Biology subjects

McJunkin, K.

Publications and source records attributed to McJunkin, K..

9 recordsLinked to original sources

bioRxiv2025

A lncRNA drives developmentally-timed decay of all members of an essential microRNA family

The spatiotemporal expression patterns of microRNAs (miRNAs) are crucial to their function. Target-directed miRNA degradation (TDMD) is an emerging regulatory module that contributes to these expression patterns wherein a specialized RNA (TDMD trigger) drives miRNA decay through base pairing and resulting recruitment of E3 ubiquitin ligase ZSWIM8/EBAX-1. Extensive base pairing to the miRNA seed region and 3 end has been proposed as a key feature that distinguishes TDMD triggers from conventional mRNA targets of miRNAs, which primarily pair with the seed. Here we identify the long noncoding RNA, tts-2, as a TDMD trigger for mir-35-42, the most abundant miRNA family in C. elegans early embryos. We demonstrate that a single site in tts-2 drives decay through base pairing with the seed sequence shared by all eight family members. A second site in tts-2 supports decay of mir-38 with incomplete seed complementarity. Our findings demonstrate that extended base pairing is not a universal requirement for TDMD, and that TDMD drives developmentally-timed clearance of abundant miRNAs at the exit of C. elegans embryogenesis.

molecular biology↗

bioRxiv2025

A noncanonical Pol III-dependent, Microprocessor-independent biogenesis pathway generates a germline enriched miRNA family

MicroRNAs (miRNAs) are short RNAs that post-transcriptionally regulate gene expression. In canonical miRNA biogenesis, primary miRNAs are transcribed from intergenic loci or intronic regions by RNA polymerase II, sequentially cleaved by the Microprocessor complex and Dicer, and resulting mature miRNAs are loaded into Argonaute to repress target mRNAs. A minority of miRNAs are generated via noncanonical biogenesis pathways that bypass the Microprocessor and/or Dicer. Here, we describe a new Pol III-dependent, Microprocessor -independent, and Dicer-dependent biogenesis pathway exemplified by the mir-1829 family in C. elegans. Although the mir-1829 family loci reside in intronic regions of protein-coding genes, we show that the miRNAs are derived from independent Pol III transcripts. Unlike other Pol III-dependent miRNAs, the mir-1829 family small RNAs are the dominant species derived from their loci, rather than fragments of a larger functional noncoding RNA. These germline-enriched miRNAs are loaded in multiple miRNA Argonautes, including the recently-characterized germline Argonaute ALG-5, which we demonstrate is repressive when tethered to a reporter transcript. We extend these findings, identifying additional Pol III-transcribed and noncanonical small RNAs in C. elegans and human datasets, including human miR-4521. These young, noncanonical miRNAs may represent an early snapshot in the evolution of de novo miRNA genes.

molecular biology↗

bioRxiv2025

An intrinsically disordered region of Drosha selectively promotes miRNA biogenesis, independent of tissue-specific Microprocessor condensates

Precise control of miRNA biogenesis is of extreme importance, since mis-regulation of miRNAs underlies or exacerbates many disease states. The Microprocessor complex, composed of DROSHA and DGCR8, carries out the first cleavage step in canonical miRNA biogenesis. Despite recent advances in understanding the molecular mechanism of Microprocessor, the N-terminal region of DROSHA is less characterized due its high intrinsic disorder. Here we demonstrate that Microprocessor forms condensates with properties consistent with liquid-liquid phase separation (LLPS) in select tissues in C. elegans. While DRSH-1/Drosha recruitment to granules is only partially dependent on its intrinsically disordered regions (IDRs), one of these N-terminal IDRs is crucial for biogenesis of a subset of miRNAs and normal development. A cis region of IDR-dependent miRNAs confers IDR-dependence to another miRNA, suggesting that the IDR recognizes sequences or structures in the miRNA primary transcript. Future studies will further elucidate the specificity of this interaction and the putative role of Microprocessor condensates.

molecular biology↗

bioRxiv2024

The RNA-binding activity of the TRIM-NHL protein NHL-2 is essential for miRNA-mediated gene regulation

The conserved TRIM-NHL protein, NHL-2, plays a key role in small RNA pathways in Caenorhabditis elegans. NHL-2 has been shown to interact with U-rich RNA through its NHL domain, but the importance to its biological function is unknown. We defined the crystal structure of the NHL domain to 1.4 [A] resolution and identified residues that affect affinity for U-rich RNA. Functional analysis of an NHL-2 RNA-binding loss-of-function mutant demonstrated defects in the heterochronic pathway, suggesting that RNA binding is essential for its role in this miRNA pathway. Processing bodies were enlarged in the NHL-2 RNA-binding mutant, suggesting a defect in mRNA decay. We also identified the eIF4E binding protein IFET-1 as a strong synthetic interactor with NHL-2 and the DEAD box RNA helicase CGH-1 (DDX6), linking NHL-2 function to translation repression. We demonstrated that in the absence of NHL-2, there was an enrichment of miRNA transcripts associated with the miRNA pathway Argonaute proteins ALG-2 and ALG-2. We demonstrate that NHL-2 RNA-binding activity is essential for let-7 family miRNA-mediated translational repression. We conclude that the NHL-2, CGH-1, and IFET-1 regulatory axes work with the core miRISC components to form an effector complex that is required for some, but not all, miRNAs.

genetics↗

bioRxiv2023

The catalytic activity of microRNA Argonautes plays a modest role in microRNA star strand cleavage in C. elegans

Many Argonaute proteins can cleave RNA ("slicing") as part of the microRNA-induced silencing complex (miRISC), even though miRNA-mediated target repression is generally independent of target cleavage. Here we use genome editing in C. elegans to examine the role of miRNA-guided slicing in organismal development. In contrast to previous work, slicing-inactivating mutations did not interfere with normal development when introduced by CRISPR. We find that unwinding and decay of miRNA star strands is weakly defective in the absence of slicing, with the largest effect observed in embryos. Argonaute-Like Gene 2 (ALG-2) is more dependent on slicing for unwinding than ALG-1. The miRNAs that displayed the greatest (albeit minor) dependence on slicing for unwinding tend to form stable duplexes with their star strand, and in some cases, lowering duplex stability alleviates dependence on slicing. Gene expression changes were consistent with negligible to moderate loss of function for miRNA guides whose star strand was upregulated, suggesting a reduced proportion of mature miRISC in slicing mutants. While a few miRNA guide strands are reduced in the mutant background, the basis of this is unclear since changes were not dependent on EBAX-1, a factor in the Target-Directed miRNA Degradation (TDMD) pathway. Overall, this work defines a role for miRNA Argonaute slicing in star strand decay; future work should examine whether this role could have contributed to the selection pressure to conserve catalytic activity of miRNA Argonautes across the metazoan phylogeny.

molecular biology↗

bioRxiv2021

The developmentally-timed decay of an essential microRNA family is seed sequence-dependent

MicroRNA (miRNA) abundance is tightly controlled by regulation of biogenesis and decay. Here we show that the mir-35 miRNA family undergoes selective decay at the transition from embryonic to larval development in C. elegans. The seed sequence of the miRNA is necessary and largely sufficient for this regulation. Sequences outside the seed (3 end) regulate mir-35 abundance in the embryo but are not necessary for sharp decay at the transition to larval development. Enzymatic modifications of the miRNA 3 end are neither prevalent nor correlated with changes in decay, suggesting that miRNA 3 end display is not a core feature of this mechanism and further supporting a seed-driven decay model. Our findings demonstrate that seed sequence-specific decay can selectively and coherently regulate all redundant members of a miRNA seed family, a class of mechanism that has great biological and therapeutic potential for dynamic regulation of a miRNA familys target repertoire.

molecular biology↗

bioRxiv2021

Screening by deep sequencing reveals mediators of miRNA tailing in C. elegans

microRNAs are frequently modified by addition of untemplated nucleotides to the 3 end, but the role of this tailing is often unclear. Here we characterize the prevalence and functional consequences of microRNA tailing in vivo, using C. elegans. MicroRNA tailing in C. elegans consists mostly of mono-uridylation of mature microRNA species, with rarer mono-adenylation which is likely added to microRNA precursors. Through a targeted RNAi screen, we discover that the TUT4/TUT7 gene family member CID-1/CDE-1/PUP-1 is required for uridylation, whereas the GLD2 gene family member F31C3.2 - here named GLD-2-related 2 (GLDR-2) - is required for adenylation. Thus, the TUT4/TUT7 and GLD2 gene families have broadly conserved roles in miRNA modification. We specifically examine the role of tailing in microRNA turnover. We determine half-lives of microRNAs after acute inactivation of microRNA biogenesis, revealing that half-lives are generally long (median=20.7h), as observed in other systems. Although we observe that the proportion of tailed species increases over time after biogenesis, disrupting tailing does not alter microRNA decay. Thus, tailing is not a global regulator of decay in C. elegans. Nonetheless, by identifying the responsible enzymes, this study lays the groundwork to explore whether tailing plays more specialized context- or miRNA-specific regulatory roles.

molecular biology↗

bioRxiv2019

The mir-35 family links maternal germline sex to embryonic viability in C. elegans

The germline sex determination pathway in C. elegans determines whether germ cells develop as oocytes or sperm, with no previously known effect on viability. The mir-35 family of microRNAs are expressed in the C. elegans germline and embryo and are essential for both viability and normal hermaphroditic sex determination, preventing aberrant male gene expression in XX hermaphrodite embryos. Here we show that combining feminizing mutations with partial loss of function of the mir-35 family results in enhanced penetrance embryonic lethality that preferentially kills XO animals. This lethal phenotype is due to altered signaling through the germline sex determination pathway, and maternal germline feminization is sufficient to induce enhanced lethality. These findings reveal a surprising pleiotropy of sperm-fate promoting pathways on organismal viability. Overall, our results demonstrate an unexpectedly strong link between sex determination and embryonic viability, and suggest that in wild type animals, mir-35 family members buffer against misregulation of pathways outside the sex determination program, allowing for clean sex reversal rather than deleterious effects of perturbing sex determination genes.

genetics↗

bioRxiv2016

A microRNA family exerts maternal control on sex determination in C. elegans

Gene expression in early animal embryogenesis is in large part controlled post-transcriptionally. Maternally-contributed microRNAs may therefore play important roles in early development. We have elucidated a major biological role of the nematode mir-35 family of maternally-contributed, essential microRNAs. We show that this microRNA family regulates the sex determination pathway at multiple levels, acting both upstream and downstream of her-1 to prevent aberrantly activated male developmental programs in hermaphrodite embryos. The predicted target genes that act downstream of the mir-35 family in this process, sup-26 and nhl-2, both encode RNA binding proteins, thus delineating a previously unknown post-transcriptional regulatory subnetwork within the well-studied sex determination pathway of C. elegans. Genome-wide profiling of SUP-26 binding targets reveals 775 mRNAs, most of which have no known role in sex determination, suggesting that the mir-35 family may modulate numerous other pathways via regulation of sup-26. Since sex determination in C. elegans requires zygotic gene expression to read the sex chromosome karyotype, early embryos must remain gender-naive; our findings show that the mir-35 family microRNAs act in the early embryo to function as a developmental timer that preserves naivete and prevents premature deleterious developmental decisions.

developmental biology↗