A paucity of structural integrity in cloned porcine blastocysts produced in vitro

Abstract

The structural integrity of blastocyst stage embryos, consisting of the inner cell mass (ICM) and trophectoderm (TE) cells, is a prerequisite for normal development after implantation in mammals. In this study, allocation of nuclear transfer (NT)-derived porcine blastocysts to the ICM and to the TE cells was examined and compared with IVF- and in vivo-derived embryos. NT-derived embryos had a lower developmental competence to the blastocyst stage than IVF-derived embryos (P < 0.05). Total cell number of NT-derived blastocysts was inferior to that of IVF-derived embryos (P < 0.05), although no difference was detected between the two groups in the ratio of ICM to total cells. However, in vivo-derived blastocysts had a higher proportion of ICM to total cells compared with in vitro-produced embryos (P < 0.01). To investigate what proportions of in vitro-produced porcine embryos represent normal structural integrity, differentially-stained blastocysts were individually classified into three presumptive groups (I: < 20%; II: 20-40%; III: > 40%) according to the ratio of ICM to total cells. Low proportions of NT- (12.5%, 7/56) and IVF-derived blastocysts (15.8%, 9/57) were assigned to Group II, presumptively having a normal range of structural integrity, whereas, almost all in vivo-derived embryos (97.5%, 39/40) were allocated to Group II. In conclusion, limited structural integrity may lead to the poor survival to term of NT- or IVF-derived porcine embryos produced in vitro. (c) 2004 Elsevier Inc. All rights reserved.