Multifunctional scaffolds in eggs: sites for localization, signal transduction and meiotic spindle polarity

Molecular scaffolds in the mammalian egg are capable of tethering specific proteins involved in regulation of early development. Scaffolds can take the form of cytoskeletal elements, or involve proteins such as MARCKs or RACKSs during important cellular transitions in the egg. Moreover, with each cellular transition (i.e. germinal vesicle breakdown, meiosis I, meiosis II, etc) comes an extensive rearrangement of architectural elements within the cell. To accomplish this regulatory elements in signaling pathways should be in close molecular proximity to other discrete signaling pathways both to increase the speed of chemical reactions and to promote crosstalk. Crosstalk between signaling pathways is essential to modulate downstream effectors as one pathway can trigger activation/inhibition of another. It also is important to sequester or restrict access to various signaling enzymes for later use. These requirements create both morphological and biochemical heterogeneity, and likely necessitate the use of molecular scaffolds. This review examines the body of literature suggesting cytoskeletal elements serve to meet the aforementioned requirements in the mammalian egg.