The construction of a mammalian oocyte involves the collaboration of a number of cells. Each oocyte is surrounded by layers of follicle cells, i.e. granulosa cells, separated from the oocyte by the zona pellucida, which is secreted by the oocyte. Microvilli from the granulosa cells cross the zona pellucida and attach to the oocyte by desmosomes and gap junctions for the transfer of proteins and nucleic acids (mRNA and rRNA) to the oocyte cytoplasm.