Paper - The Comparative Behavior of Mammalian Eggs in Vivo and in Vitro

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Pincus G. and Enzmann EV. The Comparative Behavior of Mammalian Eggs in Vivo and in Vitro. (1935) J Exp Med. 62(5):665-75. PMID 19870440

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The Comparative Behavior of Mammalian Eggs In Vivo And In Vitro

I. The Activation of Ovarian Eggs

By Gregory Pincus, S.D., And E. V. Enzmann, Ph.D.

(From the Biological Laboratories, Harvard University, Cambridge)

This investigation has been aided by a grant from the National Research Council Committee for Problems of Sex.

PLATES 29 AND 30

(Received for publication, July 17, 1935)

The eggs of most mammals are shed from the ovary with the first polar body formed. The mechanism controlling this stage of maturation has never been investigated in detail. Furthermore, under normal conditions only shed ova are fertilized. Does this indicate that the first maturation division is an essential prelude to fertilization? Or may ovarian eggs in fact be activated before the first meiotic division?

This investigation concerns itself with these problems, and falls into two parts dealing with: (1) the mechanism controlling the first meiotic division; (2) the capacity for fertilization of ovarian eggs. Superficially unrelated, these two studies are aspects of the broad problem of the fundamental nature of the activation process.

Experimental

The rabbit is especially favorable material for this study since it ovulates only after copulation. It has been established that copulation results in a stimulation of pituitary secretion, and that the amount of anterior pituitary secretion necessary to induce ovulation occurs during the 1st hour after copulation (Deansley, Fee, and Parkes, 1930). The injection of pituitary extracts or of prolan induces ovulation (Friedman, 1929); and furthermore, ovulation induced by stimulating hormones occurs at 10 hours after injection (Bellerby, 1929). Ova are normally shed with the first polar body at 10 hours after copulation. According to Heape (1905) both polar bodies are formed at 9 hours after copulation.

Heape’s statement is but partially correct. Only one polar body is formed. We have investigated this situation in detail, and our data are summarized in Table I. Before copulation occurs the ovum contains a single large vesicular nucleus about 30 microns in diameter (Fig. 1). At 2 hours after copulation some of the ripe ova show signs of the initiation of maturation. The diakinesis-like chromatin begins to condense into tetrads, but the nuclear membrane remains intact (Fig. 2). The separation of strands of follicle cells adjacent to the corona radiata begins to be manifest. By 4 hours after copulation the tetrads of the first polar spindle are formed and the nuclear membrane is ordinarily dissolved (Figs.

Table I

Progressive Changes in M aturing Ovarian Eggs during the Time Interval between Capulaticm and Ovulation

Time No. of elfigggd cases Condition of the egg Condition of the follicles copulation °b5e”°d hrs.

0 10 Egg fully grown. Nucleus ve- Average diameter 970 p.. The sicular, in some cases vesicu- follicular epithelium forms a lar tetrads present spider web. In some cases the

egg is in a cumulus

2 9 The vesicular nucleus present in Spider web arrangement of granu- most cases. In all cases tet- losa. Liquor folliculi increas- rads present ing in amount. Disintegration of follicle cells adjacent to corona begins

4 7 Vesicular membranes have dis- Average diameter 1045 p. Fol- appeared. Only traces pres- licular epithelium changing ent. Tetrads free in cyto- from spider web to cumulus plasm type

6 6 Chromatic material decreases Most follicles in cumulus type. very much in size and forms The liquor folliculi becomes in- the first spindle. No trace of creasingly viscous nuclear membrane left

7 4 First polar body extruded in As in preceding type many cases. The remaining chromatin moves sideways

8 10 First polar body present in all Average diameter 1125 p cases

9 4 First polar body present. Sec- Average diameter 1310 p. Egg

and spindle in place and ready to form the second polar body almost free in follicle

3, 4, and 5). The metaphase plate is found in all maturing ova by 6 hours after copulation, and the freeing of the egg and corona from the connecting follicular strands is almost complete. The fiI'3t polar body is given off between 7 and 8 hours after copulation (Fig. 6). The second polar spindle is formed during the 9th hour post coitum and the ripe ovum (Fig. 7) is shed between 9:} and 10% hours.

Plate 1

FIG. 1. Ovarian egg obtained by puncture of a follicle from the ovary of an unmated rabbit.

FIG. 2. Ovarian egg obtained by puncture of a follicle from the ovary of a doe mated 2 hours previously. The chromatin material condenses to tetrads. The vesicular membrane is still present.

FIG. 5. Ovarian egg from a doe mated 6 hours previously. The first polar spindle begins to form.

FIG. 6. Ovarian egg from a doe mated 8 hours previously. The first polar body has been given off.

FIG. 9. Ovarian egg from a doe which had received 2 cc. thyroxin intravenously. Tetrads have formed in a vesicular nucleus.

FIG. 10. Ovarian egg from unmated doe, inseminated with normal sperm in vitro. Sperm penetration has occurred. Note sperm head at lower right periphery.

Plate 2

FIG. 3. Ovarian egg from a doe mated 4 hours previously. Tetrads fully formed and vesicular nucleus dissolved.

FIG. 4. Ovarian egg from a doe mated 5 hours previously. The tetrads have become smaller and arranged themselves in a plate. All traces of the vesicular membrane have disappeared.

FIG. 7. Ovarian egg from a doe mated 9 hours previously. First polar body and second polar spindle.

FIG. 8. Ovarian egg cultured for 24 hours in Ringer-Locke solution containing maturity hormone. Note apparent fusion nuclei.

FIG. 11. Ovarian egg from a doe mated 6 hours previously and inseminated in vitro with normal sperm. Male and female pronuclei present side by side.

FIG. 12. Ovarian egg from a doe mated 8 hours previously and inseminated with normal sperm. The first polar body has formed and sperm penetration occurred. The entering spermatozoan has formed a male pronucleus (centre left).

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