RanBP2 Colocalizes with HK1, Cox11, and mHsp70 in the Retina and Cultured Neurons
In addition to its presence at the vicinity of NPCs, we have shown previously that RanBP2 is localized to and abundant in the mitochondria-rich ellipsoid subcellular compartment of photosensory (photoreceptor) neurons of the retina [19]. We extended the subcellular colocalization studies on RanBP2 and its novel partners by immunocytochemistry to determine if RanBP2, Cox11, HKI, and mHsp70 colocalize in hippocampal neurons (Figure 3A–3C), cerebral cortex neurons (Figure 3D–3F), ellipsoid (mitochondria-rich) subcellular compartments of photosensory neurons of the retina (Figure 3G–3O), and dissociated primary glia and neuron cultures from the brain (Figure 3P–3Z). Double immunostaining with antibodies against these proteins showed that they colocalize to the mitochondria (Figure 3A–3Z).
Figure 3  Localization of RanBP2 and Its LD Molecular Partners
(A–F) are thin cryosections of an area of the hipocampus (CA1 neurons) and cerebral cortex, respectively, immunostained against HKI (A and D), RanBP2 (B and E), and merged images thereof (C and F). Note that while RanBP2 and HKI are widely expressed among and colocalize to hippocampal neurons (C), HKI expression and localization with RanBP2 is restricted to a subset of cortical neurons (likely interneurons) (F). Images of the distal region of bovine retinal cryosections comprising part of the nuclear layer of photoreceptor neurons and their inner (myoid and ellipsoid) segment compartment (G–O) are immunostained against mHsp70 (G) and RanBP2 (H), mHsp70 (J) and Cox11 (K), HKI (M) and Cox11 (N), and merged images thereof (I–O). Note the prominent localization of RanBP2, mHsp70, and Cox11 at the mitochondria-rich ellipsoid compartment of photoreceptors and the colocalization of RanBP2 and Cox11 with mHsp70 (I and L), while HKI colocalization with Cox11 was limited to restricted foci (R, arrowheads). High-resolution images of dissociated primary cerebral neurons and glial cells confirmed that the colocalization of HKI and Cox11 was highly restricted (P–R), while RanBP2 extensively colocalized with HKI (S–U) and mHsp70 (V–Z). Scale bars in A–O and P–Z are 40 and 10 μm, respectively. ONL, outer nuclear layer.