Germ Line Development in the Grasshopper Schistocerca gregaria: vasa As a Marker

Abstract

Vasa is a widely conserved germline marker, both in vertebrates and invertebrates. We identify a vasa orthologue, Sgvasa, and use it to study germline development in the grasshopper Schistocerca gregaria, a species in which no germ plasm has been identified. In adults, Sgvasa is specifically expressed in the ovary and testis. It is expressed at high levels during early oogenesis, but no detectable vasa RNA and little Vasa protein are present in mature unlaid eggs. None appears to be localized to any defined region of the egg cortex, suggesting that germline specification may not depend on maternal germ plasm expressing vasa. Vasa protein is expressed in most cleavage energids as they reach the egg surface and persists at high levels in most cells aggregating to form the embryonic primordium. However, after gastrulation, Vasa protein persists only in extraembryonic membranes and in cells at the outer margin of the late heart-stage embryo. In the embryo, it then become restricted to cells at the dorsal margin of the forming abdomen. In older embryos, these Vasa-positive cells move toward the midline; Vasa protein accumulates asymmetrically in their cytoplasm, a pattern closely resembling that of germ cells in late embryonic gonads. Thus, we suggest that the Vasa-stained cells in the abdominal margin are germ cells, as proposed by Nelson (1934), and not cardioblasts, as has been proposed by others.

Differential expression of vasa RNA and protein during spermatogenesis and oogenesis in the gibel carp (Carassius auratus gibelio), a bisexually and gynogenetically reproducing vertebrate

“…In contrast, Vasa peaks at the early spermatocyte stage in chicken and mouse (Toyooka et al, 2000), and is weakly stained in spermatogonia in Drosophila and grasshopper (Chang et al, 2002). During oogenesis, the gibel carp Vasa persists through oogonia to mature oocyte, with strong staining in oogonia, compared with weak straining in oogonia of Drosophila and grasshopper (Chang et al, 2002), and to the strongest staining in primary oocytes in the chicken and mouse (Toyooka et al, 2000). Vasa protein expression during zebrafish oogenesis (Knaut et al, 2000) closely resembles our observation in the gibel carp.…”

“…Vasa is an RNA helicase of the DEAD (Asp-Glu-Ala-Asp) family and is thought to be implicated in translational control. The Drosophila vasa homolog has been identified in the hydra (Mochizuki et al, 2001), silkworm (Nakao, 1999), grasshopper (Chang et al, 2002), oyster (Fabioux et al, 2004), Xenopus , chicken , mouse (Fujiwara et al, 1994), and human (Castrillon et al, 2000). Specifically, vasa RNA has been demonstrated to be a germ cell marker in the zebrafish (Olsen et al, 1997;Yoon et al, 1997;Knaut et al, 2000;Raz, 2003), trout (Yoshizaki et al, 2000), tilapia (Kobayashi et al, 2000), and medaka (Shinomiya et al, 2002).…”

Transient occurrence of vasa-expressing cells in nongenital segments during embryonic development in the oligochaete annelid Tubifex tubifex

“…In this study, to gain an insight into expression of Ttu-vas protein, in terms of the Ttu-vas transcripts, we stained Tubifex embryos with an anti-Vasa antibody named formosa 2, which was raised to Schistocera Vasa protein (Chang et al 2002). According to these authors, the amino acid sequence of the polypeptide used to raise this antibody included six of the eight conserved DEAD-box protein motifs as well as the EARKF motif; we find that this sequence shows 53% identity to the corresponding domain of the predicted Ttu-vas protein (data not shown).…”

“…This diversity is manifested especially by comparing vasa expression pattern in arthropods such as fruit fly (Dme; Lasko and Ashburner 1988), red flour beetle (Tca; Schröder 2006), silk moth (Bmo; Nakano 1999), grasshopper (Sgr; Chang et al 2002), spider mite (Tur; Dearden et al 2003), branchiopod (Dma;Sagawa et al 2005) and amphipod (Pha; Extavour 2005). For instance, vasa transcripts are maternally contributed to the egg in Dme, Tca and Bmo, but not in Sgr, Tur and Dma.…”

Germ-plasm specification and germline development in the parthenogenetic pea aphid Acyrthosiphon pisum: Vasa and Nanos as markers

“…However, in some insects such as the grasshopper Schistocerca gregaria, no maternal germ plasm can be identified and germ cells are segregated at much later developmental stages in the abdominal margin when segmentation is initiated in the abdomen. It is believed that the formation of these primordial germ cells is induced by signals from adjacent somatic cells (Chang et al, 2002). In other insects such as Bombyx mori (Lepidoptera) (Nakao, 1999), Apis mellifera (Hymenoptera) (Nelson, 1915) and Hydrophilus piceus (Coleoptera) (Hegner, 1908), germ-cell segregation is also not detected until late gastrulation.…”