19 research outputs found
A Comparative Analysis of Extra-Embryonic Endoderm Cell Lines
Prior to gastrulation in the mouse, all endodermal cells arise from the primitive
endoderm of the blastocyst stage embryo. Primitive endoderm and its derivatives
are generally referred to as extra-embryonic endoderm (ExEn) because the
majority of these cells contribute to extra-embryonic lineages encompassing the
visceral endoderm (VE) and the parietal endoderm (PE). During gastrulation, the
definitive endoderm (DE) forms by ingression of cells from the epiblast. The DE
comprises most of the cells of the gut and its accessory organs. Despite their
different origins and fates, there is a surprising amount of overlap in marker
expression between the ExEn and DE, making it difficult to distinguish between
these cell types by marker analysis. This is significant for two main reasons.
First, because endodermal organs, such as the liver and pancreas, play important
physiological roles in adult animals, much experimental effort has been directed
in recent years toward the establishment of protocols for the efficient
derivation of endodermal cell types in vitro. Conversely,
factors secreted by the VE play pivotal roles that cannot be attributed to the
DE in early axis formation, heart formation and the patterning of the anterior
nervous system. Thus, efforts in both of these areas have been hampered by a
lack of markers that clearly distinguish between ExEn and DE. To further
understand the ExEn we have undertaken a comparative analysis of three ExEn-like
cell lines (END2, PYS2 and XEN). PYS2 cells are derived from embryonal
carcinomas (EC) of 129 strain mice and have been characterized as parietal
endoderm-like [1], END2 cells are derived from P19 ECs and
described as visceral endoderm-like, while XEN cells are derived from blastocyst
stage embryos and are described as primitive endoderm-like. Our analysis
suggests that none of these cell lines represent a bona fide
single in vivo lineage. Both PYS2 and XEN cells represent mixed
populations expressing markers for several ExEn lineages. Conversely END2 cells,
which were previously characterized as VE-like, fail to express many markers
that are widely expressed in the VE, but instead express markers for only a
subset of the VE, the anterior visceral endoderm. In addition END2 cells also
express markers for the PE. We extended these observations with microarray
analysis which was used to probe and refine previously published data sets of
genes proposed to distinguish between DE and VE. Finally, genome-wide pathway
analysis revealed that SMAD-independent TGFbeta signaling through a TAK1/p38/JNK
or TAK1/NLK pathway may represent one mode of intracellular signaling shared by
all three of these lines, and suggests that factors downstream of these pathways
may mediate some functions of the ExEn. These studies represent the first step
in the development of XEN cells as a powerful molecular genetic tool to study
the endodermal signals that mediate the important developmental functions of the
extra-embryonic endoderm. Our data refine our current knowledge of markers that
distinguish various subtypes of endoderm. In addition, pathway analysis suggests
that the ExEn may mediate some of its functions through a non-classical MAP
Kinase signaling pathway downstream of TAK1
TAK1 inhibition-induced RIP1-dependent apoptosis in murine macrophages relies on constitutive TNF-α signaling and ROS production
A gradient of Bmp7 specifies the tonotopic axis in the developing inner ear
The auditory systems of animals that perceive sounds in air are organized to separate sound stimuli into their component frequencies. Individual tones then stimulate mechanosensory hair cells located at different positions on an elongated frequency (tonotopic) axis. During development, immature hair cells located along the axis must determine their tonotopic position in order to generate frequency-specific characteristics. Expression profiling along the developing tonotopic axis of the chick basilar papilla (BP) identified a gradient of Bmp7. Disruption of that gradient in vitro or in ovo induces changes in hair cell morphologies consistent with a loss of tonotopic organization and the formation of an organ with uniform frequency characteristics. Further, the effects of Bmp7 in determination of positional identity are shown to be mediated through activation of the Mapk, Tak1. These results indicate that graded, Bmp7-dependent, activation of Tak1 signaling controls the determination of frequency-specific hair cell characteristics along the tonotopic axis