IMMUNOLOCALIZATION OF CENTRIN DURING FERTILIZATION AND THE FIRST CELL-CYCLE IN FUCUS-DISTICHUS AND PELVETIA-COMPRESSA (FUCALES, PHAEOPHYCEAE)

Antibodies that recognize the centrosome-associated protein centrin we re used to characterize centrosomal origin and positioning during fert ilization and the first cell cycle in Fucus distichus subsp. evanescen s (C. Agardh) Powell and Pelvetia compressa (J. Agardh) Be Tent. Centr in was identified in sperm, eggs, and zygotes on protein blots, indica ting the protein is present in both gametes. Using immunofluorescence microscopy, centrin was found in discrete foci in sperm. In contrast, eggs lack centrosomes and centrin was not detectable by immunofluoresc ence, indicating that centrin was probably dispersed in the cytoplasm. Two foci of centrin were present on the nuclear envelope of zygotes, but microtubules remained dispersed over the zygotic nucleus. Centrin foci separated over the nuclear envelope as the first cell cycle progr essed. Microtubules became concentrated at the centrin foci to form ce ntrosomes that gave rise to the spindle poles at mitosis.