What do mouse eggs look like? - briefly
Mouse oocytes are roughly 70–80 µm in diameter, appearing spherical and translucent under a light microscope, surrounded by a thin zona pellucida. The cytoplasm contains a centrally located nucleus and is filled with fine granules and organelles.
What do mouse eggs look like? - in detail
Mouse oocytes are spherical cells with a diameter of approximately 70–80 µm at the germinal‑vesicle (GV) stage and 80–85 µm after meiotic maturation to the metaphase‑II (MII) stage. The plasma membrane is smooth, enclosing a clear, homogeneous cytoplasm that contains a central nucleus (the germinal vesicle) in immature cells. Upon completion of meiosis I, the nucleus condenses into a metaphase plate, and the cell extrudes the first polar body, leaving a smaller second polar body attached to the oocyte surface.
Key structural features observable under light or differential‑interference contrast microscopy include:
- Zona pellucida: a translucent, glycoprotein envelope 5–7 µm thick that surrounds the oocyte, appearing as a faint halo.
- Perivitelline space: a narrow fluid-filled gap between the zona pellucida and the plasma membrane, often visualized as a thin dark line.
- Cytoplasmic granularity: occasional lipid droplets and vesicles create a mildly speckled appearance, more pronounced in older females.
- Mitochondrial distribution: clusters of mitochondria aggregate near the cortex, giving the peripheral cytoplasm a slightly denser look in high‑resolution images.
When stained with DNA‑binding dyes (e.g., Hoechst 33342) and examined by fluorescence microscopy, the chromatin of the GV stage forms a compact, centrally located fluorescent mass, whereas the MII stage displays a distinct metaphase plate with aligned chromosomes at the animal pole. Immunofluorescent labeling of the actin cortex reveals a thin, uniform band beneath the plasma membrane, contributing to the cell’s rounded contour.
Electron microscopy provides further detail: the plasma membrane shows a typical lipid bilayer; the zona pellucida consists of interwoven filaments; the cytoplasm contains abundant rough endoplasmic reticulum, Golgi stacks, and a high density of mitochondria with dense cristae. The cortical region exhibits a dense array of microfilaments that support polarity and facilitate fertilization.
Overall, mouse oocytes present as uniformly round, translucent cells with a well‑defined zona pellucida, a clear cytoplasm, and stage‑specific nuclear morphology, all of which are consistently observed across standard microscopic techniques.