title: Role of the mesonephros as a transient haematopoietic organ in the bovine embryo.
abstract: During vertebrate embryogenesis, haematopoietic stem cells (HSC) arise in the aorta-gonads-mesonephros (AGM) region. In the present study, we examined serial sections of 22-34 days post-insemination (dpi) bovine embryos, a species with a well-developed and functional mesonephros. We describe the temporo-spatial distribution of presumptive c-kit positive HSC and the occurrence of haematopoietic foci in the mesonephros and fetal liver using specific antibodies directed against haematopoietic cell markers and conventional electron microscopy. In the mesonephros, presumptive HSC were found at 23-24 dpi in the blood stream, in the endothelial lining of the filtering capillaries and in the septal stroma of the cranial part of the mesonephros, the mesonephric giant corpuscle (MGC), suggesting a colonalization via the blood stream from the haematopoietic clusters of the dorsal aorta. From 25 to 30 dpi, presumptive HSC predominate in the septal stroma of the MGC, were they first expand but then decline and disappear following 32 dpi. In parallel, we found ongoing erythropoiesis and myelopoiesis starting in the MGC at 24 dpi and extending during the complete observation period. In the embryonic liver, colonization with presumptive c-kit positive HSC occurs slightly later, at 25 dpi. Active formation of blood cells in the liver increases following 30 dpi. In conclusion, the mesonephros of bovine embryos, in particular its MGC, functions as a primitive haematopoietic organ, temporarily intercalated between extraembryonic erythropoiesis and haematopoiesis within in the fetal liver, thus recapitulating for a short period a phylogenetically old site of blood formation.
authors.affiliation: Institute of Anatomy, University of Regensburg, 93040 Regensburg, Germany. mk@zihak.de
authors.forename: M
authors.initials: M
authors.lastname: Kritzenberger
authors.forename: K-H
authors.initials: KH
authors.lastname: Wrobel
mesh_terms: D000818:Animals; D002417:Cattle / Q000196:embryology*; D004622:Embryo, Mammalian / Q000033:anatomy & histology; D004900:Erythroblasts / Q000166:cytology; D004920:Erythropoiesis; D005865:Gestational Age; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000648:ultrastructure; D007124:Immunoenzyme Techniques; D008099:Liver / Q000166:cytology / Q000196:embryology / Q000648:ultrastructure; D008533:Megakaryocytes / Q000166:cytology; D008650:Mesonephros / Q000033:anatomy & histology / Q000166:cytology / Q000196:embryology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D013194:Staining and Labeling; D034061:Thrombopoiesis