLSD1 by a novel, selective, and potent LSD1 synthetic inhibitor MC3935 is detrimental to the survival of juvenile and adult worms.
MC3935 was synthesized based on the scaffold of the nonselective and irreversible monoamine oxidase (MAO) inhibitor tranylcypromine (TCP) (29, 42) . Tranylcypromine is a mechanism-based suicide inhibitor of MAO and LSD1; it covalently binds to the FAD cofactor embedded within the protein, thus abolishing enzymatic catalysis (43) . Importantly, MC3935 showed a 1,000 fold higher inhibitory activity than TCP, in vitro. In addition, our in silico molecular docking indicated that MC3935 could indeed be an effective SmLSD1 inhibitor and that the inhibition also relied on the amino-oxidase-like catalytic domain.
Toxicity assays on S. mansoni parasites using each of our 11 synthetic putative LSD1 inhibitors, as well as TCP, revealed MC3935 as the most powerful, with TCP showing the lowest toxicity toward the worms. This was a surprising result if we consider that both MC3935 and TCP (44) should adopt a similar orientation in their binding to the catalytic site of SmLSD1, based on our in silico molecular docking. However, one could always assume that the lack of toxicity of TCP was due to its lower permeability to the tegument of S. mansoni or that it is more metabolically labile. Indeed, MC3935 fills better the catalytic tuibe of the enzyme than TCP, due to its addiotional ethynylbenzamide portion, which allows additional interaction into the tube. Importantly, our western blot analyses indicated that MC3935 specifically inhibited H3K4 mono-and dimethylation, which are known LSD1 targets, but not H3K4 trimethylation, a mark that is targeted by the histone demethylases of the Jumonji family (doi: 10.1101/gad.1652908).
Genetic studies in numerous models have suggested that LSD1 plays a significant role in developmental processes (45) . LSD1 has also been reported to have a role in the DNA damage response (46) , repression of mitochondrial metabolism, lipid oxidation energy expenditure programs (47, 48) , and smooth muscle regeneration (49) . Additionally, germline murine knockouts exhibit embryonic lethality before E7.5: the egg cylinder fails to elongate and gastrulate, resulting in development arrest (50) . In C. elegans, the homolog spr-5 regulates Notch signaling (51, 52) , and maintains transgenerational epigenetic memory and fertility (53) . The yeast spLsd1/2 (54) and Drosophila Su(var)3-3 (55) homologs regulate gene silencing, which is required to guarantee normal oogenesis (56) and spermatogenesis (57) in Drosophila.
Taking into account the phenotypic effects observed in schistosomula or adult worms under the treatment with the LSD1 inhibitor MC3935, it can be assumed that SmLSD1 also plays important roles in the development and homeostasis of the tegument, muscle and sexual organs of S. mansoni. Although inhibition of SmLSD1 can have more pronounced effects on many other key biological processes or structures in S. mansoni, the tegument disruption would alone represent a desirable LSD1 target. The tegument of S. mansoni plays a crucial role in its protection against the host immune system (58) ; it is capable of absorbing nutrients and molecules, as well as excreting metabolites and synthesizing proteins (59, 60) . Inhibition of SmLSD1 activity, either by irreversible MC3935 binding (Fig 3A and B) or by partial knockdown of the SmLSD1 gene ( Supplementary Fig S6A and B) , generated pronounced damage in schistosomula or adult worms (Fig 5, Fig 7, and Supplementary Fig S6) , which likely made a major contribution to the observed mortality of the parasites within a short period of time (Fig 2, Fig 4, Supplementary Fig S3, Supplementary Fig S6, and Supplementary videos).
The musculatory activity is essential in several aspects of S. mansoni biology and physiology, including infection, pairing, feeding, regurgitation, reproduction and egg laying (61) (62) (63) . Our transmission electron microscopy revealed a complete lack of muscle layers in schistosomula treated with the LSD1 inhibitor (Fig 6) , which was accompanied by phenotypic defects observed in treated-worms, such as lack of motility, sucker adherence, egg laying and vitellaria contraction (Fig 2, Supplementary Fig S6 and Supplementary video S4) , that could be related to the compromised muscle structures.
Interestingly, the role of LSD1 in oogenesis and spermatogenesis seems to be conserved among different organisms, including human, C. elegans, Drosophila, and S. mansoni (this paper). Our confocal microscopy revealed significant alterations in the sexual organs of treated worm pairs, such as a reduced number of spermatocytes and oocytes (Fig 7H  and J) . These data are in agreement with the incapacity of the worms to produce eggs, even when remaining paired during the treament (see Supplementary Fig S4) .
Several diseases have been associated with aberrant histone methylation/demethylation patterns. Thus, considering that juvenile or adult S. mansoni are highly transcriptionally active and that SmLSD1 is expected to control the expression of a variety of different genes to maintain the homeostasis of the parasites, we compared their global transcriptional profiles after incubation with a sublethal dose of MC3935. Our RNAseq analysis revealed that inhibition of SmLSD1 led to the differential expression of genes involved in several different biological processes. These data suggest that SmLSD1 is recruited to target gene promoters by different transcription factors. Among the genes that were downregulated upon SmLSD1 inhibition in schistosomula, females and males, several proteases stood out (Tables S9-S11, shaded in green), mainly from the cathepsin family, including two hemoglobinases in female worms. This is an important finding considering that proteases are key components of the pathogenicity of the parasite; they facilitate tissue penetration and determine the nutritional sources of the parasite within intermediate and human hosts (64) . Importantly, two protease inhibitors were upregulated in females and males (Tables S9 and S10, shaded in dark green). That SmLSD1 controls the expression of genes of the digestive system of female or male worms was supported by the fact that a number of genes encoding enzymes or proteins of the digestive tract of the parasite (65) had modified expression in treated parasites (Tables S9-S11, shaded in green and with *). In this regard, it is noteworthy that blood digestion seemed to be severely compromised in females (see Supplementary Video S4).
Interestingly, we identified the SMDR2 gene as significantly downregulated in female worms treated with the LSD1 inhibitor (Table S9 , shaded in green and with #). SMDR2 is the schistosome homolog of P-glycoprotein (PgP) (66) , an ATP-dependent efflux pump, and its downregulation upon treatment might be involved in the high toxicity of MC3935 observed in females (see Supplementary Video S4).
Importantly, a significant number of proteins involved in RNA metabolism seemed to be specifically upregulated in schistosomula (Table S11, shaded in blue). This finding is of great importance since, although histone methylation has been only recently coupled to RNA processing (67) , this is the first report suggesting a role for LSD1 in regulating RNA metabolism.
The epigenetic regulation of chromatin affects many fundamental biological pathways.
Therefore, the realization that the deregulation of chromatin is harmful to S. mansoni should spark significant efforts to develop selective epigenetic drugs against schistosomiasis. The present study further promotes SmLSD1 as a strong candidate.