Involved in neural development by regulating the establishment of proper connectivity within the nervous system (PubMed:17478416, PubMed:17803360, PubMed:23028443, PubMed:25406022, PubMed:22499796, PubMed:29414938). Acts in both pre- and postsynaptic neurons in the hippocampus to control the assembly of a precise topographic projection: required in both CA1 and subicular neurons for the precise targeting of proximal CA1 axons to distal subiculum, probably by promoting homophilic cell adhesion (PubMed:29414938). Promotes homophilic adhesion in a splicing isoform-dependent manner: most isoforms (isoform-type A and type-B) can mediate homophilic interaction (PubMed:29414938). Promotes axon guidance (PubMed:23028443). Required for proper dendrite morphogenesis and axon targeting in the vertebrate visual system, thereby playing a key role in the development of the visual pathway (PubMed:17803360, PubMed:23028443, PubMed:25406022, PubMed:22499796). Regulates the formation in ipsilateral retinal mapping to both the dorsal lateral geniculate nucleus (dLGN) and the superior colliculus (SC) (PubMed:17803360, PubMed:23028443). May also be involved in the differentiation of the fibroblast-like cells in the superficial layer of mandibular condylar cartilage into chondrocytes (PubMed:20636325). Homodimer; disulfide-linked; to mediate homophilic cell adhesion (PubMed:29414938, PubMed:12000766). Most isoforms (isoform-type A and type-B) can mediate homophilic interaction (PubMed:29414938). Heterodimer with either TENM1 or TENM2 (PubMed:12000766). May also form heterodimer with TENM4 (PubMed:12000766). Isoform A0B0: Does not form homodimer to mediate homophilic cell adhesion. Isoform A0B0: Heterodimer with ADGRL3 (PubMed:29414938). 8 different isoforms are produced by the inclusion or exclusion of 'exon 12' and 'exon 20' (at splice sites A and B, respectively). The different isoforms probably mediate a combination of specific homophilic and/or heterophilic interactions. In brain, expressed in highly specific regions of the postnatal brain: expressed in restricted domains of the developing hippocampal region, including proximal CA1, distal subiculum, and medial entorhinal cortex (at protein level) (PubMed:29414938). Expression matches with topographic connectivity between entorhinal cortex, CA1, and subiculum (at protein level) (PubMed:29414938). Also specifically expressed in subregions of the presubiculum, parasubiculum, medial mammillary nucleus and anteroventral thalamic nucleus that are topographically connected with subiculum or entorhinal cortex (at protein level) (PubMed:29414938). Expressed in neurons of the developing visual pathway (at protein level). Expressed in the dorsal and ventral lateral geniculate nucleus (dLGN and vLGN) and optic tract at birth. Expressed in ipsilateral retinal axons of terminal zones (TZs) in the developing superior colliculus (SC) throughout the first postnatal week. Expressed in the layer V of the visual caudal cortex. Expressed in the femoral and mandibular condylar cartilages. Strongly expressed in fibrous and proliferating chondrocytes. Poorly expressed in mature chondrocytes. Not expressed in hypertrophic chondrocytes (PubMed:12915301, PubMed:17478416, PubMed:17803360, PubMed:20636325, PubMed:23028443). Expressed in the neural plate at 7.5 dpc. Expressed in the forebrain and telencephalon at 8.5 dpc. Expressed in the diencephalon, spinal cord and midbrain at 12.5 dpc. Expressed in the retinal ganglion cell (RGC) layer and the dorsal lateral geniculate nucleus (dLGN) at 16 dpc. Expressed in ipsilateral retinal axons of terminal zones (TZs) in the developing superior colliculus (SC) at 16 dpc, onward. EGF-like domains 2 and 5 which have an odd number of cysteines might enable the formation of intermolecular disulfide bonds. Cytoplasmic proline-rich regions could serve as docking domains for intracellular SH3-containing proteins. Mice show impair binocular vision, consistent with altered ipsilateral retinal neuron projections both into the ventrolateral region of the lateral geniculate nucleus (dLGN) and the superior colliculus (SC) (PubMed:17803360, PubMed:23028443). The distribution of ipsilateral drive in V1 is altered, leading to an expanded but visuotopically misaligned binocular zone (PubMed:22499796). Conditional knockout mice lacking Tenm3 in CA1 neurons display proximal CA1 axons spread throughout the entire subiculum, instead of projecting only to distal regions (PubMed:29414938). When Tenm3 is absent from a subset of distal subicular cells, Tenm3-containing proximal CA1 axons do not target Tenm3 and instead innervate nearby Tenm3 regions (PubMed:29414938). Belongs to the tenascin family. Teneurin subfamily. Truncated N-terminus.