THE KINESIN-RELATED PROTEIN EG5 ASSOCIATES WITH BOTH INTERPHASE AND SPINDLE MICROTUBULES DURING XENOPUS EARLY DEVELOPMENT

We have examined the changing abundance and distribution of the kinesi n-related protein Eg5 during oogenesis and early development in Xenopu s laevis. Antibodies raised against proteins synthesized from parts of a novel Eg5 gene expressed in eggs were used for Western blotting and immunofluorescence. Eg5 protein was highly enriched in oocytes and eg gs compared with other adult tissues. It accumulated during the latter stages of oogenesis and increased a further threefold during oocyte m aturation. Its level then gradually declined during early development. In oocytes, eggs, and early embryos, Eg5 protein could be detected th roughout the cytoplasm and in subcortical aggregates. Eg5 staining was found concentrated in meiotic and mitotic spindles, mainly toward the poles. Some Eg5 staining colocalized with microtubules in interphase cells, including the aligned subcortical microtubules in fertilized eg gs implicated in the cortical rotation that specifies the dorsoventral axis. Interphase association of Eg5 with microtubules during early de velopment was confirmed by copelleting the protein with microtubules f rom egg homogenates. In tadpoles and tissue culture cells, Eg5 colocal ized with spindle microtubules throughout mitosis but not with interph ase microtubules. These results suggest that the Eg5 microtubule motor may function in meiosis, mitosis, and interphase during early develop ment. (C) 1994 Academic Press, Inc.