THE GENETIC CONSTITUTION OF MULTINUCLEAR BLASTOMERES AND THEIR DERIVATIVE DAUGHTER BLASTOMERES

The presence of multinuclear blastomeres (MNB) has been widely reporte d in in-vitro-cultured embryos. Multinucleation at the first mitotic d ivision and affecting both blastomeres is considered abnormal and such embryos are not transferred, The objective of this study was to use f luorescent in-situ hybridization (FISH) and probes specific for chromo somes X, Y and 18 to examine the genetic constitution of embryos devel oping from the 2-cell stage in which both blastomeres were bi- or mult inuclear. Initially, 2-cell embryos in which both blastomeres were bi- or multinuclear were cultured further. Of 101 embryos, 89 (88.1%) cle aved further and were analysed at the 3- to 8-cell stage on day 2 or 3 , Among embryos analysed, 30.4% contained only mononuclear diploid bla stomeres, 35.9% had a combination of mononuclear diploid and non-diplo id blastomeres, and 33.7% had non-diploid blastomeres, indicative of c haotic division. Results obtained were similar with embryos derived fr om in-vitro fertilization (IVF) or intracytoplasmic sperm injection (I CSI), Also, no significant differences were found between 2-cell embry os with bi- or multinuclear blastomeres or between slowly or normally cleaved embryos. Twelve (11.9%) embryos arrested at the 2-cell stage o n day 3; of these, one had diploid blastomeres and the others were abn ormal and highly polyploid, Subsequently, 59 embryos were analysed at the 2-cell stage. Initial observations related to the high number of n uclei in metaphase at the moment of spreading, notably when multinucle ar blastomeres were observed, Genetic analysis showed 44.7% of embryos to be susceptible to analysis; the genetic constitution corresponded in both blastomeres to a diploid status, A combined diploid blastomere and abnormal blastomere was found in 4.3% of embryos; both blastomere s were abnormal in 51%, These data show that the genetic constitution of bi- or multinuclear blastomeres, and the daughter cells developing from them, are not always abnormal.