Synthesis of Spindle-associated Proteins in Early Cleavage

Synthesis of mitotic spindle proteins is probably one of the normal preparations for division in higher cells (Mazia, 1961). Not so clear, however, is the situation in early embryonic development. The most widely accepted point of view, based upon several independent lines of evidence, is that the unfertilized egg contains a store of preformed spindle precursors, and that the controlling process is assembly, rather than biosynthetic elaboration, of the working mitotic apparatus (MA). The evidence is very thoroughly reviewed in Mazia's monograph (1961). Protein synthesis begins in sea urchin eggs immediately after fertilization (Nakano and Mon-