Zmiz2 modulates the positioning of somata across the outer nuclear layer

Abstract

Purpose : ZMIZ2 is a PIAS-like domain protein that serves as a transcriptional co-regulator, shown to modulate the transcriptional activity of nuclear hormone receptors as well as β-catenin. It is expressed in neural tissues during early development, then down-regulated in the mouse embryo after the 2^nd week of gestation. Zmiz2 is, however, expressed in both rod and cone photoreceptors during postnatal development and in maturity. The present study examined the consequences of Zmiz2 overexpression in photoreceptors to investigate its potential role during development.

Methods : Retinal electroporation was conducted in neonatal mice (P2), targeting rod photoreceptors, using pCAGIG plasmids containing the Zmiz2 coding sequence followed by an IRES-EGFP cassette; control mice were electroporated using plasmids containing only the IRES-EGFP sequence. Mice were examined after the retinal architecture was established at P21, or during development at P5 or P10, using antibodies to label ZMIZ2, mCAR or GFP.

Results : Immunostaining for ZMIZ2 protein confirmed that GFP+ cells exhibited conspicuous immunoreactivity beyond endogenous expression, expression that was absent in GFP+ cells in control retinas. P21 retinas from experimental and control mice showed comparable ratios of GFP+ cells in the ONL and INL, and those in the ONL showed terminals reaching into the OPL, as well as differentiated inner and outer segments extending beyond the OLM. Interestingly, those cells in the ONL receiving Zmiz2-encoding plasmids exhibited a tendency to be positioned nearer the OLM, whereas control retinas showed a distribution of GFP+ cells positioned across the width of the ONL. These cells had not simply failed to translocate their nuclei into the ONL during development, because experimental and control retinas examined at P5 and P10 showed comparable distributions across the width of the retina.

Conclusions : The somata of rod photoreceptors overexpressing Zmiz2 become positioned in the outer parts of the ONL, where cone somata are normally positioned. As cones normally exhibit higher levels of Zmiz2 relative to rods, perhaps Zmiz2 participates in the specification of their positioning; this hypothesis will be explored through future loss-of-function studies.

This is a 2020 ARVO Annual Meeting abstract.