vasa and piwi are required for mitotic integrity in early embryogenesis in the spider Parasteatoda tepidariorum

• Published in: Developmental biology 2015-06, Vol.402 (2), p.276-290
• Main Authors: Schwager, Evelyn E., Meng, Yue, Extavour, Cassandra G.
• Format: Article
• Language: English
• Subjects: Achaearanea; Animals; Argonaute Proteins - genetics; Argonaute Proteins - metabolism; Base Sequence; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Chelicerata; Cloning, Molecular; DEAD-box RNA Helicases - genetics; DEAD-box RNA Helicases - metabolism; DNA Primers - genetics; Embryo, Nonmammalian - metabolism; Germ Cells - growth & development; Image Processing, Computer-Assisted; Immunohistochemistry; In Situ Hybridization; Mitosis; Mitosis - genetics; Mitosis - physiology; Molecular Sequence Data; Oocytes - metabolism; Phylogeny; piwi; Polymerase Chain Reaction; RNA Interference; Sequence Alignment; Sequence Analysis, DNA; Spiders - embryology; Spiders - enzymology; Spiders - genetics; Spindle; Time-Lapse Imaging; vasa
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2014.08.032

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. •Spider vasa and piwi are expressed ubiquitously in oocytes and early embryos.•Spider vasa and piwi expression patterns suggest that primordial germ cells arise late in embryogenesis.•Germ cells emerge as paired clusters in opisthosomal segments 2–6.•Spider vasa and piwi are required for egg laying and early embryonic mitoses.