Biology subjects

Grosshans, H.

Publications and source records attributed to Grosshans, H..

16 recordsLinked to original sources

bioRxiv2026

Large transgene arrays cause aberrant transcription and synthetic molting defects with myrf-1 mutation

Multicopy transgene arrays remain widely used in C. elegans research. It is usually assumed that they behave neutrally, not impacting the phenotype under investigation. Here, we reveal that a previously reported heterochronic extra-molt phenotype associated with myrf-1(mg412) depends on the presence of the integrated molting reporter mgIs49. Nanopore long-read sequencing shows that mgIs49 is a massive 8.8-Mb insertion - around 50% of the size of its host chromosome - which disrupts the prmt-9 gene. Both mgIs49 and another array, maIs105, cause dysregulation of the transcriptome and accumulation of reads mapping to the promoter sequences used as components of the array. We identify additional arrays exceeding 4 Mb and show that variable molting defects occur across different transgenic lines when combined with myrf-1(mg412), implicating array size or composition in the synthetic phenotype. Our results underscore the necessity of replacing multicopy reporters in developmental studies with single-copy insertions or endogenous tagging whenever possible.

genetics↗

bioRxiv2026

let-7 miRNA and lin-46 mRNA are the two essential targets of the LIN28 RNA-binding protein in developmental timing

The RNA-binding protein (RBP) LIN28 is a key regulator of temporal cell fates, promoting stem cell identity and suppressing differentiation. It regulates the processing of the let-7 miRNA but additionally binds thousands of mRNAs, suggesting a model of coordinated regulation across many targets. Yet, direct evidence for such a network function is scarce for both LIN28 and other broadly binding RBPs. Here, we show that in C. elegans larvae, loss of LIN28 leaves the levels of most LIN28-bound transcripts unchanged. The only exceptions are the lin-46 mRNA and the let-7 miRNA. Comprehensive genetic analyses identify these two as the functionally essential LIN28 targets: lin-28; lin-46; let-7 triple null mutant animals exhibit complete suppression of the lin-28(0) precocious heterochronic phenotypes and recapitulate the retarded lin-46; let-7 double mutant phenotypes. Conversely, simultaneous overexpression of lin-46 and let-7 mimics LIN28 loss. Unexpectedly, LIN28 controls not only cell identity but also the tempo of development, using the same two targets. These findings establish a close functional link between the heterochronic pathway and the clock regulating developmental tempo and demonstrate that an RBP can achieve complex biological outcomes through a small set of targets.

developmental biology↗

bioRxiv2025

Cleavage of MEP-1 by DPF-3 Reveals Novel Substrate Specificity and Its Impact on Reproductive Fitness

Proteases are enzymes that catalyse the hydrolysis of peptide bonds in proteins for their functional, modification or degradation. Members of the Dipeptidyl Peptidase IV (DPPIV) family are exopeptidases that cleave dipeptides off the N-termini of their substrate peptides, typically after proline or alanine. Recently, we showed that human DPP4 and Caenorhabditis elegans DPF-3 have a larger target repertoire in vitro, permitting cleavage after additional amino acids. Here, we use TAILS (Terminal Amine Isotopic Labelling of Substrates) to identify DPF-3 targets in vivo and observe cleavage of MEP-1 after threonine, confirming a broader substrate specificity of DPF-3 also in vivo. Demonstrating physiological relevance, we show that rendering MEP-1 resistant to cleavage disrupts its stability, leading to developmental abnormalities such as defective gonadal migration and reproductive issues. Collectively, our findings highlight a previously unappreciated complexity in the substrate specificity of DPPIV family proteases and suggest that their physiological roles may extend beyond what is currently known. IMPORTANTO_LIManuscripts submitted to Review Commons are peer reviewed in a journal-agnostic way. C_LIO_LIUpon transfer of the peer reviewed preprint to a journal, the referee reports will be available in full to the handling editor. C_LIO_LIThe identity of the referees will NOT be communicated to the authors unless the reviewers choose to sign their report. C_LIO_LIThe identity of the referee will be confidentially disclosed to any affiliate journals to which the manuscript is transferred. C_LI GUIDELINESO_LIFor reviewers: https://www.reviewcommons.org/reviewers C_LIO_LIFor authors: https://www.reviewcommons.org/authors C_LI CONTACTThe Review Commons office can be contacted directly at: office@reviewcommons.org

molecular biology↗

bioRxiv2025

A scheduler for rhythmic gene expression

Genetic oscillators drive precisely timed gene expression, crucial for development and physiology. Using the C. elegans molting clock as a model, we investigate how oscillators can schedule the orderly expression of thousands of genes. Single cell RNA sequencing reveals a broad peak phase dispersion in individual issues, mirrored by rhythmic changes in chromatin accessibility at thousands of regulatory elements identified by time-resolved ATAC-seq. We develop a linear model to predict chromatin dynamics based on the binding of >200 transcription factors. This identifies nine key regulators acting additively to determine the peak phase and amplitude of each regulatory element. Strikingly, these factors can also generate constitutive, non-rhythmic activity through destructive interference. Validating its power, the model accurately predicts the impact of GRH-1/Grainyhead perturbation on both chromatin and transcript dynamics. This work provides a conceptual framework for understanding how combinatorial, non-cooperative transcription factor binding schedules complex gene expression patterns in development and other dynamic biological processes.

systems biology↗

bioRxiv2024

A conserved chronobiological complex times C. elegans development

The mammalian PAS-domain protein PERIOD (PER) and its C. elegans orthologue LIN-42 have been proposed to constitute an evolutionary link between two distinct, circadian and developmental, timing systems. However, while the function of PER in animal circadian rhythms is well understood molecularly and mechanistically, this is not true for LIN-42s function in timing rhythmic development. Here, using targeted deletions, we find that the LIN-42 PAS domains are dispensable for the proteins function in timing molts. Instead, we observe arrhythmic molts upon deletion of a distinct sequence element, conserved with PER. We show that this element, designated CK1{delta}-binding domain (CK1BD), mediates stable binding to KIN-20, the C. elegans CK1{delta}/{varepsilon} orthologue. We demonstrate that CK1{delta} phosphorylates LIN-42 and define two conserved helical motifs in the CK1BD, CK1BD-A and CK1BD-B, that have distinct roles in controlling CK1{delta}-binding and kinase activity in vitro. KIN-20 and the LIN-42 CK1BD are required for proper molting timing in vivo, and loss of LIN-42 binding changes KIN-20 subcellular localization. The interactions mirror the central role of a stable circadian PER-CK1 complex in setting a robust [~]24-hour period. Hence, our results establish LIN-42/PER - KIN-20/CK1{delta}/{varepsilon} as a functionally conserved signaling module of two distinct chronobiological systems.

developmental biology↗

bioRxiv2023

Massively parallel mapping of substrate cleavage sites defines dipeptidyl peptidase four subsite cooperativity

Substrate specificity determines protease functions in physiology and in clinical and biotechnological application, yet quantitative cleavage information is often unavailable, biased, or limited to a small number of events. Here, we develop qPISA (quantitative Protease specificity Inference from Substrate Analysis) to study Dipeptidyl Peptidase Four (DPP4), a key regulator of blood glucose levels. We use mass spectrometry to quantify its effects on >40,000 peptides from a complex, commercially available peptide mixture. By determining substrate turnover instead of focusing on product identification, we can reveal cooperative interactions within DPP4s active pocket and derive a sequence motif that predicts activity quantitatively. qPISA distinguishes DPP4 from the related C. elegans DPF-3 (a DPP8/9 orthologue), and we relate the differences to structural features of the two enzymes. We demonstrate that qPISA can direct protein engineering efforts like stabilization of GLP-1, a key DPP4 substrate used in treatment of diabetes and obesity. Thus, qPISA offers a versatile approach for profiling protease and especially exopeptidase specificity, facilitating insight into enzyme mechanisms and biotechnological and clinical applications.

biochemistry↗

bioRxiv2023

Convergence of multiple RNA-silencing pathways on GW182/TNRC6

The RNA-binding protein TRIM71/LIN-41 is a phylogenetically conserved developmental regulator that functions in mammalian stem cell reprogramming, brain development and cancer. TRIM71 recognizes target mRNAs through hairpin motifs and silences them through molecular mechanisms that await identification. Here, we uncover that TRIM71 silences its targets by recruiting TNRC6/GW182, a core component of the miRNA-induced silencing complex (miRISC). Co-immunoprecipitation reveals interaction of TNRC6A with additional RNA-binding proteins and we demonstrate that AGO2, TRIM71, and UPF1 each recruit TNRC6 to specific, largely distinct sets of transcripts to silence them. As cellular TNRC6 levels are limiting, competition occurs among the silencing pathways, such that loss of AGO2 protein, or of AGO2 binding to TNRC6, enhances the activities of the other pathways. We conclude that a miRNA-like silencing activity is shared among different mRNA silencing pathways and that use of TNRC6 as a central hub provides a means to integrate their activities.

molecular biology↗

bioRxiv2022

The Grainyhead/LSF transcription factor GRH-1 is rhythmically required for molting

Molting, that is, the synthesis and shedding of a cuticular exoskeleton, is a defining characteristic of ecdysozoa. In nematodes such as C. elegans, molts rhythmically terminate each of four larval stages. The molting cycle is tightly coupled to the rhythmic accumulation of thousands of transcripts. Here, using chromatin immunoprecipitation coupled to sequencing (ChIP-seq) and quantitative reporter assays, we show that these dynamic gene expression patterns rely on rhythmic transcription. To gain insight into the relevant gene regulatory networks (GRNs), we performed an RNAi-based screen for transcription factors required for molting to identify potential components of a molting clock. We find that depletion of GRH-1, BLMP-1, NHR-23, NHR-25, MYRF-1 or BED-3 impairs progression through the molting cycle. We characterize GRH-1, a Grainyhead/LSF transcription factor whose orthologues in other animals are key epithelial cell fate regulators. We show that GRH-1 depletion causes a dose-dependent extension of molt duration, defects in cuticle formation and shedding, and larval death. Coincident with its rhythmic accumulation, GRH-1 is required repetitively for each molt, during specific time windows preceding lethargus. These findings are consistent with a function of GRH-1 in a molting cycle GRN. As its mammalian orthologues, as well as those of BLMP-1 and NHR-23, have been implicated in rhythmic homeostatic skin regeneration in mouse, the mechanisms underlying rhythmic C. elegans molting may apply beyond nematodes.

developmental biology↗

bioRxiv2021

The BLMP-1 transcription factor promotes oscillatory gene expression to achieve timely molting

Gene expression oscillators can coordinate developmental events in space and time. In C. elegans, a gene expression oscillator directs rhythmic accumulation of [~]25% of the transcriptome, and thus thousands of transcripts, presumably to control molting, a process of rhythmic skin regeneration. Recently, a reverse genetic screen identified several transcription factors important for molting. Here, we characterize one of these, BLMP-1, orthologous to the mammalian transcription repressor PRDM1. We find it to be important for timely molting, and oscillatory gene expression. We propose a dual function for BLMP-1 in shaping oscillatory gene expression and coupling it to a set of direct targets, which ensures cuticular integrity. With mammalian PRDM1/BLIMP1 promoting regular cycles of postnatal hair follicle regeneration, our findings point to the possible existence of a fundamentally conserved clock mechanism in control of rhythmic skin regeneration.

developmental biology↗

bioRxiv2021

A folder mechanism ensures size uniformity among C. elegans individuals by coupling growth and development

Animals increase by orders of magnitude in their volume during development. Hence, even small differences in the growth rates between individuals could generate large differences in their adult body size. Yet, such volume divergence among individuals is usually not observed in nature. We combined theory and experiment to understand the mechanisms of body size uniformity. Using live imaging, we measured the volume growth of hundreds of individuals of C. elegans over the entire span of their postembryonic development. We find that C. elegans grows exponentially in volume with a coefficient of variation of the growth rate of [~]7%, but that individuals diverge much less in volume than expected from this heterogeneity. The mechanism counteracting size divergence does not involve size thresholds for developmental milestones. Instead, an inverse coupling of the growth rate and the duration of development produces a constant volume fold change per larval stage. The duration of larval stages of C. elegans is determined by the period of a developmental oscillator. Using mathematical modelling, we show that an anti-correlation between the growth rate and the oscillatory period emerges as an intrinsic property of a genetic oscillator. We propose that the robustness of body volume fold change is a hard-wired characteristic of the oscillatory circuit and does not require elaborate mechanisms of size control by cellular signalling. Indeed, the coupling of growth and development was unaltered by mutation of canonical pathways of growth control. This novel concept of size homeostasis may broadly apply to other multicellular systems controlled by genetic oscillators.

developmental biology↗

bioRxiv2020

Protease-mediated processing of Argonaute proteins controls small RNA association

Small RNA pathways defend the germlines of animals against selfish genetic elements and help to maintain genomic integrity. At the same time, their activity needs to be well-controlled to prevent silencing of self genes. Here, we reveal a proteolytic mechanism that controls endogenous small interfering (22G) RNA activity in the Caenorhabditis elegans germline to protect genome integrity and maintain fertility. We find that WAGO-1 and WAGO-3 Argonaute (Ago) proteins are matured through proteolytic processing of their unusually proline-rich N-termini. In the absence of DPF-3, a P-granule-localized N-terminal dipeptidase orthologous to mammalian DPP8/9, processing fails, causing a change of identity of 22G RNAs bound to these WAGO proteins. Desilencing of repeat- and transposon-derived transcripts, DNA damage and acute sterility ensue. These phenotypes are recapitulated when WAGO-1 and WAGO-3 are rendered resistant to DFP-3-mediated processing, identifying them as critical substrates of DPF-3. We conclude that N-terminal processing of Ago proteins regulates their activity and promotes discrimination of self from non-self by ensuring association with the proper complement of small RNAs. Graphical Abstract: The role of DPF-3 in the fertility of the animals O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY In wild type animals, the WAGO-1 and WAGO-3 Argonaute proteins are produced as immature pro-proteins with N-termini (N) that are unusually rich in prolines (P). N-terminal processing by DPF-3 is required for loading of the proper small RNA cargo and stabilization of WAGO-3. Accordingly, loss of this processing activity causes desilencing of transposable elements (TE), cell death and sterility.

molecular biology↗

bioRxiv2019

Two parallel arms of the heterochronic pathway direct coordinated juvenile-to-adult transition through distinct LIN-29 isoforms

Robust organismal development relies on temporal coordination of disparate physiological processes. In Caenorhabditis elegans, the timely transition from juvenile to adult is controlled by the heterochronic pathway, a regulatory cascade of conserved proteins and small RNAs. The heterochronic pathway culminates in accumulation of the transcription factor LIN-29, which triggers coordinated execution of juvenile-to-adult (J/A) transition events. Here, we reveal that two LIN-29 isoforms fulfill distinct functions during the J/A transition. We show that the functional differences between the isoforms do not stem from differences in their sequences, but from their distinct spatiotemporal expression, and we propose that distinct LIN-29 dose sensitivities of the individual J/A transition events help to ensure their temporal ordering. We demonstrate that unique lin-29 isoform expression patterns are generated by the RNA-binding protein LIN-41 for lin-29a, and the transcription factor HBL-1 for lin-29b. By regulating both HBL-1 and LIN-41, the RNA-binding protein LIN-28 coordinates LIN-29 isoform activity. Thus, our findings reveal that a coordinated transition from juvenile to adult involves branching of a linear pathway to achieve timely control of multiple events.

developmental biology↗

bioRxiv2019

State transitions of a developmental oscillator

Gene expression oscillators can structure biological events temporally and spatially. Different biological functions benefit from distinct oscillator properties. Thus, finite developmental processes rely on oscillators that start and stop at specific times; a poorly understood behavior. Here, we have characterized a massive gene expression oscillator comprising >3,700 genes in C. elegans larvae. We report that oscillations initiate in embryos, arrest transiently after hatching and in response to perturbation, and cease in adults. Experimental observation of the transitions between oscillatory and non-oscillatory states at a resolution where we can identify bifurcation points reveals an oscillator operating near a Saddle Node on Invariant Cycle (SNIC) bifurcation. These findings constrain the architecture and mathematical models that can represent this oscillator. They also reveal that oscillator arrests occur reproducibly in a specific phase. Since we find oscillations to be coupled to developmental processes, including molting, this characteristic of SNIC bifurcations thus endows the oscillator with the potential to halt larval development at defined intervals, and thereby execute a developmental checkpoint function.

systems biology↗

bioRxiv2018

let-7 controls the transition to adulthood by releasing select transcriptional regulators from repression by LIN41

Development of multicellular organisms relies on faithful temporal control of cell fates. In Caenorhabditis elegans, the heterochronic pathway governs temporal patterning of somatic cells. This function may be phylogenetically conserved as several heterochronic genes have mammalian orthologues, and as the heterochronic let-7 miRNA and its regulator LIN28 appear to time the onset of puberty in mice and humans. Here, we have investigated how let-7 promotes the transition to adulthood in C. elegans. We find that let-7 controls each of three relevant processes, namely male and female sexual organ morphogenesis as well as changes in skin progenitor cell fates, through the same single target, lin-41. LIN41 in turn silences two pairs of targets post-transcriptionally, by binding and silencing their mRNAs. The EGR-type transcription factor LIN-29a and its co-factor, the NAB1/2 orthologous MAB-10, mediate control of progenitor cell fates and vulval integrity. By contrast, male tail development depends on regulation of the DM domain-containing transcription factors DMD-3 and MAB-3. Our results provide mechanistic insight into an exemplary temporal patterning pathway, demonstrate that let-7 - LIN41 function as a versatile regulatory module that can be connected to different outputs, and reveal how several levels of post-transcriptional regulation ultimately achieve effects through controlling transcriptional outputs.

developmental biology↗

bioRxiv2018

Timing mechanism of sexually dimorphic nervous system differentiation

In all animals, sexual differentiation of somatic tissue is precisely timed, yet the molecular mechanisms that control the timing of sexual differentiation, particularly in the brain, are poorly understood. We have used sexually dimorphic molecular, anatomical and behavioral features of the C. elegans nervous system to decipher a regulatory pathway that controls the precise timing of sexual differentiation. We find that the sexually dimorphic differentiation of postmitotic neurons in the male nervous system is abrogated in animals that carry a mutation in the miRNA let-7 and prematurely executed in animals either lacking the let-7 inhibitor lin-28, or the direct let-7 target lin-41, an RNA-binding, posttranscriptional regulator. We show that an isoform of a phylogenetically conserved transcription factor, lin-29a, is a critical target of LIN-41 in controlling sexual maturation of sex-shared neurons. lin-29a is expressed in a male-specific manner in a subset of sex-shared neurons at the onset of sexual maturation. lin-29a acts cell-autonomously in these neurons to control the expression of sexually dimorphic neurotransmitter switches, sensory receptor expression, neurite anatomy and connectivity, and locomotor behavior. lin-29a is not only required but also sufficient to impose male-specific features at earlier stages of development and in the opposite sex. The temporal, sexual and spatial specificity of lin-29a expression is controlled intersectionally through the lin-28/let-7/lin-41 heterochronic pathway, sex chromosome configuration and neuron type-specific terminal selector transcription factors. Two Doublesex-like transcription factors represent additional neuron-type specific targets of LIN-41 and are regulated in a similar intersectional manner, indicating the existence of modular outputs downstream of the heterochronic pathway. In conclusion, we have provided insights into the molecular logic of the timing of sexual differentiation in the C. elegans nervous system. Remarkably, the lin28/let7 axis also controls the timing of sexual differentiation in mice and humans thereby hinting toward a striking universality of the control mechanisms of sexual differentiation.

neuroscience↗

bioRxiv2017

Interplay of target site architecture and miRNA abundance determine miRNA activity and specificity

The recognition that the miRNA seed sequence is a major determinant of miRNA activity has greatly advanced the ability to predict miRNA targets. However, it has remained unclear to what extent miRNAs act redundantly when they are members of the same family and thus share a common seed. Using in vivo studies in C. elegans, we uncover features that drive specific target repression by individual miRNA family members. We find that seed-distal complementarity to a specific family member promotes specificity. However, the extent and robustness of specificity are greatly increased by seed match imperfections, such as bulges and G:U wobble base pairs. Depending on the seed match architecture, specificity may be overcome by increasing the levels of a miRNA lacking seed-distal complementarity. Hence, in contrast to a binary distinction between functional and non-functional target sites, our data support a model where functionality depends on a combination of target site quality and miRNA abundance. This emphasizes the importance of studying miRNAs under physiological conditions in their endogenous contexts.

molecular biology↗