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Ermak styela clava renewal blood cells experientia 1975

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Ermak styela clava renewal blood cells experientia 1975

  1. 1. a- Separatum TXPERITNTIA 3/, 837 (1975) Birkhduser Verlag, Basel (Schweiz) An Autoradio$raphic Demonstration of Blood Cell Renewal in Styela claaa (tJrochordata: Ascidiacea) The blood cells of ascidians circulate in the blood chan- Mnterials and meth,ods. Specimens of Styeta claua were nels and wander throughout the tissues and the tunic. collected from Mission Bry, San Diego, California, IJSA Although some blood cell types are common to all asci- and inj ected intra-atrially with 1 pCi of tritiated thymidine dians, other blood ceIl types often differ from species to (New England Nuclear corp.) per g fresh weight. The species. The number of blood cells described in any one aqueous solution of tritiated thymidine (specific activitv species also varies with the morphological criteria of the 6.7 Cilrrrlw) was diluted with an equal volume of 2 times authors. With iight microscopy, 8 types have been describ- concentrated sea water before use" 3 individuals were ed in Styela claual while 5 types have been described in sacrificed by fixation in Bouins fluid at each of the follow- Styela plicataz " ing time intervals : J- h, La, 20 and 60 days. The body wall The origin and renewal of ascidian blood cells have been and digestive tract were dissected out, dehydrated,, and the subject of controversy. The neural gtand3 and haemo- embedded in paraffin" 7 pm sections were cor.ered with blasts in the connective tissue a have been reportecL as Kodak Nuclear Track Emulsion type NBT-2 by the sites of biood cell formation. Several authors have dipping method and stored at 4 oC for periods of 2 weeks remarked on the absence of mitotic figures in the blood to 2 months" Autoradiograms were developed in Kodak spaces 5, 6" There is general agreement that the lymphocyte D-l9 developer (3 min), and sections were stained through is the progenitor biood cell type. Vhether l1mphocyte cell the emulsion with hematoxylin" division occurs only in the lymph nodules of the body wall Resrtlts. 3 types of blood cells can be recognrzed in and digestive tract6 or both in the lymph nodules and in autoradiograms: the lymphocyte, the leucocyte, and the the circulating blood 1, 2 has not been established. In vacuolated cell. A11 3 blood cell types occur free in the either case, the lymphocytes are presumed to differentiate circulating blood and clustered in lymph nodules within into the other cetrI types by the loss of the nucleolus, an the connective tissue of the body. In the body wall, the increase in the amount of crrtoplasm, and the acquisition lymph nodules occur in patches immediateiy adjacent to of various cytoplasmic inclusions and vacuoles. The the atrial epithelium (the internal lining of the body wa1l). transformations of one blood cell type to another have In the digestive tract, they are most concentrated in the been deduced from morphological criteria alon e2, ? . branchiai wall" rn the present investigation, autoradiography with tritiated thymidine was used to locahze sites of blood cell proliferation and determine possibie blood cell transforma- rW. C. GronGE, Q. J1. microsc. Sci. Bl,391_ (1939). tions in the ascidian Styela claua. A short exposure to 2 T" onuvn, Sci. Rep. Res. Insts Tohuku t]niv., Bio1. l l, rgr (1936). 3 L. Cuf Nor, Archs ZooI" exp. gdn. g, 13 (189j ). tritiated thymidine labeled blood cells engaged in pre- * J. M. Pfnis, Annis Inst. oc6anogr., Monaco 2/,229 (19,t3). mitotic DNA synthesis. By sampling tissues at increasing 5 M. Korr.lra.x, Annls Sci. nat., Zoo7.8, 1 (1908). time intervals after this short exposure, the fate of the 6 R" H" Mrrran, L.hI.B.c. {ern. typ.Br. mar. pl. Anim. ss, (1953). proliferating cells was f ollowed " 7 R" ExDEAN, Q. Jl.microsc. Sci. /0l , M (1960). "u* *=*"+*n .jii,ffi:,,,,,,,, $::::Iri:::::::::::::: : ] :: :::::::i::: F ig. 1. An autoradiogram of the lymph nodules in the body wall of Fig. 2. An autoradiogram of the lymph nodules in the body wali of Styela claua t h after the injection of tritiated thymidine. x 600" Styela claua 60 days after the injection of tritiated thymidine. The blood celis are no longer labeled although several atrial epithelial celis (arrows) are still labeled. m, muscle. x 600.
  2. 2. /- 838 Specialia ExpBnrBNrrA 3tl7 Lymphocytes are small, round to oval cells approximate- labeled, but few lymphocytes were labeled any longer. ly 6-8 pm in diameter with a large nucleolated nucleus. Most of the labeled cells, both in the lymph nodules and The nucleus fills most of the cell and is surrounded by a in the circulating blood, were leucocytes and vacuolated small amount of basophilic cytoplasm. Several lymphocy- cells. At 60 days after the administration of tritiated tes frequently cluster together in the interior of the lymph thymidine, most of the blood cells in the lymph nodules nodules. Cell boundaries are difficult to distinguish as the were unlabeled (Figure 2). llowever a few scattered Iarge basophilic nuclei of adjacent cells crowd each other labeled leucocytes and vacuolated cells occurred in the with little intervening cytoplasm. connective tissue below the atrial epithelium and in the Leucocytes are large blood cells about L}-L+ pm in blood channels. diameter with a small, basophilic nucleus which is eccen- Discussion. The blood cells of. Styela claua constitute a trically displaced and lacks a conspicuous nucleolus. renewing 8 cell system with a renewal time on the order of Most of the cell is filled with slightly basophilic cytoplasm. several weeks. As suggested by other authors 1 2, blood Leucocytes range in shape from spherical to oval and cell proliferation occurs both in the lymph nodules and in may have several cytoplasmic processes. The cytoplasm the blood channels. The possible blood cell transforma- may be granular or transparent and may contain a large tions are shown in Figure 3. Although both lymphocytes basophilic inclusion. Leucocytes probably include several and leucocytes proliferate, the lymphocyte is probably cell types which are difficult to distinguish from each the more primitive blood cell type. It is ultrastructurally other. In the lymph nodules, the abundant cytoplasm the most undifferentiated blood cell type e and may also around each nucleus produces regions of light basophilia be capable of differentiating into germinal cells 10 and and makes the leucocyte nucleus easily distinguished from somatic cells other than blood cells 11. Presumably the the lymphocyte nucleus. lymphocytes differentiate into leucocytes. llowever, Vacuolated cells are the largest of the blood cells, being since the leucocytes divide and also probably represent roughly 16-18 pm long. The nucleus is eccentrically several separate cell types, the leucocytes themselves placed and lacks a conspicuous nucleolus. Within the might be composed of stem, dividing transit, or non- cytoplasm, the vacuolated cells contain numerous vacu- dividing transit 12 components. Since the differentiated oles which are clear or yellow in hematoxylin stained vacuolated cells do not divide, they must be differentiating sections and which have a high index of refraction. from a precursor cell type; whether this precursor is a Vacuolated cells frequently lie embed d ed between the lymphocyte or a leucocyte could not be determined in the atrial epithelium and the connective tissue of the body present investigation. Based upon morphological criteria, wall. however, vacuolated cells have been reported to differen- A t h exposure to tritiated thymidine labeled many tiate from intermediate cell types and not from lympho- blood cells in the body. Blood cells were labeled. both in cytes in other ascidians 7 , L3. the lymph nodules and in the blood channels. In the Blood cells are renewed in insects 1a and mammals 15 Iymph nodules, both lymphocytes and leucocytes wero but not in echinoderms 16 where blood cells have charac- labeled (Figure 1), and labeled nuclei were frequentlv teristics of expandirg* cell populations. In mammals, clustered in small groups. Probably no vacuolated cells proliferating cells are most concentrated in the bone were labeled at this time ; however, positive reaction s marrow, lymph nodes, and spleen, but, like tn Styela, they were difficult to detect in autoradiograms as the vacuoles also occur in the circulating blood and in the connective appear very similar to out-of-focus silver grains. ti$sue. In Styela, other elements of the vascular system By 20 days after injection, most of the labeled cells in (the heart and connective tissue lining the blood channels) the lymph nodules occurred in the peripheral parts of the comprise expanding cell populations 17. nodules. Some vacuolated cells were now unequivocally Surnrnary. The blood cells of Styela claua were shown by autoradiography r,vith tritiated thymidine to be renew- ed after several weeks. Proliferating lymphocytes and leucocytes occurred in the lymph nodules and blood channels of the body. Vacuolated cells did not proliferate but differentiated from a precursor cell type. T. H. ERnrax 18 Diuision, of Marine Biology, Scri,pps Institution of Oceanography, La Jolla (Cali,fornia 92037, USA), 5 March 7 975. I f, 8 e B. MBSSTER and C. P. LBnroND, Am. J. Anat. 106,247 (1960). J. OvnRroN, J. Morph.779,305 (1966). 10 A. T. NBwBERRv, 11 G. FnnBnreN, tJ. E. Cr,Bevnn, J. Morph.726, t23 (1,968). J. exp. Zool.756,I57 (7964). Thyrnid,ine Metabol,ism and, CeII, Kinetics (John Wiley & Sons, fnc., New York 1,967). 13 A. SansA.nrN, Arch. ital. Anat. Embriol . 60,33 (1955). 14 E. P. CnoNKrrE, V. P. BoNn, T. M. Fr,rBnNnn and J. R. RunrNr, Lab. fnvest. 8,263 (1959). 15 S. C. SsnrvASrAvA and A. G. RrcsARD, Biol. Bull. 728,337 (1965). 16 N. D. Holr,AND, J. H. Pnrr-r,rps and A. C. Grnsr, Biol. Bull. 128, zse (Le6s). L7 T. H. Ennar, Ph. D. Diss. (1975). Fig. 3. Transformation of blood cell typesin Styela claaa. A, lympho- 18 Present address: Department of. ZooIogy, University of California, cyte; B, leucocyte; C, vacuolated cell. Berkeley, California 94720, USA.