The Mechanism of Regulated Release of Lasso/Teneurin-2

Teneurins are large cell-surface receptors involved in axon guidance. Teneurin-2 (also known as latrophilin-1-associated synaptic surface organizer (Lasso)) interacts across the synaptic cleft with presynaptic latrophilin-1, an adhesion G-protein-coupled receptor that participates in regulating neurotransmitter release. Lasso-latrophilin-1 interaction mediates synapse formation and calcium signaling, highlighting the important role of this trans-synaptic receptor pair. However, Lasso is thought to be proteolytically cleaved within its ectodomain and released into the medium, making it unclear whether it acts as a proper cell-surface receptor or a soluble protein. We demonstrate here that during its intracellular processing Lasso is constitutively cleaved at a furin site within its ectodomain. The cleaved fragment, which encompasses almost the entire ectodomain of Lasso, is potentially soluble; however, it remains anchored on the cell surface via its non-covalent interaction with the transmembrane fragment of Lasso. Lasso is also constitutively cleaved within the intracellular domain (ICD). Finally, Lasso can be further proteolytically cleaved within the transmembrane domain. The third cleavage is regulated and releases the entire ectodomain of Lasso into the medium. The released ectodomain of Lasso retains its functional properties and binds latrophilin-1 expressed on other cells; this binding stimulates intracellular Ca2+ signaling in the target cells. Thus, Lasso not only serves as a bona fide cell-surface receptor, but also as a partially released target-derived signaling factor

Proteolytically released Lasso/teneurin-2 induces axonal attraction by interacting with latrophilin-1 on growth cones

A presynaptic adhesion G-protein-coupled receptor, latrophilin-1, and a postsynaptic transmembrane protein, Lasso/teneurin-2, are implicated in trans-synaptic interaction that contributes to synapse formation. Surprisingly, during neuronal development, a substantial proportion of Lasso is released into the intercellular space by regulated proteolysis, potentially precluding its function in synaptogenesis. We found that released Lasso binds to cell-surface latrophilin-1 on axonal growth cones. Using microfluidic devices to create stable gradients of soluble Lasso, we show that it induces axonal attraction, without increasing neurite outgrowth. Using latrophilin-1 knockout in mice, we demonstrate that latrophilin-1 is required for this effect. After binding latrophilin-1, Lasso causes downstream signaling, which leads to an increase in cytosolic calcium and enhanced exocytosis, processes that are known to mediate growth cone steering. These findings reveal a novel mechanism of axonal pathfinding, whereby latrophilin-1 and Lasso mediate both short-range interaction that supports synaptogenesis, and long-range signalling that induces axonal attraction

Latrophilin fragments behave as independent proteins that associate and signal on binding of LTX(N4C)

Heptahelical, or G-protein-coupled, receptors control many cellular functions and normally consist of one polypeptide chain. In contrast, heptahelical receptors that belong to the long N-terminus, group B (LNB) family are cleaved constitutively into two fragments. The N-terminal fragments (NTFs) resemble cell-adhesion proteins and the C-terminal fragments (CTFs) are typical G-protein-coupled receptors (GPCRs) with seven transmembrane regions. However, the functional roles of this cleavage and of any subsequent NTF–CTF interactions remain to be identified. Using latrophilin, a well-studied member of the LNB family, we now demonstrate that cleavage is critical for delivery of this receptor to the cell surface. On the plasma membrane, NTF and CTF behave as separate membrane proteins involved, respectively, in cell-surface reception and signalling. The two fragments can also internalise independently. However, separated NTF and CTF can re-associate on solubilisation. Agonist binding to NTF on the cell surface also induces re-association of fragments and provokes signal transduction via CTF. These findings define a novel principle of structural and functional organisation of the cleaved, two-subunit GPCRs

ADGRL1 haploinsufficiency causes a variable spectrum of neurodevelopmental disorders in humans and alters synaptic activity and behavior in a mouse model

ADGRL1/latrophilin-1, a well-characterized adhesion G protein-coupled receptor, has been implicated in synaptic development, maturation and activity. However, the role of ADGRL1 in human disease has been elusive. Here, we describe 10 individuals with variable neurodevelopmental features including developmental delay, intellectual disability, attention deficit hyperactivity and autism spectrum disorders, and epilepsy, all featuring heterozygous variants in ADGRL1. In vitro, human ADGRL1 variants expressed in neuroblastoma cells showed faulty ligand-induced regulation of intracellular Ca2+ influx, consistent with haploinsufficiency. In vivo, Adgrl1 was knocked out in mice and studied on two genetic backgrounds. On a non-permissive background, mice carrying a heterozygous Adgrl1 null allele exhibited neurological and developmental abnormalities while homozygous mice were non-viable. On a permissive background, the null allele also appeared at sub-Mendelian frequency, but many Adgrl1 null mice survived the gestation and reached adulthood. The Adgrl1-/- mice demonstrated stereotypic behaviors, sexual dysfunction, bimodal extremes of locomotion, augmented startle reflex and attenuated pre-pulse inhibition, which responded to risperidone. Ex vivo synaptic preparations displayed increased spontaneous exocytosis of dopamine, acetylcholine and glutamate, but Adgrl1-/- neurons formed synapses in vitro poorly. Overall, our findings demonstrate that ADGRL1 haploinsufficiency leads to consistent developmental, neurological and behavioral abnormalities in mice and humans