Differentiation Tendency Research Articles

Prestalk/prespore differentiation tendency of Dictyostelium discoideum cells as detected by a stalk-specific monoclonal antibody

By the use of a prestalk- and stalk-specific monoclonal antibody, production of prestalk antigen was examined with non-glucose grown [G(−)] and glucose grown [G(+)] cells of Dictyostelium discoideum AX2. Unlike wild type (NC4), some growth phase cells of AX2 were reactive with the antibody. However, G(−) cells contained much more antigen than G(+) cells and the difference between the two remained during the preaggregation period. Besides glucose, the addition of metabolizable, but not nonmetabolizable sugars to both growth phase and preaggregation cells suppressed the production of the prestalk antigen on the one hand and stimulated the accumulation of glycogen on the other hand. When mixed, G(−) cells which produced more prestalk antigen during the preaggregation period remained prestalk cells after aggregation, while G(+) cells which produced less antigen were converted to prespore cells. G(+) cells collected at the stationary phase [G(+)st] were stronger in prestalk sorting tendency than G(+) cells but weaker than G(−) cells. The prestalk antigen content of G(+)st cells prior to aggregation was an intermediate between those of G(−) and G(+) cells. These lead to the conclusion that the prestalk antigen content of preaggregation cells reflect the tendency of the cells toward either prestalk or prespore differentiation after aggregation.

Ameloblastoma. Light and electron microscopic study.

Light and electron microscopic studies of ameloblastoma were reviewed. The 21 cases of ameloblastoma examined were classified into 12 cases of the plexiform type and nine of the follicular type. The average age of the patients with the plexiform type was 25.3 years, while that of those with the follicular type was 54.4 years. Histologically, in the follicular type, the tumor cells consisted of two cell types, central polyhedral and star-shaped cells resembling the stellate reticulum and peripheral cuboidal and columnar cells similar to the inner enamel epithelium. The resemblance between the tumor follicle and enamel organ was confirmed electron microscopically. In the plexiform type, however the tumor cells did not show two cell types, but resembled squamous epithelium. Electron microscopically, all cells of the tumor strands had relatively numerous bundles of tonofilaments and were joined together by desmosomes. Differentiation of tumor cells to squamous epithelium less evident than in normal surface epithelium. We speculate that these histological differences between plexiform and follicular types represent the differentiation tendency of the remnant of the dental lamina at the time of neoplastic transformation. What decides the histological pattern is unknown but age may be a factor. Central epidermization with keratinization or microcytic changes was frequently seen in the follicular type. Keratinization and microcystic changes rarely occurred in the plexiform type. We do not believe that these changes are a form of involution or result from multipotentiality of the tumor cells.

Properties of the primary organization field in the embryo of Xenopus laevis: IV. Pattern formation and regulation following early inhibition of mitosis

ABSTRACT Visual observation of early blastulae, and counting of cell suspensions from the late blastula and subsequent stages of Xenopus development, have shown that exposure to either colcemid or mitomycin C can sustain blockage of the mitotic cycle, and hence prevent the normal increase in cell number. Such blockage is essentially complete within a period, following introduction of the drugs, which is short compared with the cell-cycle time normal to post-blastular stages. Although the cell-counting data do not allow a statistical demonstration, there is a suggestion that mitomycin C allows a greater proportion of cells to divide once, after its introduction, than does colcemid. This is in accord with its putative mode of action, in causing only intrachromatid cross-linkage within chromosones, but there are no data on the status of DNA replication within nuclei of the non-dividing cells under either drug. If blockage is begun not earlier than stage 10+, some 20 min after dorsal lip formation, essentially normal morphogenesis ensues up to tail-bud stages around 27, including histodifferentiation of ectodermal structures and notochord, and twitching of somitic muscle. Such embryos are described. In describing those arresting at earlier stages following blockage in blastulae, the possibility is mentioned that morphogenesis may fail for mechanical reasons due to low cell number and large cell size, rather than to lack of a normal field as such. Cell counting reveals that blocked embryos with qualitatively normal pattern formation by stages 22-24, in having a total cell number appropriate to stage 10+ or 10J, show about a seventh or an eighth of the number of cells normal to their stage. Between then and stage 27 when histogenesis, particularly of twitching muscle, is more clearly seen, the direct method of estimating cell number can no longer be used, but histology reveals no mitotic metaphases in any blocked embryos. In the same experiments, operations of two types described in previous papers are performed on early gastrulae so that regulation is required in the embryonic field after the cessation of mitosis. The results are as seen in the normal presence of the cell cycle, revealing that, in response to changes of positional information value, host material may change its presumptive differentiation tendency and final commitment, in the absence of cell division as such. There is some indication that the proportional numbers of cells assigned to different structures in an individuation field may deviate from normal when overall cell number is limiting.