Notch signaling is inactive but inducible in human embryonic stem cells.

The NOTCH signaling pathway performs a wide range of critical functions in a number of different cell types during development and differentiation. The role of NOTCH signals in human embryonic stem cells (hESCs) has not been tested. We measured the activity of canonical NOTCH signaling in undifferentiated embryonic stem (ES) cells and tested the requirement for NOTCH activity in hESC self-renewal or differentiation by growing hESCs in the presence of gamma-secretase inhibitors. Our results suggest that NOTCH signaling is not required for the propagation of undifferentiated human ES cells but instead is required for the maintenance of the differentiating cell types that accumulate in human ES cell cultures. Our studies suggest that NOTCH signaling is not required in human embryonic differentiation until the formation of extraembryonic, germ layer, or tissue-specific stem cells and progenitors.

Karyotypic stability, genotyping, differentiation, feeder-free maintenance, and gene expression sampling in three human embryonic stem cell lines derived prior to August 9, 2001.

The number of human embryonic stem cell (hESC) lines available to federally funded U.S. researchers is currently limited. Thus, determining their basic characteristics and disseminating these lines is important. In this report, we recovered and expanded the earliest available cryopreserved stocks of the BG01, BG02, and BG03 hESC lines. These cultures exhibited multiple definitive characteristics of undifferentiated cells, including long-term self-renewal, expression of markers of pluripotency, maintenance of a normal karyotype, and differentiation to mesoderm, endoderm, and ectoderm. Each cell line exhibited a unique genotype and human leukocyte antigen (HLA) isotype, confirming that they were isolated independently. BG01, BG02, and BG03 maintained in feederfree conditions demonstrated self-renewal, maintenance of normal karyotype, and gene expression indicative of undifferentiated pluripotent stem cells. A survey of gene expression in BG02 cells using massively parallel signature sequencing generated a digital read-out of transcript abundance and showed that this line was similar to other hESC lines. BG01, BG02, and BG03 hESCs are therefore independent, undifferentiated, and pluripotent lines that can be maintained without accumulation of karyotypic abnormalities.

Directed neuronal differentiation of human embryonic stem cells.

BACKGROUND: We have developed a culture system for the efficient and directed differentiation of human embryonic stem cells (HESCs) to neural precursors and neurons.HESC were maintained by manual passaging and were differentiated to a morphologically distinct OCT-4+/SSEA-4- monolayer cell type prior to the derivation of embryoid bodies. Embryoid bodies were grown in suspension in serum free conditions, in the presence of 50% conditioned medium from the human hepatocarcinoma cell line HepG2 (MedII). RESULTS: A neural precursor population was observed within HESC derived serum free embryoid bodies cultured in MedII conditioned medium, around 7-10 days after derivation. The neural precursors were organized into rosettes comprised of a central cavity surrounded by ring of cells, 4 to 8 cells in width. The central cells within rosettes were proliferating, as indicated by the presence of condensed mitotic chromosomes and by phosphoHistone H3 immunostaining. When plated and maintained in adherent culture, the rosettes of neural precursors were surrounded by large interwoven networks of neurites. Immunostaining demonstrated the expression of nestin in rosettes and associated non-neuronal cell types, and a radial expression of Map-2 in rosettes. Differentiated neurons expressed the markers Map-2 and Neurofilament H, and a subpopulation of the neurons expressed tyrosine hydroxylase, a marker for dopaminergic neurons. CONCLUSION: This novel directed differentiation approach led to the efficient derivation of neuronal cultures from HESCs, including the differentiation of tyrosine hydroxylase expressing neurons. HESC were morphologically differentiated to a monolayer OCT-4+ cell type, which was used to derive embryoid bodies directly into serum free conditions. Exposure to the MedII conditioned medium enhanced the derivation of neural precursors, the first example of the effect of this conditioned medium on HESC.

Inhibitory effect of recombinant iNOS gene expression on vasomotor function of canine basilar artery.

The present study was designed to determine the effect of recombinant inducible nitric oxide (NO) synthase (iNOS) gene expression on vasomotor function in cerebral arteries. Isolated canine basilar arteries were exposed ex vivo (30 min at 37 degrees C) to an adenoviral vector [10(7), 10(8), or 10(9) plaque-forming units (pfu)/ml] encoding either the iNOS gene or the beta-galactosidase reporter gene. Twenty-four hours after transduction, Western blot analysis demonstrated expression of iNOS protein only in iNOS (10(9) pfu/ml)-transduced arteries. Immunohistochemical analysis localized iNOS expression predominantly in adventitia. Vascular reactivity of isolated basilar arteries was studied by isometric force recording. Concentration-response curves to UTP (10(-9)-10(-3) M) and diethylaminodiazen-1-ium-1,2-dioate (10(-10)-10(-5) M) were significantly shifted to the right in iNOS gene (10(9) pfu/ml)-transduced rings compared with control and beta-galactosidase-transduced rings (P < 0.05, n = 5-6). Endothelium-dependent relaxation to bradykinin was significantly attenuated in iNOS-transduced rings (P < 0.001, n = 8). The basal level of cGMP and superoxide anion (O(2)(-).) production were elevated in iNOS-transduced rings (P < 0.05, n = 7 for cGMP; P < 0.01, n = 6-9 for O(2)(-). production). Our results suggest that expression of recombinant iNOS in cerebral arteries reduces vasomotor reactivity to both vasoconstrictor and vasodilator agonists. Attenuation of contractions is most likely due to functional antagonism between UTP and cGMP. Reduction of endothelium-dependent relaxation to bradykinin appears to be mediated in part by reduced reactivity of smooth muscle cells to NO.

Expression and function of recombinant S1179D endothelial nitric oxide synthase in canine cerebral arteries.

BACKGROUND AND PURPOSE: Bovine endothelial nitric oxide synthase (eNOS) is phosphorylated directly by the protein kinase Akt at serine 1179. Mutation of this residue to the negatively charged aspartate (S1179DeNOS) increases nitric oxide (NO) production constitutively in the absence of agonist stimulus. The present study was designed to determine the effect of mutant S1179DeNOS gene expression on vasomotor function of canine cerebral arteries. METHODS: Isolated basilar and middle cerebral arteries were exposed ex vivo (30 minutes at 37 degrees C) to an adenoviral vector (10(10) plaque-forming units per milliliter) encoding the S1179DeNOS gene (AdCMVS1179DeNOS), the wild-type eNOS gene (AdCMVeNOS), or the green fluorescent protein (GFP) reporter gene (AdCMVGFP). Twenty-four hours after transduction, arteries were suspended in an organ chamber for isometric force recording, and levels of cGMP were measured by radioimmunoassay. RESULTS: Transgene protein expression was detected mainly in the vascular adventitia. In AdCMVS1179DeNOS-transduced arteries, basal levels of cGMP were significantly elevated compared with those in control (nontransduced), AdCMVGFP-, or AdCMVeNOS-transduced vessels (n=8; P<0.01). The elevation of cGMP was abolished by a NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), or by incubation in the calcium-free medium in the presence of calcium chelators. In AdCMVS1179DeNOS-transduced arteries, contractions to endothelin-1 (10(-10) to 10(-8) mol/L) were significantly reduced compared with those in control and AdCMVGFP-transduced arteries (n=7; P<0.05). The vasoconstrictor effect of endothelin-1 was restored in the presence of the NOS inhibitor L-NAME. CONCLUSIONS: Our results suggest that in cerebral arteries, expression of recombinant S1179DeNOS increases basal production of NO and inhibits the vasoconstrictor effect of endothelin-1. This effect may have therapeutic application in prevention and treatment of cerebrovascular diseases.