Morphometric analysis of the zona pellucida and ooplasm of squirrel monkey (Saimiri sciureus) eggs

The objective of this study was to correlate the thickness of the zona pellucida (zona) with egg (oocyte) maturity determined through a widely-used method of assessing oocyte maturation namely, the evidence for cumulus and corona cells expansion. Measurements of the zona of cultured oocytes were recorded at 0, 3, 6, 24, and 48 hr after laparoscopic oocyte retrieval from hormonallystimulated squirrel monkeys. The results indicated that at the time of oocyte retrieval, oocytes that were classified as mature had thicker zonae compared with immature oocytes. The zona layer of the mature oocyte expanded to a maximum after 6 hr of incubation while the zona layer of the immature oocyte became compressed. The diameter of the mature oocyte (minus the zona and perivitelline space) became smaller with time while the immature oocyte diameter remained relatively unchanged. The correlation between the maturational state of the oocyte and the thickness of the zona layer suggest the possible application of zona morphometric evaluations as an indicator of oocyte maturation.