Embryo Fragmentation 胚胎碎片

The presence of anuclear small cellular fragmentation is the norm in in vitro cultured human embryos. The degree of fragmentation varies from 5% to 10% to 100%, the fragments may be either localized or scattered and initially appear from the first mitotic division on. However, when the degree of fragmentation exceeds 10% of the embryonic volume it can have a negative effect on development.

体外培养的人类胚胎出现无核小细胞碎片非常常见。不同胚胎细胞的碎片率有很大差别，可能是5% 至10%或至100%，碎片从第一次有丝分裂便开始出现，可能为局部碎片或分散化碎片。不过，当碎片率超过胚胎体积的10%时，碎片可能会对胚胎发育产生负面影响。

Large fragments that are found in the cells of a 2- or 4-cell embryo are due to the electrondensity of the mitochondria in each fragment. Mitochondria are more electrondense in later stages of development than in earlier stages. When large fragments are released in the early stages of development the embryo loses important organelles such as the mitochondria. When fragmentation occurs the section of the cell that is left with the nucleus can arrest due to the loss of important organelles (1).

在2或4细胞胚胎的细胞中发现的大块碎片是由于每个片段中线粒体的电子密度造成的。线粒体的电子密度在发育的后期比早期高。在发育的早期阶段释放大碎片时，胚胎会失去重要的细胞器，例如线粒体。当碎片产生时，留下细胞核的细胞部分可能会由于重要细胞器的丢失而停育(1)。

Fragmentation has also been attributed to spermatozoa (2). Spermatozoa were implicated as a cause of fragmentation through DNA damage occurring before fertilization (3), whereas others have reported that metabolic disturbances in the oocyte may play a role (4). Fragmentation percentage has also been known to be associated with chromosome abnormalities. Both apoptotic and necrotic processes have been suggested as causes of blastomere fragmentation in human embryos (5).

碎片的产生也与精子有关(2)。有人认为精子细胞如果在受精前发生DNA损伤会导致碎片(3)，也有人认为卵子细胞如果出现代谢紊乱可能也会造成碎片(4)。胚胎碎片率与染色体异常有关。凋亡和坏死过程都被认为是造成人类胚胎卵裂球出现碎片的原因 (5)。

According to Van Royen et al., a top quality embryo will have no multinucleated blastomeres; four or five blastomeres on days 2; and <20% fragments. The presence of large fragments was found to be harmful to the developing embryo (6). On the other hand small and scattered or localized fragements did not significantly impact implantation potential (7).

Van Royen等人认为，优质胚胎不会有多核卵裂球;第2天有4或5个卵裂球;以及<20%的碎片率。大碎片的存在会影响胚胎发育(6)。另一方面，一些小且分散的碎片或者局部碎片对胚胎植入潜力没有显著影响(7)。

Fragments can be removed by microsurgical techniques, which improves the developmental potential because the spatial relationship between the blastomeres is restored. Frozen embryos also show fragmentation and detriment to the embryo. Elliott et al. showed that by removing lysed cells in mouse embryos the developmental potential was restored to that of the control (8). Lysed cells in frozen/thawed embryos are thought to interfere with cell to cell communication.

胚胎碎片可以通过显微外科技术去除，去除后卵裂球之间的空间关系得到恢复，可以提高胚胎的发育潜力。胚胎冷冻也会导致碎片及对胚胎的损害。Elliott等人发现，去除小鼠胚胎中的裂解细胞后，其发育潜力恢复到对照组小鼠细胞水平(8)。冷冻/解冻胚胎中的裂解细胞被认为会干扰细胞间通讯。

References

参考文献

1. Alikani M, Cohen J, Tomkin G, et al. Human embryo fragmentation in vitro and its implications for pregnancy and implantation. Fertil Steril 1999;71:836-42.

2. Janny L, Menezo Y. Evidence for a strong paternal effect on human preimplantation embryo development and blastocyst formation. Mol Reprod Dev 1994;38:36-42.

3. Munne S, Estop AM. The effect of in-vitro ageing on mouse sperm chromosomes. Hum Reprod 1991;6:703-8.

4. Van Blerkom J, Davis PW, Lee J. ATP content of human oocytes and developmental potential and outcome after in-vitro fertilization and embryo transfer. Hum Reprod 1995;10:415-24.

5. Juriscova A, Varmuza S, Casper R. Programmed cell death and human embryo fragmentation. Mol Hum Reprod 1996;2:93-8.

6. Van Royen E, Mangelscots K, De Neubourg D, et al. Characterization of a top quality embryo, a step towards single embryo transfer. Hum Reprod 1999;14:2345-9.

7. Van Blerkom J, DavisP, Alexander S. A microscopic and biochemical study of fragmentation phenotypes in stage appropriate human embryos. Hum Reprod 2001;16:719-29.

8. Elliott TA, Colturato LFA, Taylor TH, et al. Lysed cell removal promotes frozen-thawed embryo development. Fert Steril 2006;87:1444-9/