Figure 2.
A subset of identified Wnt pathway genes are required for proper orientation of the EMS spindle. Isolated P1 blastomeres from different mutant strains were cultured in vitro; on P1 division, P2 and EMS were left in contact and the angle of the EMS spindle was measured. Spindle angles were scored and recorded as described in Materials and Methods. The left-most quadrant shows wild-type control data, with spindle angles ranging from 0° to 19°. The range of spindle angles in EMS blastomeres from embryos mutant for mom-1/porc (1°–88°), mom-5/fz (0°–90°), mom-3 (1°–90°), and gsk-3 (1°–90°) are wider than wild-type, indicating a lack of orientation with respect to the plane of contact with P2. The defects in EMS may represent a randomization of spindle orientation, or an incompletely penetrant failure to rotate the nucleus/centrosome complex. In some cases, endoderm induction occurred in the absence of correct EMS spindle orientation, and vice versa. Examples of such situations have been indicated for mom-1/porc, mom-3, and mom-5/fz. A (+) next to a spindle angle mark indicates the production of endoderm in spite of abnormal EMS spindle orientation and a (−) indicates the lack of endoderm in some partial embryos with normal EMS spindle angles. mom-4 experiments yielded a wide range of EMS spindle angles (0°–90°). Only 4/26 were abnormal, whereas the majority of spindles oriented properly. A one-sided Student t-test comparing wild-type with mom-4 yields a P-value of 0.18, indicating that the mom-4 data set is not significantly different from wild type. Spindle angle ranges for mom-2/wg (0°–28°), apr-1/APC (3°–34°), wrm-1/arm (1°–17°), pop-1/pan (1°–32°), and the apr-1;wrm-1 double (0°–13°) were similar to wild type. Mammalian and Drosophila genes names are aligned below their C. elegans homologs. mom-3 and mom-4 have not yet been cloned.