Figure 3.

The mitotic type of cell cycles proceed after meiosis I in Mos-deficient 1-MeAde-treated unfertilized starfish oocytes. (A) Abortive spindle formation at a stage corresponding to metaII in Mos-deficient oocytes. After 1-MeAde addition to oocytes that had been injected with either antisense or sense mos, a spindle was frequently detectable at metaI with antitubulin staining but thereafter could not be detected, and condensed chromosomes were located in the middle of each oocyte. (Insets) Meiotic spindles and condensed chromosomes at higher magnification. White arrow indicates the first polar body. (B) Repeated fluctuation of histone H1 kinase activity after 1-MeAde addition in starfish oocytes injected with antisense mos. (Upper) Autoradiograms (AS, antisense mos; S, sense mos). (Lower) Radioactivity of the excised histone H1 bands (closed squares, antisense mos; open circles, sense mos). (C) Dynamics of cyclins B and A, Cdc25, Tyr phosphorylation in Cdc2 and MAP kinase after 1-MeAde addition in starfish oocytes injected with antisense mos. P-MAPK and P-Cdc2, immunoblots with antiphospho MAP kinase and antiphospho-Tyr-15 of Cdc2, respectively. (D) DNA replication occurs when histone H1 kinase activity drops to minimal levels after 1-MeAde addition to starfish oocytes injected with antisense mos. BrdUrd incorporation by pulse labeling for 30 min indicated below each panel was detectable rarely immediately after meiosis I (see also Fig. 4A) and always thereafter in antisense mos-injected oocytes; in contrast, it was undetectable through 180 min continuous labeling in control sense mos-injected oocytes. Each oocyte was double stained with 4′,6-diamidino-2-phenylindole (DAPI). (E) Several rounds of cleavage in antisense mos-injected, 1-MeAde-treated, unfertilized starfish oocytes. Nuclear divisions and furrowing occurred normally in some blastomeres and abnormally in others within an embryo. Thus, although they were abnormal as a whole, these oocytes developed to the two-cell stage almost invariably and to the blastula stage at 10%. Presence of nucleus is shown by accumulation of FITC-conjugated BSA coupled with nucleoplasmin NLS peptide, which was injected into immature oocytes (Left). (F) Development to 64-cell stage embryo in 1-MeAde- and U0126-treated unfertilized starfish oocytes. Almost all of these embryos developed to bipinnaria larvae, even though abnormal cleavages were partially observed. Note the absence of elevation of the fertilization envelope.