Ptf1a+,ela3l− cells are developmentally maintained progenitors for exocrine regeneration following extreme loss of acinar cells in zebrafish larvae

Abstract

The exocrine pancreas displays a significant capacity for regeneration and renewal. In humans and mammalian model systems, the partial loss of exocrine tissue, such as after acute pancreatitis or partial pancreatectomy induces rapid recovery via expansion of surviving acinar cells. In mouse it was further found that an almost complete removal of acinar cells initiates regeneration from a currently not well-defined progenitor pool. Here, we used the zebrafish as an alternative model to study cellular mechanisms of exocrine regeneration following an almost complete removal of acinar cells. We introduced and validated two novel transgenic approaches for genetically encoded conditional cell ablation in the zebrafish, either by caspase-8-induced apoptosis or by rendering cells sensitive to diphtheria toxin. By using the ela3l promoter for exocrine-specific expression, we show that both approaches allowed cell-type-specific removal of >95% of acinar tissue in larval and adult zebrafish without causing any signs of unspecific side effects. We find that zebrafish larvae are able to recover from a virtually complete acinar tissue ablation within 2 weeks. Using short-term lineage-tracing experiments and EdU incorporation assays, we exclude duct-associated Notch-responsive cells as the source of regeneration. Rather, a rare population of slowly dividing ela3l-negative cells expressing ptf1a and CPA was identified as the origin of the newly forming exocrine cells. Cells are actively maintained, as revealed by a constant number of these cells at different larval stages and after repeated cell ablation. These cells establish ela3l expression about 4-6 days after ablation without signs of increased proliferation in between. With onset of ela3l expression, cells initiate rapid proliferation, leading to fast expansion of the ela3l-positive population. Finally, we show that this proliferation is blocked by overexpression of the Wnt-signaling antagonist dkk1b. In conclusion, we show a conserved requirement for Wnt signaling in exocrine tissue expansion and reveal a potential novel progenitor or stem cell population as a source for exocrine neogenesis after complete loss of acinar cells.

Tcf7l2 plays pleiotropic roles in the control of glucose homeostasis, pancreas morphology, vascularization and regeneration

“…For functional in vivo studies we used the following fish lines, that where crossed with the tcf4hu892 or tcf4 exI / exI mutant 19 : Tg ( fli1a:EGFP ) y1 28 , Tg ( kdrl:mcherry ) is5 55 , Tg ( ins:EGFP ) 56 , Tg ( 7xTCF-Xla . Siam:GFP ) ia4 26 , Tg ( ptf1a:EGFP ) jh1 , Tg ( ptf1a:DsRed ) ia6 , Tg ( gcga:GFP ) ia1 25 Tg ( ela3l:caspase ; ela3l:E2Crimson ) (line abbreviated to Tg ( ela3l:E2Crimson )) 57 , Tg ( −1 . 2ins:DsRed ) 56 referred to as Tg ( ins:DsRed ), and Tg ( ins:NTR-mCherry ) ml10 (Dirk Meyer’s Lab) expressing a nitroreductase (NTR)-mCherry fusion protein in β cells.…”

Inducible Mosaic Cell Labeling Provides Insights Into Pancreatic Islet Morphogenesis

“…To define the spaces occupied by pancreatic tissue compartments, we generated triple-transgenic zebrafish in which endocrine, duct and exocrine compartments are labeled by cytoplasmically localized fluorescent reporters. A previously generated line using the far red E2-Crimson fluorophore labels exocrine tissue (ela:E2-Crimson, Schmitner et al, 2017), and can be distinguished from a DsRed transgene expressed in endocrine cells (pax6b:DsRed). Ductal progenitors are labeled by the Tp1:GFP transgene (Parsons et al, 2009).…”

Spotlight on zebrafish: the next wave of translational research

“…In cancer, the White laboratory presents an exciting new method for generating adult zebrafish cancer models called transgene electroporation in adult zebrafish (TEAZ), which helps to better model somatic gene mutations in a spatially defined tissue (Callahan et al, 2018). The Meyer laboratory achieved conditional, genetically encoded, cell-specific ablation of exocrine cells in zebrafish using transgenic lines expressing the human diphtheria toxin receptor or, alternatively, a membrane-localized Caspase 8-FKBP fusion, in which apoptosis could be pharmacologically induced (Schmitner et al, 2017). In addition to robust, conditional ablation of exocrine tissue, these tools allow a detailed examination of progenitor populations during regenerative processes.…”