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J B Turpen

Publications and source records attributed to J B Turpen.

28 records · Page 2Linked to original sources
PubMed1979

Experimental studies on hemopoiesis in the pronephros of Rana pipiens.

Embryogenesis of hemopoietic cell populations in the pronephros of Rana pipiens was examined during embryonic and early larval development. Differential cell counts of Wright-Giemsa-stained cell suspensions demonstrated that granulopoiesis is the predominant hemopoietic activity in the pronephros, erythropoiesis accounts for a minor component of the hemopoietic activity (less than 10%), and lymphopoiesis within the organ is negligible. Microdensitometric analysis of Feulgen-DNA stained granulocyte populations in pronephroses from larvae that had received chromosomally labeled pronephric analgen transplants between 84 and 96 h of development demonstrated that hemopoiesis in this organ is dependent on colonization by an extrinsic hemopoietic stem cell. A similar analysis of pronephric hemopoiesis in larvae which had received chromosomally labeled, presumptive ventral blood island transplants between 62 and 67 h of development, indicates that granulopoietic cells are not derived from the embryonic blood islands. It is proposed that the pronephros may be the initial site of granulocyte differentiation during early embryogenesis. Although the embryonic origin of the hemopoietic stem cell is unknown, indirect evidence from this study indicates a dorsal stem cell compartment.

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PubMed1975

Thymus: central role in the immune system of the frog.

In the leopard frog (Rana pipiens), the thymus profoundly influences immunologic development by providing virtually all the progenitor lymphocytic cells for the bone marrow and other peripheral lymphoid organs. The thymus houses a self-perpetuating population of lymphopoietic cells that originally self-differentiated in that gland.

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PubMed1973

Ontogeny and peripheralization of thymic lymphocytes.

Reciprocal transplantation of undifferentiated thymic primordia between diploid and triploid chromosomally marked frog embryos has revealed that thymic lymphocytes are ontogenically derived from elements of the thymic primordium rather than from blood-borne stem cells that migrated into the developing organ. Virtually all the lymphocytes in the spleen, kidneys, and bone marrow of adult frogs are descendants of these original thymic stem lymphocytes.

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PubMedDate not supplied

Characterization of lineage restricted forms of a Xenopus CD45 homologue.

The leukocyte common antigen, also known as CD45, is a structurally heterogenous molecule ranging in molecular weight from 180 to 220 kDa. CD45 belongs to a family of high molecular weight, cell surface glycoproteins expressed on all hematopoietic lineages with the exception of mature erythrocytes. In higher vertebrates, the highly conserved cytoplasmic domain of CD45 exhibits protein tyrosine phosphatase activity and has been implicated in lymphocyte activation through dephosphorylation of critical tyrosine residues on substrates associated with signal transduction pathways. The monoclonal antibody CL21 recognizes a high molecular weight determinant expressed on the surface of Xenopus leukocytes which was postulated to be a CD45 homologue. In order to determine if lymphocyte subpopulations expressed different molecular weight variants, splenic B cells were identified and isolated on the basis of surface IgM and the CL21 determinant expressed by these cells was compared to the determinant expressed by thymocytes. Immunoprecipitation revealed that IgM + B cells expressed a 220 kDa molecular weight variant whereas thymocytes and IgM-cells expressed a 180 kDa variant. Bone marrow myeloid cells, isolated on the basis of light scatter properties, expressed a determinant which ranged from 150 to 160 kDa. Dephosphorylation experiments utilizing p-nitrophenyl phosphate, 32P-labeled Raytide [tyr(P)], or Kemptide [ser(P)] as substrates demonstrated that immunoprecipitated CL21 antigen exhibited tyrosine specific phosphatase activity which was inhibited by sodium orthovanadate. Thus, data based on the presence of enzymatic activity and lineage restricted molecular weight variants support the hypothesis that the CL21 determinant is the amphibian homologue of mammalian CD45, and suggest that both structural and functional elements of CD45 have been conserved during vertebrate evolution.

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PubMedDate not supplied

Induction and early development of the hematopoietic and immune systems in Xenopus.

This paper reviews several aspects of the development of the hematopoietic and lymphoid systems in Xenopus. The developmental biology of hematopoietic stem cells and the early development of the thymus and B-cells are discussed. Recent advances in the development of molecular indices of the hematopoietic program are also considered. Previous studies as well as new data demonstrate that the hematopoietic program is initiated at the time of gastrulation. Recent advances suggest that both positive and negative regulation is necessary for the appropriate spatial and temporal expression of the hematopoietic program during development.

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PubMedDate not supplied

Thymus: primary site of lymphopoiesis.

The thymus of the leopard frog is the primary, if not the sole, source of progenitor lymphocytic cells that normally colonize the spleen. Following embryonal parabiosis, a high level of cell chimerism exists in the thymus glands of each member of the parabiotic pair. Evidently, there can be an appreciable amount of cross-circulation of thymic cells between thymus glands.

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PubMedDate not supplied

Alternate sites of lymphopoiesis in the amphibian embryo.

The presumptive ventral blood islands were reciprocally transplanted between chromosomally labelled 72-hour-old leopard frog embryos. At 10 days of development, the differentiating epithelial thymus glands were surgically removed. Following metamorphosis, the spleen and bone marrow from juvenile frogs were analysed cytophotometrically. During normal ontogeny, the vast majority of peripheral lymphocytes are derived from the thymus, not the ventral blood islands. In the absence of the thymus, the ventral blood islands made the major lymphocyte contribution to the peripheral lymphoid organs. Thus, removal of the thymus appears to initiate an alternate pathway of lymphocyte differentiation in the leopard frog.

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