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Gibson SB, Ness-Cohn E, Andersen EC. Benzimidazoles cause lethality by inhibiting the function of Caenorhabditis elegans neuronal beta-tubulin. Int J Parasitol Drugs Drug Resist 2022; 20:89-96. [PMID: 36332489 PMCID: PMC9771835 DOI: 10.1016/j.ijpddr.2022.10.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 10/17/2022] [Accepted: 10/18/2022] [Indexed: 11/08/2022]
Abstract
Parasitic nematode infections cause an enormous global burden to both humans and livestock. Resistance to the limited arsenal of anthelmintic drugs used to combat these infections is widespread, including benzimidazole (BZ) compounds. Previous studies using the free-living nematode Caenorhabditis elegans to model parasitic nematode resistance have shown that loss-of-function mutations in the beta-tubulin gene ben-1 confer resistance to BZ drugs. However, the mechanism of resistance and the tissue-specific susceptibility are not well known in any nematode species. To identify in which tissue(s) ben-1 function underlies BZ susceptibility, transgenic strains that express ben-1 in different tissues, including hypodermis, muscles, neurons, intestine, and ubiquitous expression were generated. High-throughput fitness assays were performed to measure and compare the quantitative responses to BZ compounds among different transgenic lines. Significant BZ susceptibility was observed in animals expressing ben-1 in neurons, comparable to expression using the ben-1 promoter. This result suggests that ben-1 function in neurons underlies susceptibility to BZ. Subsetting neuronal expression of ben-1 based on the neurotransmitter system further restricted ben-1 function in cholinergic neurons to cause BZ susceptibility. These results better inform our current understanding of the cellular mode of action of BZs and also suggest additional treatments that might potentiate the effects of BZs in neurons.
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Affiliation(s)
- Sophia B. Gibson
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA
| | - Elan Ness-Cohn
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA,Driskill Graduate Program in Life Sciences, Northwestern University, Chicago, IL, 60611, USA
| | - Erik C. Andersen
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA,Corresponding author. Department of Molecular Biosciences Northwestern University 4619 Silverman Hall 2205 Tech Drive Evanston, IL, 60208, USA.
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2
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Widespread employment of conserved C. elegans homeobox genes in neuronal identity specification. PLoS Genet 2022; 18:e1010372. [PMID: 36178933 PMCID: PMC9524666 DOI: 10.1371/journal.pgen.1010372] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 08/03/2022] [Indexed: 11/20/2022] Open
Abstract
Homeobox genes are prominent regulators of neuronal identity, but the extent to which their function has been probed in animal nervous systems remains limited. In the nematode Caenorhabditis elegans, each individual neuron class is defined by the expression of unique combinations of homeobox genes, prompting the question of whether each neuron class indeed requires a homeobox gene for its proper identity specification. We present here progress in addressing this question by extending previous mutant analysis of homeobox gene family members and describing multiple examples of homeobox gene function in different parts of the C. elegans nervous system. To probe homeobox function, we make use of a number of reporter gene tools, including a novel multicolor reporter transgene, NeuroPAL, which permits simultaneous monitoring of the execution of multiple differentiation programs throughout the entire nervous system. Using these tools, we add to the previous characterization of homeobox gene function by identifying neuronal differentiation defects for 14 homeobox genes in 24 distinct neuron classes that are mostly unrelated by location, function and lineage history. 12 of these 24 neuron classes had no homeobox gene function ascribed to them before, while in the other 12 neuron classes, we extend the combinatorial code of transcription factors required for specifying terminal differentiation programs. Furthermore, we demonstrate that in a particular lineage, homeotic identity transformations occur upon loss of a homeobox gene and we show that these transformations are the result of changes in homeobox codes. Combining the present with past analyses, 113 of the 118 neuron classes of C. elegans are now known to require a homeobox gene for proper execution of terminal differentiation programs. Such broad deployment indicates that homeobox function in neuronal identity specification may be an ancestral feature of animal nervous systems.
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Caenorhabditis elegans sine oculis/SIX-type homeobox genes act as homeotic switches to define neuronal subtype identities. Proc Natl Acad Sci U S A 2022; 119:e2206817119. [PMID: 36067313 PMCID: PMC9478639 DOI: 10.1073/pnas.2206817119] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Anatomical and molecular studies have revealed that in many animal nervous systems, neuronal cell types can often be subclassified into highly related subtypes with only small phenotypic differences. We decipher here the regulatory logic of such cell type diversification processes. We show that identity features of neurons that are highly similar to one another are controlled by master regulatory transcription factors and that phenotypic differences between related cell types are controlled by downstream acting transcription factors that promote or antagonize the ability of master regulatory factors to control unique identity features. Our findings help explain how neuronal cell types diversify and suggest hypothetical scenarios for neuronal cell-type evolution. The classification of neurons into distinct types reveals hierarchical taxonomic relationships that reflect the extent of similarity between neuronal cell types. At the base of such taxonomies are neuronal cells that are very similar to one another but differ in a small number of reproducible and select features. How are very similar members of a neuron class that share many features instructed to diversify into distinct subclasses? We show here that the six very similar members of the Caenorhabditis elegans IL2 sensory neuron class, which are all specified by a homeobox terminal selector, unc-86/BRN3, differentiate into two subtly distinct subclasses, a dorsoventral subclass and a lateral subclass, by the toggle switch–like action of the sine oculis/SIX homeobox gene unc-39. unc-39 is expressed only in the lateral IL2 neurons, and loss of unc-39 leads to a homeotic transformation of the lateral into the dorsoventral class; conversely, ectopic unc-39 expression converts the dorsoventral subclass into the lateral subclass. Hence, a terminal selector homeobox gene controls both class- as well as subclass-specific features, while a subordinate homeobox gene determines the ability of the class-specific homeobox gene to activate subtype-specific target genes. We find a similar regulatory mechanism operating in a distinct class of six motor neurons. Our findings underscore the importance of homeobox genes in neuronal identity control and invite speculations about homeotic identity transformations as potential drivers of evolutionary novelty during cell-type evolution in the brain.
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Leyva-Díaz E, Hobert O. Robust regulatory architecture of pan-neuronal gene expression. Curr Biol 2022; 32:1715-1727.e8. [PMID: 35259341 PMCID: PMC9050922 DOI: 10.1016/j.cub.2022.02.040] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 02/04/2022] [Accepted: 02/10/2022] [Indexed: 12/17/2022]
Abstract
Pan-neuronally expressed genes, such as genes involved in the synaptic vesicle cycle or in neuropeptide maturation, are critical for proper function of all neurons, but the transcriptional control mechanisms that direct such genes to all neurons of a nervous system remain poorly understood. We show here that six members of the CUT family of homeobox genes control pan-neuronal identity specification in Caenorhabditis elegans. Single CUT mutants show barely any effects on pan-neuronal gene expression or global nervous system function, but such effects become apparent and progressively worsen upon removal of additional CUT family members, indicating a critical role of gene dosage. Overexpression of each individual CUT gene rescued the phenotype of compound mutants, corroborating that gene dosage, rather than the activity of specific members of the gene family, is critical for CUT gene family function. Genome-wide binding profiles, as well as mutation of CUT homeodomain binding sites by CRISPR/Cas9 genome engineering show that CUT genes directly control the expression of pan-neuronal features. Moreover, CUT genes act in conjunction with neuron-type-specific transcription factors to control pan-neuronal gene expression. Our study, therefore, provides a previously missing key insight into how neuronal gene expression programs are specified and reveals a highly buffered and robust mechanism that controls the most critical functional features of all neuronal cell types.
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Datta RR, Rister J. The power of the (imperfect) palindrome: Sequence-specific roles of palindromic motifs in gene regulation. Bioessays 2022; 44:e2100191. [PMID: 35195290 PMCID: PMC8957550 DOI: 10.1002/bies.202100191] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 02/01/2022] [Accepted: 02/03/2022] [Indexed: 12/22/2022]
Abstract
In human languages, a palindrome reads the same forward as backward (e.g., 'madam'). In regulatory DNA, a palindrome is an inverted sequence repeat that allows a transcription factor to bind as a homodimer or as a heterodimer with another type of transcription factor. Regulatory palindromes are typically imperfect, that is, the repeated sequences differ in at least one base pair, but the functional significance of this asymmetry remains poorly understood. Here, we review the use of imperfect palindromes in Drosophila photoreceptor differentiation and mammalian steroid receptor signaling. Moreover, we discuss mechanistic explanations for the predominance of imperfect palindromes over perfect palindromes in these two gene regulatory contexts. Lastly, we propose to elucidate whether specific imperfectly palindromic variants have specific regulatory functions in steroid receptor signaling and whether such variants can help predict transcriptional outcomes as well as the response of individual patients to drug treatments.
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Affiliation(s)
- Rhea R Datta
- Department of Biology, Hamilton College, Clinton, New York, USA
| | - Jens Rister
- Department of Biology, University of Massachusetts Boston, Integrated Sciences Complex, Boston, Massachusetts, USA
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6
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Poupault C, Choi D, Lam-Kamath K, Dewett D, Razzaq A, Bunker J, Perry A, Cho I, Rister J. A combinatorial cis-regulatory logic restricts color-sensing Rhodopsins to specific photoreceptor subsets in Drosophila. PLoS Genet 2021; 17:e1009613. [PMID: 34161320 PMCID: PMC8259978 DOI: 10.1371/journal.pgen.1009613] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 07/06/2021] [Accepted: 05/19/2021] [Indexed: 11/18/2022] Open
Abstract
Color vision in Drosophila melanogaster is based on the expression of five different color-sensing Rhodopsin proteins in distinct subtypes of photoreceptor neurons. Promoter regions of less than 300 base pairs are sufficient to reproduce the unique, photoreceptor subtype-specific rhodopsin expression patterns. The underlying cis-regulatory logic remains poorly understood, but it has been proposed that the rhodopsin promoters have a bipartite structure: the distal promoter region directs the highly restricted expression in a specific photoreceptor subtype, while the proximal core promoter region provides general activation in all photoreceptors. Here, we investigate whether the rhodopsin promoters exhibit a strict specialization of their distal (subtype specificity) and proximal (general activation) promoter regions, or if both promoter regions contribute to generating the photoreceptor subtype-specific expression pattern. To distinguish between these two models, we analyze the expression patterns of a set of hybrid promoters that combine the distal promoter region of one rhodopsin with the proximal core promoter region of another rhodopsin. We find that the function of the proximal core promoter regions extends beyond providing general activation: these regions play a previously underappreciated role in generating the non-overlapping expression patterns of the different rhodopsins. Therefore, cis-regulatory motifs in both the distal and the proximal core promoter regions recruit transcription factors that generate the unique rhodopsin patterns in a combinatorial manner. We compare this combinatorial regulatory logic to the regulatory logic of olfactory receptor genes and discuss potential implications for the evolution of rhodopsins. Each type of sensory receptor neuron in our body expresses a specific sensory receptor protein, which allows us to detect and discriminate a variety of environmental stimuli. The regulatory logic that controls this spatially precise and highly restricted expression of sensory receptor proteins remains poorly understood. As a model system, we study the mechanisms that control the expression of different color-sensing Rhodopsin proteins in distinct subtypes of Drosophila photoreceptors, which is the basis for color vision. Compact promoter regions of less than 300 base pairs are sufficient to reproduce the non-overlapping rhodopsin patterns. However, the regulatory logic that underlies the combination (sometimes called ‘grammar’) of the cis-regulatory motifs (sometimes called ‘vocabulary’) within the rhodopsin promoters remains poorly understood. Here, we find that specific combinations of cis-regulatory motifs in the distal and the proximal core promoter regions of each rhodopsin direct its unique expression pattern.
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Affiliation(s)
- Clara Poupault
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Diane Choi
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Khanh Lam-Kamath
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Deepshe Dewett
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Ansa Razzaq
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Joseph Bunker
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Alexis Perry
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Irene Cho
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
| | - Jens Rister
- Department of Biology, Integrated Sciences Complex, University of Massachusetts Boston, Boston, Massachusetts, United States of America
- * E-mail:
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7
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Mathews EA, Stroud D, Mullen GP, Gavriilidis G, Duerr JS, Rand JB, Hodgkin J. Allele-specific suppression in C. elegans reveals details of EMS mutagenesis and a possible moonlighting interaction between the vesicular acetylcholine transporter and ERD2 receptors. Genetics 2021; 218:6259149. [PMID: 33914877 PMCID: PMC8664489 DOI: 10.1093/genetics/iyab065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 04/17/2021] [Indexed: 11/12/2022] Open
Abstract
A missense mutant, unc-17(e245), which affects the Caenorhabditis elegans vesicular acetylcholine transporter UNC-17, has a severe uncoordinated phenotype, allowing efficient selection of dominant suppressors that revert this phenotype to wild-type. Such selections permitted isolation of numerous suppressors after EMS (ethyl methanesulfonate) mutagenesis, leading to demonstration of delays in mutation fixation after initial EMS treatment, as has been shown in T4 bacteriophage but not previously in eukaryotes. Three strong dominant extragenic suppressor loci have been defined, all of which act specifically on allele e245, which causes a G347R mutation in UNC-17. Two of the suppressors (sup-1 and sup-8/snb-1) have previously been shown to encode synaptic proteins able to interact directly with UNC-17. We found that the remaining suppressor, sup-2, corresponds to a mutation in erd-2.1, which encodes an endoplasmic reticulum retention protein; sup-2 causes a V186E missense mutation in transmembrane helix 7 of ERD-2.1. The same missense change introduced into the redundant paralogous gene erd-2.2 also suppressed unc-17(e245). Suppression presumably occurred by compensatory charge interactions between transmembrane helices of UNC-17 and ERD-2.1 or ERD-2.2, as previously proposed in work on suppression by SUP-1(G84E) or SUP-8(I97D)/synaptobrevin. erd-2.1(V186E) homozygotes were fully viable, but erd-2.1(V186E); erd-2.2(RNAi) exhibited synthetic lethality (like erd-2.1(RNAi); erd-2.2(RNAi)), indicating that the missense change in ERD-2.1 impairs its normal function in the secretory pathway but may allow it to adopt a novel moonlighting function as an unc-17 suppressor.
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Affiliation(s)
- Eleanor A Mathews
- Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA
| | - Dave Stroud
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
| | - Gregory P Mullen
- Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA
| | | | - Janet S Duerr
- Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA.,Department of Biological Sciences, Ohio University, Athens, Ohio 45701, USA
| | - James B Rand
- Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA.,Oklahoma Center for Neuroscience, Oklahoma City, Oklahoma 73104, USA
| | - Jonathan Hodgkin
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
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8
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Aghayeva U, Bhattacharya A, Sural S, Jaeger E, Churgin M, Fang-Yen C, Hobert O. DAF-16/FoxO and DAF-12/VDR control cellular plasticity both cell-autonomously and via interorgan signaling. PLoS Biol 2021; 19:e3001204. [PMID: 33891586 PMCID: PMC8099054 DOI: 10.1371/journal.pbio.3001204] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 05/05/2021] [Accepted: 03/23/2021] [Indexed: 01/08/2023] Open
Abstract
Many cell types display the remarkable ability to alter their cellular phenotype in response to specific external or internal signals. Such phenotypic plasticity is apparent in the nematode Caenorhabditis elegans when adverse environmental conditions trigger entry into the dauer diapause stage. This entry is accompanied by structural, molecular, and functional remodeling of a number of distinct tissue types of the animal, including its nervous system. The transcription factor (TF) effectors of 3 different hormonal signaling systems, the insulin-responsive DAF-16/FoxO TF, the TGFβ-responsive DAF-3/SMAD TF, and the steroid nuclear hormone receptor, DAF-12/VDR, a homolog of the vitamin D receptor (VDR), were previously shown to be required for entering the dauer arrest stage, but their cellular and temporal focus of action for the underlying cellular remodeling processes remained incompletely understood. Through the generation of conditional alleles that allowed us to spatially and temporally control gene activity, we show here that all 3 TFs are not only required to initiate tissue remodeling upon entry into the dauer stage, as shown before, but are also continuously required to maintain the remodeled state. We show that DAF-3/SMAD is required in sensory neurons to promote and then maintain animal-wide tissue remodeling events. In contrast, DAF-16/FoxO or DAF-12/VDR act cell-autonomously to control anatomical, molecular, and behavioral remodeling events in specific cell types. Intriguingly, we also uncover non-cell autonomous function of DAF-16/FoxO and DAF-12/VDR in nervous system remodeling, indicating the presence of several insulin-dependent interorgan signaling axes. Our findings provide novel perspectives into how hormonal systems control tissue remodeling.
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Affiliation(s)
- Ulkar Aghayeva
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Abhishek Bhattacharya
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Surojit Sural
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Eliza Jaeger
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Matthew Churgin
- Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Christopher Fang-Yen
- Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
- * E-mail:
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9
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Brovkina MV, Duffié R, Burtis AEC, Clowney EJ. Fruitless decommissions regulatory elements to implement cell-type-specific neuronal masculinization. PLoS Genet 2021; 17:e1009338. [PMID: 33600447 PMCID: PMC7924761 DOI: 10.1371/journal.pgen.1009338] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 03/02/2021] [Accepted: 01/04/2021] [Indexed: 01/12/2023] Open
Abstract
In the fruit fly Drosophila melanogaster, male-specific splicing and translation of the Fruitless transcription factor (FruM) alters the presence, anatomy, and/or connectivity of >60 types of central brain neurons that interconnect to generate male-typical behaviors. While the indispensable function of FruM in sex-specific behavior has been understood for decades, the molecular mechanisms underlying its activity remain unknown. Here, we take a genome-wide, brain-wide approach to identifying regulatory elements whose activity depends on the presence of FruM. We identify 436 high-confidence genomic regions differentially accessible in male fruitless neurons, validate candidate regions as bona fide, differentially regulated enhancers, and describe the particular cell types in which these enhancers are active. We find that individual enhancers are not activated universally but are dedicated to specific fru+ cell types. Aside from fru itself, genes are not dedicated to or common across the fru circuit; rather, FruM appears to masculinize each cell type differently, by tweaking expression of the same effector genes used in other circuits. Finally, we find FruM motifs enriched among regulatory elements that are open in the female but closed in the male. Together, these results suggest that FruM acts cell-type-specifically to decommission regulatory elements in male fruitless neurons. Courtship behavior in male Drosophila melanogaster is controlled by a well-defined neural circuit that is labeled by the male-specific transcription factor Fruitless (FruM). While FruM is known to change the number, anatomy and connectivity of neurons which comprise the circuit and has been suggested to repress the expression of a few gene targets, the mechanism of how FruM regulates genes across many different kinds of neurons is unknown. Using an approach to identify gene regulatory elements based on their chromatin accessibility states (ATAC-seq), we identified a large set of chromatin accessibility changes downstream of Fruitless. By examining the activity of these regulatory elements in vivo, we found that their activity was 1) sexually dimorphic and 2) specific to a single class of FruM neurons, suggesting that FruM acts on different chromatin targets in different neuron classes comprising the courtship circuit. Further, we found a known FruM-regulated enhancer of the FruM-repressed gene Lgr3 to have closed chromatin specifically in FruM neurons. Combined with an enrichment of FruM motifs in regions which are closed in FruM neurons, we present a mechanism where FruM directs the decommissioning of sex-shared regulatory elements to masculinize neurons in a cell-type specific manner.
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Affiliation(s)
- Margarita V. Brovkina
- Graduate Program in Cellular and Molecular Biology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Rachel Duffié
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York, United States of America
- Mortimer B. Zuckerman Mind Brain and Behavior Institute, Columbia University, New York, New York, United States of America
| | - Abbigayl E. C. Burtis
- Department of Molecular, Cellular, and Developmental Biology, The University of Michigan, Ann Arbor, Michigan, United States of America
| | - E. Josephine Clowney
- Department of Molecular, Cellular, and Developmental Biology, The University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail:
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10
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Abstract
Large amounts of effort have been invested in trying to understand how a single genome is able to specify the identity of hundreds of cell types. Inspired by some aspects of Caenorhabditis elegans biology, we implemented an in silico evolutionary strategy to produce gene regulatory networks (GRNs) that drive cell-specific gene expression patterns, mimicking the process of terminal cell differentiation. Dynamics of the gene regulatory networks are governed by a thermodynamic model of gene expression, which uses DNA sequences and transcription factor degenerate position weight matrixes as input. In a version of the model, we included chromatin accessibility. Experimentally, it has been determined that cell-specific and broadly expressed genes are regulated differently. In our in silico evolved GRNs, broadly expressed genes are regulated very redundantly and the architecture of their cis-regulatory modules is different, in accordance to what has been found in C. elegans and also in other systems. Finally, we found differences in topological positions in GRNs between these two classes of genes, which help to explain why broadly expressed genes are so resilient to mutations. Overall, our results offer an explanatory hypothesis on why broadly expressed genes are regulated so redundantly compared to cell-specific genes, which can be extrapolated to phenomena such as ChIP-seq HOT regions.
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Affiliation(s)
- Carlos Mora-Martinez
- Evo-devo Helsinki community, Centre of Excellence in Experimental and Computational Developmental Biology, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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