Reproductive Technology

Nuclear-Cytoplasmic Interactions Affect In Utero Developmental Capacity, Phenotype, and Cellular Metabolism of Bovine Nuclear Transfer Fetuses

Abstract
We generated a clone of bovine somatic cell nuclear transfer embryos using oocyte pools from defined maternal sources to study nuclear-cytoplasmic interactions. Nucleocytoplasmic hybrids were reconstructed with Bos taurus (Brown Swiss) granulosa cells and oocytes that contained B. taurus A (Simmental), B. taurus B (Simmental), or B. indicus (Dwarf Zebu) cytoplasm. Another set of embryos was reconstructed with randomly selected Brown Swiss (B. taurus R) oocytes. Embryo transfer resulted in 9 (12.5%), 9 (13.8%), 3 (50%) and 11 (16.7%) day 80 fetuses, of which 8 (11.1%), 3 (4.6%), 3 (50%), and 10 (15.2%) were viable. The proportion of viable fetuses was affected by cytoplasm (likelihood ratio test P<0.02) and was higher for embryos with B. indicus cytoplasm than for the B. taurus A (P<0.05) and B (P<0.01) groups. Furthermore, the proportion of surviving day 80 fetuses was reduced for B. taurus B as compared to B. taurus A and B. taurus R cytoplasm (P<0.05 and P<0.02). Body weight of nucleocytoplasmic hybrid fetuses was not significantly different from Brown Swiss control fetuses produced by AI, but fetuses reconstructed with random cytoplasts of the same breed as the nuclear donor exhibited fetal overgrowth (P<0.01) and a higher coefficient of variation in weight. Furthermore, body weight, crown rump length, thorax circumference (P<0.05), and femur length (P<0.01) of fetuses with B. taurus A cytoplasm differed from fetuses with B. taurus R cytoplasms. Fetal skin, heart and liver cells with B. indicus cytoplasm showed a greater increase in number per time period (P<0.001) and oxygen consumption rate per cell (skin and liver P<0.001, heart P<0.08) in comparison to their counterparts with B. taurus A cytoplasm. These data point to complex oocyte cytoplasm-dependent epigenetic modifications and/or nuclear DNA-mtDNA interactions with relevance to nuclear transfer and other reproductive technologies such as ooplasmic transfer in human assisted reproduction.

Key words: Assisted Reproductive Technology • Pregnancy • Conceptus • Developmental biology

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