A partial hydatidiform mole with 2N/3N mosaicism identified by molecular analysis

Parental genomes segregate into distinct blastomeres during multipolar zygotic divisions leading to mixoploid and chimeric blastocysts

Background

During normal zygotic division, two haploid parental genomes replicate, unite and segregate into two biparental diploid blastomeres.

Results

Contrary to this fundamental biological tenet, we demonstrate here that parental genomes can segregate to distinct blastomeres during the zygotic division resulting in haploid or uniparental diploid and polyploid cells, a phenomenon coined heterogoneic division. By mapping the genomic landscape of 82 blastomeres from 25 bovine zygotes, we show that multipolar zygotic division is a tell-tale of whole-genome segregation errors. Based on the haplotypes and live-imaging of zygotic divisions, we demonstrate that various combinations of androgenetic, gynogenetic, diploid, and polyploid blastomeres arise via distinct parental genome segregation errors including the formation of additional paternal, private parental, or tripolar spindles, or by extrusion of paternal genomes. Hence, we provide evidence that private parental spindles, if failing to congress before anaphase, can lead to whole-genome segregation errors. In addition, anuclear blastomeres are common, indicating that cytokinesis can be uncoupled from karyokinesis. Dissociation of blastocyst-stage embryos further demonstrates that whole-genome segregation errors might lead to mixoploid or chimeric development in both human and cow. Yet, following multipolar zygotic division, fewer embryos reach the blastocyst stage and diploidization occurs frequently indicating that alternatively, blastomeres with genome-wide errors resulting from whole-genome segregation errors can be selected against or contribute to embryonic arrest.

Conclusions

Heterogoneic zygotic division provides an overarching paradigm for the development of mixoploid and chimeric individuals and moles and can be an important cause of embryonic and fetal arrest following natural conception or IVF.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02763-2.

[Twin pregnancy with complete mole and coexisting fetus: Reach fetal viability is possible]

Twin pregnancies combining complete hydatidiform mole and coexistent fetus are a rare situation (incidence in 1/20,000 in 1/100,000 pregnancies) and a challenge for diagnosis. Their complications can be important - bleeding, preeclampsia, miscarriage - and their management remains complex and controversial. In case of continuing the pregnancy, nearly 40% of women have lives babies. Three quarters of fetal loss occur before 24weeks gestation. We report here three new cases; only one of these cases had a favorable outcome.