Super-Enhancers and CTCF in Early Embryonic Cell Fate Decisions

Cell fate decisions are the backbone of many developmental and disease processes. In early mammalian development, precise gene expression changes underly the rapid division of a single cell that leads to the embryo and are critically dependent on autonomous cell changes in gene expression. To understand how these lineage specifications events are mediated, scientists have had to look past protein coding genes to the cis regulatory elements (CREs), including enhancers and insulators, that modulate gene expression. One class of enhancers, termed super-enhancers, is highly active and cell-type specific, implying their critical role in modulating cell-type specific gene expression. Deletion or mutations within these CREs adversely affect gene expression and development and can cause disease. In this mini-review we discuss recent studies describing the potential roles of two CREs, enhancers and binding sites for CTCF, in early mammalian development.

Genome-wide decoupling of H2Aub and H3K27me3 in early mouse development

Polycomb group (PcG) proteins are crucial chromatin regulators during development. H2Aub and H3K27me3 are catalyzed by Polycomb-repressive Complex 1 and 2 (PRC1/2) respectively, and largely overlap in the genome due to mutual recruitment of the two complexes. However, whether PRC1/H2Aub and PRC2/H3K27me3 can function independently remains obscure. Here we uncovered a genome-wide decoupling of H2Aub and H3K27me3 in preimplantation mouse embryos, at both canonical PcG targets and broad distal domains. H2Aub represses future bivalent genes without H3K27me3 but does not contribute to maintenance of H3K27me3-dependent non-canonical imprinting. Our study thus revealed their distinct and independent functions in early mammalian development.

Enhancement of Developmental Competence of Immature Oocytes Supplemented with Growth Factors in Culture Media

Background: In vitro embryo production is a valuable tool for understanding early mammalian development, therapeutic applications, excellent source for research in the field of developmental biology and production of valuable animals. The purpose of this study is to improve the production of in vitro cattle embryos using fibroblast and platelet derived growth factor as media supplement. Methods: Ovaries were collected from local abattoir in 0.9% saline (30-35°C) supplemented with antibiotics. Cumulus oocyte complexes were aspirated, washed 5-6 times and placed in maturation media supplemented with growth factors and cultured in 5% CO2 incubator at 38.5°C with maximum humidity. After 24 h oocytes were co-incubated with in vitro capacitated sperms for fertilization for 15-18 h and then presumptive zygotes were cultured for embryo development. Cleavage was observed after 40-42 h and embryos were co-cultured with oviductal cells for 7-9 days. Result: The highest cleavage and blastocyst formation rates were 55.93 ± 4.75, 57.06 ± 4.78, 51.24 ± 4.12 and 3.26 ±1.53, 2.42 ± 1.02, 2.70 ± 1.17 in FGF (1ng ml-1), PDGF (10 ng ml-1) and in combination of FGF and PDGF (1ng ml-1 each) respectively. It can be concluded that PDGF (10 ng ml-1) enhanced cleavage rate and FGF (1ng ml-1) enhanced blastocyst formation rate.

EKLF/KLF1 expression defines a unique macrophage subset during mouse erythropoiesis

Erythroblastic islands are a specialized niche that contain a central macrophage surrounded by erythroid cells at various stages of maturation. However, identifying the precise genetic and transcriptional control mechanisms in the island macrophage remains difficult due to macrophage heterogeneity. Using unbiased global sequencing and directed genetic approaches focused on early mammalian development, we find that fetal liver macrophages exhibit a unique expression signature that differentiates them from erythroid and adult macrophage cells. The importance of erythroid Krüppel-like factor (EKLF)/KLF1 in this identity is shown by expression analyses in EKLF-/- and in EKLF-marked macrophage cells. Single-cell sequence analysis simplifies heterogeneity and identifies clusters of genes important for EKLF-dependent macrophage function and novel cell surface biomarkers. Remarkably, this singular set of macrophage island cells appears transiently during embryogenesis. Together, these studies provide a detailed perspective on the importance of EKLF in the establishment of the dynamic gene expression network within erythroblastic islands in the developing embryo and provide the means for their efficient isolation.

EKLF/KLF1 expression defines a unique macrophage subset during mouse erythropoiesis

ABSTRACTErythroblastic islands are a specialized niche that contain a central macrophage surrounded by erythroid cells at various stages of maturation. However, identifying the precise genetic and transcriptional control mechanisms in the island macrophage remains difficult due to macrophage heterogeneity. Using unbiased global sequencing and directed genetic approaches focused on early mammalian development, we find that fetal liver macrophage exhibit a unique expression signature that differentiates them from erythroid and adult macrophage cells. The importance of EKLF/KLF1 in this identity is shown by expression analyses in EKLF-/- and in EKLF-marked macrophage cells. Single cell sequence analysis simplifies heterogeneity and identifies clusters of genes important for EKLF-dependent macrophage function and novel cell surface biomarkers. Remarkably, this singular set of macrophage island cells appears transiently during embryogenesis. Together these studies provide a detailed perspective on the importance of EKLF in establishment of the dynamic gene expression network within erythroblastic islands in the developing embryo and provide the means for their efficient isolation.