Many members of the C1q family, including complement C1q and adiponectin, and the structurally related tumor necrosis factor family are secreted and play crucial roles in intercellular signaling. Among them, the Cbln (precerebellin) and C1q-like (C1ql) subfamilies are highly and predominantly expressed in the central nervous system. Although the Cbln subfamily serve as essential trans-neuronal regulators of synaptic integrity in the cerebellum, the functions of the C1ql subfamily (C1ql1-C1ql4) remain unexplored. Here, we investigated the gene expression of the C1ql subfamily in the adult and developing mouse brain by reverse transcriptase-polymerase chain reaction and high-resolution in-situ hybridization. In the adult brain, C1ql1-C1ql3 mRNAs were mainly expressed in neurons but weak expression was seen in glia-like structures in the adult brain. The C1ql1 mRNA was predominantly expressed in the inferior olive, whereas the C1ql2 and C1ql3 mRNAs were strongly coexpressed in the dentate gyrus. Although the C1ql1 and C1ql3 mRNAs were detectable as early as embryonic day 13, the C1ql2 mRNA was observed at later embryonic stages. The C1ql1 mRNA was also expressed transiently in the external granular layer of the cerebellum. Biochemical characterization in heterologous cells revealed that all of the C1ql subfamily proteins were secreted and they formed both homomeric and heteromeric complexes. They also formed hexameric and higher-order complexes via their N-terminal cysteine residues. These results suggest that, like Cbln, the C1ql subfamily has distinct spatial and temporal expression patterns and may play diverse roles by forming homomeric and heteromeric complexes in the central nervous system.
"A single particle negative stain EM reconstruction of adiponectin revealed an 18-mer superstructure involving six globular C1q domains in a ring-like arrangement (Radjainia et al., 2008). Moreover, superstructures of the C1QL protein family higher than hexamer were observed by SDS gel electrophoresis (Bolliger et al., 2011; Iijima et al., 2010). Within the C1q/TNF superfamily , superstructure formation is mostly attributed to the N-terminally located conserved cysteine residues and the collagen-stalk region. "
"On sorting the genes based on p values (Additional file 3: Sheet S2), we found several genes that are specific to AMC such as, genes involved in transcriptional repression (Mbd1 which binds to methylated sites on DNA) [47,48], vesicular trafficking (Snx6, a component of the retromer complex) , and microtubule depolymerization (Stmn1) . RMC express genes involved in immune functions such as RT1-A2, which is the MHC of rat and C1ql3, a protein of the complement system [51,52], calcium ion signaling pathway protein, Camk2 [53,54] and sodium dependent glucose transporter gene Slc5a11, known to interact with immune-related genes . "
[Show abstract][Hide abstract] ABSTRACT: Microglia, the resident immune cells of the central nervous system (CNS), have two distinct phenotypes in the developing brain: amoeboid form, known to be amoeboid microglial cells (AMC) and ramified form, known to be ramified microglial cells (RMC). The AMC are characterized by being proliferative, phagocytic and migratory whereas the RMC are quiescent and exhibit a slow turnover rate. The AMC transform into RMC with advancing age, and this transformation is indicative of the gradual shift in the microglial functions. Both AMC and RMC respond to CNS inflammation, and they become hypertrophic when activated by trauma, infection or neurodegenerative stimuli. The molecular mechanisms and functional significance of morphological transformation of microglia during normal development and in disease conditions is not clear. It is hypothesized that AMC and RMC are functionally regulated by a specific set of genes encoding various signaling molecules and transcription factors.
To address this, we carried out cDNA microarray analysis using lectin-labeled AMC and RMC isolated from frozen tissue sections of the corpus callosum of 5-day and 4-week old rat brain respectively, by laser capture microdissection. The global gene expression profiles of both microglial phenotypes were compared and the differentially expressed genes in AMC and RMC were clustered based on their functional annotations. This genome wide comparative analysis identified genes that are specific to AMC and RMC.
The novel and specific molecules identified from the trancriptome explains the quiescent state functioning of microglia in its two distinct morphological states.
[Show abstract][Hide abstract] ABSTRACT: Several C1q family members, especially the Cbln and C1q-like subfamilies, are highly and predominantly expressed in the central nervous system. Cbln1, a member of the Cbln subfamily, plays two unique roles at parallel fiber (PF)-Purkinje cell synapses in the cerebellum: the formation and stabilization of synaptic contact, and the control of functional synaptic plasticity by regulating the postsynaptic endocytotic pathway. The delta2 glutamate receptor (GluD2), which is predominantly expressed in Purkinje cells, plays similar critical roles in the cerebellum. In addition, viral expression of GluD2 or the application of recombinant Cbln1 induces PF-Purkinje cell synaptogenesis in vitro and in vivo. Antigen-unmasking methods were necessary to reveal the immunoreactivities for endogenous Cbln1 and GluD2 at the synaptic junction of PF synapses. We propose that Cbln1 and GluD2 are located at the synaptic cleft, where various proteins undergo intricate molecular interactions with each other, and serve as a bidirectional synaptic organizer.
European Journal of Neuroscience 07/2010; 32(2):191-7. DOI:10.1111/j.1460-9568.2010.07346.x · 3.18 Impact Factor
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