Evolution of marrow regeneration as revealed by transplantation studies

An in situ study of CD34(+) cells in human fetal bone marrow

The purpose of this study was to characterize the spatial distribution, number and size of CD34(+) cells in fetal bone marrow. Thin sections of normal fetal bone marrow from lumbar vertebrae were stained using CD34 antibody QBend/10. Sections were used under light microscopy with various eyepiece graticules to make measurements of CD34(+) cells in situ. Results showed that at mid- and late gestation, approximately 2% and 0.5% of fetal bone marrow cells were CD34(+) respectively. The mean distance of CD34(+) cells from the nearest trabecular bone surface was 61 +/- 4 and 46 +/- 4 microm, respectively, for mid- and late gestation. The mean distance to the nearest neighbour was 46 +/- 5 and 105 +/- 15 microm, and the mean distance to the nearest blood vessel was 13 +/- 1 and 17 +/- 2 microm respectively. The concentration of CD34(+) cells in the peripheral region was 6.5 times greater than that at the centre of the sections. Overall, the percentage number of CD34(+) cells decreased with gestational age. The cellular and nuclear diameters of CD34(+) cells remained unchanged throughout mid- and late gestation at 5.4 +/- 0.1 and 3.8 +/- 0.1 microm respectively. This information will be used to calculate the natural background alpha-radiation dose to haemopoietic stem cells.

Initiation and enhancement of bone formation. A review

Knowledge of some of the fundamental biochemical factors that may influence the initiation and continued growth of bone-forming cell lines is presented. The discussion is limited to those factors shown experimentally to be present locally in bone tissue and synthesized in the environment of bone-forming cells. The current state of knowledge of basic research findings on osteogenic factors is given in detail. Cooperative actions of these locally produced and systemic factors are the primary stimuli that result in increased bone growth and volume.

Induction of chondrogenesis in muscle, skin, bone marrow, and periodontal ligament by demineralized dentin and bone matrix in vivo and in vitro

Induction of chondrogenesis in vivo by rolls of demineralized dentin implanted in muscle, subcutaneous connective tissue of skin, medullary cavity of femur, and periodontal ligament of rat was investigated. Specimens were examined at various times up to 21 days after implantation, using light microscopy and morphometric analysis. Induction of cartilage occurred most quickly in muscle, followed by subcutaneous connective tissue of skin and medullary cavity of femur, and most slowly in periodontal ligament. Significantly more cartilage was found in muscle than in subcutaneous connective tissue of skin and medullary cavity of femur at the times examined, and least of all in periodontal ligament. Outgrowth of cells from rat muscle, dermis and subcutaneous tissue, bone marrow and periodontal ligament cultured in vitro on demineralized bone matrix for up to 35 days produced similar results.

Bone lining cells and hematopoiesis: an electron microscopic study of canine bone marrow

Hematopoietic bone marrow in the dog is enclosed by a nearly complete and rather complex layer of endosteum, consisting of a diverse group of cells collectively called bone lining cells (BLC). Cell types comprising BLC include osteoblasts and osteoclasts, and other cell types, among which are elongated, flat cells with a spindle-shaped nucleus, and small cytoplasmic vesicles. The composition and thickness of the layer of BLC varies along the perimeter of the marrow. The layer may be simple or stratified. Occasionally a zone of tightly packed regularly arranged collagenous fibers lies between the bone lining cells and bone. Hematopoiesis, particularly neutrophilic, often occurs in the bone marrow next to the BLC. Cytoplasmic processes of BLC occasionally extend into the hematopoietic spaces and stromal cells in the hematopoietic compartment may extend processes to the layer of BLC. Occasionally cells of the BLC are similar in appearance to stromal cells within the marrow. Our observations together with the experimental findings of others (that fibroblastic stromal cells contribute to the hematopoietic inductive microenvironment, that hematopoietic stem cells are concentrated subosteally, that cells responsible for regeneration of the marrow stroma are derived from the endosteal layer, and that high concentrations of hematopoietic colony-stimulating factors are produced there) indicate that the hematopoietic capacities of bone marrow may be regulated by BLC.

Studies on bone marrow histogenesis: morphometric and autoradiographic studies of regeneration marrow stroma in extramedullary autoimplants and after evacuation of marrow cavity

The marrow cavity of the rat tibia was mechanically evacuated and autoimplanted to the subcutaneous tissue. The regenerative process which restored the integrity of marrow stroma and hemopoiesis, was morphometrically evaluated in whole mount of tibia. Following evacuation, the clot filled the cavity. The granulation tissue then appeared and expanded, penetrating and replacing the clot. The fibroblasts of the granulation tissue differentiated into osteoblasts forming osteoid bone. Within its interstices, the primordial marrow consisting of loose connective tissue and vascular sinuses appeared and hemopoiesis resumed. Expansion of hemopoiesis resulted in the resorption of bone and within three weeks the tibial cavity was restored to the pre-evacuation state. Autoradiography indicated that the labeling index was initially high in fibroblasts and osteoblasts but was subsequently reduced while it increased in osteocytes, cells of Haversian canals, stromal and hemopoietic cells of marrow. The finding is in disagreement with the view that the regenerative process originates from the Haversian canal. When the label was introduced on day 4 post-operatively, it subsequently appeared in osteocytes, cells of Haversian canal, stromal elements of the marrow, but not in the hemopoietic cells. This indicates complete dissociation of marrow stroma and hemopoietic stem cell.

Architecture of the marrow vasculature in three amphibian species and its significance in hematopoietic development

Architecture of the bone marrow vasculature, particularly that of the femur, was analyzed in three amphibian species in relation to the early phylogeny of marrow hematopoiesis. A dye-injection method and histological techniques, including both serial sectioning and reconstruction methods, were used for this purpose. From these observations the following conclusions may be drawn. (1) Marrow hematopoiesis is absent from the femur of the urodelan (Triturus pyrrhogaster) and appears first in the femur of the primitive anuran (Xenopus laevis) (2) The site of primitive hematopoiesis (granulopoiesis) is the subendosteal region where the venous vascular net develops. (3) The primitive vascular architecture observed in the femur of Xenopus is characterized by the absence of a central vein. Subendosteal veins drain the blood from the bone marrow. A vein collateral to the primary artery appears in the femur of Rana catesbeiana, an advanced anuran, in which further development of both the subendosteal venous plexus and hematopoietic activity are noted. In both anura examined, the primitive blood sinuses form near the mid-shaft of the femur. The proliferation of mesenchymal elements containing dark pigment, presumably melanin, was also noted in this area. (4) The architecture of marrow vessels in Rana approaches the structure noted in mammalian bone marrow. (5) Fat tissue is observed in the urodelan bone marrow prior to the appearance of hematopoietic activity. This indicates that the formation of marrow fat is phylogenetically unrelated to the development of hematopoiesis. The present investigation on primitive hematopoiesis suggests that the development of hematopoietic activity is intimately related to the development of the marrow vasculature, particularly that of the subendosteal venous plexus. A favorable vascular arrangement may be necessary to allow active hematopoiesis.