Differential expression of the mRNAs of the axonal glycoproteins axonin-1 and NgCAM in the developing chick retina

Cell adhesion molecules expressed on the axonal membrane have been thought to be involved in the guidance of axons to their target area. In the chick, axonin-1 and NgCAM have been shown to promote, through reciprocal interactions, neurite outgrowth in vitro. We have recently shown that chick retinal ganglion cells (RGC) express both proteins as early as the axonal elongation begins. Their expression continues throughout the development of the retinotectal system synchronously with the chronotopic spread of axons. To further investigate the spatiotemporal distribution of axonin-1 and NgCAM in the retina, we have analysed the expression of their mRNAs in the present study. From stage 36 (E10) until hatching photoreceptors express axonin-1 but not NgCAM. In the inner nuclear layer groups of amacrine cells were strongly labelled with both probes but they seemed to belong to different subgroups. These patterns of expression might indicate a differential influence of the two proteins on the development of the local neural circuits of the retina.     

Developmental expression patterns of bone morphogenetic proteins, receptors, and binding proteins in the chick retina

Bone morphogenetic proteins (BMPs), a large subfamily of the transforming growth factor-beta (TGF-beta) superfamily of growth factors, have been implicated in patterning of the central nervous system, but their role in the retina is much less well known. As an initial step in addressing this issue, we have investigated by in situ hybridization the expression patterns of BMP-2, -4, -5, -6, and -7, BMP receptor kinases (BRKs) -1, -2, and -3, and BMP binding proteins noggin and chordin, in the chick embryonic eye at embryonic day 3 (E3), and in isolated retinas at E6, E8, and E18. Strikingly, all mRNAs examined had spatially restricted patterns of expression in the early eye, with the receptors found primarily in the ventral portion of the retina and in the optic stalk, and the ligands and binding proteins localized to other regions of the retina and/or retinal pigment epithelium. Dorso-ventrally restricted patterns of expression persisted at E8, but were no longer apparent at E18, whereas layer-specific patterns of expression were detectable at both E8 and E18. This distribution of BMP family members, receptors, and binding proteins within the retina appears consistent with a possible role in patterning and/or differentiation of this tissue.     

Differential expression of neurexin genes in the mouse brain

Synapses, highly specialized membrane junctions between neurons, connect presynaptic neurotransmitter release sites and postsynaptic ligand-gated channels. Neurexins (Nrxns), a family of presynaptic adhesion molecules, have been characterized as major regulators of synapse development and function. Via their extracellular domains, Nrxns bind to different postsynaptic proteins, generating highly diverse functional readouts through their postsynaptic binding partners. Not surprisingly given these versatile protein interactions, mutations and deletions of Nrxn genes have been identified in patients with autism spectrum disorders, intellectual disabilities, and schizophrenia. Therefore, elucidating the expression profiles of Nrxns in the brain is of high significance. Here, using chromogenic and fluorescent in situ hybridization, we characterize the expression patterns of Nrxn isoforms throughout the brain. We found that each Nrxn isoform displays a unique expression profile in a region-, cell type-, and sensory system-specific manner. Interestingly, we also found that αNrxn1 and αNrxn2 mRNAs are expressed in non-neuronal cells, including astrocytes and oligodendrocytes. Lastly, we found diverse expression patterns of genes that encode Nrxn binding proteins, such as Neuroligins (Nlgns), Leucine-rich repeat transmembrane neuronal protein (Lrrtms) and Latrophilins (Adgrls), suggesting that Nrxn proteins can mediate numerous combinations of trans-synaptic interactions. Together, our anatomical profiling of Nrxn gene expression reflects the diverse roles of Nrxn molecules.     

Coordinate expression of insulin-like growth factor system components by neurons and neuroglia during retinal and cerebellar development.

The interactions of insulin-like growth factors (IGFs) with the type I IGF receptor are modulated by a family of high-affinity IGF binding proteins (IGFBPs). One of these, IGFBP2, demonstrates a striking spatiotemporal relationship with IGF-I during cerebellar and retinal development. IGF-I mRNA is transiently expressed in large projection neurons--cerebellar Purkinje and retinal ganglion cells--while IGFBP2 mRNA is selectively expressed by contiguous neuroglia--Bergmann glia in the cerebellum and Müller cells and astrocytes of the nerve fiber layer in the retina. IGF-I and IGFBP2 gene expression is not only neuroanatomically coordinated but also temporally synchronized, peaking together during the postnatal maturation of these structures. This pattern of IGF system expression suggests that IGFBP2 is closely related to IGF-I's action in the developing nervous system.     

Differential expression of the PSD-95 gene family in electrosensory neurons

The PSD-95 family of membrane-associated guanylate kinase (MAGUK) proteins are involved in the assembly and organization of neurotransmitter receptors at excitatory synapses in the vertebrate nervous system. We have isolated partial cDNAs for five PSD-95 family members from Apteronotus leptorhynchus brain RNA using a degenerate PCR method. The amino acid sequences deduced indicate that A. leptorhynchus neurons express homologues of the mammalian PSD-93, SAP-97, and SAP-102 MAGUKs and two homologues of mammalian PSD-95. In situ hybridization experiments have been carried out to localize the cellular expression of all five MAGUK mRNAs in the central nervous system of A. leptorhynchus. In the cerebellum the expression patterns are highly similar to patterns reported for mammalian cerebellum, suggesting an evolutionary conservation of the functional roles in this gene family. Cellular levels of expression of the PSD-95 MAGUK mRNAs and the NMDAR-1 mRNA were highly correlated in neurons of the dorsal forebrain but were not correlated in neurons of the electrosensory lateral line lobe (ELL) or the cerebellum. These results suggest that the expression of PSD-95 MAGUK genes in forebrain neurons may provide mechanisms for synaptic organization that are not shared by neurons in the ELL and cerebellum.     

Expression of basal lamina protein mRNAs in the early embryonic chick eye

Laminin, collagen IV, collagen XVIII, agrin, and nidogen are major protein constituents of the chick retinal basal lamina. To determine their sites of synthesis during de novo basal lamina assembly in vivo, we localized their mRNA expression in the eye during maximum expansion of the retina between embryonic day (E) 2.5 and E6. Our in situ hybridization studies showed that the expression pattern of every basal lamina protein mRNA in the developing eye is unique. Collagen IV and perlecan originate predominantly from the lens epithelium, whereas collagen XVIII, nidogen, and the laminin gamma 1 and beta1 chains are synthesized mainly by the ciliary body. Agrin, collagen XVIII, collagen IV, and laminin gamma 1 also originate from cells of the optic disc. The only basal lamina protein that is synthesized by the neural retina throughout development is agrin with ganglion cells as its main source. Some of the mRNAs have short, transient expressions in the retina, most notably that of collagen IV and laminin gamma 1, both of which appear in the ventral retina between E4 and E5. That most retinal basal lamina proteins originate from extraretinal tissues infers that the basal lamina proteins have to be shed from the lens, optic disc, and ciliary body into the vitreous body. The assembly of the retinal basal lamina then occurs by the binding of these proteins by cellular receptor proteins on the vitreal endfeet of the retinal neuroepithelial cells.     

Developmental pattern of the neuronal intermediate filament inaa in the zebrafish retina

α‐Internexin is a member of the neuronal intermediate filament (nIF) protein family, which also includes peripherin and neurofilament (NF) triplet proteins. Previous studies found that expression of α‐internexin precedes that of the NF triplet proteins in mammals and suggested that α‐internexin plays a key role in the neuronal cytoskeleton network during development. In this study, we aimed to analyze the expression patterns and function of internexin neuronal intermediate filament protein‐alpha a (inaa), the encoding gene of which is a homolog of the mammalian α‐internexin, during retinal development in zebrafish. Via in vitro and in vivo studies, we demonstrated that zebrafish inaa is an α‐internexin homolog that shares characteristics with nIFs. An immunohistochemical analysis of zebrafish revealed that inaa was distributed dynamically in the developing retina. It was widely localized in retinal neuroepithelial cells at 1 day postfertilization (dpf), and was mainly found in the ganglion cell layer (GCL) and inner part of the inner nuclear layer (INL) from 3–9 dpf; after 14 dpf, it was restricted to the outer nuclear layer (ONL). Moreover, we demonstrated for the first time that inaa acted distinctively from the cytoskeletal scaffold of zebrafish cone photoreceptors during development. In conclusion, we demonstrated the morphological features of a novel nIF, inaa, and illustrated its developmental expression pattern in the zebrafish retina. J. Comp. Neurol. 524:3810–3826, 2016. © 2016 Wiley Periodicals, Inc.