Biology subjects

Lynch, J. A.

Publications and source records attributed to Lynch, J. A..

7 recordsLinked to original sources

bioRxiv2024

Novel structure and composition of the unusually large germline determinant of the wasp Nasonia vitripennis

Specialized, maternally derived ribonucleoprotein (RNP) granules play an important role in specifying the primordial germ cells in many animal species. Typically, these germ granules are small ([~]100 nm to a few microns in diameter) and numerous; in contrast, a single, extremely large granule called the oosome plays the role of germline determinant in the wasp Nasonia vitripennis. The organizational basis underlying the form and function of this unusually large membraneless RNP granule remains an open question. Here we use a combination of super-resolution and transmission electron microscopy to investigate the composition and morphology of the oosome. We show that the oosome has properties of a viscous liquid or elastic solid. The most prominent feature of the oosome is a branching mesh-like network of high abundance mRNAs that pervades the entire structure. Homologs of the core polar granule proteins Vasa and Oskar do not appear to nucleate this network, but rather are distributed adjacently as separate puncta. Low abundance RNAs appear to cluster in puncta that similarly do not overlap with the protein puncta. Several membrane-bound organelles, including lipid droplets and rough ER-like vesicles, are incorporated within the oosome, whereas mitochondria are nearly entirely excluded. Our findings show that the remarkably large size of the oosome is reflected in a complex sub-granular organization and suggest that the oosome is a powerful model for probing interactions between membraneless and membrane-bound organelles, structural features that contribute to granule size, and the evolution of germ plasm in insects.

developmental biology↗

bioRxiv2023

Dynamic protein assembly and architecture of the large solitary membraneless organelle during germline development in the wasp Nasonia vitripennis

Germ cells in different animals assemble characteristic membraneless organelles referred to as germ granules, which contain RNA and proteins required for germline development. Typically, the germ granules are small spherical or amorphous cytoplasmic granules and often, they assemble around membrane-bound organelles such as nuclei, mitochondria and endoplasmic reticulum. In particular, in egg chambers of the fruit fly Drosophila, nurse cells assemble perinuclear granules, referred to as nuage, along with multiple small germ granules formed at the posterior pole of the oocyte (polar granules). Nuage is assembled in a very similar way in the wasp Nasonia vitripennis, despite the long evolutionary distance from Drosophila. In contrast, Nasonia forms a very different single germ granule, called the oosome, at the posterior, which is about 40 times larger than a homologous Drosophila polar granule. Here, using molecular and super-resolution imaging approaches, we provide insights into protein assembly and architecture of the oosome during germline development. Interestingly, unlike the fly, the wasp utilizes alternatively spliced RNA-helicase Vasa isoforms during germline development and oosome formation. The isoforms differ by an unstructured region, containing repeats of phenylalanine and glycine, that is similar to functional domains characteristic of nucleoporins. In addition, while other conserved components of germ granules, such as Oskar, Aubergine and Tudor proteins are recruited to the oosome, these polypeptides show a distinct and specific localization within the oosome. Of particular note, Tudor protein forms a shell encapsulating the oosome, while small Oskar/Vasa/Aubergine granules occur inside the oosome core. Also, in surprising contrast to Drosophila egg chambers, we found that a subset of the wasp nurse cells located in anterior show dramatic DNA damage and assemble higher levels of nuage than their posterior counterparts. The characteristics of two distinct nurse cell populations suggest a mechanistic link between the higher amounts of nuage assembled in anterior nurse cells and their need to silence transposable elements in the presence of double-strand DNA breaks. Our results point to the high degree of plasticity in the assembly of membraneless organelles, which adapt to specific developmental needs of different organisms, and suggest that novel molecular features of conserved proteins result in the unique architecture of the oosome in the wasp.

cell biology↗

bioRxiv2021

Knockdown of Dnmt1 links Gene body DNA methylation to regulation of gene expression and maternal-zygotic transition in the wasp Nasonia

Gene body methylation (GBM) is an ancestral aspect of DNA methylation (Sarda, Zeng, Hunt, & Yi, 2012; Yi, 2012; Zemach, McDaniel, Silva, & Zilberman, 2010) whose role in development has been obscured by the more prominent roles of promoter and CpG island methylation. The wasp Nasonia has little promoter and CpG island methylation, yet retains strong GBM (Park et al., 2011; Wang et al., 2013; Werren et al., 2010), making it an excellent model for elucidating the role of GBM. Here we show that Nasonia DNA methyl transferase 1a (Nv-Dnmt1a) knockdown leads to failures in cellularization and gastrulation of the embryo. Both of these disrupted events are hallmarks of the maternal-zygotic transition (MZT) in insects. Analysis of the embryonic transcriptome and methylome revealed strong reduction of GBM and widespread disruption of gene expression during embryogenesis after Nv-Dnmt1a knockdown. There was a strong correlation between loss of GBM and reduced gene expression in thousands of methylated loci, while affected unmethylated genes tended to be upregulated. We propose that reduced GBM and subsequent lower expression levels of methylated genes was the direct effect of Nv-Dnmt1 knockdown, and that this disruption led to widespread downstream dysregulation of MZT, and manifesting in developmental failure at gastrulation. Significance StatementThe importance of gene-body methylation (GBM) in development is unclear, due to the difficulty in teasing apart the effects of cis-regulatory methylation from those of GBM in vertebrate model systems. Unlike vertebrate models, the methylation machinery in the jewel wasp Nasonia vitripennis appears to exclusively mediate GBM, thus simplifying interpretation of the role of GBM in development. Knockdown of DNMT1 (Nv-Dnmt1a) in Nasonia leads to embryonic lethality, which we show is caused by a failure of cellularization and gastrulation. Nv-Dnmt1a knockdown resulted in a global loss of GBM in the embryo, which was strongly correlated with a down-regulation of gene expression. We propose that GBM facilitated by Nv-Dnmt1a is required for proper zygotic genome activation in the wasp.

genomics↗

bioRxiv2020

Striking parallels between dorsoventral patterning in Drosophila and Gryllus reveal a complex evolutionary history behind a model gene regulatory network

Dorsoventral pattering relies on Toll and BMP signalling in all insects studied so far, with variations in the relative contributions of both pathways. Drosophila and the beetle Tribolium share extensive dependence on Toll, while representatives of more distantly related lineages like the wasp Nasonia and bug Oncopeltus rely more strongly on BMP signalling. Here, we show that in the cricket Gryllus bimaculatus, an evolutionarily distant outgroup, Toll has, like in Drosophila, a direct patterning role for the ventral half of the embryo. In addition Toll polarizes BMP signalling, although this does not involve the conserved BMP inhibitor Sog/Chordin. Finally, Toll activation relies on ovarian patterning mechanisms with striking similarity to Drosophila. Our data suggest two surprising hypotheses: 1) that Tolls patterning function in Gryllus and Drosophila is the result of convergent evolution or 2) a Drosophila-like system arose early in insect evolution, and was extensively altered in multiple independent lineages.

evolutionary biology↗

bioRxiv2019

Genetic, morphometric, and molecular analyses of interspecies differences in head shape and hybrid developmental defects in the wasp genus Nasonia

Males in the parasitoid wasp genus Nasonia (N. vitripennis, N. giraulti, N. longicornis) have distinct, species specific, head shapes. Fertile hybrids among the species are readily produced in the lab allowing genetic analysis of the evolved differences. In addition, the obligate haploidy of males makes these wasps a uniquely powerful model for analyzing the role of complex gene interactions in development and evolution. Previous analyses have shown that complex gene interactions underpin different aspects of the shape differences, and developmental incompatibilities that are specific to the head in F2 haploid hybrid males are also governed by networks of gene interaction. Here we use the genetic tools available in Nasonia to extend our understanding of the gene interactions that affect development and morphogenesis in male heads. Using artificial diploid male hybrids, we show that alleles affecting head shape are codominant, leading to uniform, averaged hybrid F1 diploid male heads, while the alleles mediating developmental defects are recessive, and are not visible in the diploid hybrids. We also determine that divergence in time, rather than in morphological disparity is the primary driver of hybrid developmental defects. In addition, we show that doublesex is necessary for the male head shape differences, but is not the only important factor. Finally we demonstrate that we can dissect complex interspecies gene interaction networks using introgression in this system. These advances represent significant progress in the complex web of gene interactions that govern morphological development, and chart the connections between genomic and phenotypic variation.

evolutionary biology↗

bioRxiv2019

Fog signaling has diverse roles in epithelial morphogenesis in insects

The Drosophila Fog pathway represents one of the best-understood signaling cascades controlling epithelial morphogenesis. During gastrulation, Fog induces apical cell constrictions that drive the invagination of mesoderm and posterior gut primordia. The cellular mechanisms underlying primordia internalization vary greatly among insects and recent work has suggested that Fog signaling is specific to the fast mode of gastrulation found in some flies. On the contrary, here we show in the beetle Tribolium, whose development is broadly representative for insects, that Fog has multiple morphogenetic functions. It modulates mesoderm internalization and controls a massive posterior infolding involved in gut and extraembryonic development. In addition, Fog signaling affects blastoderm cellularization, primordial germ cell positioning and cuboidal-to-squamous cell shape transitions in the extraembryonic serosa. Comparative analyses with two other distantly related insect species reveals that Fogs role during cellularisation is widely conserved and therefore might represent the ancestral function of the pathway.

developmental biology↗

bioRxiv2018

Transcriptomic and functional analysis of the oosome, a unique form of germplasm in the wasp Nasonia vitripennis

BackgroundThe oosome is the germline determinant in the wasp Nasonia vitripennis and is homologous to the polar granules of Drosophila. Despite a common evolutionary origin and developmental role, the oosome is morphologically quite distinct from polar granules. It is a solid sphere that migrates within the cytoplasm before budding out and forming pole cells.\n\nResultsTo gain an understanding of both the molecular basis of the novel form of the oosome, and the conserved essential features of germ plasm, we quantified and compared transcript levels between embryo fragments that contained the oosome, and those that did not. The identity of the localized transcripts indicated that Nasonia uses different molecules to carry out conserved germ plasm functions. In addition, functional testing of a sample of localized transcripts revealed potentially novel mechanisms of ribonucleoprotein assembly and pole cell cellularization in the wasp.\n\nConclusionsOur results demonstrate that numerous novel and unexpected molecules have been recruited in order produce the unique characteristics of the oosome and pole cell formation in Nasonia. This work will serve as the basis for further investigation into the patterns of germline determinant evolution among insects, the molecular basis of extreme morphology of ribonucleoproteins, and the incorporation of novel components into developmental networks.

developmental biology↗