The placenta is a transient organ that plays a critical role in sustaining pregnancy and supporting fetal growth and nutrition. The placental epithelium is comprised of trophoblast cells. Trophoblast cells are the first cell type to differentiate during embryogenesis and ultimately diversify into a heterogeneous population of cells specializing in distinct functions essential for placentation. The emergence of the trophoblast lineage and subsequent specialization into distinct trophoblast sublineages is tightly regulated by transcription factors. This chapter will provide an overview of transcription factors that regulate trophoblast development and function. The chapter is divided into three sections. In the first section, a generalized outline of trophoblast ontogeny and a functional description of different trophoblast sublineages will be provided. In the second section, transcription factors involved in emergence of the trophoblast lineage and maintenance of trophoblast stem cells will be discussed. In the third section, transcription factors implicated in the formation and function of villous and extravillous cytotrophoblast lineages will be described.
Functional cell-based assays are useful for comparing the effect of a treatment, drug, or condition on cells in culture. Cell lines are a commonly used model to replicate a normal biological process or a pathological condition. Trophoblasts within the placenta are required to perform a variety of functions, which include proliferation, differentiation, migration, and invasion for efficient placentation to occur. These functions are impaired in trophoblasts from preeclamptic pregnancies, and therefore functional cell-based assays can be utilized to measure differences and dissect molecular regulatory pathways.
Abstract The steroid hormone 17β-estradiol is an estrogen that influences multiple aspects of placental function and fetal development in humans. During early pregnancy it plays a role in the regulation of blastocyst implantation, trophoblast differentiation and invasiveness, remodeling of uterine arteries, immunology and trophoblast production of hormones such as leptin. Estradiol exerts some effects through the action of classical estrogen receptors ERα and ERβ, which act as ligand-activated transcription factors and regulate gene expression. In addition, estradiol can elicit rapid responses from membrane-associated receptors, like activation of protein-kinase pathways. Thus, the cellular effects of estradiol will depend on the specific receptors expressed and the integration of their signaling events. Leptin, the 16,000 MW protein product of the obese gene, was originally considered an adipocyte-derived signaling molecule for the central control of metabolism. However, pleiotropic effects of leptin have been identified in reproduction and pregnancy. The leptin gene is expressed in placenta, where leptin promotes proliferation and survival of trophoblastic cells. Expression of leptin in placenta is highly regulated by key pregnancy molecules as hCG and estradiol. The aim of this paper is to review the molecular mechanisms underlying estrogen functions in trophoblastic cells; focusing on mechanisms involved in estradiol regulation of placental leptin expression.
Abstract Invasion of extravillous trophoblast cell types into maternal uterine tissues is essential for successful human placental development and progression of pregnancy. Whereas endovascular trophoblasts migrate into the maternal spiral arteries, interstitial trophoblasts invade the decidual stroma, colonize the vessels from outside and communicate with diverse uterine cell types such as decidual stromal cells, macrophages and uterine NK cells. For example, interstitial trophoblasts expressing polymorphic human leukocyte antigen-C interact with uterine NK cells through binding to their killer immunoglobulin-like receptors which likely plays a role in trophoblast invasion and reproductive success of pregnancy. Both extravillous trophoblast subtypes are critically involved in the vascular transformation of the spiral arteries into dilated conduits ensuring appropriate blood flow into the intervillous space. Failures in this remodeling process are thought to be associated with severe forms of fetal growth restriction, preeclampsia and other pregnancy complications warranting studies on the molecular regulation of extravillous trophoblast differentiation. Moreover, interstitial trophoblast-derived hormones may regulate diverse biological functions in the decidua. In particular, human chorionic gonadotrophin has been shown to promote angiogenesis and to suppress apoptosis of endometrial stromal cells. In return, decidual cells produce a plethora of soluble factors controlling trophoblast invasion in a time- and distance-dependent manner. However, the underlying mechanisms have not been fully elucidated. Here, we will summarize autocrine as well as paracrine factors regulating invasion of extravillous trophoblasts and discuss critical signaling cascades involved. In addition, we will focus on key regulatory transcription factors controlling cell column proliferation and differentiation of the human extravillous trophoblast.
Understanding cell fate patterning and morphogenesis in the mammalian embryo remains a formidable challenge. Recently, in vivo models based on embryonic stem cells (ESCs) have emerged as complementary methods to quantitatively dissect the physical and molecular processes that shape the embryo. Here we review recent developments in using ESCs to create both two- and three-dimensional culture models that shed light on mammalian gastrulation.