Abstract
Purpose :
The ability to successfully repair eye structures varies amongst species, even closely related ones. Thus it has been a challenge to identify the molecular mechanisms used for productive repair. Using experimental animal models of eye repair, we found that Xenopus laevis embryos regrow eyes after ablation, an ability only reported in animals with simple eyes like planarians. We compared embryonic Xenopus and adult planarians to assess if there are conserved mechanisms used for eye repair.
Methods :
The adult Schmidtea mediterranea eye (photoreceptors and pigment cells) or stage 27 Xenopus embryonic eye (eye cup and differentiating lens placode) were excised and regrowth followed 5 days (Xenopus) or 14 days (planaria) post surgery. For each, the contralateral uninjured eye served as internal control and n≥15. Repair was characterized by antibody staining of neural tissues (Xen1, Xenopus; arrestin, planaria) and in situ hybridization for eye tissue markers. Membrane voltage was visualized by 100μM DiBAC4(3), with DMSO vehicle controls, and quantified by signal intensity. Ectopic hyperpolarization was achieved by RNAi to H,K-ATPase in planaria (with GFP-RNAi controls) and by NaV overexpression (OE) in Xenopus (GFP OE controls). Planaria were ectopically depolarized with 1μM ivermectin (DMSO vehicle controls) and Xenopus with 20nM concanamycin A (DMSO vehicle controls). Student’s T-test or two sample T-test between percents used for significance.
Results :
Our data show that like Xenopus, planarian eye fields are hyperpolarized (p<0.001, n=6) and ectopic hyperpolarization results in ectopic eye formation (71.4%, SEp=0.085, p<0.001). Following eye ablation, we show that both embryonic Xenopus and adult planarians undergo directed repair. By 5 days in Xenopus and 14 days in planarians, ablated animals possess eye tissues and innervation similar to controls. However, ectopic depolarization prevented eye repair following ablation (planaria: 69.7%, SEp=0.079, p<0.0001; Xenopus: 49.7%, SEp=0.104, p<0.001).
Conclusions :
Our data reveal that both adult planarians and embryonic Xenopus are capable of productive repair of the eye. Furthermore, we found that hyperpolarization is necessary and sufficient for eye growth in both models, implicating ion transport as a conserved repair mechanism. These data suggest that manipulation of biophysical mechanisms (such as ion transport) may be a suitable target for eye repair strategies.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.