| Successful duplication of a cell requires appropriate increase in mass and duplication and transmission of cellular organelles to daughter cells. Two constituents, namely, DNA and the centriole, exist in low copy number and are duplicated precisely once in the cell cycle. Much like DNA, centrioles arise from pre-existing centrioles and their duplication occurs once and only once during cell duplication. This thesis provides insights into both these questions. By modulating activities of cell cycle regulators in Drosophila embryos, we discovered that progression through steps in the centriole cycle require activities of cell cycle regulators. Changes in the activities of these cell cycle regulators set the order of events in the DNA replication cycle, thus enforcing the ‘once-and-only-once’ mode of DNA replication. The requirements that we have uncovered ensure coordination of progression through one round of centriole and cell duplication and could underlie the ‘once-and-only-once’ more of centriole replication.; How does a centriole, an open cylindrical structure, contribute to organization of a new centriole? Specifically, how is a unique site chosen for daughter elaboration, how is the length of the daughter specified and how is the elaboration of new daughters regulated with respect to centriole pair separation? We discovered that a centriole can, indeed, assemble centrioles from multiple sites. Furthermore, mother-daughter centriole pair separation is not essential for embarking on a new round of centriole replication. Lastly, centriole length determination is regulated and is not an intrinsic feature of centriole replication. These observations provide insights into the mode of centriole replication and raise further issues about how steps in the centriole replication are regulated. |
