Molecular Biology of the Stress Response in the Early Embryo and its Stem Cells

Abstract

Stress is normal during early embryogenesis and transient, elevated stress is commonplace. Stress in the milieu of the peri-implantation embryo is a summation of maternal hormones, and other elements of the maternal milieu, that signal preparedness for development and implantation. Examples discussed here are leptin, adrenaline, cortisol, and progesterone. These hormones signal maternal nutritional status and provide energy, but also signal stress that diverts maternal and embryonic energy from an optimal embryonic developmental trajectory. These hormones communicate endocrine maternal effects and local embryonic effects although signaling mechanisms are not well understood. Other in vivo stresses affect the embryo such as local infection and inflammation, hypoxia, environmental toxins such as benzopyrene, dioxin, or metals, heat shock, and hyperosmotic stress due to dehydration or diabetes. In vitro, stresses include shear during handling, improper culture media and oxygen levels, cryopreservation, and manipulations of the embryo to introduce sperm or mitochondria. We define stress as any stimulus that slows stem cell accumulation or diminishes the ability of cells to produce normal and sufficient parenchymal products upon differentiation. Thus stress deflects downwards the normal trajectories of development, growth and differentiation. Typically stress is inversely proportional to embryonic developmental and proliferative rates, but can be proportional to induction of differentiation of stem cells in the peri-implantation embryo. When modeling stress it is most interesting to produce a 'runting model' where stress exposures slow accumulation but do not create excessive apoptosis or morbidity. Windows of stress sensitivity may occur when major new embryonic developmental programs require large amounts of energy and are exacerbated if nutritional flow decreases and removes energy from the normal developmental programs and stress responses. These windows correspond to zygotic genome activation, the large mRNA program initiated at compaction, ion pumping required for cavitation, the differentiation of the first lineages, integration with the uterine environment at implantation, rapid proliferation of stem cells, and production of certain lineages which require the highest energy and are most sensitive to mitochondrial inhibition. Stress response mechanisms insure that stem cells for the early embryo and placenta survive at lower stress exposures, and that the organism survives through compensatory and prioritized stem cell differentiation, at higher stress exposures. These servomechanisms include a small set of stress enzymes from the 500 protein kinases in the kinome; the part of the genome coding for protein kinases that hierarchically regulate the activity of other proteins and enzymes. Important protein kinases that mediate the stress response of embryos and their stem cells are SAPK, p38MAPK, AMPK, PI3K, Akt, MEK1/2, MEKK4, PKA, IRE1 and PERK. These stress enzymes have cytosolic function in cell survival at lo...

Commonly used fertility drugs, a diet supplement, and stress force AMPK-dependent block of stemness and development in cultured mammalian embryos

“…However, Met [97], Asa [98], and BR-DIM [60,99] reach pharmacokinetic peaks within 30-144 min of ingestion but are cleared within 12 h. It will be important to expose gestational females to these drugs and remove embryos at the timing of the peak to test for potency factor loss. We previously showed that shear stress by mouth pipetting causes activation of stress-activated protein kinase (SAPK) to levels as high as highest activation dose of hyperosmotic sorbitol, about a 10-fold increase [30]. However, this dose has no effect of mouth pipetting for 15 min on cell number 24 h later [100].…”

“…The cloning of the first stress enzymes in mammals also used hyperosmotic stress, and this has been used as the positive control by many labs that study stress enzymes in somatic cells or study stress or stress enzymes in reproductive systems [30][31][32]. Use of hyperosmotic stress enables comparison of results between stem cells and embryos and is universal stress for all cells.…”

“…Of significance is that small variations in Oct4 level, including loss in the levels caused by stress, change the fate of the ESC [52]. Rex1 is expressed in the ICM also and, although not necessary for embryo survival, is lost when ICM cells follow either of its immediate cell fates, extraembryonic primitive endoderm, or primitive ectoderm that produces all tissues at gastrulation [30]. Thus, it is important to move from potency factor loss of TSC potency factors to testing for the loss of ESC potency factors that will mark and control the pluripotency of stem cells in the embryo that ultimately produce the neonate.…”

Id2 Mediates Differentiation of Labyrinthine Placental Progenitor Cell Line, SM10

“…In this investigation, the expression of Id isoforms in the SM10 labyrinthine progenitor cell line and the effect of Id2 overexpression and knockdown on TGF-b-induced differentiation were examined. The expression of Id proteins is essential for normal development and differentiation of several cell types [28,51,[75][76][77][78][79][80]. Id isoforms are also expressed in the placenta, and this suggests their importance in directing trophoblast self-renewal and differentiation [15,[29][30][31][32]43,76].…”

“…The expression of Id proteins is essential for normal development and differentiation of several cell types [28,51,[75][76][77][78][79][80]. Id isoforms are also expressed in the placenta, and this suggests their importance in directing trophoblast self-renewal and differentiation [15,[29][30][31][32]43,76]. Even though mice that are deficient in a single Id isoform are viable, double deficiency of Id1, Id2, and/or Id3 isoforms leads to embryonic lethality, implying functional redundancy of expression [48,49,[81][82][83][84][85][86][87].…”