Another stressor that greatly impacts embryo
development is the use of culture media. Its goal is to enhance its probability
of developing embryos to achieve successful maturity (Gruber and Klein, 2011).
A culture medium is considered to be a foreign environment for the
establishment of an embryo. Thus, the design underlying the media is severely
complicated because the components within must be selected whilst maintaining
their determined concentrations in an attempt to minimize stress for the
cultured embryo (Gruber and Klein, 2011). Within the reproductive tract, the
embryo is likely to be exposed to autocrine, paracrine and endocrine mediators.
Conversely, paracrine and endocrine embryotrophic mediators are excluded from
culture in simple defined medium (Gandolfi et. al., 1994).
A review by Morbeck et. al. suggested that,
“culture without protein is a definite prerequisite to effectively ascertain
the ability of culture medium to support embryo development because protein is
known to have significant undefined and defined variability” (Morbeck et. al.
2014). Protein consists of unknown components that could alleviate deficiencies
produced by certain media formulations (Morbeck et. al. 2014). Although culture
media have improved over the last two decades, they still activate
significantly more stress-activated protein kinase (SAPK) such as SAPK/JNK
(Xie, Puscheck and Rappolee, 2006). Media increases SAPK/JNK phosphorylation
and these levels negatively correlate with embryonic development (Wang et. al.,
2005). Stress tests for SAPK/JNK phosphorylation may be conducted to new media
in attempt to control the established medium (Wang et. al., 2005). It’s
possible to use SAPK/JNK inhibitors to prevent stress induced cultures and
significantly reduce apoptosis and embryo toxicity (Xie, Puscheck and Rappolee,
Summers and Biggers (2003) suggested that,
“manufacturers of human embryo culture media follow either the ‘back to nature’
sequential or the ‘let the embryo choose’ global single-step philosophy or
an empirical optimization approach” (Summers and Biggers, 2003). There isn’t
any evidence to suggest which media is preferably better, however, depending on
the culture system and other factors, there can be a preference. Table 1
highlights the importance of both mediums in relation to embryonic development.