ALTERNATIVE SPLICING DURING RETINAL DEVELOPMENT

Rahul Kanadia (Postdoctoral Fellow)

Many types of regulatory processes must produce the repetoire of retinal cell types. Transcription regulation, chromatin structure, RNA processinug and stability, as well as the many levels of regulation of proteins all must play a role. We have recently begun to investigate the role of alternative splicing (AS). AS is the primary mechanism by which a limited number of protein coding genes can generate proteome diversity. In our first study fo AS, we investigated the role of an alternative splicing factor, Sfrs1, an arginine/serine (SR) rich-protein family member, during retinal development (Kanadia et al., 2008). We found that loss of Sfrs1 function during embryonic retinal development had a profound effect such that it led to a small retina at birth. In addition, the retina underwent further degeneration in the postnatal period. Loss of Sfrs1 function resulted in the death of retinal neurons that were born during early and mid-embryonic development. Ganglion cells, cone photoreceptors, horizontal cells and amacrine cells were produced and initiated differentiation. However, these neurons subsequently underwent cell death through apoptosis. In contrast, Sfrs1 was not required for the survival of the neurons generated later, including later born amacrine cells, rod photoreceptors, bipolar cells and Müller glia. Our results highlight the requirement of Sfrs1-mediated AS for the survival of retinal neurons, with sensitivity defined by the window of time in which the neuron was generated. Future studies are aimed at defining the targets of Sfrs-1 as well as the functions of additional AS factors.

Figure 1. The eye from a mouise with a conditional knock-out allele of sfrs-1 crossed to a retinal Cre line was obviously smaller than its wild type counterpart. From Kanadia et al., 2008.

Figure 2. The Sfrs-1 CKO retina had fewer of the early born cell types. Here, immunohistochemistry for Pax 6 (green), which marks ganglion cells, amacrine cells, and horizontal cells shows this reduction. From Kanadia et al., 2008.

Figure 3. Role of Sfrs1 during retinal development A) The expression pattern of the two Sfrs1 isoforms (Sfrs1a, Sfrs1b) during development and the requirement (dark gray) and the lack (light gray) of Sfrs1 function. B) A single progenitor in the wild-type retina is shown undergoing cell divisions and producing neurons and glia from E10.5 to P14. Mitotic cells are shown as , while postmitotic cells are shown as . The black line denotes time with P0 indicating birth. Below the black line there are boxes depicting the birth order of each cell type. The lower panel shows a progenitor cell in the Sfrs1-cKO retina undergoing cell division and producing neurons with denoting cell death (B,C).