Transport-associated pathway responses in ovine fetal membranes to changes in amniotic fluid dynamics

The role of embryonic stem cells, transcription and growth factors in mammals: A review

Mammals represent a relevant species in worldwide cultures with significant commercial value. These animals are considered an attractive large animal model for biomedical and biotechnology research. The development of large animal experimental models may open alternative strategies for investigating stem cells (SCs) physiology and potential application in the veterinary field. The embryonic stem cells (ESCs) are known to possess natural pluripotency that confers the ability to differentiate into various tissues in vivo and in vitro. These notable characteristics can be useful for research and innovative applications, including biomedicine, agriculture and industry. Transcription factors play a crucial role in preserving stem cell self-renewal, whereas growth factors are involved in both growth and differentiation. However, to date, many questions concerning pluripotency, cellular differentiation regulator genes, and other molecules such as growth factors and their interactions in many mammalian species remain unresolved. The purpose of this review is to provide an overall review regarding the study of ESCs in mammals and briefly discuss the role of transcription and growth factors.

Pluripotency and Growth Factors in Early Embryonic Development of Mammals: A Comparative Approach

The regulation of early events in mammalian embryonic development is a complex process. In the early stages, pluripotency, cellular differentiation, and growth should occur at specific times and these events are regulated by different genes that are expressed at specific times and locations. The genes related to pluripotency and cellular differentiation, and growth factors that determine successful embryonic development are different (or differentially expressed) among mammalian species. Some genes are fundamental for controlling pluripotency in some species but less fundamental in others, for example, Oct4 is particularly relevant in bovine early embryonic development, whereas Oct4 inhibition does not affect ovine early embryonic development. In addition, some mechanisms that regulate cellular differentiation do not seem to be clear or evolutionarily conserved. After cellular differentiation, growth factors are relevant in early development, and their effects also differ among species, for example, insulin-like growth factor improves the blastocyst development rate in some species but does not have the same effect in mice. Some growth factors influence genes related to pluripotency, and therefore, their role in early embryo development is not limited to cell growth but could also involve the earliest stages of development. In this review, we summarize the differences among mammalian species regarding the regulation of pluripotency, cellular differentiation, and growth factors in the early stages of embryonic development.

Altered proteomics profile in the amnion of patients with oligohydramnios

In pregnancy, idiopathic oligohydramnios is an obstetrical complication that compromises maternal health with poor perinatal outcome. Effective therapeutic treatment of this condition has been hampered by the unknown etiology and lack of understanding of cellular and molecular mechanisms that underlie idiopathic oligohydramnios. Amniotic fluid volume (AFV) is determined by intramembranous (IM) transport of amniotic fluid across the amnion and this pathway is regulated to maintain AFV within the normal range. To gain understanding of the causes of idiopathic oligohydramnios, we performed proteomics analysis of the human amnion to investigate the changes in protein expression profiles of cellular transport pathways and regulators in patients with oligohydramnios. Placental amnions from five patients with normal pregnancies and five patients with oligohydramnios were subjected to proteomics experiments followed by bioinformatics analysis. Using Ingenuity Pathway Analysis (IPA) software, five categories of biological functions and multiple canonical pathways within each category were revealed. The top differentially expressed proteins that participate in mediating these pathways were identified. The functional pathways activated include: (a) cellular assembly and organization, (b) cell signaling and energy metabolism, and (c) immunological, infectious, and inflammatory functions. Furthermore, the analysis identified the category of pathways that facilitate molecular endocytosis and vesicular uptake. Under oligohydramniotic conditions, the mediators of clathrin vesicle-mediated uptake and transport as well as intracellular trafficking mediators were up-regulated. These findings suggest that idiopathic oligohydramnios may be associated with alternations in cellular organization and immunological functions as well as increases in activity of vesicular transport pathways across the amnion.

Multiomics analyses of vesicular transport pathway-specific transcripts and proteins in ovine amnion: responses to altered intramembranous transport

Amniotic fluid volume (AFV) is determined by the rate of intramembranous (IM) transport of amniotic fluid (AF) across the amnion. This transport is regulated by fetal urine-derived stimulators and AF inhibitors. Our objective was to utilize a multiomics approach to determine the IM transport pathways and identify the regulators. Four groups of fetal sheep with experimentally induced alterations in IM transport rate were studied: control, urine drainage (UD), urine drainage with fluid replacement (UDR), and intra-amniotic fluid infusion (IA). Amnion, AF, and fetal urine were subjected to transcriptomics (RNA-Seq) and proteomics studies followed by Ingenuity Pathway Analysis. The analysis uncovered nine transport-associated pathways and four groups of differentially expressed transcripts and proteins. These can be categorized into mediators of vesicular uptake and endocytosis, intracellular trafficking, pathway activation and signaling, and energy metabolism. UD decreased IM transport rate and AFV in conjunction with enhanced expression of vesicular endocytosis regulators but reduced expression of intracellular trafficking mediators. With UDR, IM transport rate decreased and AFV increased. Energy metabolism activators increased while trafficking mediators decreased in expression. IA increased IM transport rate and AFV together with enhanced expressions of vesicular endocytosis and trafficking mediators. We conclude that IM transport across the amnion is regulated by multiple vesicular transcytotic and signaling pathways and that the mediators of intracellular trafficking most likely play an important role in determining the rate of IM transport. Furthermore, the motor protein cytoplasmic dynein light chain-1, which coexpressed in AF and fetal urine, may function as a urine-derived IM transport stimulator.

Regulation of amniotic fluid volume: insights derived from amniotic fluid volume function curves

Recent advances in understanding the regulation of amniotic fluid volume (AFV) include that AFV is determined primarily by the rate of intramembranous absorption (IMA) of amniotic fluid across the amnion and into fetal blood. In turn, IMA rate is dependent on the concentrations of yet-to-be identified stimulator(s) and inhibitor(s) that are present in amniotic fluid. To put these concepts in perspective, this review 1) discusses the evolution of discoveries that form the current basis for understanding the regulation of AFV, 2) reviews the contribution of IMA to this regulation, and 3) interprets experimentally induced shifts in AFV function curves and amnioinfusion function curves in terms of the activity of the amniotic fluid stimulator and inhibitor of IMA. In the early 1980s, it was not known whether AFV was regulated. However, by the late 1980s, IMA was discovered to be a "missing link" in understanding the regulation of AFV. Over the next 25 years the concept of IMA evolved from being a passive process to being an active, unidirectional transport of amniotic fluid water and solutes by vesicles within the amnion. In the 2010s, it was demonstrated that a renally derived stimulator and a fetal membrane-derived inhibitor are present in amniotic fluid that regulate IMA rate and hence are the primary determinants of AFV. Furthermore, AFV function curves and amnioinfusion function curves provide new insights into the relative efficacy of the stimulator and inhibitor of IMA.

Transport-associated pathway responses in ovine fetal membranes to changes in amniotic fluid dynamics

Current evidence suggests that amniotic fluid volume (AFV) is actively regulated by vesicular transport of amniotic fluid outward across the amnion and into the underlying fetal vasculature in the placenta. Our objective was to determine whether gene expression profiles of potential stimulators, inhibitors, and mediators of vesicular transport are altered in response to changes in intramembranous absorption (IMA) rate. Samples of ovine amnion and chorion were obtained from fetal sheep with normal, experimentally reduced or increased AFVs and IMA rates. Amnion and chorion levels of target mRNAs were determined by RT‐qPCR. In the amnion, caveolin‐1 and flotillin‐1 mRNA levels were unchanged during alterations in IMA rate. However, levels of both were significantly higher in amnion than in chorion. Tubulin‐α mRNA levels in the amnion but not in chorion were reduced when IMA rate decreased, and amnion levels correlated positively with IMA rate (P < 0.05). Dynamin‐2 mRNA levels were not altered by experimental conditions. Vascular endothelial growth factor (VEGF₁₆₄ and VEGF₁₆₄b) mRNA levels increased during both increases and decreases in IMA rate, whereas soluble Flt‐1 levels did not change. Neither HIF‐1α nor PBEF mRNA levels in the amnion were correlated with VEGF₁₆₄ expression levels and were not related to IMA rate. Collectively, our findings suggest that changes in amnion microtubule expression may be important in the regulation of transcellular vesicular transport of amniotic fluid and thus modulate IMA rate. Further, our results are consistent with the concept that the amnion is the rate‐limiting layer for amniotic fluid transport.