Downregulation of Endothelin Receptor B Contributes to Defective B Cell Lymphopoiesis in Trisomy 21 Pluripotent Stem Cells.

Individuals with Trisomy 21 (T21) exhibit numerous hematological abnormalities, including reductions in numbers of circulating B and T lymphocytes. To elucidate molecular mechanisms underlying these phenotypes, we differentiated human isogenic disomic and trisomic pluripotent cells, and observed that trisomic cells showed defects in B cell, but not T cell differentiation. Global gene expression of differentiated, trisomic B cells revealed reduced expression of genes encoding endothelin signaling components, namely the Endothelin Receptor B (EDNRB), and its ligand Endothelin1 (EDN1).

Gene correction of reversed Kostmann disease phenotype in patient-specific induced pluripotent stem cells.

Severe congenital neutropenia (SCN, Kostmann disease) is a heritable disorder characterized by a granulocytic maturation arrest. Biallelic mutations in () are frequently detected in affected individuals, including those of the original pedigree described by Kostmann in 1956. To date, no faithful animal model has been established to study SCN mediated by HAX1 deficiency.

Hematopoietic stem cells develop in the absence of endothelial cadherin 5 expression.

Rare endothelial cells in the aorta-gonad-mesonephros (AGM) transition into hematopoietic stem cells (HSCs) during embryonic development. Lineage tracing experiments indicate that HSCs emerge from cadherin 5 (Cdh5; vascular endothelial-cadherin)(+) endothelial precursors, and isolated populations of Cdh5(+) cells from mouse embryos and embryonic stem cells can be differentiated into hematopoietic cells. Cdh5 has also been widely implicated as a marker of AGM-derived hemogenic endothelial cells.

Altered hematopoiesis in trisomy 21 as revealed through in vitro differentiation of isogenic human pluripotent cells.

Trisomy 21 is associated with hematopoietic abnormalities in the fetal liver, a preleukemic condition termed transient myeloproliferative disorder, and increased incidence of acute megakaryoblastic leukemia. Human trisomy 21 pluripotent cells of various origins, human embryonic stem (hES), and induced pluripotent stem (iPS) cells, were differentiated in vitro as a model to recapitulate the effects of trisomy on hematopoiesis. To mitigate clonal variation, we isolated disomic and trisomic subclones from the same parental iPS line, thereby generating subclones isogenic except for chromosome 21.

A human stem cell model of early Alzheimer's disease pathology in Down syndrome.

Human cellular models of Alzheimer's disease (AD) pathogenesis would enable the investigation of candidate pathogenic mechanisms in AD and the testing and developing of new therapeutic strategies. We report the development of AD pathologies in cortical neurons generated from human induced pluripotent stem (iPS) cells derived from patients with Down syndrome. Adults with Down syndrome (caused by trisomy of chromosome 21) develop early-onset AD, probably due to increased expression of a gene on chromosome 21 that encodes the amyloid precursor protein (APP).

The role of CYP26 enzymes in defining appropriate retinoic acid exposure during embryogenesis.

Retinoic acid (RA) is a pleiotropic derivative of vitamin A, or retinol, which is responsible for all of the bioactivity associated with this vitamin. The teratogenic influences of vitamin A deficiency and excess RA in rodents were first observed more than 50 years ago. Efforts over the last 15-20 years have refined these observations by defining the molecular mechanisms that control RA availability and signaling during murine embryonic development.

Analysis of Cyp26b1/Rarg compound-null mice reveals two genetically separable effects of retinoic acid on limb outgrowth.

The role of retinoic acid (RA) in limb development is unclear, although it has been suggested to be a proximalizing factor which plays a morphogenetic role in pattern formation. Exogenous RA produces a teratogenic effect on limb morphology; similarly, changes in the endogenous distribution of RA following genetic ablation of the RA-metabolizing enzyme, CYP26B1, result in phocomelia accompanied by changes in expression of proximo-distal (P-D) patterning genes, increased cell death, and delayed chondrocyte maturation. Here we show that disruption of RA receptor (RAR) gamma in a Cyp26b1(-/-) background is able to partially rescue limb skeletal morphology without restoring normal expression of proximo-distal patterning genes.

Cyp26b1 expression in murine Sertoli cells is required to maintain male germ cells in an undifferentiated state during embryogenesis.

In mammals, germ cells within the developing gonad follow a sexually dimorphic pathway. Germ cells in the murine ovary enter meiotic prophase during embryogenesis, whereas germ cells in the embryonic testis arrest in G0 of mitotic cell cycle and do not enter meiosis until after birth. In mice, retinoic acid (RA) signaling has been implicated in controlling entry into meiosis in germ cells, as meiosis in male embryonic germ cells is blocked by the activity of a RA-catabolizing enzyme, CYP26B1.

Genetic disruption of CYP26B1 severely affects development of neural crest derived head structures, but does not compromise hindbrain patterning.

Cyp26b1 encodes a cytochrome-P450 enzyme that catabolizes retinoic acid (RA), a vitamin A derived signaling molecule. We have examined Cyp26b1(-/-) mice and report that mutants exhibit numerous abnormalities in cranial neural crest cell derived tissues. At embryonic day (E) 18.

Apoptotic extinction of germ cells in testes of Cyp26b1 knockout mice.

Cyp26b1 encodes a retinoic acid (RA) metabolizing cytochrome P450 enzyme that is expressed in embryonic tissues undergoing morphogenesis, including the testes. We have generated transgenic mice lacking Cyp26b1 and have observed increased RA levels in embryonic testes. Cyp26b1(-/-) germ cells prematurely enter meiosis at embryonic d 13.

Transcriptional co-operativity between distant retinoic acid response elements in regulation of Cyp26A1 inducibility.

Cyp26A1 encodes an RA (retinoic acid)-catabolizing CYP (cytochrome P450) protein that plays a critical role in regulating RA distribution in vivo. Cyp26A1 expression is inducible by RA, and the locus has previously been shown to contain a RARE (RA response element), R1, within the minimal promoter [Loudig, Babichuk, White, Abu-Abed, Mueller and Petkovich (2000) Mol. Endocrinol.

Developing with lethal RA levels: genetic ablation of Rarg can restore the viability of mice lacking Cyp26a1.

We have previously reported that the retinoic acid (RA) catabolizing enzyme CYP26A1 plays an important role in protecting tail bud tissues from inappropriate exposure to RA generated in the adjacent trunk tissues by RALDH2, and that Cyp26a1-null animals exhibit spina bifida and caudal agenesis. We now show that, in the absence of Cyp26a1, retinoic acid receptor gamma (RARgamma) mediates ectopic RA-signaling in the tail bud. We also show that activated RARgamma results in downregulation of Wnt3a and Fgf8, which integrate highly conserved signaling pathways known for their role in specifying caudal morphogenesis.

Differential expression of the retinoic acid-metabolizing enzymes CYP26A1 and CYP26B1 during murine organogenesis.

We recently cloned the murine homologue of Cyp26B1, a novel retinoic acid (RA)-metabolizing enzyme and showed that its gene expression pattern is unique from that of Cyp26A1 during early embryogenesis. Here, we complete this comparative expression analysis from embryonic day (E) 12 to postnatal stages. Cyp26B1 expression was found in developing tendons and precartilaginous elements and in perichondrium by E14.