The potential redundant roles of AP-2α and AP-2β in the developing and postnatal neural retina

Abstract

Purpose: Previous studies from our lab have shown that the Activating Protein- 2 (AP-2) family of transcription factors are important in retinal development. For example, double mutants with both AP-2α and AP-2β deleted from the retina were generated by crossing retina-specific AP-2α conditional knockouts (KO) onto a AP-2β germ-line knockout background and examined from embryonic day (E)16.5 to post natal day (P)0. These double mutants exhibited interesting anomalies in the inner nuclear layer, which involved the horizontal and amacrine cells. Since AP-2β germline KOs die prenatally (due to kidney disease), the role of AP-2a and AP-2β in retinogenesis could not been examined post-natally in these mutants. The purpose of this study was to utilize a floxed AP-2β line to study retinal development in double AP-2α/AP-2β mutants in stages past birth.

Methods: To generate double AP-2α/AP-2β retinal mutants, Pax6 α-Cre mice were used to conditionally delete one floxed allele of AP-2α and AP-2β at E10.5. The second allele of AP-2α/AP-2β was deleted as a germ-line knockout. The developing neural retina of the AP-2^αKI/flox/AP-2β^-/flox mice was examined using histological and immunofluorescent techniques at post-natal stages to examine retinogenesis upon its completion.

Results: Double AP-2α/AP-2β retinal mutants displayed both morphological and cellular abnormalities that were not present in the single gene mutants. Morphologically, double AP-2α/AP-2β retinal mutants at P17 displayed unilateral retinal dysplasia in the peripheral retina: an inside-out retina, folded back on itself at the retinal margin, a thick and twisted retina with a pigmented layer within the twist, and retinal whorls. On a cellular level, these double mutants displayed a lack of horizontal cells at P14, as examined by cell markers including LIM1, Calbindin and neurofilament medium chain. Furthermore, there was reduced immunostaining of the cholinergic amacrine cell markers, SOX2 and Isl1/2 at both P14 and P17.

Conclusions: These data demonstrate the potential redundant roles of AP-2α and AP-2β in neural retinogenesis and suggest that, together, these genes have an intrinsic role in the development of horizontal cells and cholinergic amacrine cells, and they impact retinal structure and lamination.

Keywords: 688 retina • 497 development