Abstract
Human cells migrate between mother and fetus during pregnancy and persist in the respective host for long-term after birth. Fetal microchimerism occurs also in twins sharing a common placenta or chorion. Whether microchimerism occurs in multiparous mammals such as the domestic pig, where fetuses have separate placentas and chorions, is not well understood. Here, we assessed cell chimerism in litters of wild-type sows inseminated with semen of transposon transgenic boars. Segregation of three independent monomeric transposons ensured an excess of transgenic over non-transgenic offspring in every litter. Transgenic siblings (n = 35) showed robust ubiquitous expression of the reporter transposon encoding a fluorescent protein, and provided an unique resource to assess a potential cell trafficking to non-transgenic littermates (n = 7) or mothers (n = 4). Sensitive flow cytometry, fluorescence microscopy, and real-time PCR provided no evidence for microchimerism in porcine littermates, or piglets and their mothers in both blood and solid organs. These data indicate that the epitheliochorial structure of the porcine placenta effectively prevents cellular exchange during gestation.
Highlights
Microchimerism refers to the presence of a small ratio of foreign cells (,1:100) within the tissues of a host organism
Fetal microchimerism was observed in monochorionic twins [11,12,13]
Each carrying three monomeric integrations of the cytomegalovirus enhancer, chicken beta actin hybrid promoter (CAGGS)-Venus transposon, were used for collection of semen, and six wild-type sows were artificially inseminated. This resulted in 5 pregnancies that went to term and yielded a total of 44 piglets, of which 35 were transgenic and 9 were non-transgenic
Summary
Microchimerism refers to the presence of a small ratio of foreign cells (,1:100) within the tissues of a host organism. The human hemochorial placenta, in which maternal blood is in direct contact with the chorionic trophoblast, facilitates trafficking of cells and/or macromolecules, such as antibodies [7,8]. Most of the domestic species possess an epitheliochorial placenta [9], which consists of maternal and fetal epithelia and is thought to be much tighter than the hemochorial placenta. Cell transfer in multiparous, multichorionic species like the domestic pig has only rarely been studied. A recent report suggested microchimerism in porcine littermates under specific experimental situations [15], in which xenogenic human cord blood derived cells had been injected into the peritoneum of porcine fetuses around day 40 of gestation. Evidence for long-term maintenance of human cells in the treated animals, and in untreated littermates was reported [15]
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