Aizu Seiei

紀要類（bulletin）departmental bulletin pape

Aizu, Seiei

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

REGENERATION OF THE ECTODERM AND ENDODERM INHYDROIDS著者 Aizu Seieijournal orpublication titleThe bulletin of the Marine Biological Stationof Asamushi, Tohoku Universityvolume 13number 3page range 161-167year 1969-03-25URL http://hdl.handle.net/10097/00131328BULLETIN OF THE MARINE BIOLOGICAL STATION OF ASAli·IUSHI, VOL. XDI, NO. 3, 1969 REGENERATION OF THE ECTODERM AND ENDODERM IN HYDROIDS1> SEmi Arzu2> £- i$ ffl * . Biological Institute, TtJhoku University, Sendai, Japan Although many studies have been published on the morphogenesis of hydroids, the emphasis has largely concerned with the problem of polarity. In this study, the nature and the ability of the ectoderm and the endoderm were investigated. The writer wishes to express his cordial thanks to Dr. Isao Motomura Profes-sor Emeritus of the T6hoku University for his kind help and valuable criticism, and to Professor Eturo Hirai of the Marine Biological· Station of the T6hoku University for his valuable advice during the course of the present study. MA'l'ERIAL AND ME'l'HOD Two species of colonial hydroids, Obelia plana and Coryne pusilla were used as materials. They were collected in Matsushima Bay, Miyagi Prefecture. They were cultured in the laboratory at 10'0 by feeding Artemia larvae. The coenosarcs were taken from the periderm by squeezing the pieces of the hydrocau!us. Then, the ectoderm was isolated from the endoderm with a fine glass knife or needle. The endodermallayer of the fed colonies was easily distinguished from the ecto-derm by its pink color. Further, the ectoderm was distinguished from the endo-derm, as the latter contained the granules of a remarkable birefringence. OBSERVATIONS AND CONSIDERA'l'IONS l. REGENERATION OF THE ISOLATED ECTODERM AND ENDODERM l. Obelia plana a. Regeneration of the ectodermal tissue fragments. The pure ectodermal cells fused readily and formed a smooth spherical mass. In the center of the mass a core of cells mass was formed by splitting from the surrounding ectoderm. Mter five days, the stem bud having a hydranth budded at its tip began to grow. The complete hydranth was formed after six to seven days. I) Contributions· from the Marine Biological Station of Asamushi, Aomori Ken, No. 359 2) Present address: Department of Anatomy, TOhoku University School of Medicine, Sendai. 161 162 REGENERATION OF HYDROIDS b. Regeneration from the endodermal tissue fragments. The endodermal fragments were cultured in the same way as the ectodermal fragments. All of the er.dodermal fragments rounded up into balls within several hours after isolation and remained in t his form until they disintegrated twenty-four to t hirty-six hours later. No sign of differentiation was observed. Fig. l. P hotomicrographs of sections showing the regeneration process of t he ectodermal fragment of Obelia. a, Section of t he ectodermal t issue fixed immedia.tely after isola.tion. b, The same, after twelve hours. c, After twenty-four hours. d, After t.hree days, showing the porous str ucture in the ectoderm. e, After four or five days, showing t he connection between the outer and the inner part. f, Complete coenosarc regenerated from the ectodermal fragmen t six days after isoJa.tion. S. AIZU 163 c. Histological observations. The arrangement of the cells of the fragments fixed immediately after isolation was complete showing contraction. The tissue fragments consisted of many epithelio-muscular cells, interstitial cells and nematocysts, whereas no endodermal cells which contained many small inclusions was observed (Fig. l a). In the specimens of the isolates fixed six to twelve hours after isolation, the tissue fragments became tightly'rounded and were covered with a thin periderm (Fig. I b). After twelve to thirty-six hours the external cells became columnar, forming a layer of cells on the surface. The cells in the central area were degenerating (Fig. l c). 1\'l.any pores were arranging continuously in a circle under the external columnar cells. A few remained forming the thin bridge of the cytoplasm con-necting the extemal columnar cells and the internal degenerating cells (Fig. ld). M tcr three to five days, the connecting cytoplasm became thick incorporating the particles which were derived from the degenerated cells (Fig. le). At the time of hydranth formation, the connecting cells became large and contained many inclusions. These cells were considered to become the endodermal cells from the fact t hat they contained many basophilic par ticles. Thus, the endodennal cells were newly formed (Fig. If). 2. Ooryne pttsilla a. Regeneration of the ectodermal tissue fragments. The isolated ectodermal tissue fragment rounded up very quickly, usually into a spherical mass, and began to adhere to the substratum. At first, the whole sphere was translucent. Soon, the center of the mass became opaque. At the same time, circulation of the hydroplasm was observed in the mass. Three to four days after isolation the stolon began to elongate from the ectodermal tissue frag-ment. Then, the hydranth bud \\'aS formed on the stolon nea1· the tip. Mter ten to fourteen days the complete hyclranth with many tentacles was formed . b. Regeneration of the endodermal fragments. All of the endodermal fragments rounded up into ball form within six hours. But they became disintegrated twelve hours later. In addition, the endodermal tissue mass "·hich was enveloped in the mesogloca membrane also showed no further differentiation. c. Histological observations in regeneration of ectoderm. The components of the ectodermal cells fixed immediately after isolation were nearly normal showing contraction. The tissue fragment consisted of many epithelio-muscular cells with large nuclei, nematocysts and a few small interstitial cells (Fig. 2a). In the specimens of the isolates fixed after twelve to t wenty-four hours after isolation, the whole tissue masses rounded up tightly and were covered with a new thin periderm. The epithelio-muscular cells arranged 164 S. AIZU Fig. 2.'t·Photomicrographs of sections showing the regeneration process of the ectodermal fragment of Coryne. a, Section of the ectodermal t issue fixed immediately after isolation. b, The same, after twelve hours. c, After twenty-four hours, increasing in number of t he interstit ial cells . d, After thirty-six hours, the interstit ial cells appearing a long t he inner margin of the external cell layer. e, Showing the extensive opening. f, T he complete coenosarc re-generated from the ectodermal fragment. around the periphery of the tissue mass (Fig. 2b). The cells of the central area remained contracted. The interstitial cells increased in numbers (Fig. 2c). Mter twenty-four to thirty-six hours, the intercellular space was formed by the degenera-tion of the central cell mass. Thirty-six to fourty-eight hours after isolation the external cells became columnar, forming a layer of cells in the surface. Many interstitial cells appeared along the inner margin of external cell layer (Fig. 2d). REGENERATION OF HYDROIDS 165 Then, the space became extensive. Further, many small particles began to appear in the cytoplasm of the external columnar cells (Fig. 2e) . After two to three days the cytoplasm of the interstitial cells became large and began to incorporate many inclusions. These cells were considered to become the endodermal cells (Fig. 2f). As mentioned above, the isolated ectoderm in Coryne was able to regenerate the lost endoderm and to produce t he new hydranth as in Obelia. The transformation of the ectoderm to the endoderm in hydroids has been known in Cordylophora (Zwill-ing, 1963). But it was not clear what kind of the cells in the ectodermal layer transformed to the enclodermal cells. The results of t he present study indicate that the interstitial cells transformed to the endodermal cells. II. THE RELATION BETWEEN THE ECTODERM AND THE ENDODERM. l. Contact of the ectoclerrnal ancl the endoclermal fragments . When the endodermal fragment came into contact with the ectodermal fragment of Cm-yne, in the case in which the former was smaller than the latter, it was incorporated by the ectodermal fragment. After six hours it became located in the center of the ectodermal fragment. Hale (1964) described that the initiation of a hydranth was possibly due to a concentration of the ectodermal cells, and that the ectodermal cells continued to migrate up the stalk. From these facts, it can be suggested that the ectodermal cells are active in morphogenetic movement. 2. The 1·elation between the regeneration index cmd the mtio of the ectodermal and the endodenncd mctsses. The isolated ectodermal and the endodermal tissue fragments were minced to obtain many small fragments of 25, 50, 75 and 100 microns in diameter, respectively. These ectodermal and endodermal fragments came into contact in combinations as shown in Table l. The regeneration from the tissue fragment could be arranged in a graded series, ranging from tissue fragment to complete hydranth. In order to obtain a numerical measure of the grade of regeneration, arbitary numerical values were assigned to six grades of regeneration (Fig. 3). The regeneration index is calculated after the formula Table 1. The combination of the ectodermal and endodermal fi·agments. Diameter of ectoderm in micra 100 50 50 25 25 25 25 Diameter of endoderm in micra 100 100 50 50 25 75 100 166 reg. index S. AIZU 100·n1 + SO·n2 + 70·n3 +50··n, + 30·n, + 10·n, N where n1, n,, .... n, are the number of the cases of the different grades of regeneration and N is the total number of the masses. Fig. 4 is _a record of the regeneration index of various combined masses. The combined masses 100-100 tissue mass consisting of the ectodermal fragment having 100 microns in diamete; and the endodermal fragment having 100 microns in diameter, produced the complete hydranth on the tenth day in more than ninety per cent of the cases. The masses 50-50 produced the hydranths in forty per cent. In the masses 25-25; no hydranth was differentiated. From this, the more the volume of the tissue mass, the faster the regeneration of the mass, in the case that the volume of the ectodermal fragments were equal to the endodermal fragment. Neither 25-100 mass nor 25-75 mass differentiated any organs, though the volumes of both masses were more than 50-50 masses. This suggested that an excess of the endodermal cells hindered the regeneration of the mass. ~ ~ P& ..... , ... jk (@% ..... :.11 ~ ... :~ .. t @W ... ::~f Fig. ·a. Six grades of regeneration to which arbitary numerical values were assigned. " ~;: z 0 \i 0: "' z "' "' ~100 80 60 40 20 % 2 3 4 5 6 DAYS 8 o--o 100-100 ...... 50-100 <r-<)_ so-so ®--@ 25-50 ~ 25-25 @--@ 25-75 m--<1> 25-100 10 Fig. 4. Record of the regeneration index of various combined. masses. SUMMARY l. The ectodermal fragment of Obelia plana and Ooryne pusilla regenerated the endoderm and formed the complete hydranth. REGENERATION OF HYDROIDS 167 2. Histological observations indicated that the new endodermal cells originated from the interstitial cells. 3. The endodermal fragment· disintegrated after isolation. 4. Mesogloea membrane is not important for the regen~ration of the endo-dermal fragment. · 5. When the endodermal fragment came into contact with the ectodermal fragment, the former was ipcorporated by the latter. 6. An excess of the endodermal cells hindered the regeneration of the tissue mass. 7. In conclusion, it was shown that the ectodermal cells have a high morphogenetic potency in comparison with the endodermal cells. REFERENCES HALE, L.J., 1964. Cell movements, cell division and growth in the hydroid Olytia johnstoni. J. Embryo!. exp. Morph., 12; 517-538. ZWILLING, E., 1963. Formation of endoderm from ectoderm in Oordylophora. Biol. Bull., 124: 368-378. 

REGENERATION OF THE ECTODERM AND ENDODERM IN HYDROIDS

Institutional Repositories DataBase (IRDB)

https://tohoku.repo.nii.ac.jp/?action=repository_action_common_download&item_id=133938&item_no=1&attribute_id=18&file_no=1

REGENERATION OF THE ECTODERM AND ENDODERM IN HYDROIDS

Abstract

Similar works

Full text

Available Versions

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Institutional Repositories DataBase (IRDB)