Behavioral components define operational suitability metric for detection dog success.

Neuronal circuits are built and remodeled through the coordinated actions of synaptic organizers—secreted or membrane‐anchored proteins that guide synapse formation, target specificity, synaptic signaling, and plasticity (Connor and Siddiqui ; Südhof ; Yuzaki ). Members of the complement component 1, q subcomponent/tumor necrosis factor (C1q/TNF) superfamily, including the complement component 1, q subcomponent‐like (C1QL) proteins, have emerged as critical regulators of synaptic structure and function across the central nervous system (CNS) and beyond (Carland and Gerwick ; Ghai et al. ; Matsuda ; Peña Palomino et al. ; Südhof ; Yuzaki , ). These proteins mediate trans‐synaptic adhesion, signaling, and the stabilization of synaptic contacts. A member of this family, C1QL3, has garnered increasing attention owing to its strong CNS enrichment and high degree of evolutionary conservation. C1QL3 (also known as CTRP13 and identified initially as K100) was first cloned in a yeast two‐hybrid screen using heat shock protein 47 (HSP47), a collagen‐specific ER chaperone, as bait (Koide et al. ). Its C‐terminal globular C1q domain (gC1q) is 100% identical between human and mouse and alone is sufficient to mediate all currently known C1QL3‐protein interactions. C1QL3 interacts with key synaptic binding partners, including the adhesion G protein‐coupled receptor B3 (ADGRB3, or BAI3), specific kainate receptor paralogs, specific neurexin‐3 splice variants, and neuronal pentraxins, placing it at the center of multiple trans‐synaptic pathways involved in synapse regulation (Bolliger et al. ; Matsuda et al. ; Miao et al. ; Sticco et al. ). Despite this, the precise endogenous protein distribution in the brain, subcellular localization, and molecular assembly state of C1QL3 remain largely unexplored. Although C1QL3 is also expressed in select peripheral tissues (e.g., adipose tissue) and has been implicated in regulating systemic metabolism, insulin secretion, and lipid/glucose homeostasis (Byerly et al. ; Chen et al. ; Gupta et al. ; Koltes et al. ; Wei et al. ), its most prominent expression is in the CNS (Iijima et al. ). Within the brain, in situ hybridization (ISH) and mRNA reporter analyses have demonstrated expression in discrete neuronal populations, including pyramidal cells of the cerebral cortex, hippocampus, and amygdala, as well as select subcortical brain regions, such as the prominent expression in the suprachiasmatic nuclei (Chew et al. ; Iijima et al. ; Martinelli et al. ). Work on its paralogs, C1QL1 and C1QL2, has further revealed that proteins of this family localize to excitatory synapses, where they contribute to synapse formation, adhesion, synaptic signaling, and regulation of behavior (Aimi et al. ; Biswas et al. ; Caro et al. ; Chew et al. ; Kakegawa et al. , Kakegawa et al. ; Koumoundourou et al. ; Martinelli et al. ; Matsuda et al. ; Pan et al. ; Paul et al. ; Sigoillot et al. ; C. Y. Wang et al. ; Zhang et al. ).