title: Evidence of haematopoiesis within the developing human diencephalon. Correlations with vertebrate phylogeny.
abstract: OBJECTIVE
  The sites of haematopoiesis during human ontogeny can be correlated to the sites where haematopoiesis occurs in vertebrate phylogeny. As haematopoiesis has been described in the diencephalon and pituitary gland of water-inhabiting vertebrates we wanted to find out whether such a phenomenon also occurs in human embryos.
  
  
  METHODS
  Paraffin-embedded specimens from the diencephalon and pituitary gland of human embryos at the 7th to 22nd gestational week and from adults were investigated by conventional histology and immunohistology for the presence of haematopoietic cells.
  
  
  RESULTS
  Cellular accumulations predominantly of erythroid and megakaryocytic lineage were identified in the floor of the developing diencephalon of the 7th/8th gestational week. At the older developmental stages of the 18th to 22nd gestational week loose aggregates of haematopoietic cells within the leptomeningeal spaces adjacent to the hypophyseal infundibulum were detected in 2 out of 7 cases analyzed.
  
  
  CONCLUSIONS
  As it has been proposed that lymphohaematopoietic clusters occasionally occur within the brain in bone marrow-less vertebrates as a response to noxious agents, we speculate that this temporal appearance of haematopoietic cell clusters within the diencephalon floor in early human ontogeny could also be due to fetal immunomodulations.
authors.affiliation: Max Planck Institute for Molecular Genetics, Universitatsmedizin Berlin, Berlin, Germany.
authors.forename: Volkhard
authors.initials: V
authors.lastname: Seitz
authors.forename: Michael
authors.initials: M
authors.lastname: Hummel
authors.forename: Harald
authors.initials: H
authors.lastname: Stein
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Papadopoulos
authors.forename: Michael
authors.initials: M
authors.lastname: Zemlin
authors.forename: Korinna
authors.initials: K
authors.lastname: Joehrens
authors.forename: Ioannis
authors.initials: I
authors.lastname: Anagnostopoulos
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D004027:Diencephalon / Q000166:cytology / Q000196:embryology* / Q000502:physiology; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology; D006413:Hematopoietic System / Q000166:cytology / Q000196:embryology / Q000502:physiology; D006801:Humans; D007155:Immunologic Factors / Q000502:physiology; D010802:Phylogeny; D010904:Pituitary Gland, Posterior / Q000166:cytology / Q000502:physiology; D012754:Sharks / Q000196:embryology / Q000502:physiology; D014714:Vertebrates / Q000196:embryology* / Q000502:physiology
chemical_list: D007155:Immunologic Factors