XPOX2-peroxidase expression and the XLURP-1 promoter reveal the site of embryonic myeloid cell development in Xenopus.
Phagocytic myeloid cells provide the principle line of immune defence during early embryogenesis in lower vertebrates. They may also have important functions during normal embryo morphogenesis, not least through the phagocytic clearance of cell corpses arising from apoptosis. We have identified two cDNAs that provide sensitive molecular markers of embryonic leukocytes in the early Xenopus embryo. These encode a peroxidase (XPOX2) and a Ly-6/uPAR-related protein (XLURP-1). We show that myeloid progenitors can first be detected at an antero-ventral site in early tailbud stage embryos (a region previously termed the anterior ventral blood island) and transiently express the haematopoetic transcription factors SCL and AML. Phagocytes migrate from this site along consistent routes and proliferate, becoming widely distributed throughout the tadpole long before the circulatory system is established. This migration can be followed in living embryos using a 5 kb portion of the XLURP-1 promoter to drive expression of EGFP specifically in the myeloid cells. Interestingly, whilst much of this migration occurs by movement of individual cells between embryonic germ layers, the rostral-most myeloid cells apparently migrate in an anterior direction along the ventral midline within the mesodermal layer itself. The transient presence of such cells as a strip bisecting the cardiac mesoderm immediately prior to heart tube formation suggests that embryonic myeloid cells may play a role in early cardiac morphogenesis.
Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
Stuart J
SJ
Smith
Surendra
S
Kotecha
Norma
N
Towers
Branko V
BV
Latinkic
Timothy J
TJ
Mohun
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D006321:Heart / Q000196:embryology; D017403:In Situ Hybridization; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D038042:Myelopoiesis / Q000235:genetics; D009195:Peroxidase / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics; D029867:Xenopus Proteins / Q000235:genetics*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C404106:MRC2 protein, human; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C489365:TAL1 protein, Xenopus; D014157:Transcription Factors; D029867:Xenopus Proteins; D009195:Peroxidase