Fertilization in the Pig: Sequence of Nuclear and Cytoplasmic Events

Abstract

The timing of sperm penetration, pronuclear formation and syngamy was examined in twenty-four gilts in which ovulation had been controlled precisely by means of an injection of hcg given during prooestrus. Animals were mated at the time of ovulation and eggs recovered at autopsy exactly 3, 4, 5 or 6 hr later.Twenty of the twenty-four animals (83 %) yielded some penetrated eggs, a total of 234 eggs being examined. The mean number of spermatozoa attached to or within the zona pellucida increased progressively from 6\m=.\8 (range 1 to 25)/egg at 3 hr to 109\m=.\2 (range 1 to 466) some 6 hr after mating. Likewise, the proportion of eggs classified as fertilized increased from 23\m=.\7% at 3 hr to 71\m=.\9%by 5 hr after mating. Developing pronuclei were observed at 4 hr and apposing pronuclei within 5 hr of mating, but most of the penetrated eggs examined at these intervals were in anaphase or telophase of the second meiotic division.The results emphasize that under conditions of induced ovulation, a population of capacitated spermatozoa first becomes available in the Fallopian tubes of oestrous pigs within 2 to 3 hr of semen deposition by way of the cervix. It is suggested that the sequence of events leading to sperm penetration may be accelerated following injection of hcg during pro-oestrus and mating at the time of ovulation.

A detailed analysis of early events during in-vitro fertilization of bovine follicular oocytes

“…This is close to the estimated time for bull sperm capacitation in vivo (Hunter, 1980), but much longer than that found in thecat (Niwaeia/., 1985). Sperm head decondensation (from pronucleus 1 to pronucleus 3) occurred within 1-2 h after penetration, and it seems that 4-6 h were required for the decondensed chromatin to develop into the subsequent pronuclear stages (from pronucleus 3 to pronucleus 6), which is similar to the 5 h found in pig (Hunter, 1972).…”

“…Two large pronuclei were found 15 h after mating in the rabbit (Zamboni & Mastroianni, 1966), and Hunter (1972) presented evidence that opposing pronuclei appeared 5 h after mating in the pig. Accurate timing of events is difficult because the time required for pronuclear development is not only species-specific, but also affected by the assessment of the ovulation time and the time required for sperm capacitation in vivo (Hyttel et al, 1988).…”

Local Action of Progesterone Leading to Polyspermic Fertilization in Pigs

“…It is unlikely that there was any permanent effect on the function of the cortical granules (see Szollosi, 1962Szollosi, , 1967 or on the block to polyspermy since only a very limited number of spermatozoa, usually two, entered the polyspermic eggs. On the other hand, the involvement of progesterone in development of the acrosome reaction has been suggested (Austin, Bavister & Edwards, 1972), and the possibility of steroid involvement in the capacitation of porcine spermatozoa has been dis¬ cussed (Hunter, 1972). If progesterone does act at the membrane level to facilitate the acrosome reaction, then this might indicate another mechanism whereby the local injections of progesterone led to an increased incidence of polyspermy.…”

Ejaculated Boar Spermatozoa Can Penetrate Oocytes Maturing In Vitro without Preincubation.

“…In the present studies, we found that the female pronucleus was already forming when oocytes were fixed 6 h after insemination with washed but otherwise untreated spermatozoa. As previous studies have shown that frozen-thawed boar spermatozoa (fully capacitated) need 2 or 3 h to penetrate oocytes in vitro [14], and Hunter [15] estimated that pronucleus formation takes place some 2 h after oocytes penetration in vivo, our re-that are not apparent. In the present experiments, a specific beneficial effect of Percoll washing might have been concealed because the sperm samples already displayed very high fertility, as demonstrated by the high rate of oocyte penetration by control-washed spermatozoa.…”