Effect of Cycloheximide on In Vitro Development of Electrically Activated Feline Oocytes

Developmental competence of cat (Felis domesticus) oocytes and embryos after parthenogenetic stimulation using different methods

The aim of this study was to compare the effects of various activating factors on feline oocytes. The study included activation within the ovary (natural), activation during in vitro maturation (spontaneous activation), chemical activation (ionomycin + 6-DMAP), activation by spermatozoa and injection (ICSI) and mechanical activation (sham ICSI). According to our results, parthenogenetic embryos could emerge at every step of in vitro embryo production (IVP) procedures. After oocyte collection, 6% of parthenogenetic embryos were observed, mainly at the 2-4-blastomere stages. After 24 h of in vitro maturation, parthenogenetic activation was observed in 7% of oocytes. Using ionomycin and 6-DMAP to artificially activate oocytes, 53% of cleaved embryos were obtained. The results after ICSI (54% cleaved embryos) were not significantly different from the results in Group III using chemical activation (53% cleaved embryos). But only after ICSI were blastocysts obtained (5/73.7%) as a result of in vitro culture. Moreover, embryos after ICSI were of the best morphological quality with minor levels of fragmentation evident in the embryos. After sham mechanical activation, 'sham ICSI', 8% of cleaved embryos were noted. Therefore, it is advised to maintain a negative control in parallel with each step of IVP techniques, to avoid misleading results. Chemical methods for artificial activation of feline oocytes are the most promising for application to the cloning and production of parthenogenetic embryos for experimental studies.

Cloning Endangered Felids by Interspecies Somatic Cell Nuclear Transfer

In 2003, the first wild felid was produced by interspecies somatic cell nuclear transfer. Since then other wild felid clone offspring have been produced by using the same technique with minor modifications. This chapter describes detailed protocols used in our laboratory for (1) the isolation, culture, and preparation of fibroblast cells as donor nucleus, and (2) embryo reconstruction with domestic cat enucleated oocytes to produce cloned embryos that develop to the blastocyst stage in vitro and, after transfer into synchronized recipients, establish successful pregnancies.

Effect of culture medium and prostaglandin I(2) (PGI(2)) analogue on in vitro development of parthenogenetically activated cat oocytes

A method of reliably producing developmentally competent cat embryos in vitro is a prerequisite for study of the physiology of early development and application of assisted reproductive techniques. Oocytes were collected and then cultured in TCM-199 + 10% FBS for 4 h. The matured oocytes were activated with a 20 microsec electric pulse at 1.2 kV/mm. The activated oocytes were incubated in 2 mM of 6-dimethylaminopurine (6-DMAP) for 4 h and were then divided randomly among the treatment groups. In experiment 1, we compared the effects of three culture systems (TCM-199, CR1-aa and Tyrode's) on the in vitro development of parthenogenetically activated cat oocytes. In experiment 2, we investigated the effect of addition of Iloprost (a stable prostaglandin I(2) analogue) to Tyrode's medium on in vitro development of parthenogenetically activated oocytes. As a control, we recovered in vivo produced blastocysts and determined their average cell number. In experiment 1, the cleavage frequency of the oocytes cultured in TCM199, CR1-aa and Tyrode's media were similar (74, 72 and 83%, respectively). However, the incidence of in vitro development to the blastocyst stage was significantly higher in Tyrode's medium (20.4%) than in TCM-199 (2.4%) or CR1-aa (11.1%). Likewise, the average cell number of in vitro activated blastocysts was higher in Tyrode's than in CR1-aa or TCM-199 (106.5 +/- 45.2 vs. 68.3 +/- 25.4 and 35.0 +/- 7.7, respectively; P<0.05). In experiment 2, the percentage of parthenogenetically activated oocytes that underwent in vitro blastocyst development was significantly improved by addition of Iloprost to the culture medium (33.6 vs. 19.1%; P<0.05). The average cell number of in vivo blastocysts (909.0 +/- 226.4) was significantly higher than those of in vitro blastocysts cultured in Tyrode's medium supplemented with or without Iloprost (103.2 +/- 31.3 and 112.2 +/- 39.3, respectively; P<0.05). This result indicated that the current culture method for cat pathogenetically activated oocytes requires further improvement.

Parthenogenetic activation of domestic cat oocytes using ethanol, calcium ionophore, cycloheximide and a magnetic field

The objective of this study was to evaluate parthenogenetic activation of domestic cat oocytes after being exposed to either ethanol, magnetic field, calcium ionophore A23187, or cycloheximide and a combination of these agents. We also wished to evaluate the usefulness of the magnetic field for oocyte activation. In vitro matured oocytes subjected to artificial activation were randomly assigned into eight groups according to activating agents: (1) 10% ethanol; (2) the magnetic field (slow-changing, homogenous magnetic field with low values of induction); (3) 10% ethanol plus magnetic field; (4) 10 microM calcium ionophore A23187; (5) 10 microM calcium ionophore A23187 plus magnetic field; (6) 10% ethanol and 10 microg/mL of cycloheximide; (7) 10% ethanol and 10 microg/mL of cycloheximide plus magnetic field; (8) oocytes were not exposed to any of the activating agents. After activation oocytes were stained with Hoechst 33258 and parthenogenetic activation was defined as oocytes containing pronuclei and second polar bodies or two to four or six nuclei (embryonic cleavage). The total activation rate by using different activation treatments was 40%. The addition of the magnetic field to ethanol or calcium ionophore treatments resulted in increased parthenogenetic activation rates from 47% to 75%, and from 19% to 48%, respectively (P<0.001). Instead, when the magnetic field was added to ethanol and cycloheximide treatment, activation rate decreased from 48% to 30%. Oocytes activated with magnetic field only gave the lowest activation rate (12%). We concluded that a magnetic field can be used as an activating agent, and the combination of ethanol and magnetic field is an effective method for domestic cat oocyte activation.

Effects of electric field strengths on fusion and in vitro development of domestic cat embryos derived by somatic cell nuclear transfer

The present study was conducted to determine the effect of electric field strength on the rate of membrane fusion between the somatic cell and cytoplast and on subsequent in vitro development of reconstructed embryos. Additionally, the in vitro developmental competence of cat oocytes artificially activated after 44 h of maturation culture was examined. An efficient fusion rate (64.2%) was obtained by applying a single pulse of 1.5 kV/cm for 50 micros, and the fusion rate remained almost constant at the higher field intensity (59.8 and 54.9% at 1.7 and 2.0 kV/cm, respectively). Although the cleavage rate of fused embryos increased with an increase of the electric field strength, there were no differences among the groups with respect to the proportion of development to the morula and blastocyst stages. In the additional experiment, oocytes at the metaphase II stage after culture for 44 h were activated by the combination of calcium ionophore (CaI) with cycloheximide (CHX). Some (11.8%) of activated oocytes developed to the blastocyst stage. Results from this study indicated that electric field strength affects the rates of fusion and cleavage but has no significant effects on the development to the blastocyst stage of reconstructed embryos. Prolonged maturation culture of cat oocytes (up to 44 h) decreased their ability to develop to the blastocyst stage.