Search results
Results From The WOW.Com Content Network
Oocyte (or ovum/egg) activation is a series of processes that occur in the oocyte during fertilization. Sperm entry causes calcium release into the oocyte. In mammals, this is caused by the introduction of phospholipase C isoform zeta (PLCζ) from the sperm cytoplasm. [ 1 ]
The first frog egg extract was reported in 1983 by Lohka and Masui. [1] This pioneering work used eggs of the Northern leopard frog Rana pipiens to prepare an extract. Later, the same procedure was applied to eggs of Xenopus laevis, becoming popular for studying cell cycle progression and cell cycle-dependent cellular events. [2]
G 1 phase is the first of the four phases of the cell cycle, and is part of interphase. While in G 1 the cell synthesizes messenger RNA (mRNA) and proteins in preparation for subsequent steps of interphase leading to mitosis. In human somatic cells, the cell cycle lasts about 18 hours, and the G 1 phase makes up about 1 / 3 of that time. [13]
Many studies show that cumulus expansion is critical for the maturation of the oocyte because the cumulus complex is the oocyte's direct communication with the developing follicle environment. It also plays a significant role in fertilization, though the mechanisms are not entirely known and are species specific. [4] [5] [6]
In the brown alga Fucus, all four egg cells survive oogenesis, which is an exception to the rule that generally only one product of female meiosis survives to maturity. In plants, oogenesis occurs inside the female gametophyte via mitosis. In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia.
The egg cell is generally asymmetric, having an animal pole (future ectoderm). It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
These chromosomes, carrying genetic information, align in the equator of the cell between the spindle poles at the metaphase plate, before being separated into each of the two daughter nuclei. This alignment marks the beginning of metaphase. [2] Metaphase accounts for approximately 4% of the cell cycle's duration. [citation needed]
Meiotic resumption is visually manifested as “germinal vesicle breakdown” (GVBD), [4] referring to the primary oocyte nucleus. [5] GVBD is the process of nuclear envelope dissolution and chromosome condensation similar to mitotic prophase. In females, the process of folliculogenesis begins during fetal development. Folliculogenesis is the ...