oocyte
gameto.site · being built
| What it is | The female germ cell, the egg, held in the ovary from fetal life until ovulation. |
|---|---|
| Comes from | Primordial germ cell |
| About | Oocytes begin meiosis during fetal development and stay arrested in prophase I until the signals that lead to ovulation. |
| Source | Nunes C, Silva JV, Silva V, Torgal I, Fardilha M. Signalling pathways involved in oocyte growth, acquisition of competence and activation. Hum Fertil (Camb). 2015;18(2):149-55. PMID: 25738216 |
| Status | being built; its twin, knowledge and helper come with gameto.site |
Where it lives
| The ovarian follicle: the oocyte at the follicle wall inside its zona pellucida, wrapped in cumulus granulosa cells, the antrum filling with fluid as the follicle grows | human · PMID 3558758 |
What it does
| Begins meiosis in the fetal ovary, arrests at the germinal vesicle stage of prophase I, and completes meiosis I only at ovulation and meiosis II at fertilisation | mammalian, review · PMID 18084010 |
| Its follicle is recruited 15 to 20 days before ovulation from a pool 2 to 5 mm across, having started its growth about 85 days earlier | human · PMID 3558758 |
What goes wrong
| Meiosis I in human oocytes carries an age-related high rate of chromosome mis-segregation, such as trisomy 21 | human · PMID 18084010 |
| Most growing follicles are lost to atresia; only the dominant follicle reaches ovulation | human · PMID 3558758 |
Pictures 3
Representative bright-field (A-D) and birefringence (A1-D1) images of metaphase II spindle-positive oocytes captured using the Oosight Imaging System. Oocytes were qualitatively classified on the basis of birefringence morphology and signal intensity in both the spindle and zona pellucida (ZP). (human; Figure 1, panels A-D (bright-field) and A1-D1 (birefringence), four quality groups of human MII oocytes.)
Lee, Chen, Lo et al 2026, Frontiers in Endocrinology · CC BY 4.0
Cytoplasmic reorganisation of oocytes treated or not with metaphase II-follicular fluid extracellular vesicles (MII-ffEVs) during in vitro maturation. TEM images of oocytes. Scale bars (A-C) 20 µm, (D) 10 µm and (E-H) 5 µm. M-SER, mitochondria smooth endoplasmic reticulum (highlighted by white dotted line); MV, mitochondria vesicle; pvs, perivitelline space; mi, microvilli; ZP, zona pellucida. (human; Figure 5, panels A-C (whole-oocyte TEM at 20 µm scale; rows 0-707 of figure).)
Makieva, Saenz-de-Juano, Almiñana et al 2026, Human Reproduction Open · CC BY 4.0
Fluorescence images of human IVM-MII oocytes by laser confocal microscopy. Scale bar, 20 um. (A) Effect of NADH on CDK2 in IVM-MII oocytes. (C) Effect of NADH on GAS6 in IVM-MII oocytes. (E) Effect of NADH on C14orf36 in IVM-MII oocytes. (G) Effect of NADH on DCM1 in IVM-MII oocytes. (I) Effect of NADH on FIGN in IVM-MII oocytes. (K) Effect of NADH on FAM9B in IVM-MII oocytes. Each panel shows immunofluorescence channel, brightfield, and merged overlay for control and NADH-treated oocytes. Adapted: micrograph panels A, C, E, G, I and K rearranged side by side; bar chart panels removed. (human (IVM-MII oocytes); Figure 7, panels A, C, E, G, I, K (confocal IF micrographs only; bar chart panels B, D, F, H, J, L excluded; left group cols 5-257 and right group cols 420-664 of full figure, stitched).)
Zhang, Yang, Yang et al 2025, Frontiers in Endocrinology · CC BY 4.0
Papers 3
- Lee CI, Chen HH, Lo WC, Huang CC, Lee TH, Lin PY, et al. Spindle-to-oocyte light retardance ratio as a noninvasive biomarker for oocyte quality assessment: a prospective cohort study. Front Endocrinol (Lausanne). 2026;17:1803476. PMID: 42165024.
- Makieva S, Saenz-de-Juano MD, Almiñana C, Bauersachs S, Bernal-Ulloa S, Xie M, et al. Treatment of human oocytes with extracellular vesicles from follicular fluid during rescue in vitro maturation enhances maturation rates and modulates oocyte proteome and ultrastructure. Hum Reprod Open. 2026;2026:hoag021. PMID: 41924634.
- Zhang Q, Yang H, Yang D, Lu H, Xiong M, Xie L, et al. NADH supplementation improves human oocyte maturation and developmental competence of resulting embryos in controlled ovarian hyperstimulation cycles: a pilot study implicating the CDK2/GAS6 signaling pathway. Front Endocrinol (Lausanne). 2025;16:1627679. PMID: 40969372.