Embryonic hematopoietic stem cells and interstitial Cajal cells in the hindgut of late stage human embryos: evidence and hypotheses.
There have been few studies on human embryos describing a specific pattern of hindgut colonization by hematopoietic stem cells (HSCs) and interstitial Cajal cells (ICCs). We aimed to study CD34, CD45 and CD117/c-kit expression in late stage human embryos, to attain observational data that could be related to studies on the aorta-gonad-mesonephros (AGM)-derived HSCs, and data on hindgut ICCs. Antibodies were also applied to identify alpha-smooth muscle actin and neurofilaments. Six human embryos of 48-56 days were used. In the 48 day embryo, the hindgut was sporadically populated by c-kit+ ICCs, but, in all other embryos, a layer of myenteric ICCs had been established. Intraneural c-kit+ cells were found in pelvic nerves and vagal trunks, suggesting that the theory of Ramon y Cajal assuming that ICCs may be primitive neurons may not be so invalid. Also in the 48 day embryo, c-kit+/CD45+ perivascular cells were found along the pelvic neurovascular axes, suggesting that not only liver, but also other organs could be seeded with HSCs from the AGM region. CD45+ cells with dendritic morphologies were found in all hindgut layers, including the epithelium. This last evidence is suggestive of an AGM contribution to the tissue resident macrophages and could be related to processes of sprouting angiogenesis which, in turn, have been found to be guided by filopodia of endothelial tip cells. Further studies on human embryonic and fetal material should be performed to attempt to clarify whether the hindgut colonization with HSCs is a transitory or definitive process.
Department of Anatomy, Faculty of Medicine, "Victor Babeş" University of Medicine and Pharmacy, Timişoara, Romania.
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Ilie
Division of Anatomy, Faculty of Dental Medicine, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania; International Society of Regenerative Medicine and Surgery (ISRMS), Bucharest, Romania. Electronic address: anatomon@gmail.com.
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Rusu
Division of Embryology, Faculty of Dental Medicine, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania.
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Didilescu
Department of Anatomy, Faculty of Medicine, "Victor Babeş" University of Medicine and Pharmacy, Timişoara, Romania.
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Motoc
Research Center for Microscopic Morphology and Immunology, Department of Morphology, University of Medicine and Pharmacy of Craiova, Craiova, Romania.
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Mogoantă
D000199:Actins / Q000378:metabolism; D000328:Adult; D003713:Dendritic Cells / Q000502:physiology; D053595:Embryonic Stem Cells / Q000502:physiology*; D005260:Female; D005333:Fetus / Q000166:cytology / Q000502:physiology*; D041981:Gastrointestinal Tract / Q000166:cytology* / Q000196:embryology / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D056885:Interstitial Cells of Cajal / Q000502:physiology*; D017493:Leukocyte Common Antigens / Q000378:metabolism; D009197:Myenteric Plexus / Q000166:cytology / Q000196:embryology; D018919:Neovascularization, Physiologic / Q000502:physiology; D011247:Pregnancy; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism
D000199:Actins; D019009:Proto-Oncogene Proteins c-kit; D017493:Leukocyte Common Antigens
Aorta-gonad-mesonephros; CD117; CD45; Endothelial tip cells; Interstitial cells of Cajal; c-Kit