Tethers the endoplasmic reticulum to the cell membrane and promotes the formation of appositions between the endoplasmic reticulum and the cell membrane. Binds glycerophospholipids in a barrel-like domain and may play a role in cellular lipid transport (By similarity). Plays a role in the rapid internalization of fgfr1 that has been activated by fgf1 binding; this occurs most likely via the AP-2 complex. Required for normal fgf signaling and the activation of downstream signaling cascades via its role in the internalization of activated fgfr1. Required for normal embryonic development via its role in fgf signaling and the downstream regulation of t/xBRA expression. Interacts with fgfr1 that has been activated by fgf1 binding. Interacts (via C2 domains) with the AP-2 complex (via an alpha subunit). Identified in a complex with the AP-2 complex and fgfr1. Localizes to endoplasmic reticulum-plasma membrane contact sites (EPCS). Recruited to the cell membrane via the third C2 domain (By similarity). Detected throughout embryonic development. In late gastrula and neurula stages, mainly expressed in head and dorsolateral mesoderm, and in eye, cranial neural crest and somites at later stages. Anchored to the endoplasmic reticulum membrane by a transmembrane hairpin structure; both N-terminus and C-terminus are cytoplasmic. The C2 domains mediate lipid and calcium binding. The N-terminal C2 domain binds calcium ions and is important for calcium-dependent lipid binding and interaction with membranes. Two calcium ions are bound at a high-affinity site and a third calcium ion is bound with lower affinity. May bind up to four calcium ions. In contrast, the second C2 domain apparently does not bind calcium (By similarity). The third C2 domain mediates interaction with membranes enriched in phosphatidylinositol 4,5-bisphosphate and is required for location at the cell membrane. The SMP-LTD domain is a barrel-like domain that binds glycerophospholipids in its interior; can bind two lipid molecules simultaneously. Binds a variety of lipids, including phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositol (By similarity). Morpholino-mediated knock-down causes severe trunk shortening, disruption of somatic muscle formation and impairs the expression of the mesodermal marker t/xBRA, similar to the effects of inhibition of fgf signaling. Belongs to the extended synaptotagmin family.