DTA-mediated targeted ablation revealed differential interdependence of endocrine cell lineages in early development of zebrafish pancreas.

Cell lineage analysis is critical in understanding the relationship between progenitors and differentiated cells as well as the mechanism underlying the process of differentiation. In order to study the zebrafish endocrine pancreas cell lineage, transgenic expression of diphtheria toxin gene A chain (DTA) under two cell type-specific promoters derived from the insulin (ins) and somatostatin2 (sst2) genes was used to ablate the two types of endocrine cells: insulin-producing beta-cells and somatostatin-producing delta-cells, respectively. We found that ablation of beta-cells resulted in a reduction of not only beta-cells but also glucagon-producing alpha-cells; in contrast, delta-cells were largely unaffected. Ablation of delta-cells led to reduction of all three types of endocrine cells: alpha-, beta-, and delta. Interestingly, alpha-cells were more profoundly affected in both beta- and delta-cell ablations and were frequently reduced together with beta- and delta-cells. By taking advantage of Tg(ins:gfp) and Tg(sst2:gfp) lines, we also monitored the changes of different types of endocrine cells in vivo after ablation and found that both beta- and delta-cell populations significantly recovered by 3dpf after their ablation and it seemed that delta-cells had a better capability of recovery than beta-cells. Thus, our current observations indicated differential interdependence of these three cell lineages. The development of zebrafish alpha-cells, but not delta-cells, is dependent on beta-cells, while the development of both alpha- and beta-cells is dependent on delta-cells. In contrast, the development of delta-cells was independent of beta-cells.