Transformation of sperm nuclei into male pronuclei in nucleate and anucleate fragments of parthenogenetic mouse eggs

Abstract

Our objective was to examine the ability of nucleate and anucleate fragments of artificially activated mouse eggs to transform sperm nucleus into male pronucleus. To this end, zona-free oocytes in metaphase II were activated by ethanol and bisected into halves (one with the spindle, the other anucleate) either within 10 to 20 min (series A) or 3 or 5 hr later (series B). In series A, the fragments were inseminated 3.5, and 8 h after activation, and in series B, 3 and 5 h after activation. Both nucleate and anucleate fragments lose the capability of transforming sperm nucleus into fully formed pronucleus sometime between 3 and 5 h after activation. In 8 h old parthenogenetic fragments, the majority of sperm nuclei remain unchanged or begin decondensation but never reach the stage of an early pronucleus. In over 1/3 of anucleate fragments of this age group, sperm nuclei develop defectively; chromatin decondenses inside the persisting nuclear envelope. In other experimental groups, the incidence of these abnormal sperm nuclei varies between 0 and 10%. In general, the anucleate fragments retain the capability to transform sperm nuclei (fully or partially) longer than their nuclear counterparts. This difference may be accounted for by a different level of substances required for pronuclear growth (extrachromosomal constituents of the germinal vesicle and nuclear lamins): high and constant in the cytoplasm of anucleate egg halves and low and progressively decreasing in the nucleate halves because of their putative uptake by the female pronucleus. However, the cytoplasmic factors responsible for the initial stages of transformation (nuclear envelope breakdown, chromatin decondensation) become eventually inactivated both in the presence and in the absence of a female pronucleus.

Spindle assembly checkpoint-related failure perturbs early embryonic divisions and reduces reproductive performance of LT/Sv mice

“…Moreover, we previously showed that the timing of MPF activation, spindle formation, mitosis duration, and the most importantly SAC inactivation do not differ between onecell parthenogenotes and fertilized embryos (Ciemerych et al 1999, Sikora-Polaczek et al 2006. Other studies also confirmed the usefulness of one-cell parthenogenotes for the analyses of different aspects of the mouse preimplantation development (Waksmundzka et al 1984, Borsuk & Tarkowski 1989, Ciemerych 1995, Winston & Maro 1995, Kalab et al 1996. However, time-lapse recordings were performed using exclusively embryos obtained after in vivo fertilization, i.e., zygotes and two-cell embryos.…”

Mammalian and avian embryology at Warsaw University (Poland) from XIX century to the present

“…These oocytes can be penetrated by spermatozoa even several hours after activation, and spermatozoa which entered these preactivated oocytes undergo at least partial transformation (Komar, 1979(Komar, ,1982. Later we demonstrated that the ability of the cytoplasm of artificially activated oocyte to decondense sperm chromatin disappears gradually during the first cell cycle of the parthenogenetic embryo (Borsuk and Tarkowski, 1989) and reappears during the first mitotic division (Maleszewski, 1992;. However, the decondensastion of sperm chromatin does not necessarily indicate that this chromatin can undergo transformation into male pronucleus.…”

“…However, the decondensastion of sperm chromatin does not necessarily indicate that this chromatin can undergo transformation into male pronucleus. In collaboration with Dan and Maryna Szollosi, we have demonstrated that the breakdown of the spermatozoon's nuclear envelope is a prerequisite for the transformation of the sperm nucleus into functional pronucleus (Borsuk and Tarkowski, 1989;Maleszewski 1990, 1992, Szollosi et al, 1990, Borsuk, 1991. However, Szollosi et al (1994) showed that the decondensation of sperm chromatin is not fully preventable by the lack of sperm nuclear envelope breakdown.…”

“…This confirmed earlier observation of Wolf (1978) who showed that in mouse a block to polyspermy can develop in fertilised, zona-free oocytes. The mechanism of the oolemma block to sperm penetration remains obscure, but it seems to be independent of oocyte activation, since the oolemmae of parthenogenetically activated oocytes remain fusible with spermatozoa much longer than those of fertilised oocytes (Komar, 1979(Komar, ,1982Borsuk and Tarkowski, 1989;Maleszewski, 1992). Several observations suggest that this block against sperm penetration is induced by sperm-oocyte fusion (Maleszewski and Bielak, 1993;Maleszewski et al, 1996;Pyrzynska et al, 1996), and can be induced in any cell that does not posses such a block (GV oocyte, MII oocyte, parthenogenetic embryo) by fusion with a cell that has already developed the block (zygote) (Krukowska et al, 1998).…”

Effects of Activation Timing on the Fertilization Rate and Early Embryo Development in Porcine ROSI Procedure

“…NEBD of a male gamete nucleus is prerequisite for the decondensation of the male gamete nucleus and subsequently for the formation of a male pronucleus (PN) (1)(2)(3). The capability of mammalian oocyte to induce NEBD of a male gamete disappears within a few hours after oocyte activation (4,5).…”