PRODUCTION OF GROWTH FACTORS BY EARLY MAMMALIAN EMBRYOS

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The roles of hormones and growth factors during the early stages of mammalian development are poorly understood. During the past decade, it has become apparent that embryos at several stages of development produce growth factors, some of which exhibit the properties of transforming growth factors (TGFs). TGFs are assayed by their ability to induce the soft agar growth of non-transformed cells, such as normal rat kidney (NRK) cells. The TGF-like growth factors from embryos were initially observed in extracts prepared from mouse embryos at mid and late stages of gestation. Recently, we have determined that embryos cultured from the blastocyst stage release growth factors that induce the soft agar growth of NRK cells. Although the precise developmental stage when production of these factors begins has not been established, the data suggest that these factors are released by cell types associated with early postimplantation embryos. However, it has not been determined whether these factors are released at earlier stages of development. Furthermore, the assay employed, although relatively sensitive, could not unambiguously identify the growth factors involved. This application proposes to address several important questions concerning TGF-like growth factors released by early mouse embryos: 1) What are their identities? 2) When are they first produced? 3) Is their release modified by conditions that interfere with development? 4) Are these factors produced by specific embryonic tissues? These questions will be addressed by employing a battery of bioassays that permit the identification of TGFs and related growth factors. The work proposed in this application will help to clarify the roles of growth factors during early development and help determine whether further study of embryonic growth factors is likely to yield assays suitable for monitoring normal preimplantation development.