Fig. 8. Phenotypes of oocytes after in vitro maturation. Examples of the various phenotypes observed in matured control and rescued oocytes (red labeling indicates F-actin detected by phalloidin, and blue labeling indicates DNA detected by DAPI). (A) Normal mature `PB1' egg, with the first polar body emitted (indicated by PB1) and the egg chromosomes organized on the metaphase II spindle. An actin-rich cap overlies the meiotic spindle (asterisk). (B,C) Two examples of `oversized polar body' phenotype. Twenty-eight percent (7/25) of the rescued eggs had this phenotype, and in six of these seven, all of the DNA was present in the polar body-like structures (arrows), with no DNA present in the egg. These polar body-like structures ranged in size from very large, containing approximately one-third of the oocyte cytoplasm (B) to somewhat more normal in size (C; compare with A). (D) An oocyte that has undergone GVBD but not emitted PB1, with chromatin near the center of the egg that appears to have failed to condense properly. In this cell, there is no actin-rich cap and instead the actin is symmetrically localized around the cell cortex, as it is in a GV-intact oocyte. (E) An oocyte that has undergone GVBD but not emitted PB1, with condensed chromatin that remains near the center of the egg (rather than having migrated to the cell periphery). This DNA appears to be poorly organized, not organized on a metaphase I spindle. As in the cell in D, the actin in this cell is symmetrically localized. (F) An oocyte that has undergone GVBD but not emitted PB1, with the metaphase I spindle having migrated to the cell periphery. The asterisk indicates the actin-rich cap over the metaphase I spindle. This oocyte appears poised to undergo PB1 emission; it is not clear if it was arrested at this stage or was simply slower than the rest of its cohort. (G) An egg that has emitted PB1 (out of the plane of focus of this image), but the egg DNA looks abnormal, as a tightly condensed wad of DNA rather than chromosomes organized on the metaphase II spindle. (Only the DAPI staining in shown in this image to show the DNA wad more clearly.) (H) A nearly normal metaphase II egg, except the chromosomes are not completely aligned on the metaphase II plate; the arrowhead indicates chromatin cluster that is not aligned. (Only the DAPI staining in shown in this image, in order to show the straggler chromosome more clearly.) (I) Percentages of the control and rescued oocytes that displayed each of the eight observed phenotypes after 19 hours in culture medium lacking dbcAMP. Values over the bars indicate the actual numbers of oocytes per total control or rescued oocytes that displayed that phenotype.