Can the formation of syncytial nuclear aggregates be studied in third trimester placental explants?

Objectives: The mechanism of syncytial nuclear aggregate (SNA) formation is unknown, but it is estimated to take 14-21 days. We hypothesise that the cytoskeleton is involved in the lateral movement of nuclei through the syncytiotrophoblast into SNAs.Methods: Term villous explants (n=6) were cultured in supplemented CMRL in either 6% or 20% O2 and samples fixed on days 0, 4, 8, 12 and 16. The number of SNAs per mm2 of tissue and size of SNAs were quantified. Immunofluoresence was performed to identify cytoskeletal components including; actin and tubulin.Results: The absolute number of SNAs per mm2 of tissue did not alter in different O2 tension or over time (median 131 SNAs/mm2 villous area) (Figure 1). Furthermore, there was no change in SNA size (median 179μm2). Immunofluorescence showed that tubulin and γ-actin localised to SNA structures (Figures 2 and 3).Conclusion: No change in SNA number may be due to a lack of de novo production in vitro or because the rate of synthesis matched the rate of loss. The former seems more likely as explants do not generate a large number of new nuclei. This would suggest that SNAs in term placental explants are stable: further work investigating material shed into the culture medium will clarify this. Finally cytoskeletal proteins including γ-actin and tubulin may be involved in nuclear movement into SNAs.