Identification and validation of SSX2IP as a MAP. (A) Workflow for the comparison of the MT interactome in interphase (stage VI X. laevis oocytes) and metaphase (unfertilized X. laevis eggs) by differential proteomics. (B) Protein abundance ratios (log2 of egg/oocyte ratio) of the 163 proteins found in five of five independent experiments. Median values of the five experiments are shown (see Table S1 for details). Note that most proteins are expressed more highly in metaphase. (C) Validation of the predicted metaphase MT association of identified proteins by immunoblotting. MAPs were purified from oocyte (interphase, I) or egg (metaphase, M) lysates by cosedimentation of taxol-stabilized MTs; nocodazole was used as a negative control. Total lysates were compared with MAP sediments, and tubulin served as a loading control. (D) Progesterone-treated, synchronously maturing X. laevis oocytes were analyzed for expression of SSX2IP, RCC1, and TPX2 (positive controls); tubulin was used as a loading control. Times are indicated with respect to nuclear (i.e., germinal vesicle) breakdown (GVBD). *, note the cross-reacting band at 55 kD in the SSX2IP blot.
