Abstract

It was more than twelve years ago when we started to use the spider Parasteatoda tepidariorum (formerly known as Achaearanea tepidariorum) as a new model organism for cell and developmental biology. At that time, we were starting to recognize significant variations existing even within the arthropod phylum. Comparison of the domain structures of classical cadherins responsible for adherens junction assembly implied that big changes had occurred at least in the lineages leading to the insects and vertebrates. Tight junctions, the junction type specific to the vertebrates and urochordates, are exceptionally observed in the chelicerate group, including spiders. In particular, old papers on experiments with spider and horseshoe crab embryos tempted us to speculate that spider embryos may have what Drosophila embryos do not have. For example, the chelicerate embryos have twinning capabilities, which require regulative mechanisms of axis formation as in the vertebrate embryos. Despite the start of spider work with great interest, it was initially not promising because we had no means to investigate gene functions. But, the turning point came when we found that repeated injections of dsRNA for short-gastrulation into adult females grossly affected dorso-ventral axis formation in the embryos. Now, many other techniques are available, including microinjection, cell labeling, embryonic RNAi, and live imaging with fluorescent proteins. Using these techniques, we have shown, in part, that the mechanisms underlying the formation of the arthropod body plan largely differ in Drosophila and Parasteatoda, which may help to fill the gaps in knowledge between the insects and vertebrates. We hope that use of the spider Parasteatoda tepidariorum will promote the understanding of not only evolutionary and developmental processes in the arthropods but also their relationships with other metazoans.