In erythropoietic differentiation, mature red blood cells are generated from specific progenitor cells through the action of specific growth regulatory molecules. To know the mechanism of differentiation, it is important to examine the control of gene expression in these progenitor cells in combination with growth regulatory molecules. We have cloned two genes expressing at a maximal level in the CFU-E (colony forming unit-erythroid), one of the erythroid progenitor cells from novel murine erythroleukemia (MEL) cell line (TSA8) which can be induced to CFU-E in vitro. The expression of these genes is well correlated with the appearance of CFU-E during induction of TSA8 cells, and is higher in the CFU-E-cells enriched from mouse fetal livers than in the more differentiated erythroid cells. Combining these with our previous results, it is suggested that in the erythropoiesis the progenitor cells have distinct patterns of gene expression. This expression is replaced through each progenitor cell rather than by the continuous increase in the expression of a set of genes specific to the mature erythroid cell following the commitment process.
In this report we examine the accumulation of glycoconjugates in the extracellular medium and insoluble matrices surrounding developing cells of the cellular slime mold Dictyostelium discoideum. Conditions were employed which permitted advanced development (slug stage and beyond) in suspension culture. Under these conditions, up to one-third of the total culture protein appeared as non-sedimentable, extracellular material over the course of 48 h of incubation. Most of the secreted molecules expressed carbohydrate antigens (glycoantigens) as detected by Western blotting, using a panel of six monoclonal antibodies. Since the glycoantigens are secreted, immunoelectron microscopy was used to localize the glycoantigens in the extracellular matrices surrounding normally developing cells, including the slime sheath, stalk tube, inner spore coat, outer spore coat, and intercellular fluid between spores. Each glycoantigen had a characteristic distribution, and each extracellular matrix space contained a unique combination of glycoantigens. Thus, although each of these matrices (except inter-spore fluid) contains cellulose as a primary component, they could be distinguished on the basis of their glycoantigen and, by inference, glycoprotein compositions. Furthermore, there were differences between anterior and posterior regions of both slime sheats and stalk tubes. These observations show that secretion as detected in suspension culture occurs under normal conditions as a part of the process of depositing extracellular matrices around the cells. The distributions show that the cell aggregate positionally regulates the expression and deposition of secretory glycoproteins; the resultant patterns of expression of unique protein-linked carbohydrate structures imply a functional role in matrix organization and possibly cell activity which can now be explored.
The chorio-allantoic grafts analysed were prepared from avian proventricular endoderm combined with its own or pancreatic mesenchyme and from re-associated pancreatic layers. Intestine developed ectopically in some grafts: in these, endocrine cells typical of intestine differentiated irrespective of the source of the endoderm or mesenchyme. In addition, endocrine cells inappropriate for the surrounding histology were detected in small numbers in grafts of all categories. Clearly it is not the mesenchyme that is responsible but perhaps some aspect of the procedure, which may relate to stressful stimuli thought to provoke intestinal metaplasia. The differentiation of inappropriate cells aids in understanding the occurrence of ectopic endocrine tumours.
