Contribution of Müller cells toward the regulation of photoreceptor outer segment assembly

Abstract

The assembly of photoreceptor outer segments into stacked discs is a complicated process, the precise regulation of which remains a mystery. It is known that the integrity of the outer segment is heavily dependent upon surrounding cell types including the retinal pigment epithelium and Müller cells; however the role played by Müller cells within this photoreceptor-specific process has not been fully explored. Using an RPE-deprived but otherwise intact Xenopus laevis eye rudiment preparation, we reveal that Müller cell involvement in outer segment assembly is dependent upon the stimulus provided to the retina. Pigment epithelium-derived factor is able to support proper membrane folding after inhibition of Müller cell metabolism by alpha-aminoadipic acid, while isopropyl beta-Dthiogalactoside, a permissive glycan, requires intact Müller cell function. These results demonstrate that both intrinsic and extrinsic redundant mechanisms exist to support the ability of photoreceptors to properly assemble their outer segments. Our study further suggests that the receptor for pigment epithelium-derived factor resides in photoreceptors themselves while that for permissive glycans is likely localized to Müller cells, which in turn communicate with photoreceptors to promote proper membrane assembly.

Astrocytes in the rat medial amygdala are responsive to adult androgens

“…Given the link between number of astrocytic processes and synapse density (Pfrieger and Barres, 1997; Mong et al, 2001; Elmariah et al, 2005), our results suggest that the neural network in the amygdala may be changing in response to circulating hormones in adults. Computer simulations in artificial neuron–neuron and neuron–glia networks suggest that the presence and number of astrocytes improves network performance, particularly as the network increases in complexity (Porto-Pazos et al, 2011).…”

“…Computer simulations in artificial neuron–neuron and neuron–glia networks suggest that the presence and number of astrocytes improves network performance, particularly as the network increases in complexity (Porto-Pazos et al, 2011). However, astrocytic complexity in vivo has been associated with both increases in synapse number (Pfrieger and Barres, 1997; Elmariah et al, 2005) and decreases in dendritic spines and axondendritic synapses (Mong et al, 2001), making it unclear whether the changes we see in astrocytes would be associated with increases or decreases in synaptic connectivity in the MePD. Given that the size of somas and dendritic arbors are correlated in androgen-responsive motoneurons (Breedlove and Arnold 1981; Kurz et al, 1986), and that adult androgens increase neuronal soma size in the MePD (Cooke et al, 2003), the androgen-induced increase in MePD astrocyte number and complexity may be associated with increased synaptic connectivity, possibly enhancing network function.…”

“…On the other hand, astrocyte complexity was affected by androgens to a greater extent in males than in females, and the effects were largely symmetrical in males, increasing most measures of astrocyte complexity in both hemispheres, while asymmetric in females. While this might indicate a uniform strengthening of neural connectivity in both hemispheres in males, an additional intriguing possibility is that hormone-induced changes in astrocyte arbor complexity act to silence one hemisphere and strengthen the other, given that increases in astrocyte complexity are associated with both increases and decreases in synaptic connectivity, depending on the brain region (Pfrieger and Barres, 1997; Mong et al, 2001; Elmariah et al, 2005). In human males, the right amygdala is dominant in several functional measures including emotional memory, response to fearful faces, and resting state functional connectivity (Cahill et al, 2001; Kilpatrick et al, 2006; Schneider et al, 2010).…”

A New CRB1 Rat Mutation Links Müller Glial Cells to Retinal Telangiectasia

“…During retinal development, RMG cells are required for photoreceptor outer segment assembly (Jablonski and Iannaccone, 2000;Wang et al, 2005) and, in the postnatal period, genetic RMG destruction led to retinal dysplasia and retinal degeneration (Dubois-Dauphin et al, 2000). Conversely, RMG proliferation in mice lacking the cell cycle inhibitor protein p27…”

Novel organotypic culture model of adult mammalian neurosensory retina in co-culture with retinal pigment epithelium

“…Even though these shortcomings restrict the information and interpretation of the data obtained, especially in studies of microglia activation, neural and Muller cell remodeling (Mertsch et al, 2001;Johansson and Ehinger, 2005) the similarity between the characteristics of retinal detachment in vivo and models of retinal degeneration in vitro allows for investigations of pharmacological and bioengineering treatment modalities (Azadi et al, 2007;Liljekvist-Larsson and Johansson, 2007). The first neural retina-RPE culture was reported by Tamai et al (1978) and a number of other investigators have published studies of neural retina-RPE cultures using embryonic or postnatal tissue from rodents (Caffe et al, 1989;Pinzon-Duarte et al, 2004;Soderpalm et al, 1999), chicken (Strangeways and Fell, 1926;Rizzolo et al, 1994;Katyal and Godbout, 2004), frog (Jablonski et al, 2001;Wang et al, 2005), and pig (Saikia et al, 2006).…”