Visceral endoderm

Another approach for cardiac differentiation is based on co-culture of undifferentiated hESCs with mouse visceral endodermal like cell line (END-2), particularly in the absence of serum [98, 99]. hES cells or clumps are co-cultured with END-2 cells instead of MEF culture for 3 weeks in serum-free media, and beating cell patches are scored from day 5 onwards. 

Mummery C, Ward-van Oostwaard D, Doevendans P et al (2003) Differentiation of human embryonic stem cells to cardiomyo-cytes—role of coculture with visceral endoderm-like cells. Circulation 107(21) 2733-2740... 

The central nervous system (CNS) of vertebrates is a very complex structure derived from a multistep process involving sequential molecular and morphogenetic events that pattern the epiblast first and the neural plate later. During early gastrulation, the concerted and sequential action of both the anterior visceral endoderm (AVE) and the node and its derivatives (axial mesendoderm, AME, and anterior definitive endoderm, ADE) (Beddington and Robertson, 1999 Bachiller et al., 2000) drives the specification of the anterior neuroectoderm, which subsequently is subdivided in three main territories (forebrain, midbrain, and hindbrain) (Gallera, 1971 Storey et al., 1992 Ruiz i Altaba, 1994 Shimamura and Rubenstein, 1997 Rubenstein and Beachy, 1998). 

A new signaling center, the anterior visceral endoderm (A VE) is necessary for... 

The requirement of the AVE for normal brain formation was definitely confirmed from chimeric studies for genes such as nodal, Otx2, Liml, and Hnf3ji. The specific absence of each of these genes in the visceral endoderm led to the induction of a neural axis lacking the most anterior values, fore- and midbrain, whilst restoration of their functions only in the visceral endoderm was sufficient to rescue the initial induction of fore- and midbrain neural markers expression at headfold stages (Varlet et al., 1997 Dufort et ah, 1998 Rhinn et al., 1998 Acampora et al., 1998b Shawlot et al., 1999). The rescue of the anterior position neural plate was... 

Acampora, D., Avantaggiato, V., Tuorto, F., Briata, P., Corte, G., Simeone, A. 1998b. Visceral endoderm-restricted translation of Otxl mediates recovering of Otx2 requirements for specification of anterior neural plate and proper gastrulation. Development 125, 5091-5104. 

Dufort, D., Schwartz, L., Harpal, K., Rossant, J. 1998. The transcription factor HNF3/S is required in visceral endoderm for normal primitive streak morphogenesis. Development 125, 3015-3025. 

Kimura, C., Yoshinaga, K., Tian, E., Suzuki, M., Aizawa, S., Matsuo, I. 2001. Visceral endoderm mediates forebrain development by suppressing posteriorizing signals. Dev. Biol. 225, 304-321. 

Perea-Gomez, A., Lawson, K.A., Rhinn, M., Zakin, L., Brulet, P., Mazan, S., Ang, S.L. 2001. Otx2 is required for visceral endoderm movement and for the restriction of posterior signals in the epiblast of the mouse embryo. Development 128, 753-765. 

Perea-Gomez, A., Shawlot, W., Sasaki, H., Behringer, R.R., Ang, S.L. 1999. HNF3/J and Liml interact in the visceral endoderm to regulate primitive streak formation and anterior-posterior polarity in the mouse embryo. Development 126, 4499 1511. 

Shawlot, W., Wakamiya, M., Kwan, M.K., Kania, A., Jessell, T.M., Behringer, R.R. 1999. Liml is required in both primitive streak-derived tissues and visceral endoderm for head formation in the mouse. Development 126, 4925 1932. 

There is also evidence to suggest that lessons learned from early cardiac differentiation in the model systems (as described above) may also apply to the hES cells. The cardiogenic inductive role of the primitive visceral endoderm (VE) was also shown to play a role in cardiomyocyte differentiation of the hES fine in an elegant study conducted by Mummery et al. [59[. Go-cultur-ing of a human ES ceU line (hES2) that does not regularly differentiate spontaneously to... 

ViraferonPeg 468 Viral vector generation 156 Virosomes 1425 Virtron 17, 468 Virus based vector 186 Virus purification 158 Virus safety 1650 Visceral endoderm 294 Viscum album 482 Visudine 1280 VitoTox 1628 Vitravene 24, 633 Vivid screening kit 1613 VNTR (variable number of tandem repeats) marker 77... 

In hepatocytes. Active P-catenin is detectable immediately prior to gastrulation at E5.5 in the extra- embryonic visceral endoderm and in a narrow region of cells in the epiblast at E6. Two associations with P-catenin are important in hepatocytes One association is the connection between P-catenin and E-cadherin at the hepatocyte membrane and the other association is that of P-catenin with the hepatocyte growth factor (HGF) and receptor c-Met. 

Visceral Endoderm Provides a Signal(s) Required for Embryonic Hematopoiesis... 

To establish more directly that visceral endoderm is required for induction of hematopoiesis in the gastrulating embryo, tissue recombination experiments were performed. A semi-quantitative RT-PCR protocol was used to assay for activation of the endogenous mouse embryonic p-like globin genes (15), Ectoderm and VE layers from individual embryos were cultured separately or in combination for two to four days. RNA was prepared from individual explants and analyzed for embryonic globin gene activation using the RT-PCR assay. 

Respecification of Anterior Ectoderm to Hematopoietic and Endothelial Cell Fates by Visceral Endoderm... 

Analysis by RT-PCR of expression of a panel of hematopoietic markers indicated that visceral endoderm signaling results in activation not only of genes characteristic of differentiated erythroid cells globin) but also of early hematopoietic genes such as GATA-1 and CD-34. The presence of VE in recombinants did not result in promiscuous activation of mesoderm differentiation markers cardiac myosin, which is expected to be expressed only in cardiac tissue (and therefore only at a later developmental stage), was not detected in anterior or posterior epiblast pieces or in recombinants during the first 4 days in culture, but was detected in an older (10.5 dpc) embryonic control. 

To determine whether cell-cell contact is required for respecification of anterior ectoderm, we carried out two types of experiment. In the first, medium conditioned by a visceral endoderm-l e cell line was tested for its ability to substitute for VE tissue in the induction assay. Indeed, activation of an embryonic p-Iike globin gene was detected using RT-PCR (our unpublished results), indicating that at least some functions of the visceral endoderm can be mediated by soluble molecules. In the second type of experiment, transgenic anterior ectoderm and non-transgenic VE were cultured on opposite sides of a... 

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