Reduced axonal localization of a Caps2 splice variant impairs axonal release of BDNF and causes autistic-like behavior in mice Tetsushi Sadakataa,b,1, Yo Shinodab,c, Megumi Okaa, Yukiko Sekinec, Yumi Satoc, Chihiro Sarutac, Hideki Miwad, Mika Tanakae, Shigeyoshi Itoharae, and Teiichi Furuichib,c,1 aAdvanced Scientific Research Leaders Development Unit, Gunma University, Maebashi, Gunma 371-8511, Japan; bJapan Science and Technology Agency (JST)/Core Research for Evolutional Science and Technology (CREST), Kawaguchi, Saitama 332-0012, Japan; cDepartment of Applied Biological Science, Tokyo University of Science, Noda, Chiba 278-8510, Japan; dDepartment of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan; and eLaboratory for Behavioral Genetics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan Edited* by Masao Ito, RIKEN Brain Science Institute, Wako, Japan, and approved October 30, 2012 (received for review June 14, 2012) + Ca2 -dependent activator protein for secretion 2 (CAPS2 or CADPS2) BDNF secretion, affecting proper brain circuit development and/ potently promotes the release of brain-derived neurotrophic factor or function, and thereby contributing to an increased susceptibility (BDNF). A rare splicing form of CAPS2 with deletion of exon3 (dex3) to autism. Our results suggest that disturbance of the alternative was identified to be overrepresented in some patients with autism. splicing patterns of Caps2 can directly affect normal brain de- Here, we generated Caps2-dex3miceandverified a severe impair- velopment and function and could contribute to a genetic back- ment in axonal Caps2-dex3 localization, contributing to a reduction ground of autism susceptibility. in BDNF release from axons. In addition, circuit connectivity, mea- sured by spine and interneuron density, was diminished globally. Results The collective effect of reduced axonal BDNF release during devel- Generation of a Mouse Line Expressing Exon 3-Skipped Caps2 (dex3). opment was a striking and selective repertoire of deficits in social- To clarify the in vivo effect of Caps2 exon 3 skipping, we used and anxiety-related behaviors. Together, these findings represent a Cre/loxP system to generate a mouse line carrying a deletion of a unique mouse model of a molecular mechanism linking BDNF- exon 3 (which encodes 111 amino acids) of the Caps2 gene, NEUROSCIENCE mediated coordination of brain development to autism-related which expresses the exon 3-skipped Caps2 (Caps2-dex3) protein. behaviors and patient genotype. A conditional Caps2-dex3 allele was generated by gene targeting in embryonic stem cells (Fig. S1A). The resultant homozygotes, psychiatry | mental disorder | dense-core vesicle | exocytosis Δ Δ called Caps2 ex3/ ex3 mice, produced a Caps2-immunoreactive protein with a slightly lower molecular weight than that of wild 2+ Δ Δ a -dependent activator protein for secretion 2 (CAPS2 or types (Fig. S1B). The Caps2 ex3/ ex3 mice in standard breeding CCADPS2) is a member of the CAPS protein family that reg- cages exhibited no differences in life expectancy from control fi Δex3/Δex3 ulates the traf cking of dense-core vesicles by binding both mice, and both male and female Caps2 mice had normal – phosphoinositides and dense-core vesicles (1 5). We initially reproductive ability. identified mouse Caps2 as a potent factor promoting the release of brain-derived neurotrophic factor (BDNF) during cerebellar de- Dex3 Mice Show a Severe Reduction in Caps2 Immunoreactivity in the velopment (6, 7). Our subsequent knockout mouse study showed Projection Areas of Caps2-Expressing Neurons. We first examined that Caps2 not only plays a role in neuronal development of the the intracellular localization of dex3 protein in vivo using an anti- cerebrum and hippocampus as well as the cerebellum, but that it is Caps2 antibody. In the cerebellum, wild-type Caps2 protein was also associated with social interaction, anxiety, and maternal and mostly localized in the granule cell axons (parallel fibers) circadian behaviors in mice (7, 8). We also showed that the ex- extending into the molecular layer (Fig. 1 A and C), whereas dex3 CAPS2 pression of an exon 3-skipped (or -spliced out) form of protein was not localized in the axons and instead accumulated in CAPS2 (designated -dex3) (8), which is now known to be a rare the cell somas in the internal granule cell layer (Fig. 1 B and D). In alternative splicing variant (9, 10), is increased in a subgroup of the cerebrum of wild-type mice, diffuse signal was widely distrib- patients with autism and is not properly localized in axons (8). uted over the cortical layers, and intense signals were observed in Thus, neurons overexpressing dex3 may fail to coordinate local the soma of a subset of interneurons scattered throughout layers BDNF release from axons properly (8, 9), resulting in improper E Caps2Δex3/Δex3 CAPS2 II/III and V (Fig. 1 ). Interestingly, in mice, the brain development and function. The human gene locus diffuse signal was almost absent and mostly localized to cell somas (7q31.32) is intriguingly located within the autism susceptibility – in layer V, in addition to some intense signaling seen in inter- locus 1 (AUTS1) (11) on chromosome 7q31 q33, one of several neurons in layers II/III and V (Fig. 1F). This supported our hy- susceptibility loci for autism (12). Moreover, an association of pothesis that full-length Caps2 protein [exon3-plus; the dominant CAPS2 with autism has been suggested recently, not only by the form in mouse (27) and human (8) brains] can be transported into presence of copy number variations in the CAPS2 gene in autistic axons, whereas dex3 protein (exon3-minus) cannot (8). patients (13–15), but also by decreased transcription of CAPS2 in the brains of people with autism (16). Thus, clarifying the bi- ological significance of dex3 expression is an important step in Author contributions: T.S. and T.F. designed research; T.S., Y. Shinoda, M.O., Y. Sekine, elucidating the association of CAPS2 with brain circuit de- Y. Sato, and C.S. performed research; T.S., Y. Shinoda, H.M., M.T., and S.I. analyzed data; velopment and behaviors related to autism. and T.S. and T.F. wrote the paper. The potential molecular risk factors for autism susceptibility The authors declare no conflict of interest. – have been increasingly reported (17 26) but are poorly charac- *This Direct Submission article had a prearranged editor. terized in animal models. In this report, we generated a mouse 1To whom correspondence may be addressed. E-mail: [email protected] or sadakata-1024@ model expressing dex3 and analyzed the cellular and autistic-like umin.ac.jp. behavioral phenotypes of dex3 mice. Our results support the in- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. volvement of the rare dex3 form of Caps2 in defective axonal 1073/pnas.1210055109/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1210055109 PNAS Early Edition | 1of6 Downloaded by guest on September 30, 2021 Fig. 1. Distribution of Caps2 immunoreactivity in the Δ Δ Caps2 ex3/ ex3 mouse cerebellum and neocortex. (A and B) Δ Δ Sagittal sections of P21 wild-type (A) and Caps2 ex3/ ex3 (B) cerebellum were immunolabeled with an anti-Caps2 antibody. (Scale bars, 300 μm.) (C and D) Sagittal sections of P21 wild- type (C)andCaps2Δex3/Δex3 (D) cerebella were immunolabeled with anti-Caps2 antibody. Immunosignal intensity of red dot- ted lines is shown by black lines in the graphs. Signal intensity from the other three images is shown in colored lines. M, molecular layer; P, Purkinje cell layer; I, internal granular layer. (Scale bars, 50 μm.) (E and F) Sagittal sections of P21 wild-type (E) and Caps2Δex3/Δex3 (F) neocortex were immunolabeled with an anti-Caps2 antibody. II/III, IV, and V represent cortical layers II/III, IV, and V, respectively. Areas outlined by dotted squares are shown in Insets. (Scale bars, 100 μm.) In the wild-type mouse hippocampus, Caps2 protein was depolarization-induced) BDNF–GFP release from transfected expressed in dentate gyrus (DG) granule cells and cornu neurons was evaluated by immunostaining with an anti-GFP ammonis region 1 (CA1) pyramidal neurons in addition to antibody before cell permeabilization and by counting immu- a subset of interneurons scattered in the DG and CA1 regions nopositive puncta on axons (Fig. 2O), as previously reported (28), as shown in Fig. S2A. The latter immunosignal was strong (29–31). The number of cell-surface (i.e., released) BDNF–GFP in the cell soma, whereas Caps2 expressed in DG granule cells puncta in KCl-stimulated cells was normalized to that in unsti- Δ Δ was localized in axons of the stratum lucidum. In Caps2 ex3/ ex3 mulated control cells. A graded increase in KCl concentration hippocampus, diffuse signal of the stratum lucidum was almost revealed an activity (depolarization)-dependent release of Δ Δ diminished, as shown in Fig. S2 B, D, and E. BDNF–GFP from the axons of wild-type but not Caps2 ex3/ ex3 cells (Fig. 2P). These results showed that regulated release of Δ Δ Decreased Axonal Localization of BDNF in dex3 Neurons. We ana- BDNF was impaired in the axons of Caps2 ex3/ ex3 neurons. lyzed the effect of dex3 expression on the axonal localization of BDNF immunoreactivity using primary-cultured hippocampal Deficits in Hippocampal and Cortical Interneurons and Dendritic Δ Δ calbindin-positive granule cells from wild-type and Caps2 ex3/ ex3 Spines in dex3 Mice. There is a report showing disrupted archi- mice. In wild-type neurons (Fig. 2 A–C), Caps2-immunopositive tecture in the gamma-aminobutyric acid (GABA)ergic in- puncta were localized in the axon, as shown by colocalization with terneuron circuit of the neocortex in autism (32). It was also Δ Δ the axonal marker Tau. However, in Caps2 ex3/ ex3 neurons, shown that differentiation of a subset of neocortical parvalbu- Caps2-positive puncta were decreased in the axons (Fig.