Transcription co-repressors Panky and Panky-like modulate ganglioside levels and are essential for retinal cone photoreceptor structure and survival

Abstract

The biological functions and mechanisms of many cell-type-specific transcriptional cofactors remain unclear. We previously identified Panky ( Ankrd33 ) as a repressive transcriptional co-factor that suppresses Crx-mediated transactivation of photoreceptor genes; however, the biological function of Panky remains unclarified. Here, we investigated the functions of Panky and its paralog, Panky-like ( Ankrd33b ), in mice of either sex. Single knockout (KO) mouse retinas of Panky or Panky-like did not show significant alterations at both histological and functional levels compared to those of control mice. We then established and examined Panky and Panky-like double knockout ( PPL DKO) mice. PPL DKO mice exhibited decreased light-evoked activities detected by electroretinogram (ERG), impaired cone photoreceptor morphology revealed by immunohistochemistry, and structural deformity of cone outer segments and synaptic terminals indicated by transmission electron microscopy (TEM), followed by cone death at a later stage. Lipidomics analysis revealed elevated ganglioside levels in PPL DKO retinas, consistent with the increased immunoreactivity of GT1b and GD3 in the outer segment layer. RNA-seq analysis was conducted in a cone-enriched context resulting from Nrl deficiency and showed that the Cerkl gene, whose mutations in humans cause retinitis pigmentosa (RP26), was upregulated in Panky/Panky-like/Nrl triple KO mice. Transcriptional assays showed that PPL suppressed Crx-mediated transactivation of Cerkl . In addition, AAV-mediated Cerkl overexpression in the mouse retina induced significant photoreceptor cell death. Taken together, these findings suggest that the repressive Panky and Panky-like co-factors, which modulate Crx transcriptional activities and thus ganglioside levels in the mouse retina, are essential for cone photoreceptor structure and maintenance. Significance statement The retina is a light-sensing neural tissue in the eye. Photoreceptor cells (PRs) in the retina receive light stimuli. Rod PRs mediate dim-light vision, whereas cone PRs are responsible for bright and color vision. The present study identified that Panky and Panky-like genes are predominantly expressed in PRs in the mouse retina. Panky and Panky-like double-knockout mice exhibit impaired cone cell morphology, cone cell death, and visual dysfunction. In addition, gangliosides, which are chemically bonded lipids and sugars essential for cell membrane stability and function, accumulate in the photoreceptor layer. This study showed that Panky and Panky-like genes regulate ganglioside levels in the retina and play essential roles in the structure and maintenance of cone photoreceptor cells.