Attempts to Produce Identical Offspring in the Sheep by Mechanical Division of the Ovum

Abstract

In an attempt to produce identical offspring artificially, the inner cell mass of ova, collected on days 4, 6 and 7 after oestrus (day 0 = day of oestrus), was mechanically divided into two equal sections.The sections were then either cultured in vitro for 2 days and the resulting apparently normal blastocysts transferred to recipient ewes or, in the case of day-7 ova, transferred to recipient ewes without a period of in vitro culture.Half sections of day-4 ova showed little further development in culture and in most the individual cells separated and dispersed. Those of day 6 and 7 showed no dispersion and 24 apparently normal blastocysts were recovered following the culture of 82 half sections. Fourteen of the normal blastocysts developed from each of both half sections of seven day-6 ova.Nineteen normal blastocysts were transferred individually to recipients following culture, but only two developed into lambs and both lambs developed from blastocysts of different ova. A further 18 half sections of day-7 ova were transferred without an intervening period of culture but none developed into lambs.Although a substantial proportion of the half sections of day-6 and day-7 ova showed apparently normal development in culture, very few showed continued normal development in recipients. It is suggested that cellular specialization within the inner cell mass may have occurred before the inner cell mass was divided.

Development of Early Porcine Embryos In Vitro and In Vivo1

“…It has also been postulated that a low oxygen tension environment has a beneficial effect on early embryo development, although the results are contradictory. Bovine [26], ovine [26,27], and porcine [28] premorula-stage embryo development was reportedly more superior under a 5% oxygen than in a 20% oxygen atmosphere. Others [29], however, were unable to confirm the beneficial effect of the reduced oxygen tension by culturing bovine embryos in the two gaseous atmospheres.…”

Role of ultrastructural studies in the analysis of cell lineage in the mammalian pre‐implantation embryo

“…The blastomeres of disaggregated 8-cell embryos appear to be totipotent in terms of the tissues they can produce in a chimera (Kelly, 1975) but do not become viable fetuses when transferred singly into foster mothers (Rossant, 1976a). In contrast, single blastomeres from 4-and 8-cell rabbit embryos are totipotent (Moore et al, 1968;Seidel, 1952), as are single blastomeres from 8-cell sheep embryos (reviewed in Papioannou and Ebert, 1986;Trounson and Moore, 1974;Willadsen, 1981). This is not the case in rat embryos, however; isolated blastomeres of 2-cell rat embryos failed to yield fetuses on transfer to foster mothers (Nicholas and Hall, 1942).…”

Current developments in embryo transfer

“…The final micromanipulation technique worthy of mention is the bisection of embryos at the morula and blastocyst stages. This technique is relatively simple and it has now been used successfully by many different groups (Trounson and Moore 1974;Willadsen, Lehn-Jehnsen, Fehilly and Newcombe 1981 ;Williams, Elsden and Seidel 1982;Ozil 1983;Willadsen and Godke 1984, and others). Pregnancy rates for bisected blastocysts are higher than for morulae and are equivalent to those achieved after transfer of whole embryos.…”