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(cell and molecular biology)
One of the two nuclear bodies of a newly fertilized ovum, the male pronucleus and the female pronucleus, the fusion of which results in the formation of the germinal (cleavage) nucleus.



the haploid nucleus of a sex cell, or gamete. During fertilization, the diploid nucleus of the zygote, or synkaryon, is formed by the fusion of two pronuclei; the chromosome sets of both pronuclei are joined in the synkaryon.

In multicellular organisms and a number of protozoans that are anisogamous, there are female and male pronuclei. The female pronucleus is the nucleus of a mature egg cell, or macro-gamete. The male pronucleus is formed by the swelling of the nucleus of a spermatozoid, or microgamete, after it has become embedded in the cytoplasm of an egg cell. In isogamous unicellular organisms, the fusing pronuclei, like the gametes themselves, are morphologically indistinguishable. During autogamy, pronuclei that have been formed in the same cell fuse; they are usually sister nuclei. During conjugation in infusorians, two pronuclei form in each partner—a stationary pronucleus and a migrating pronucleus. There is first an exchange of migrating pronuclei between partners through a cytoplasmic bridge, which is followed by the fusion of the pronuclei in each of the partners.

References in periodicals archive ?
>2PN: oocytes with more than 2 pronuclei. TABLE III EFFECT OF THE SUPPLEMENT IN THE CULTURE MEDIUM MSOFAACI ON DEVELOPMENT OF BOVINE EMBRYOS IVP Total zygotes > 4 cells Total cleaved Morulae Blastocyst in IVC embryos embryos D3 D6 D7 (mSOFaaci) n n n n n (%) (%) (%) (%) PVA 94 190 65 67 262 (35.8) (a) (72.51) (a) (24.8) (a) (25.4) BSA 102 199 83 90 287 (35.5) (a) (69.33) (a) (28.9) (a) (31.3) FCS 20 60 33 37 137 (14.59) (b) (43.79) (b) (24.08) (b) (27) Different letters in the same column differ significantly (a,b) P<0.05).
No statistically significant differences were found in the time from ICSI to the extrusion of the second polar body, the time from ICSI to the appearance of the pronuclei, the time from ICSI to the fading of the pronuclei, the times from ICSI to the first frames in which 2-and 3-cell stage were observed, and the duration of the first cell cycle.
Normal fertilization was determined 16-20 hours after ICSI by presence of two pronuclei and FR estimated by number of fertilized oocytes per number of microinjected oocytes.7,14 Embryos were evaluated on alternate days and were transferred in the blastocysts stage.
The nuclei of fish eggs are small and difficult to visualize, the chorion, hardens soon after fertilization [12] and in many fish species the pronuclei of fertilized eggs is not visible and transgenes are usually injected into the egg cytoplasm.
According to the genomic imprinting map, it appeared highly probable that the responsible gene for the parthenogenetic death should be located on mouse proximal Chr6, because this is the only imprinted region that causes early embryonic lethality upon maternal duplication, like the parthenogenetic embryos, with two maternally derived pronuclei (Fig.
Differential H4 acetylation of paternal and maternal chromatin precedes DNA replication and differential transcriptional activity in pronuclei of 1-cell mouse embryos.
Thus, pronuclei, which are generated only after polar bodies are fully formed, do not appear to play a vital role in terminating the calcium signal in nemerteans, unlike in some mammalian oocytes where pronuclear formation is involved in the cessation of calcium oscillations (Marangos et al., 2003).
A recent report has shown that the rapid loss of 5-mC from mouse paternal pronuclei was accompanied by an accumulation of genomewide 5-hmC (34).
Previously, Herbert and her colleagues had performed a similar technique using fertilized human eggs, extracting and transferring the "pronuclei"--the nuclei from the parents' egg and sperm before the two have fused-into healthy donor eggs.
This gradient of [Ca.sup.+] ion concentration promotes membrane fusion of the male and female pronuclei (Munehara and others 1989).
(24) A healthy fertilized egg will have two identifiable pronuclei and two polar bodies.
Three then are implanted, while the remaining eggs are frozen before the two "pronuclei" have combined at about 20 hours after fertilization.