Temporal expression of cell cycle-related proteins during spermatogenesis: establishing a timeline for onset of the meiotic divisions.

During spermatogenesis, the complex events of the first meiotic prophase and division phase bring about dramatic changes in nuclear organization. One factor frustrating mechanistic dissection of these events is lack of knowledge about precisely what events occur, in what order they occur, and how they may be interrelated by temporal sequence; in other words, a precise timeline is lacking. This temporal ordering problem can be tackled by following expression and localization in mouse spermatocytes of proteins critical to events of the meiotic cell division process. These include ones that are primarily chromosomal and related to pairing and recombination, as well as kinases and substrates that mediate the cell cycle transition. Distinct and protein-specific patterns occur with respect to expression and localization throughout meiotic prophase and division and dramatic relocalization of proteins occurs as spermatocytes enter the meiotic division phase. This information provides a foundation for a meiotic timeline that can be augmented to provide, eventually, a complete catalog of meiotic events and their temporal sequence. Such a framework can clarify mechanisms of normal meiosis as well as mutant phenotypes and aberrations of the meiotic process that lead to aneuploidy.