Biology subjects

Frand, A. R.

Publications and source records attributed to Frand, A. R..

5 recordsLinked to original sources

bioRxiv2026

FOXO/DAF-16 modulates the transcription factor ROR/NHR-23 and inhibits the let-7 microRNA to maintain multipotency during dauer

Animals rapidly reprogram gene expression to adapt development to environmental stress. How gene regulatory programs that drive continuous development are repressed during stress-induced developmental arrest remains poorly understood. In Caenorhabditis elegans, starvation and overcrowding trigger entry into the stress-resistant, quiescent dauer stage. Here, we identify interactions among the conserved transcription factors DAF-16/FOXO and NHR-23/ROR, and the let-7 family of microRNAs as key regulators of the switch from continuous development to dauer. We show that loss of daf-16 during dauer causes elevated let-7 family microRNAs and premature expression of the adult collagen reporter col-19p::GFP. Reducing let-7 family activity suppresses this phenotype, whereas dauer-specific let-7 expression is sufficient to induce col-19p::GFP expression. Mechanistically, DAF-16 inhibits let-7 transcription in part by repressing nhr-23, which encodes a transcriptional activator of the let-7 family and molting-cycle genes. ChIP-seq analysis reveals DAF-16 binding upstream of nhr-23, and daf-16; daf-7 mutant dauers exhibit increased nhr-23 mRNA and NHR-23 protein, supporting a model in which DAF-16 directly represses nhr-23. Integrated ChIP-seq and transcriptomic analyses identify 1,183 genes activated and 681 genes repressed by DAF-16 during dauer. Repressed targets are enriched for pro-growth genes involved in mitotic DNA replication and translational elongation. DAF-16 targets include 59 transcription factors that may mediate broader transcriptional reprogramming during dauer to maintain multipotency and establish quiescence. Together, these findings reveal that DAF-16/FOXO establishes stress-induced developmental arrest by coupling activation of protective pathways with repression of conserved developmental timing, growth, and differentiation programs. Significance statementAnimals often pause development during environmental stress and then resume normal development when conditions improve. How developmental programs are temporarily halted without disrupting later cell fates remains poorly understood. We show that, during stress-induced dauer arrest in C. elegans, the conserved FOXO transcription factor DAF-16 represses the differentiation-promoting let-7 microRNA pathway. DAF-16 inhibits the ROR homolog NHR-23, which normally activates let-7 and molting-cycle genes. Genome-wide analyses further show that DAF-16 both activates stress-response genes and represses growth and developmental genes. These findings reveal how a conserved stress-responsive factor coordinates survival, developmental arrest, and maintenance of cellular multipotency.

molecular biology↗

bioRxiv2021

A transient apical extracellular matrix relays cytoskeletal patterns to shape permanent acellular ridges on the surface of adult C. elegans

Apical extracellular matrices can form protruding structures such as denticles, ridges, scales, or teeth on the surfaces of epithelia. The mechanisms that shape these structures remain poorly understood. Here, we show how the actin cytoskeleton and a provisional matrix work together to sculpt acellular longitudinal alae ridges in the cuticle of adult C. elegans. Transient actomyosin-dependent constriction of the underlying lateral epidermis accompanies deposition of the provisional matrix at the earliest stages of alae formation. Actin is required to pattern the provisional matrix into longitudinal bands that are initially offset from the pattern of longitudinal actin filaments. These bands appear ultrastructurally as alternating regions of adhesion and separation within laminated provisional matrix layers. The provisional matrix is required to establish these demarcated zones of adhesion and separation, which ultimately give rise to alae ridges and their intervening valleys, respectively. Provisional matrix proteins shape the alae ridges and valleys but are not present within the final structure. We propose a morphogenetic mechanism wherein cortical actin patterns are relayed mechanically to the laminated provisional matrix to set up distinct zones of matrix layer separation and accretion that shape a permanent and acellular matrix structure.

developmental biology↗

bioRxiv2020

A multi-layered and dynamic apical extracellular matrix shapes the vulva lumen in Caenorhabditis elegans

Biological tubes must develop and maintain their proper diameter in order to transport materials efficiently. These tubes are molded and protected in part by apical extracellular matrices (aECMs) that line their lumens. Despite their importance, aECMs are difficult to image in vivo and therefore poorly understood. The C. elegans vulva has been a paradigm for understanding many aspects of organogenesis. Here we describe the vulva luminal matrix, which contains chondroitin proteoglycans, Zona Pellucida (ZP) domain proteins, and other glycoproteins and lipid transporters related to those in mammals. Confocal and transmission electron microscopy revealed, with unprecedented detail, a complex and dynamic aECM. Different matrix factors assemble on the apical surfaces of each vulva cell type, with clear distinctions seen between Ras-dependent (1{degrees}) and Notch-dependent (2{degrees}) cell types. Genetic perturbations suggest that chondroitin and other aECM factors together generate a structured scaffold that both expands and constricts lumen shape.

developmental biology↗

bioRxiv2018

A Regulatory Loop between the Retinoid-Related Orphan Nuclear Receptor NHR-23 and let-7 family microRNAs Modulates the C. elegans Molting Cycle

Animal development requires coordination among cyclic processes, sequential cell fate specifications, and once-a-lifetime morphogenic events, but the underlying mechanisms are not well understood. C. elegans undergo four molts at regular 8-10 h intervals. The pace of the cycle is governed by PERIOD/lin-42 and other as-yet unknown factors. Cessation of the cycle in young adults is controlled by the let-7 family of microRNAs and downstream transcription factors in the heterochronic pathway. Here, we characterize a negative feedback loop between NHR-23, the worm homolog of mammalian retinoid-related orphan receptors (RORs), and the let-7 family of microRNAs that regulates both the frequency and finite number of molts. The molting cycle is decelerated in nhr-23 knockdowns, accelerated in let-7(-) mutants, and similar to wild type animals in let-7(-) nhr-23(-) double mutants. NHR-23 binds response elements (ROREs) in the let-7 promoter and activates transcription. In turn, let-7 dampens nhr-23 expression across development via a complementary let-7 binding site (LCS) in the nhr-23 3' UTR. The molecular interactions between NHR-23 and let-7 hold true for other let-7 family microRNAs. Either derepression of nhr-23 transcripts by LCS deletion or high gene dosage of nhr-23 leads to protracted behavioral quiescence and extra molts in adults. NHR-23 and let-7 also co-regulate scores of genes required for execution of the molts, including lin-42. In addition, ROREs and LCSs isolated from mammalian ROR and let-7 genes function in C. elegans, suggesting conservation of this feedback mechanism. We propose that this feedback loop unites the molting timer and the heterochronic gene regulatory network possibly by functioning as a cycle counter.

developmental biology↗

bioRxiv2018

Non-canonical apical constriction shapes emergent matrices in C. elegans

Specialized epithelia produce apical matrices with distinctive topographies by enigmatic mechanisms. Here, we describe a holistic mechanism that integrates cortical actomyosin dynamics with apical matrix remodeling to pattern C. elegans cuticles. Therein, axial AFBs appear near the surface of lateral epidermal syncytia during an interval of transverse apical constriction (AC). AC gives rise to three temporary semi-circular cellular protrusions beneath a provisional matrix (sheath). In turn, sheath components pattern durable ridges along the midline of adult cuticles (alae). We propose that forces generated by AC are relayed via the sheath to sculpt the the acellular adult cuticle manifest several hours later. Furthermore, we provide evidence that circumferential actin filament bundles (CFBs) near the surface of the adjacent syncytia (hyp7) are largely dispensable for the propagation of annular cuticle structures from one larval stage to the next. Rather, the temporary CFBs extend from actin bundles overlying body wall muscles, which are situated between Ce. hemidesmosomes. Similar mechanisms may contribute to the morphogenesis of integumentary organs in higher metazoans.

developmental biology↗