Characterization of myelid cells derived from the anterior ventral mesoderm in the Xenopus laevis embryo

Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan.
Development Growth and Regeneration (Impact Factor: 2.42). 11/2006; 48(8):499-512. DOI: 10.1111/j.1440-169X.2006.00885.x
Source: PubMed


A recent study revealed the presence of a unique population of myeloid cells in the anterior ventral (AV) mesoderm of Xenopus laevis embryo, as characterized by the expression of peroxidase 2 (POX2), which encodes for a leukocyte-specific enzyme. The current report further characterized the POX2-positive cells in terms of their contribution to hematopoiesis in tadpole and regulatory mechanism in differentiation. Grafting experiments with cytogenetically labeled tissues revealed that AV-derived mesoderm supplies a transient population of migrating leukocytes in the mesenchyme of early tadpole. These cells were rarely found in blood vessels at any stages. Using a ventral marginal zone explant system, we demonstrated that dkk1, shown as a heart inducer in this system, has a strong ability to induce the expression of POX2. Injection of a high dose dkk1 RNA induced a heart marker while a low dose of dkk1 preferentially induced the expression of POX2, suggesting that dkk1 works as a morphogen to determine the different lineages. Overall results indicate that wnt signal inhibitors induce leukocytes at the early neurula stage and that these cells spread to the entire body and exist until the ventral blood island-derived leukocytes appear in the body.

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    • "At the protein level, a leukocyte-specific mAb, XL-1, has similarly identified a widely dispersed population of nonlymphoid leukocytes in X. laevis tadpoles before the onset of cardiovascular circulation at the tail bud stage (Ohinata et al., 1989). Another mAb, XL-2, also recognizes an even earlier type of leukocyte at st 26 (Miyanaga et al., 1998); it is quite possible that these two mAbs recognize the same cell population (Tashiro et al., 2006). Although these different results are consistent with the establishment, during early development, of a rudimentary or transitory innate type of immune cell effector of the myeloid lineage, the heterogeneity and fate of these myelocytes at later stages of development, as well as their mode of action remain to be determined. "
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    ABSTRACT: Xenopus laevis is the model of choice for evolutionary, comparative, and developmental studies of immunity, and invaluable research tools including MHC-defined clones, inbred strains, cell lines, and monoclonal antibodies are available for these studies. Recent efforts to use Silurana (Xenopus) tropicalis for genetic analyses have led to the sequencing of the whole genome. Ongoing genome mapping and mutagenesis studies will provide a new dimension to the study of immunity. Here we review what is known about the immune system of X. laevis integrated with available genomic information from S. tropicalis. This review provides compelling evidence for the high degree of similarity and evolutionary conservation between Xenopus and mammalian immune systems. We propose to build a powerful and innovative comparative biomedical model based on modern genetic technologies that takes take advantage of X. laevis and S. tropicalis, as well as the whole Xenopus genus. Developmental Dynamics 238:1249-1270, 2009. (c) 2009 Wiley-Liss, Inc.
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