Hindbrain Progenitors Produce Retinal Cell Types When Transplanted Into Developing Zebrafish Retina

Abstract

Abstract: : Purpose: To test the lineage restriction and specification of retinal progenitors. The neural retina develops from the eye field –– a region of the anterior neural tube delineated by the overlapping expression of several transcription factors implicated in retinal determination. In order to test the capacity of neural progenitors that do not normally express retinal determination factors to differentiate into retinal cell types, we have examined the fates of hindbrain progenitors transplanted into the developing zebrafish retina. Methods: Donor zebrafish embryos were injected with the lineage tracer FluoRuby at the 2–16 cell stage to uniformly label all cells. Hindbrain progenitors were removed from donor embryos at 14, 24, 48 or 72 hours post fertilization and injected into the developing retina of unlabeled host embryos at 14, 24, 48 or 72 hours post fertilization. After allowing 4–6 days for cellular differentiation, host retinas were sectioned and labeled with markers for differentiated retinal cell types. Results: Hindbrain progenitors survived in the host retinas and were capable of producing cells in all layers of the retina. Both calretinin–positive neurons and GFAP–positive Müller glia derived from the donor cells could be found in the appropriate layers of the retina of the host fish when 14– or 24–hour progenitors were transplanted isochronically. In addition, when transplanted isochronically 14– or 24–hour hindbrain progenitors were able to produce cells in the photoreceptor layer expressing zpr–1, a specific marker of zebrafish double cone photoreceptors. When hindbrain cells from 72–hour fish were transplanted into 72–hour retinas, which were laminated and differentiated, few transplanted cells survived. Conclusions: Progenitors from young hindbrain (14 or 24 hours post fertilization) retain the capacity to respecify as retinal progenitors and produce neurons, glia, and photoreceptors in the appropriate positions in the retina. Few cells from older hindbrain (72 hpf) survived in the retina, suggesting that the window for conversion of hindbrain into retina may be limited to early stages prior to retinal differentiation. Heterochronic transplants will be used to further dissect the timing of specification of hindbrain and retinal progenitors. These experiments suggest that cell fate as retina is not determined early, and that cells transplanted into the developing retina can respond to environmental cues therein to change their fates and produce retinal–specific cell types.

Keywords: retinal development • transplantation • cell-cell communication