摘要:

AbstractExperiments were carried out to determine whether chick embryonic cells have the capacity to lodge preferentially in their homologous organ after intravascular dissemination in host embryos. Chick embryos incubated for five and one‐fourth days were used as donor and hosts. Donors were labeled with tritiated thymidine and selected organs were dissociated into single cells with trypsin. In separate experiments, labeled cells of mesonephros, limb, or heart ventricle were injected into hosts via a large chorioallantoic vein. The hosts were sacrificed 6 and 24 hours later. In each experiment, autoradiographs were prepared from serial sections of these three organs and the labeled cells in each organ were counted.The distribution of cells among the three organs was found to be almost identical for the three types of cells and at both time periods. Approximately 65–78% of the cells found in the three organs were in the mesonephros; about 21–31% were in the limbs; and about 1–4% were in the ventricle. Thus the cells failed to show a tendency to home; their distribution was completely independent of their organ source. These results suggest that homing is not a general property of embryonic cells, and their lodging properties offer no support for the hypothesis that embryonic cells of different types have highly type‐specific adhesive pr

ISSN:0022-104X    

DOI:10.1002/jez.1401670102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractCutting and grafting experiments on the ciliateStentor coeruleusduring division stages indicated or demonstrated the following: (1) Unequal division after excision of one cell end showed that the location of the fission line usually remains predetermined but this line is not an indispensable constriction organelle. (2) The fission line is always smooth in spite of irregularities in the cell surface and it cannot extend across gaps. (3) A transequatorial piece of a divider can go on to divide anywhere on a divider in the same stage of division but its fission is not autonomous because it can be affected if the host cell is in a very different stage of division or is a non‐divider. (4) After removing half the presumptive or actual fission line or furrow a stentor can still divide along the line of healing. (5) Transverse cuts, though resembling a division line, do not serve for fission. These results suggest a morphogenetic hypothesis of cell division in Stento

ISSN:0022-104X    

DOI:10.1002/jez.1401670103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractUnlike acute skin allograft reactions observed in most randomly breeding ectothermic and endothermic vertebrates, a basic pattern of intermediate to prolonged chronic skin graft rejection characterized the alloimmune response of representatives of at least five genera of salamanders from three different families (Salamandridae, Ambystomatidae, and Proteidae). First‐set median survival times (MST's) ranged from 33 to 55 days at 25°C. Individual zero end points (total melanophore destruction) occurred between 17 and 120 days. Several grafts appeared to have survived indefinitely (>300 days) with full to partial viability.MST's of second‐set grafts were significantly shorter than first‐set MST's for all salamanders exceptAmbystoma tigrinum.For this species, the small sample of seven repeat grafts all exhibited either prolonged survivalvis‐a‐visfirst‐set grafts or were destroyed well within the range of first‐set rejections. About 25% of the combined individualTarichaandNecturusrepeat grafts were completely destroyed at the same postoperative time as or significantly later than first‐set grafts from the same donor. Only curtailed survival ofCynopssecond‐set grafts was noted. When the post transplantation period was resolved into a latent phase and a rejection phase, the curtailed survival of 50% of theTrarichaand 60% of theCynopssecond‐set grafts was attributable solely ot a comparatively shorter latent period. The curtailed zero end points of otherTaricharepeat grafts resulted from both shorter latent and shorter rejection intervals. The overall prolonged second‐set survival noted for someTarichaallografts was referable only to longer rejection phases; the latent phases for these repeat grafts were either shorter than or similar to those of the corres

ISSN:0022-104X    

DOI:10.1002/jez.1401670104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractIn order to determine whether chondrocytes are stable as to type during limb regeneration and whether any cells from limb muscle become chondrocytes in the regenerate, labeled cartilage and muscle were transplanted into limbs which were then allowed to regenerate. Transplanted cells were identified after redifferentiation in the regenerate by three kinds of label: H3‐thymidine detected by radioautography; triploidy as judged by the presence of three nucleoli per nucleus; or a combination of the two.The results of this investigation indicate that limb chondrocytes are intrinsically stable with respect to cell type, for grafts of both triploid and H3‐thymidine labeled chondrocytes gave rise to morphologically dedifferentiated blastema cells which almost exclusively differentiated into chondrocytes. The small percentage of labeled noncartilage cells observed could have been the result of metaplasia, although it is more likely that all or most of them arose as spontaneous polyploids or as contaminants of the original grafts. Isotope dilution in H3‐thymidine labeled chondrocytes indicated that they had usually divided at least five times. Hence, the basis for the intrinsic stability of chondrocytes must be heritable.Chondrocytes from the coracoid, scapula, and visceral arch cartilages also contributed cells to cartilage of limb regenerates, and the available evidence indicates that cells released from these cartilages are similarly stable as to type. These cartilages did not dedifferentiate and participate in limb regeneration to the same extent as did limb cartilage.Results from transplanted limb muscle, labeled by all three methods used in this study, indicate that certain cells of muscle can become chondrocytes during limb regeneration. The exact cellular origin of these chondrocytes, however, is uncertain, for muscle is a mixture of cell

ISSN:0022-104X    

DOI:10.1002/jez.1401670105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractHeart determination is a gradual, cumulative process involving inductive and suppressive interactions between the heart mesoderm and nearby embryonic tissues. Our analysis of heart determination in the California newt,Taricha torosa, includes defect and otherin vivoexperiments, and explants in epidermal vesicles and into hanging drops.Explants of presumptive heart mesoderm from neurulae into hanging drops of a completely defined salt solution (Niu‐Twitty solution) produce beating hearts only infrequently. The addition of various other tissues and fractions of tissue homogenates changes the frequency and the rate of differentiation. These two parameters were used to assess the stimulatory and suppressive effects of tissues and tissue fractions on the differentiation of the presumptive heart mesoderm.At least three different factors are active in eliciting and regulating heart differentiation. A specific heart inductor in anterior endoderm increases the rate and the freqency of heart differentiation. A general stimulatory factor in epidermis and other embryonic tissues increases the frequency, but not the rate, of heart differentiation. An inhibitory agent in cranial fold and neural plate tissues delays or prevents heart differentiation. These three factors operate from intact tissues in the embryo or when explanted in vesicles or hanging drops, and are effectively present in a fraction (from sephadex column chromatography) of homogenates of the appropriate tissue

ISSN:0022-104X    

DOI:10.1002/jez.1401670106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractAxolotl females homozygous foroproduce eggs which cleave normally, but never develop beyond gastrulation. This cessation of development is due to a cytoplasmic deficiency which can be corrected by injecting eggs ofo/ofemales with cytoplasm from normal eggs. When so injected, the recipient eggs develop beyond gastrulation and may attain larval stages. The corrective component of normal cytoplasm has the following characteristics: 1. It remains in the supernatant of normal egg homogenates after two hours of centrifugation at 105g, but is gradually sedimented thereafter. 2. The corrective activity persists for at least eight days when preparations are stored at O°C. It is abolished on heating for one hour at 50° to 55°, and on incubation with crystalline trypsin. 3. The active material is customarily extracted from egg homogenates in 0.1 M or 0.2 M KCl, with 0.01 M Tris, pH. 7.6. It can be precipitated by 2M to 3M ammonium sulfate and retains its corrective activity. It is also precipitated by distilled water, but is then irreversibly denatured. 4. The corrective component is found mainly within the germinal vesicle of large oocytes; then in the egg cytoplasm or extracts thereof following germinal vesicle breakdown. Comparable extracts of blastulae show a reduced corrective activity. Attempts to extract the active material from older embryos and from organs of adults have so far failed. These results suggest that the corrective material, presumably a product of the normal allele ofo, depends upon a protein or proteins for its activity. It is produced during oogenesis and later plays an indispensible role in early organogenes

ISSN:0022-104X    

DOI:10.1002/jez.1401670107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractZebrafish embryos at six developmental stages were exposed to the supernatant of homogenates of zebrafish embryos, 5‐day chick embryos and 9 mm frog larvae. Extracts of embryos bring about developmental arrest of the zebrafish embryo at stages 17–18. The effect is reversible. Arrested embryos returned to buffered water recover and develop normally to hatching, delayed by a time equal to the time of exposure to extracts. Two fractions of the embryo extract are produced by G‐75 Sephadex gel filtration. The inhibitory effect is limited to one of these fractions. The inhibitory factor in embryo extract has characteristics compatible with those of nucleases but the effect on embryos is unlike that of ribonuc

ISSN:0022-104X    

DOI:10.1002/jez.1401670108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1401670101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY