Project description:The signaling cascades that direct the morphological differentiation of the vascular system during early embryogenesis are not well defined. To further understand the role of Notch signaling during endothelial differentiation, this study uses both an in vivo gain-of-function and in vivo loss-of-function approach. At embryonic day 9.5, embryos with activated Notch1 signaling in the endothelia display a variety of growth and cardiovascular defects, and die soon after E10.5. Most notably, the extra-embryonic vasculature of the yolk sac displays remodeling differentiation defects. In the wild-type yolk sac, the primary vascular network has begun to reorganize, forming the large primary vessels and the smaller capillaries. In the activated Notch1 embryos remodeling is defective; the vasculature have an enlarged surface with decreased inter-vessel space. Embryos with ablated Notch signaling also display growth and vascular defects at E9.5 similar to the activated Notch1 embryos, however they exhibit a lack of vascular remodeling in the yolk sac, retaining the simple vascular plexus seen at E8.5. These results indicate that Notch signaling plays a critical role in the remodeling of the vasculature in the early embryo, particularly in the extra embryonic region. A conditional transgenic system was used in this study to activate Notch signaling. The ubiquitous ROSA26Notch transgene with a Neo/stop cassette flanked by loxP sites, followed by the N1-ICD cDNA, was recombined with a Tie2-CRE mouse, resulting in the removal of the STOP cassette and the subsequent activation of the Notch1-intracellular domain. This allowed for the overexpression and expansion of Notch signaling in all endothelial cells. Male Tie2-Cre mice were mated with female ROSA26Notch mice and resulting embryos were dissected at embryonic day 9.5. To ablate Notch signaling, Tie2-Cre mice were used in a two generation cross to obtain Tie2-Cre; Rbpj flox/flox embryos. These embryos lack RBPJ binding activity in the endothelia. In both instances embryos were used for genotyping and the yolk sac were separated and used to isolate total RNA with an RNeasy mini kit. The RNA was analyzed with the Mouse Genome 430A Array from Affymetrix. Samples were performed in duplicate, and RNA from wild type yolk sac tissues was compared to activated Notch and RBPJ loss-of-function yolk sac tissues.

Project description:KLF2 is a Krüppel-like zinc-finger transcription factor required for blood vessel, lung, T-cell, and erythroid development. KLF2-/- mice die by embryonic day 14.5 (E14.5), due to hemorrhaging and heart failure. Embryonic -like globin gene expression is reduced in KLF2-/- embryos compared to wildtype (WT), and E10.5 erythroid cells exhibit abnormal morphology. Other KLF2 target genes were identified by comparing E9.5 KLF2-/- and WT yolk sac erythroid cells, using laser capture microdissection and microarray assays. One hundred and ninety-six genes exhibited significant differences in expression; eighty-nine of these are downregulated in KLF2-/- compared to WT. Genes involved in cell migration, differentiation and development are over-represented in the KLF2-regulated gene list. Previously identified erythroid-enriched regulatory genes such as reelin, adenylate cyclase 7, cytotoxic T lymphocyte-associated protein 2 alpha, and CD24a antigen are downregulated in KLF2-/- compared to WT. SOX2, a pluripotency factor in ES cells, is also a KLF2 target in embryonic erythroid cells. We investigated whether reelin, which has an established role in neuronal migration and proliferation, has a role in embryonic erythropoiesis. Luciferase reporter assays demonstrated that KLF2 directly transactivates the reelin promoter, but reelin mutant mice have no apparent abnormalities in embryonic erythroid morphology or globin gene expression. Timed-pregnant KLF2+/- females were anesthetized and sacrificed. E9.5 yolk sacs were dissected from the embryo, cryoprotected in 20% sucrose in PBS and frozen in OCT media. A small portion of the embryo tail was used for PCR genotyping. Eight micron KLF2-/- frozen yolk sac sections were obtained and laser capture microdissection (LCM) was used to isolate primitive erythroid precursors. For each biological replicate, 2 to 4 yolk sacs from 2 different litters were used. Total RNA was isolated from 4 different KLF2-/- erythroid samples and hybridized to Affymetrix 430 A 2.0 microarrays

Project description:The Krüppel-like factors, KLF1 and KLF2, positively regulate embryonic β-globin expression, and have additional overlapping roles in embryonic (primitive) erythropoiesis. KLF1-/-KLF2-/- double knockout mice are anemic at embryonic day 10.5 (E10.5) and die by E11.5, in contrast to single knockouts. To investigate the combined roles of KLF1 and KLF2 in primitive erythropoiesis, expression profiling of E9.5 erythroid cells was performed. A limited number of genes had a significantly decreasing trend of expression in wild-type, KLF1-/- and KLF1-/-KLF2-/-. Among these, c-myc emerged as a central node in the most significant gene network. c-myc expression is synergistically regulated by KLF1 and KLF2, and both factors bind the c-myc promoters. To characterize the role of c-myc in primitive erythropoiesis, ablation was performed specifically in mouse embryonic proerythroblast cells. After E9.5, these embryos exhibit an arrest in the normal expansion of circulating red cells and develop anemia analogous to KLF1-/-KLF2-/-. In the absence of c-myc, circulating erythroid cells do not show the normal increase in α- and β-like globin expression, but interestingly, have accelerated erythroid maturation, between E9.5 and E11.5. This study reveals a novel regulatory network by which KLF1 and KLF2 regulate c-myc, to control the primitive erythropoietic program. Timed-pregnant KLF1+/-, KLF1+/- KLF2+/- females were anesthetized and sacrificed. E9.5 yolk sacs were dissected from the embryo, cryoprotected in 20% sucrose in PBS and frozen in OCT media. A small portion of the embryo tail was used for PCR genotyping. Eight micron frozen yolk sac sections were obtained and laser capture microdissection (LCM) was used to isolate primitive erythroid precursors. For each biological replicate, 2 to 4 yolk sacs from 2 different litters were used. Total RNA was isolated from 8 different wild-type, 3 KLF1-/-, 3 KLF1-/- KLF2-/- erythroid samples and hybridized to Affymetrix 430 A 2.0 microarrays.

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Mus musculus

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