17Post-traumatic stress disorder (PTSD) is a psychological illness characterized by 18 recalling a feeling of distress when re-experiencing the original trauma-related 19 cues. This associative fear response plays an important role in some psychiatric 20 disorders and elucidation of the underlying mechanisms is of great importance. 21Here, we constructed Pyk2 null mice and found that these mutant mice showed 22 enhancement in contextual-fear memory, but no changes in auditory-cued and 23 spatial-referenced learning and memory. Moreover, using kinase mutant mice, we 24 observed that Pyk2 suppressed contextual fear memory in a kinase-independent 25 pathway. Using high-throughput RNA sequencing, we found that immediate early 26 genes (IEGs), such as Npas4, cFos, Zif268/Egr1, Arc, and Nr4a1, were enhanced 27 in Pyk2 null mice. We further demonstrated that Pyk2 disruption affected pyramidal 28 neuronal complexity and spine dynamics. Thus, we demonstrated that Pyk2 is a 29 novel fear memory suppressor molecule and Pyk2 null mice provides a model for 30understanding fear-related disorders. 31 32 between the same sets of clustered Pcdh proteins may lead to repulsion, thus self-56 avoidance and even spacing, between neurites from same neurons through 57 cytoskeletal rearrangement [14,15]. The mechanisms underlying the adhesive 58 recognition-lead repulsion is not known but may involve signaling molecules such 59 as cell-adhesion kinases. 60Pyk2 is a non-receptor tyrosine kinase and is very abundantly expressed in the 61 hippocampus of postnatal rats, reaching maximal levels in adulthood [16]. We and 62 others recently found that Pyk2 plays important roles in dendritic and spine 63 morphogenesis [7,17,18]. Pyk2 is post-synaptic located and interacts with NMDA 64 receptors [19] or PSD95 [20], implicating a role of Pyk2 in both LTP [21,22] and 65 LTD [23]. Recently, Pyk2 was also identified as a susceptibility locus for Alzheimer 66 diseases and dementias based on genome-wide association studies [24,25]. Here, 67we found Pyk2 as a repressor of contextual fear memory based on behavior 68 studies using gene modified mice by CRISPR. 69
403We thank Wuming Wang for the initial work on the project, Prof. Weidong Li (SJTU) 404 for allowing us to use his fear-conditioning testing equipment, Dr. Wenjie Bian (ION) 405 for advice on the Golgi staining, and Prof. Aaron Hsueh (Stanford) for linguistic 406 help on the manuscript. 407 408 Author Contributions 409 Mice generation: LS YXZ. 410 Study design: LS JZ YXZ QW. 411 Primary culture and biochemistry experiment: LS YXZ. 412 Animal behavior tests: LS JZ LLJ. 413 Golgi staining and picture collection: LS JZ. 414 Data analyses: LS YXZ JZ. 415 Study supervision: YPK QW. 416
