Joubert syndrome (JS) is a developmental brain disorder characterized by cerebellar vermis hypoplasia, abnormal eye movement, ataxia and mental retardation. Mutations in CEP290 mutations are responsible for the cerebello-oculo-renal subtype of JS that includes kidney cysts and retinal degeneration, two phenotypes commonly linked to ciliopathies. CEP290 mutations are also associated with Meckel-Gruber syndrome and Bardet-Biedl syndrome (BBS). Here we demonstrate that CEP290 interacts with a centriolar satellite protein PCM-1, which is implicated in BBS4 function. CEP290 binds to PCM-1 and localizes to centriolar satellites in a PCM-1- and microtubule-dependent manner. The depletion of CEP290 disrupts subcellular distribution and protein complex formation of PCM-1. In accord with PCM-1's role in microtubule organization, CEP290 knockdown causes the disorganization of the cytoplasmic microtubule network. Moreover, we show that both CEP290 and PCM-1 are required for ciliogenesis and are involved in the ciliary targeting of Rab8, a small GTPase shown to collaborate with BBS protein complex to promote ciliogenesis. Our results suggest that PCM-1 is a potential mediator that may link CEP290 with BBS proteins in common molecular pathways.

Single-cell sequencing methods have emerged as powerful tools for identification of heterogeneous cell types within defined brain regions. Application of single-cell techniques to study the transcriptome of activated neurons can offer insight into molecular dynamics associated with differential neuronal responses to a given experience. Through evaluation of common whole-cell and single-nuclei RNA-sequencing (snRNA-seq) methods, here we show that snRNA-seq faithfully recapitulates transcriptional patterns associated with experience-driven induction of activity, including immediate early genes (IEGs) such as Fos, Arc and Egr1. SnRNA-seq of mouse dentate granule cells reveals large-scale changes in the activated neuronal transcriptome after brief novel environment exposure, including induction of MAPK pathway genes. In addition, we observe a continuum of activation states, revealing a pseudotemporal pattern of activation from gene expression alone. In summary, snRNA-seq of activated neurons enables the examination of gene expression beyond IEGs, allowing for novel insights into neuronal activation patterns in vivo.

A protocol is described for sequencing the transcriptome of a cell nucleus. Nuclei are isolated from specimens and sorted by FACS, cDNA libraries are constructed and RNA-seq is performed, followed by data analysis. Some steps follow published methods (Smart-seq2 for cDNA synthesis and Nextera XT barcoded library preparation) and are not described in detail here. Previous single-cell approaches for RNA-seq from tissues include cell dissociation using protease treatment at 30 °C, which is known to alter the transcriptome. We isolate nuclei at 4 °C from tissue homogenates, which cause minimal damage. Nuclear transcriptomes can be obtained from postmortem human brain tissue stored at −80 °C, making brain archives accessible for RNA-seq from individual neurons. The method also allows investigation of biological features unique to nuclei, such as enrichment of certain transcripts and precursors of some noncoding RNAs. By following this procedure, it takes about 4 d to construct cDNA libraries that are ready for sequencing.

Joubert syndrome-related disorders (JSRD) are a group of syndromes sharing the neuroradiological features of cerebellar vermis hypoplasia and a peculiar brainstem malformation known as the 'molar tooth sign'. We identified mutations in the CEP290 gene in five families with variable neurological, retinal and renal manifestations. CEP290 expression was detected mostly in proliferating cerebellar granule neuron populations and showed centrosome and ciliary localization, linking JSRDs to other human ciliopathies.