Plays a crucial role in the formation of lipid droplets (LDs) which are storage organelles at the center of lipid and energy homeostasis (By similarity).In association with LDAF1, defines the sites of LD formation in the ER (By similarity). Also required for growth and maturation of small nascent LDs into larger mature LDs (By similarity). Mediates the formation and/or stabilization of endoplasmic reticulum-lipid droplets (ER-LD) contacts, facilitating protein and lipid delivery from the ER into growing LDs (By similarity). Regulates the maturation of ZFYVE1-positive nascent LDs and the function of the RAB18-ZFYVE1 complex in mediating the formation of ER-LD contacts (By similarity). Binds anionic phospholipids including phosphatidic acid (By similarity). Plays an important role in the differentiation and development of adipocytes (PubMed:18458148, PubMed:19574402, PubMed:21551454, PubMed:22269949). Undecamer (an oligomer having eleven subunits) (By similarity). Oligomerization is important for its function in lipid droplet formation (By similarity). Interacts with LDAF1 to form an oligomeric complex (By similarity). Interacts with RAB18 (By similarity). Interacts with ZFYVE1 in a RAB18-dependent manner (By similarity). Localizes at endoplasmic reticulum-lipid droplets (ER-LD) contact sites. Expressed in the paraventricular nucleus of the hypothalamus (PVN) and brainstem dorsal vagal complex (DVC) in oxytocin and catecholaminergic neurons (at protein level). Highest expression detected in subcutaneous and epididymal white adipose tissue, brown adipose tissue and testis. Also expressed in brain, skeletal muscle and adrenal gland, with lower levels detected in liver, heart, kidney, spleen, lung and small intestine. In brain, detected in piriform cortex, olfactory tubercle, islands of Calleja, lateral septal nucleus, medial septal nucleus, nucleus of the vertical limb of the diagonal band, nucleus of the horizontal limb of the diagonal band, preoptic area, paraventricular thalamic nucleus, lateral globus pallidus, supraoptic nucleus, suprachiasmatic nucleus, subfornical organ, paraventricular nucleus of the hypothalamus, zona incerta, dorsomedial nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, arcuate nucleus of the hypothalamus, basomedial amygdaloid nucleus, medial amygdaloid nucleus, medial habenular, pyramidal cell layer of the hippocampus, granular layer of the dentate gyrus, posterior hypothalamus, supramammilliary nucleus, premammillary nucleus, nucleus of Darkschewitsch, Edinger-Westphal nucleus, ventral tegmental area, dorsal raphe nucleus, periaqueductal gray, median raphe nucleus, lateral parabrachial nucleus, dorsal tegmental nucleus, laterodorsal tegmental nucleus, locus coeruleus, Barrington's nucleus, medial vestibular nucleus, ambiguous nucleus, dorsal vagal complex and hypoglossal nucleus. Up-regulated during in vitro adipocyte differentiation. Mutant mice display increased early postnatal mortality rate, reduction of total body fat mass, nearly total absence of gonadal fat and great reduction in subcutaneous fat. Mice have enlarged visceral organs, markedly steatotic liver, decreased adipocyte size and number, and display decreased levels of plasma adiponectin and leptin, glucose intolerance and insulin resistance but not hypertriglyceridemia. Belongs to the seipin family. Extended N-terminus. Truncated N-terminus. Extended N-terminus.