Abstract
Abstract: :
Purpose: Retinal development requires the production of correct numbers of differentiated cells, as well as their orderly distribution in a laminar pattern. The mechanisms controlling the establishment of this retinal pattern are poorly understood, and we are investigating them using a loss–of–function approach to determine the possible involvement of activin/BMP family members. Methods: On embryonic day (ED) 2.5 (Hamburger–Hamilton [HH] stages 16–18), chick embryos were injected in the right eye with RCAS retroviruses encoding either follistatin (FS, an activin/BMP7 binding protein and inhibitor), or alkaline phosphatase (AP, as a control). After further development until ED 8–15, eyes were examined in toto, and either cryo–sectioned or dissociated for analysis by immunocytochemistry (ICC) with cell–type specific antibodies. Results: At ED 8, FS–treated retinas showed a decrease in the number of amacrine cells and a delay in inner plexiform layer formation, but their overall structure and organization appeared otherwise normal. This changed by ED 9–10, with the onset of a profound distortion of retinal organization, accompanied by rosette formation in as many as 70% of FS–treated embryos, but in none of the controls. Rosettes were visible through the RPE, appeared first in a small fundal region, and spread peripherally over time. Histologically, they appeared to form by invagination of the outer nuclear layer towards the vitreal surface of the retina. The extent of retinal disorganization appeared to correlate with the degree of FS infection. Analysis by ICC showed abundant visinin–positive photoreceptors in the rosettes, with concomitant displacement of inner nuclear layer neurons labeled with a variety of markers. Amacrine cells were less abundant in FS–treated retinas than in controls. Several other cell types appeared unchanged, but pilot observations suggested a decrease in CHX10 (+) cells. Conclusions: Loss–of–function experiments have disclosed a role for activin/BMP7 in the patterning of retinal layers. We are currently investigating the mechanisms of these effects, as well as possible interactions between activin/BMP7 with WNTs and Sonic Hedgehog, which have also been reported to influence retinal lamination.
Keywords: retinal development • growth factors/growth factor receptors • degenerations/dystrophies