Department of Reproductive Medicine and Gynaecology, University Medical Centre, Utrecht, The Netherlands.
Hum Reprod. 2010 Aug;25(8):1916-26. doi: 10.1093/humrep/deq139. Epub 2010 Jun 2.
Post-zygotic chromosome segregation errors are very common in human embryos after in vitro fertilization, resulting in mosaic embryos. However, the significance of mosaicism for the developmental potential of early embryos is unknown. We assessed chromosomal constitution and development of embryos from compaction to the peri-implantation stage.
From 112 cryopreserved Day 4 human embryos donated for research, 21 were immediately fixed and all cells were analysed by fluorescent in situ hybridization (FISH) for chromosomes 1, 7, 13, 15, 16, 18, 21, 22, X and Y. The remaining 91 embryos were thawed, with 54 embryos undergoing biopsy of one or two cells which were fixed and analysed by FISH. Biopsied embryos were kept in standard culture conditions for 24 h. Embryos arrested before cavitation (n = 24) were fixed whereas developing Day 5 blastocysts (n = 24) were co-cultured for a further 72 h on an endometrial monolayer followed by fixation. Cell numbers were counted and all nuclei were analysed by FISH. Data from a previous FISH analysis on cryopreserved good-quality Day 5 blastocysts (n = 36) were also included in the present study.
FISH analysis was successful for 18 Day 4 fixed embryos and, according to our definition, 83% were mosaic and 11% showed a chaotic chromosomal constitution. FISH analysis of two blastomeres from Day 4 developing embryos showed that 54% were mosaic, 40% were normal and 6% were abnormal. Analysis of Day 4, 5 and 8 whole embryos showed a decrease in incidence of mosaicism over time, from 83% on Day 4 to 42% on Day 8. A significant positive correlation was observed between the total cell number and the percentage of normal cells in developing Day 5 and Day 8 embryos but not in developing Day 4 or embryos arrested before cavitation.
These data suggest that both the developmental arrest of a significant proportion of mosaic embryos on Day 4, and the cell death or reduced proliferation of aneuploid cells within an embryo may be responsible for the observed decrease of aneuploid blastomeres from compaction to the peri-implantation stage.
体外受精后人类胚胎合子后染色体分离错误非常常见，导致嵌合体胚胎的出现。然而，嵌合体对于早期胚胎发育潜能的意义尚不清楚。我们评估了胚胎从致密化到着床前阶段的染色体组成和发育情况。
从 112 个冷冻的第 4 天人类胚胎中，21 个胚胎立即固定，并用荧光原位杂交（FISH）分析所有细胞的染色体 1、7、13、15、16、18、21、22、X 和 Y。其余 91 个胚胎解冻后，其中 54 个胚胎进行单细胞或双细胞活检，然后固定并进行 FISH 分析。活检后的胚胎在标准培养条件下培养 24 小时。对于未发生囊胚腔形成的胚胎（n=24）进行固定，对于发育至第 5 天的囊胚（n=24）进行共培养 72 小时，随后进行固定。计数细胞数量，并对所有核进行 FISH 分析。本研究还纳入了之前对冷冻良好的第 5 天囊胚（n=36）进行的 FISH 分析数据。
18 个第 4 天固定胚胎的 FISH 分析成功，根据我们的定义，83%为嵌合体，11%表现为染色体组成混乱。对第 4 天发育胚胎的两个卵裂球进行 FISH 分析显示，54%为嵌合体，40%为正常，6%为异常。对第 4、5 和 8 天的整个胚胎进行分析显示，随着时间的推移，嵌合体的发生率逐渐降低，从第 4 天的 83%降至第 8 天的 42%。在发育至第 5 天和第 8 天的胚胎中，总细胞数与正常细胞百分比之间呈显著正相关，但在发育至第 4 天的胚胎或未发生囊胚腔形成的胚胎中无此相关性。
这些数据表明，大量嵌合体胚胎在第 4 天的发育停滞，以及胚胎内非整倍体细胞的死亡或增殖减少，可能是导致从致密化到着床前阶段，胚胎中异常卵裂球数量减少的原因。
