Hegde Aparna, Behr Barry
Department of OB/GYN, Division of Reproductive Endocrinology and Infertility, Stanford University, Stanford, CA, USA.
Methods Mol Biol. 2012;912:177-98. doi: 10.1007/978-1-61779-971-6_11.
Despite the fact that the fundamental principle underlying the most common method of culture media constitution is that of mimicking the natural environment of the preimplantation embryo, one major difference that remains between current embryo culture media and in vivo conditions is the absence of growth factors in vitro. Numerous growth factors are known to be present in the in vivo environment of human and nonhuman preimplantation embryos, often with peak concentrations corresponding to when fertilization and preimplantation embryo growth would occur. Although these growth factors are found in very small concentrations, they have a profound effect on tissue growth and differentiation through attachment to factor-specific receptors on cell surfaces. Receptors for many different growth factors have also been detected in human preimplantation embryos. Preimplantation embryos themselves express many growth factors. The growth factors and receptors are metabolically costly to produce, and thus their presence in the environment of the preimplantation embryo and in the embryo respectively strongly implies that embryos are designed to encounter and respond to the corresponding factors. Studies of embryo coculture also indirectly suggest that growth factors can improve in vitro development. Several animal and human studies attest to a probable beneficial effect of addition of growth factors to culture media. However, there is still ambiguity regarding the exact role of growth factors in embryonic development, the optimal dose of growth factors to be added to culture media, the combinatorial effect and endocrine of growth factors in embryonic development.
尽管构成培养基最常用方法的基本原理是模拟植入前胚胎的自然环境，但目前的胚胎培养基与体内条件之间仍存在一个主要差异，即体外缺乏生长因子。已知在人类和非人类植入前胚胎的体内环境中存在多种生长因子，其浓度峰值通常与受精和植入前胚胎生长的时间相对应。尽管这些生长因子的浓度非常低，但它们通过附着在细胞表面的因子特异性受体上，对组织生长和分化具有深远影响。在人类植入前胚胎中也检测到了许多不同生长因子的受体。植入前胚胎自身会表达多种生长因子。生长因子和受体的产生在代谢上成本很高，因此它们分别存在于植入前胚胎的环境和胚胎中，这强烈表明胚胎注定要接触并对相应因子作出反应。胚胎共培养研究也间接表明生长因子可以改善体外发育。一些动物和人类研究证明向培养基中添加生长因子可能具有有益效果。然而，关于生长因子在胚胎发育中的确切作用、添加到培养基中的生长因子的最佳剂量、生长因子在胚胎发育中的组合效应和内分泌作用，仍然存在模糊之处。
