55 PRELIMINARY STUDIES ON THE DEVELOPMENT OF RECONSTRUCTED EMBRYOS AFTER NUCLEAR TRANSFER IN DROMEDARY CAMEL (CAMELUS DROMEDARIUS)

Abstract

Experiments were conducted to study the in vitro development of reconstructed dromedary camel embryos after nuclear transfer by a modified zona-free method. Cumulus oocyte complexes, collected from slaughterhouse ovaries were cultured in TCM199 at 38.5°C in an atmosphere of 5% CO₂ in air for 32 to 36 h. Matured oocytes were denuded of cumulus cells by repeated pipetting and the zona pellucida was removed by brief incubation in 5 mg mL^–1 pronase dissolved in Ca- and Mg-free PBS. Zona-free oocytes were stained with 5 mg mL^–1 Hoechst 33342 in H199 supplemented with 7.5 μg mL^–1 cytochalasin B and 10% FCS. They were enucleated under constant UV-light exposure in H199 supplemented with cytochalasin B and 10% FCS. The granulosa cells at passage numbers 4 to 15 were used as nuclear donors. The zona-free cytoplasts were individually washed for a few seconds in 300 μg mL^–1 of Phytohemagglutinin in H199, then quickly dropped on a single donor cell settled to the bottom of a drop of H199 with 0.5% FCS and pushed together with the mouth pipette. Couplets were electrically fused, at room temperature, with two DC pulses of 100 V cm^–1 for 15 μs. Reconstructs were activated 2 h post-fusion, with 5 μm ionomycin for 3 min followed by culture in 6-diethylaminopurine for 4 h. The reconstructs were then cultured individually in either 5 μL drops under oil, in agar wells or in wells of wells (WOW) in a well of 4-well culture plate. Embryo culture medium consisted of TCM-199 supplemented with 0.15 mg mL^–1 L-glutamine, 2.1 mg mL^–1 sodium bicarbonate, 0.22 mg mL^–1 pyruvate, 50 μg mL^–1 gentamycine, 1% insulin-transferrin-selenium (ITS), and 15% estrous dromedary serum. The number of oocytes that had cleaved was recorded on day 2, whilst those developing to morulae and blastocysts were recorded on day 7 of culture. For cell count, the blastocysts were stained with Hoechst and cells counted under a fluorescent microscope at ×400. Data obtained was analysed by chi-square test. About 92% (349/380) of the oocytes were successfully enucleated and 76% (259/340) fused with the attached cells. The cleavage rate was significantly lower (P < 0.05) in reconstructed embryos cultured in droplets (10/72, 14%) as compared with those cultured in agar wells (37/87, 42%) or WOW system (42/96, 44%). The proportions of cleaved embryos reaching morula stage were 0, 83, and 89% in droplets, agar wells, and WOW, respectively. However, only 8% and 5% of the cleaved embryos developed to the blastocyst stage in the agar well and WOW culture systems, respectively. No difference was observed in the cell number of blastocysts produced in agar wells (77.3 ± 8.02) or WOW (78.0 ± 4.2) culture system. To the best of our knowledge, this is the first report of embryo production up to the blastocyst stage after NT in camelids and it shows that NT can be successfully applied for embryo production in camelids. Further studies are needed to optimize the parameters and to improve the efficiency for production of transferable blastocysts in this species.

This study was kindly sponsored by H.H. General Sheikh Mohammed bin Rashid Al Maktoum, Ruler of Dubai.