Ciliary signaling proteins are mislocalized in the brains of Bardet-Biedl syndrome 1-null mice

Abstract

In the brain, primary cilia are found on most, if not all, central neurons. The importance of neuronal cilia is underscored by the fact that human diseases caused by primary cilia dysfunction, which are known as ciliopathies, are associated with neuropathologies, including neuropsychiatric disorders and learning and memory deficits. Neuronal cilia are enriched for certain G protein-coupled receptors and their downstream effectors, suggesting they sense and respond to neuromodulators in the extracellular milieu. GPCR ciliary localization is disrupted in neurons from mouse models of the ciliopathy Bardet-Biedl syndrome, with GPCRs failing to localize to cilia, indicating the Bardet-Biedl syndrome proteins are required for trafficking of G protein-coupled receptors into neuronal cilia. Yet, dopamine receptor 1 accumulates in cilia in the absence of Bardet-Biedl syndrome proteins, suggesting Bardet-Biedl syndrome proteins are required for normal ciliary import and export. To further explore the roles of the Bardet-Biedl syndrome proteins in neuronal cilia, we examined localization of ciliary signaling proteins in a new constitutive Bbs1 knockout mouse model. Interestingly, we find that two additional ciliary G protein-coupled receptors (Gpr161 and Gpr19) abnormally accumulate in cilia on Bardet-Biedl syndrome neurons. In addition, we find that the GPCR signaling protein β-arrestin accumulates in a subset of cilia in the brain, suggesting the presence of additional unidentified ciliary G protein-coupled receptors. These results confirm the importance of the Bardet-Biedl syndrome proteins in establishing ciliary GPCR pathways and indicate that loss of Bbs1 leads to complex changes in the localization of signaling proteins in the brain.

Alignment of spatial transcriptomics data using diffeomorphic metric mapping

“…To assess the performance of our atlas alignment and lift-over annotations, we first confirmed the enrichment of genes within certain brain regions. Consistent with previous studies, we found Grm2 to be visually primarily enriched in the dentate gyrus 11 , Sstr2 to be enriched in cerebral cortical layers 5 and 6 12 , and Gpr161 to be enriched in the CA1 13 Next, we took a more agnostic approach to assess the performance of our atlas alignment and lift-over annotations by evaluating the consistency of cell-type compositional heterogeneity within brain structures across replicates. Consistent with previous studies 14 , we observed cell-types to be spatially and compositionally variable across brain regions.…”

GPR161 structure uncovers the redundant role of sterol-regulated ciliary cAMP signaling in the Hedgehog pathway

“…Second, it is entirely possible that cAMP production by GPR161 has roles in adult tissues outside of the Hedgehog pathway. Indeed, GPR161 is expressed in many different cell types in adult tissues that are not hedgehog regulated, such as the adult hippocampus CA1 region 59 . GPR161 has also been reported to localize to cilia of hippocampal neurons 1,59,60 .…”

“…Indeed, GPR161 is expressed in many different cell types in adult tissues that are not hedgehog regulated, such as the adult hippocampus CA1 region 59 . GPR161 has also been reported to localize to cilia of hippocampal neurons 1,59,60 . Ciliary peptidergic GPCR signaling in the CA1 pyramidal neurons has been recently shown to regulate chromatin accessibility 61 , but the role of cAMP signaling mediated by cilia remains unknown.…”

Neuronal primary cilia integrate peripheral signals with metabolic drives

“…It has been implicated in regulating the enrichment of GPCRs within the cilium. For example, SSTR3, NPY2R and MCHR1 fail to accumulate in neuronal cilia in multiple brain regions in the absence of BBS1, BBS2, and BBS4 ( Berbari et al, 2008 ; Loktev et al, 2013 ), and BBSome disruption induces ciliary accumulation of DR1R, GRP19, and hedgehog pathway receptors ( Domire et al, 2011 ; Ye et al, 2018 ; Stubbs et al, 2023 ). Overall, it appears that the BBSome may select proteins for IFT-dependent trafficking and contribute to IFT train formation at the base and tip, potentially through stabilizing interactions between IFT-A and IFT-B ( Blacque et al, 2004 ; Wei et al, 2012 ; Williams et al, 2014 ).…”