Control of inhibin production by dispersed human luteal cells in vitro

Media composition: growth factors

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.

The importance of growth factors for preimplantation embryo development and in-vitro culture

PURPOSE OF REVIEW

The present paper reviews evidence that preimplantation embryos are naturally exposed and designed to respond to growth factors during preimplantation development.

RECENT FINDINGS

Recent studies have demonstrated that in-vivo human preimplantation embryos are exposed to a mixture of many different growth factors, expressed by the follicles, oviducts and endometrium. Receptors for many of these growth factors have also been shown to be expressed by preimplantation embryos, suggesting a functional role during preimplantation development. Studies of in-vitro fertilization in both animals and humans indicate that in-vitro culture of embryos in conventional media lacking growth factors can result in suboptimal growth and a variety of short-term and long-term developmental abnormalities. Studies of embryo coculture indirectly suggest that growth factors can improve in-vitro development. Many studies of defined growth factor supplements demonstrate that their inclusion in culture media can substantially improve preimplantation development and efficacy of in-vitro fertilization, and may reduce long-term developmental abnormalities as well.

SUMMARY

Embryos are naturally exposed to a complex mixture of growth factors that play an important role in preimplantation embryo development and that are likely to be of substantial benefit if added to in-vitro culture media.

Inhibin/activin subunit mRNA expression in human granulosa-luteal cells

We studied the expression of inhibin/activin subunit mRNAs in granulosa-luteal cells of preovulatory ovarian follicles obtained from women undergoing in vitro fertilization, and in corpus luteum tissue samples of early pregnancy. Northern analysis of granulosa-luteal cell and corpus luteum RNA with single-stranded cDNA or cRNA probes revealed an 1.6-kb mRNA for the alpha subunit and about 6.0-, 4.0-, 2.8-, and 1.7-kb transcripts for the beta A subunit. No clear hybridization signal for the beta B subunit could be detected. The relative expression levels of alpha and beta A subunit mRNAs were determined at 2-day intervals in granulosa-luteal cells cultured for 5 to 11 days. The levels of alpha subunit mRNAs declined steadily with increasing culture age, whereas those of beta A remained unchanged. Reverse transcription-polymerase chain reaction analysis with 35 amplification cycles confirmed the expression of alpha and beta A subunit mRNAs in cultured granulosa-luteal cells. The beta B transcripts were also weakly detectable by this sensitive assay. In situ hybridization of human early pregnancy corpus luteum revealed intense hybridization with the alpha cRNA probe and a weaker signal for the beta A subunit in the granulosa cell compartment. We conclude that: (1) the inhibin alpha and beta A subunits (and to a lesser extent beta B) are expressed in cultured human granulosa-luteal cells; (2) during extended culture periods the alpha/beta A mRNA expression ratio decreases; and that (3) the alpha and beta A subunit mRNA expression is observed in the granulosa cell compartment of early pregnancy corpora lutea.