Xenopus system stability

When the duplicated centrosomes have become aligned, formation of the spindle proceeds, driven by simultaneous events at centrosomes and chromosomes. As just discussed, the centrosome facilitates spindle formation by nucleating the assembly of the spindle microtubules. In addition, the (—) ends of microtubules are gathered and stabilized at the pole by dynein-dynactin working with the nuclear/mitotic apparatus protein. The role of dynein in spindle pole formation has been demonstrated by reconstitution studies in which bipolar spindles form in Xenopus egg extracts in the presence of centrosomes, microtubules, and sperm nuclei. The addition of antibodies against cytosolic dynein to this in vitro system releases and splays the spindle microtubules but leaves the cen-trosomal astral microtubules in position (Figure 20-35). 

Our current understanding of the transport, metabolism, and function of specific RNA molecules has been greatly facilitated by in vitro transcription systems that produce biochemical quantities of pure, radiolabeled or chemically modified RNA molecules. In this chapter we describe procedures that will enable investigators to synthesize specific RNAs, inject theseRNAs into Xenopus oocyte nuclei or cytoplasms, and determine their nucleocytoplasmic distribution, stability, protein associations, and covalent modifications. 

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