A MOLECULAR MARKER FOR CENTRIOLE MATURATION IN THE MAMMALIAN-CELL CYCLE

The centriole pair in animals shows duplication and structural maturat ion at specific cell cycle points. In G(1), a cell has two centrioles. One of the centrioles is mature and was generated at least two cell c ycles ago. The other centriole was produced in the previous cell cycle and is immature. Both centrioles then nucleate one procentriole each which subsequently elongate to full-length centrioles, usually in S or G(2) phase. However, the point in the cell cycle at which maturation of the immature centriole occurs is open to question. Furthermore, the molecular events underlying this process are entirely unknown. Here, using monoclonal and polyclonal antibody approaches, we describe for t he first time a molecular marker which localizes exclusively to one ce ntriole of the centriolar pair and provides biochemical evidence that the two centrioles are different. Moreover, this 96-kD protein, which we name Cenexin (derived from the Latin, senex for ''old man,'' and Ce nexin for centriole) defines very precisely the mature centriole of a pair and is acquired by the immature centriole at the G(2)/M transitio n in prophase. Thus the acquisition of Cenexin marks the functional ma turation of the centriole and may indicate a change in centriolar pote ntial such as its ability to act as a basal body for axoneme developme nt or as a congregating site for microtubule-organizing material.