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Schwager, Evelyn

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Schwager

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Evelyn

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Schwager, Evelyn
Author's Publications: search.filters.isAuthorOfPublication.e9ed7b82-264f-48c9-b8a4-952327b44b9b

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    vasa and piwi are required for mitotic integrity in early embryogenesis in the spider Parasteatoda tepidariorum
    (Elsevier BV, 2015) Schwager, Evelyn; Meng, Yue; Extavour, Cassandra
    Studies in vertebrate and invertebrate model organisms on the molecular basis of primordial germ cell (PGC) specification have revealed that metazoans can specify their germ line either early in development by maternally transmitted cytoplasmic factors (inheritance), or later in development by signaling factors from neighboring tissues (induction). Regardless of the mode of PGC specification, once animal germ cells are specified, they invariably express a number of highly conserved genes. These include vasa and piwi, which can play essential roles in any or all of PGC specification, development, or gametogenesis. Although the arthropods are the most speciose animal phylum, to date there have been no functional studies of conserved germ line genes in species of the most basally branching arthropod clade, the chelicerates (which includes spiders, scorpions, and horseshoe crabs). Here we present the first such study by using molecular and functional tools to examine germ line development and the roles of vasa and piwi orthologues in the common house spider Parasteatoda (formerly Achaearanea) tepidariorum. We use transcript and protein expression patterns of Pt-vasa and Pt-piwi to show that primordial germ cells (PGCs) in the spider arise during late embryogenesis. Neither Pt-vasa nor Pt-piwi gene products are localized asymmetrically to any embryonic region before PGCs emerge as paired segmental clusters in opisthosomal segments 2–6 at late germ band stages. RNA interference studies reveal that both genes are required maternally for egg laying, mitotic progression in early embryos, and embryonic survival. Our results add to the growing body of evidence that vasa and piwi can play important roles in somatic development, and provide evidence for a previously hypothesized conserved role for vasa in cell cycle progression.
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    Distal-less and Dachshund Pattern both Plesiomorphic and Apomorphic Structures in Chelicerates: RNA Interference in the Harvestman Phalangium opilio (Opiliones)
    (Wiley-Blackwell, 2013-04-08) Sharma, Prasahant P.; Schwager, Evelyn; Giribet, Gonzalo; Jockusch, Elizabeth L.; Extavour, Cassandra
    The discovery of genetic mechanisms that can transform a morphological structure from a plesiomorphic (=primitive) state to an apomorphic (=derived) one is a cardinal objective of evolutionary developmental biology. However, this objective is often impeded for many lineages of interest by limitations in taxonomic sampling, genomic resources, or functional genetic methods. In order to investigate the evolution of appendage morphology within Chelicerata, the putative sister group of the remaining arthropods, we developed an RNA interference (RNAi) protocol for the harvestman Phalangium opilio. We silenced the leg gap genes Distal-less(Dll) and dachshund (dac) in the harvestman via zygotic injections of double-stranded RNA, and used in situ hybridization to confirm RNAi efficacy. Consistent with the conserved roles of these genes in patterning the proximo-distal axis of arthropod appendages, we observed that embryos injected with Dll dsRNA lacked distal parts of appendages and appendage-like structures, such as the labrum, the chelicerae, the pedipalps, and the walking legs, whereas embryos injected with dac dsRNA lacked the medial podomeres femur and patella in the pedipalps and walking legs. In addition, we detected a role for these genes in patterning structures that do not occur in well-established chelicerate models (spiders and mites). Dll RNAi additionally results in loss of the preoral chamber, which is formed from pedipalpal and leg coxapophyses, and the ocularium, a dorsal outgrowth bearing the eyes. In one case, we observed that an embryo injected with dac dsRNA lacked the proximal segment of the chelicera, a plesiomorphic podomere that expresses dac in wild type embryos. This may support the hypothesis that loss of the cheliceral dac domain underlies the transition to the two-segmented chelicera of derived arachnids.