Xenopus egg extract

[1] This pioneering work used eggs of the Northern leopard frog Rana pipiens to prepare an extract.

[2] Extracts derived from eggs of the Japanese common toad Bufo japonicus[3] or of the Western clawed frog Xenopus tropicalis[4] have also been reported.

The cell cycle of unfertilized eggs of X. laevis is arrested highly synchronously at metaphase of meiosis II.

[5] Unfertilized eggs in a buffer containing the Ca2+ chelator EGTA (ethylene glycol tetraacetic acid) are packed into a centrifuge tube.

When demembranated sperm nuclei are incubated with this extract, it undergoes a series of structural changes and is eventually converted into a set of M phase chromosomes with bipolar spindles.

Figure 1. An egg extract is prepared by crushing X. laevis eggs by centrifugation
Figure 2. An interphase nucleus (left) and a cluster of mitotic chromosomes (right) produced in a cycling extract. Bar, 10 μm.