In vitro culture of rabbit ova fertilized by epididymal sperms in chemically defined media

Sperm-egg interaction and fertilization: past, present, and future

Fifty years have passed since the findings of capacitation and acrosome reaction. These discoveries and the extensive effort of researchers led to the success of in vitro fertilization, which has become a top choice for patients at infertility clinics today. The effort to understand the mechanism of fertilization is ongoing, but the small number of eggs and similarly small quantity of spermatozoa continue to hinder biochemical experiments. The emergence of transgenic animals and gene disruption techniques has had a significant effect on fertilization research. Factors considered important in the early years were shown not to be essential and were replaced by newly found proteins. However, there is much about sperm-egg interaction which remains to be learned before we can outline the mechanism of fertilization. In fact, our understanding of sperm-egg interaction is entering a new stage. Progress in transgenic spermatozoa helped us to observe the behavior of spermatozoa in vivo and/or at the moment of sperm-egg fusion. These advancements are discussed together with the paradigm-shifting research in related fields to help us picture the direction which fertilization research may take in the future.

Artificial insemination with frozen epididymal sperm in cats

Artificial insemination with frozen cauda epididymal sperm was performed in cats. Sperm were transmigrated from the epididymides in 10 male cats. The mean sperm motility and viability were 67% and 82.5%, respectively, and 11.6 x 10(7) sperm were recovered. The mean sperm motility after thawing was 24.0%. Eleven female cats received unilateral intrauterine insemination of 5 x 10(7) sperm, and the conception rate was 27.3% (3/11). This was the first case of conception obtained with frozen epididymal sperm in cats.

Calcium concentration and fertilization by subzonal insemination of a single spermatozoon in mouse oocytes

The effect of calcium concentration in culture medium on the fertilization of subzonally microinseminated mouse oocytes was examined. Oocytes were injected with a single spermatozoon so that the sperm head was forced to adhere onto the ooplasmic membrane with a micromanipulation technique. For the inseminations, epididymal spermatozoa preincubated in culture medium and those treated with ionophore A23187 were used. Inseminated oocytes were cultured using media with three different calcium concentrations of 1.71, 3.42, and 5.13 mM; 40.0%, 71.6%, and 47.9% of oocytes microinjected with preincubated sperm were fertilized after incubation with those media, respectively. When the oocytes inseminated with ionophore-treated sperm were incubated in media containing 1.71 and 3.42 mM calcium, their fertilization rates were 58.2% and 87.5%. Thus fertility of subzonally microinseminated oocytes was obviously enhanced when cultured in medium with 3.42 mM of calcium, irrespective of being inseminated with preincubated sperm (P < 0.01) or with ionophore-treated sperm (P < 0.005). Some of the microinseminations with preincubated sperm were performed without sperm adhered to the oolemma. In these cases, the incidence of fertilization was not improved by incubating the inseminated oocytes in medium containing 3.42 mM calcium (32.6%) as compared to those incubated in medium with 1.71 mM calcium (28.3%). These results suggest that the concentration of extracelluar calcium exerts an important effect on the progress of fertilization events subsequent to sperm adherence onto the ooplasmic membrane. Almost 80% of the zygotes fertilized via incubation in medium with 3.42 mM of calcium developed into blastocysts after culturing in vitro.

Subzonal insemination with a single spermatozoon using manipulation assisted sperm adhesion onto the ooplasmic membrane in mouse ova

A simple and successful method of microinjection of a single spermatozoon under the zona pellucida of a mouse oocyte has been developed. A characteristic of this method is that the tip of the sperm injection needle pierces the zona pellucida without touching the ooplasmic membrane. All the ova (277) used for this series of experiments had normal morphology after the injection procedure. Spermatozoa preincubated in culture medium for capacitation and those treated with ionophore A23187 for induction of acrosome reaction were used. In combination with some of these injections, a manipulation assisting the adhesion of the sperm head onto the ooplasmic membrane was employed. The fertilization rate (67.3%) of the ova injected with the ionophore-treated sperm using the sperm-adhesion treatment was significantly higher (P less than 0.005) than that obtained by the injection of the preincubated sperm without applying the adhesion treatment (23.6%). All three of the recipients that received the 24 fertilized ova became pregnant and gave birth to 11 offspring (45.8%). The inseminations performed with the sperm-adhesion treatment using the immotile sperm from the preincubated population and/or those from the ionophore-treated population did not result in fertilization in any case. These results suggest that the fertilization rate of subzonal insemination with motile ionophore-treated sperm can be improved by applying the sperm-adhesion treatment and that sperm motility might be involved in the establishment of fertilization, even after the adhesion of the sperm head with the mouse ovum membrane.

The survival of whole and bisected rabbit morulae after cryopreservation by the vitrification method

The survival of whole and bisected rabbit morulae cryopreserved by the vitrification method was investigated. The embryos were loaded in a column of vitrification solution (VS, a mixture of 25% glycerol and 25% 1, 2-propanediol in PBS+16% calf serum), which was located between two columns of 1 M sucrose solution in a plastic straw. The embryos were frozen by being plunged into liquid nitrogen and thawed in a water bath at 20 degrees C. Two methods of loading embryos into straws were used: the single and double column vitrification solution methods. The embryonic survival rates between these two methods were compared. Seventy-one (86.6%) out of 82 morulae vitrified in double column straws developed into the blastocyst stage in vitro. Eleven (18.3%) live fetuses were obtained after the transfer of 60 frozen-thawed morulae to four recipients. By contrast, the survival rate (36.5%, 27 74 ) of embryos vitrified in the single column straws was significantly lower (P<0.05). The vitrification solution of the single column straws became opaque, indicating ice-crystal formation, upon thawing in 5 of 11 straws, which was assumed to have damaged the embryos. More than 80% (29 36 ) of the bisected morulae frozen and thawed in the double column straws developed to the blastocyst stage in vitro when cryoprotectant was diluted stepwise with 1 M and 0.25 M sucrose solution. When the cryoprotectant was removed by one-step dilution with 1 M sucrose solution, swelling in blastomeres was observed and the development rate of the recovered embryos decreased (45.8%, 11 24 ). These results indicate that the vitrification method employed in our experiment is not only efficient for the cryopreservation of rabbit morulae, but it can also be used for the preservation of bisected rabbit morulae, which had not been successful using previous methods.

Retention of labelled DNA precursor by murine cells after a single administration of tritium labelled thymidine

The central zone of the rat lens epithelium, extending half way from the centre to the periphery of a whole mount preparation, normally has less than 1% of the cells in the cell cycle at any given time. Mechanical wounding initiates a burst of proliferation in the central zone. DNA synthesis begins 14 hr after wounding followed by mitosis 10 hr later. When [3H]TdR was applied at 2 hr prior to S phase, some moderately heavy and some light labelling was observed after the onset of S phase. When [3H]TdR was applied 5 hr before S phase (9 hr after wounding), all the cells were lightly labelled. Only small amounts of the label were available to these cells 5 hr after application. It is significant that there was labelling in this group because it indicates the persistence of relatively small intracellular pools of [3H]TdR for several hours after the initial 'pulse' labelling of cells. Determinations of the duration of S phase were based on the assumption that pulse labelling may be affected by the persistence of the pools of [3H]TdR and consequent light labelling of the cells.

A long-lived thymidine pool in epithelial stem cells

The labelling index (LI) of the individual basal cell positions of the anterior column of mouse tongue filiform papillae was assessed with time after an injection of [3H]TdR at 12.00 hours (the minimum point in the circadian LI rhythm). An initial doubling of the LI in the stem cell zone due to cell division was followed by a second rise of 14-16% 16 hr after injection and this occurred even in the presence of vincristine. Although the uptake of [3H]TdR and the initial LI doubling were largely prevented by a preceding injection of hydroxyurea, the 14-16% LI rise was still observed. The possible explanations are discussed, the favoured one being that an average of one of the six or seven cells (the stem cell) in each stem cell zone can store [3H]TdR in a long-lived precursor pool for at least 16 hr before being utilized for DNA synthesis. This complements previously published work which suggested that one cell in each stem cell zone may selectively segregate DNA at mitosis.

Potential pitfalls of [3H]thymidine techniques to measure cell proliferation

Pitfalls and artifacts in the use of [3H]thymidine in the measurement of cell proliferation kinetics in vitro and in vivo are reviewed. These pitfalls are of particular significance for the study of inhibitors of cell proliferation including chalones.