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During their embryogenesis, marsupials transiently develop a unique structure, the shoulder arch, which provides the structural support and muscle-attachments necessary for the newborn's crawl to the teat. One of the most pronounced and functionally important aspects of the shoulder arch is an enlarged coracoid. The goal of this study is to determine the molecular basis of shoulder arch formation in marsupials. To achieve this goal, this study investigates the relative expression of several genes with known roles in shoulder girdle morphogenesis in a marsupial-the opossum, Monodelphis domestica-and a placental, the mouse, Mus musculus. Results indicate that Hoxc6, a gene involved in coracoid patterning, is expressed for a longer period of time and at higher levels in opossum relative to mouse. Functional manipulation suggests that these differences in Hoxc6 expression are independent of documented differences in retinoic acid signaling in opossum and mouse forelimbs. Results also indicate that Emx2, a gene involved in scapular blade condensation, is upregulated in opossum relative to mouse. However, several other genes involved in shoulder girdle patterning (e.g., Gli3, Pax1, Pbx1, Tbx15) are comparably expressed in these species. These findings suggest that the upregulation of Hoxc6 and Emx2 occurs through independent genetic modifications in opossum relative to mouse. In summary, this study documents a correlation between gene expression and the divergent shoulder girdle morphogenesis of marsupial (i.e., opossum) and placental (i.e., mouse) mammals, and thereby provides a foundation for future research into the genetic basis of shoulder girdle morphogenesis in marsupials. Furthermore, this study supports the hypothesis that the mammalian shoulder girdle is a highly modular structure whose elements are relatively free to evolve independently.
© 2013 Wiley Periodicals, Inc.
Simple experiments demonstrate that the development of an organism is both a genetic and a physical process. This statement is so obvious that it is seldom stated explicitly, and yet, there has been little progress toward integrating what should be complementary viewpoints. This paper focuses on the mechanical aspects of morphogenesis-highlighting those areas where mechanics and molecular genetics are converging toward a much-needed synthesis.
Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is emerging as a powerful tool for investigating the distribution of molecules within biological systems through the direct analysis of thin tissue sections. Unique among imaging methods, MALDI-IMS can determine the distribution of hundreds of unknown compounds in a single measurement. We discuss the current state of the art of MALDI-IMS along with some recent applications and technological developments that illustrate not only its current capabilities but also the future potential of the technique to provide a better understanding of the underlying molecular mechanisms of biological processes.
Stem cells are defined by their ability to both self-renew and give rise to multiple lineages in vivo and/or in vitro. As discussed in other chapters in this volume, the embryonic neural crest is a multipotent tissue that gives rise to a plethora of differentiated cell types in the adult organism and is unique to vertebrate embryos. From the point of view of stem cell biology, the neural crest is an ideal source for multipotent adult stem cells. Significant advances have been made in the past few years isolating neural crest stem cell lines that can be maintained in vitro and can give rise to many neural crest derivatives either in vitro or when placed back into the context of an embryo. The initial work identifying these stem cells was carried out with premigratory neural crest from the embryonic neural tube. Later, neural crest stem cells were isolated from postmigratory neural crest, presumably more restricted in developmental potential. More recently it has been demonstrated that neural crest stem cell progenitors persist in the adult in at least two differentiated tissues, the enteric nervous system of the gut and the whisker follicles of the facial skin. In all cases, the properties of the stem cells derived reflect their tissue of origin and the potential of the progenitors becomes more restricted with age. In this chapter we will review this work and speculate on future possibilities with respect to combining our knowledge of neural crest gene function in the embryo and the manipulation of adult neural crest stem cells in vitro and eventually in vivo.