Fate of Mammalian Morula Cells (p. 106/107)
Role of the Egg Cortex in Positioning the Mitotic Spindle (p. 112/113)
See Movies on Cleavage on Movies page.
p. 115, legend to Fig. 5.25 should begin "Centrosome replication and movements..."
p. 123, paragraph 2, line 2 from below, should read "meroblastic cleavage..."
Paria B.C., Reese J., Das S.K., and Dey S.K. (2002) Deciphering the cross-talk of implantation: Advances and challenges. Science 296: 2185-2188
Schuyler S.C., Pellman D. (2001) Search, capture and signal: games microtubules and centrosomes play. J. Cell Sci. 114: 247-255
Sisson J.C., Rothwell W. and Sullivan W. (1999) Cytokinesis: Lessons from Rappaport and the Drosophila embryo. Cell Biology International 23: 871-876
Lehmann D.A., Patterson B., Johnston L.A., Balzer T., Britton J.S., Saint R. and Edgar B.A. (1999) Cis-regulatory elements of the mitotic regulator, string/Cdc25. Development 126: 1793-1803
In Drosophila embryos past the midblastula trasition, mitosis in most cells is triggered by bursts of transcription of string+, which encodes a phosphatase that activates the mitotic kinase CDK1 (see text Fig. 5.34). It is expected that mitotic divisions are differentially regulated so as to allow cell turnover and regional proliferation, to support morphogenetic movements, and to avoid interference with cell differentiation. In accord with the expected complexity in the control of string+, Lehmann et al. (1999) found that the gene's transcription is controlled by an unusually large regulatory region (more than 30kb) containing a plethora of regulatory elements. They identified regulatory elements specific to subsets of epidermal cells, mesoderm, trachea, nurse cells, and in particular the nervous system.
Korinek W.S., Copeland M.J., Chaudhuri A. and Chant J. (2000) Molecular linkage underlying microtubule orientation toward cortical sites in yeast. Science 287: 2257-2259
Lee L., Tirnauer J.S., Li J., Schuyler S.C., Liu J.Y. and Pellman D. (2000) Positioning of the mitotic spindle by a cortical-microtubule capture mechanism. Science 287: 2260-2262
The asymmetrical cleavage patterns observed in many embryos require the correct positioning and orientation of mitotic spindles. The latter may be facilitated by a search-and-capture mechanism, in which dynamic microtubules are stabilized through interactions with specific sites of submembrane cortex. In yeast, oriented microtubules align the mitotic spindle between the mother cell and its bud. Korinek et al. and Lee et al. found independently that a cortical protein, Kar9, localizes to the bud tip and interacts with Bim1, a phylogeneticlly conserved protein that occurs specifically at the free (plus) ends of microtubules. A similar cortical-microtubule capture mechanism seems to exist in animal cells.
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