Early embryonic development, including germ‐disk stage, in the theridiid spider Achaearanea japonica (Bös. et Str.)

Abstract

Early embryonic development, from the first cleavage to the germ-disk stage, in the theridiid spider Achaearanea japonica was examined by light and electron microscopy. The eggs are syncytial during the first four cleavages, and then invaginations of cell membranes fuse to generate the blastomeres at the sixteen-nucleus stage. The cleavage pattern is a modified type of total cleavage. It appears that radial bundles of microtubules that radiate from the perinuclear cytoplasm may participate in the migration of cleavage nuclei for the formation of the blastoderm. The large yolk granules are sequestered by cell membranes from the blastomeres or blastoderm cells into the interior of the embryo together with various organelles and glycogen granules. Most of the blastoderm cells converge in the upper hemisphere to form the germ disk, whereas a few cells remain in the lower hemisphere. The embryo at the germ-disk stage contains many spherical germ-disk cells. Almost no large yolk granules are found in these cells, but the flat remaining cells each contain several large yolk granules. These remaining cells may preserve a flat shape to cover the surface of the embryo that does not include the germ disk. © 1995 Wiley-Liss, Inc.

Embryonic development and staging of the cobweb spider Parasteatoda tepidariorum C. L. Koch, 1841 (syn.: Achaearanea tepidariorum; Araneomorphae; Theridiidae)

“…Also, the staging systems previously provided for early stages of P. tepidariorum (Akiyama- Oda 2003, 2006;up to 60 h;Yamazaki et al 2005;Kanayama et al 2010) as well as the staging through approximately half of the development (McGregor et al 2008) were reassessed and emended. Furthermore, the precise description of early cleavage stages of the closely related species Achaearanea japonica (Suzuki and Kondo 1995) was taken into account. As P. tepidariorum develops nearly twice as fast as C. salei and the developmental stages of both species are not duplicates, we defined several new stages by focussing on developing organ systems (e.g.…”

Progressive activation of Delta-Notch signaling from around the blastopore is required to set up a functional caudal lobe in the spiderAchaearanea tepidariorum

“…By contrast, our previous and present studies with the spider Achaearanea highlight the importance of cell-cell communication mediated by Dpp and Sog in dorsoventral patterning (Akiyama- Oda and Oda, 2006) and by Delta-Notch signaling in mesoderm and caudal specification. The necessity for cell-cell communication in early spider embryos may be due to early completion of cellularization (Kondo, 1969;Suzuki and Kondo, 1995). Based on Achaearanea studies, the blastopore region is particularly important, because cells producing Dpp signals originate from that region and progressive activation of Delta-Notch signaling starts there.…”

Early patterning of the spider embryo: a cluster of mesenchymal cells at the cumulus produces Dpp signals received by germ disc epithelial cells

“…The energids give rise to a germ disc of relatively uniform epithelial cells. Although when the cellularization is completed in the species used has not been examined, a previous work on a closely related spider species, Achaearanea japonica, showed that every nucleus was already enclosed with plasma membrane at the 16-blastomere stage (Suzuki and Kondo, 1995). At the center of the germ disc, a white spot is seen (Fig.…”