Molecular Insights Into Evolution of the Vertebrate Gut: Focus on Stomach and Parietal Cells in the Marsupial, Macropus eugenii

Gastrulation in vertebrate embryos results in the formation of the primary germ layers: ectoderm, mesoderm and endoderm, which contain the progenitors of the tissues of the entire fetal body. Extensive studies undertaken in Xenopus, zebrafish and mouse have revealed a high degree of conservation in the genes and cellular mechanisms regulating endoderm formation. Nodal, Mix and Sox gene factor families have been implicated in the specification of the endoderm across taxa. Considerably less is known about endoderm development in marsupials. In this study we review what is known about the molecular aspects of endoderm development, focusing on evolution and development of the stomach and parietal cells and highlight recent studies on parietal cells in the stomach of Tammar Wallaby, Macropus eugenii. Although the regulation of parietal cells has been extensively studied, very little is known about the regulation of parietal cell differentiation. Intriguingly, during late-stage forestomach maturation in M. eugenii, there is a sudden and rapid loss of parietal cells, compared with the sharp increase in parietal cell numbers in the hindstomach region. This has provided a unique opportunity to study the development and regulation of parietal cell differentiation. A PCR-based subtractive hybridization strategy was used to identify candidate genes involved in this phenomenon. This will allow us to dissect the molecular mechanisms that underpin regulation of parietal cell development and differentiation, which have been a difficult process to study and provide markers that can be used to study the evolutionary origin of these cells in vertebrates. J. Exp. Zool. (Mol. Dev. Evol.) 312B:613-624, 2009. (C) 2008 Wiley-Liss, Inc.