Cellular scaffolds in mammalian eggs

Cellular scaffolds serve as structural components to which various elements of signal transduction pathways can be associated. The association of components on a scaffold can have several important functions, for example they can: 1) associate upstream regulatory components in a cascade that can increase the speed of response to a stimulus; 2) restrict access of substrates to enzymes associated with the scaffold; 3) permit cross talk between distinct signaling pathways, and; 4) aid in the establishment of cellular polarity. The conversion of the mammalian egg into the zygote requires many rapid alterations during a distinct time frame to mediate the biochemical and structural changes that occur. Cellular scaffolds provide a mechanism that can perform these rapid, highly orchestrated changes. They can permit interaction between distinct calcium-dependent pathways and also can provide a means for the calcium signal, that is initiated by fertilization, to act on calcium-independent pathways. This review considers various lines of evidence suggesting that in the mammalian egg, the meiotic spindle serves as a cellular scaffold that permits coordination among several signaling pathways essential for fertilization and the initiation of early development.