RBX2 maintains final retinal cell position in a DAB1-dependent and -independent fashion

Abstract

The laminated structure of the retina is fundamental for the organization of the synaptic circuitry that translates light input into patterns of action potentials. However, the molecular mechanisms underlying cell migration and layering of the retina are poorly understood. Here, we show that RBX2, a core component of the E3 ubiquitin ligase CRL5, is essential for retinal layering and function. RBX2 regulates the final cell position of rod bipolar cells, cone photoreceptors and Muller glia. Our data indicate that sustained RELN/DAB1 signaling, triggered by depletion of RBX2 or SOCS7 - a CRL5 substrate adaptor known to recruit DAB1 - causes rod bipolar cell misposition. Moreover, whereas SOCS7 also controls Muller glia cell lamination, it is not responsible for cone photoreceptor positioning, suggesting that RBX2, most likely through CRL5 activity, controls other signaling pathways required for proper cone localization. Furthermore, RBX2 depletion reduces the number of ribbon synapses and disrupts cone photoreceptor function. Together, these results uncover RBX2 as a crucial molecular regulator of retina morphogenesis and cone photoreceptor function.

CRL5-dependent regulation of Arl4c and Arf6 controls hippocampal morphogenesis

“…As expected, efficient and extensive depletion of Rbx2 was observed in Rbx2cKO-Emx1 samples at P1 when tested by western blotting (Figure 4C and Figure S1A). Furthermore, Rbx2cKO-Emx1 telencephalons accumulated tyrosine phosphorylated (pY)-Dab1, Dab1, and Fyn, and showed the same layering defects as previously described for Rbx2cKO-Nes pups (Figure S1) (Fairchild et al, 2018; Simo and Cooper, 2013). These results indicate that Rbx2cKO-Emx1 mice faithfully recapitulate the phenotypes observed in Rbx2cKO-Nes mice without the morbidity caused by hydrocephalus.…”

“…Our previous studies indicate that Rbx2 regulates neuron positions in the retina through cell autonomous and non-autonomous mechanisms (Fairchild et al, 2018). To test whether CRL5 regulates hippocampal development cell autonomously, we used in utero electroporation (IUE) to deplete CRL5 activity in individual PNs.…”

“…First, we confirmed that pY-Dab1/Dab1 accumulated in the Rbx2cKO-Emx1 hippocampus (Figure 4C) and in shCul5-electroporated neurons (Figure S3A). To test whether sustained Reelin/Dab1 signaling is sufficient to promote PN over-migration, we used the SOCS7 knock out mouse (Fairchild et al, 2018). SOCS7 is a CRL5 substrate adaptor that recruits and targets pY-Dab1 for degradation in the developing telencephalon (Simo and Cooper, 2013).…”

“…The core CRL5 components Cul5 and Rbx2 are ubiquitously expressed during development and in the adult central nervous system (CNS), and functionally active during development (Fairchild et al, 2018; Hino et al, 2018; Simo and Cooper, 2013). Importantly, CRL5 substrate adaptors are dynamically regulated during development, directing CRL5 activity to specific substrates at different times and areas in the CNS (Cembrowski et al, 2016).…”

Genetic control of cellular morphogenesis in Müller glia

“…The high level of genetic conservation of glia in the animal kingdom suggests there may be basic principles of glial biology (Charlton‐Perkins et al, ), and the finding here that several conserved genes are involved during particular temporal windows of MG morphogenesis, suggest that there may also be conserved programs of differentiation. A recent study has implicated some proteins found here in mouse MG morphology and tiling including Rbx2, Dab1, and SOCS7 (Fairchild et al, ). Another excellent example of this conserved function is Pax2, which in the eye is primarily known for its function in optic stork formation, and whose expression has been noted in mature MG of chick but not guinea pigs or dogs (Boije, Ring, López‐Gallardo, Prada, & Hallböök, ; Stanke, Moose, El‐Hodiri, & Fischer, ).…”