Neuronatin Promotes Neural Lineage in ESCs via Ca2+ Signaling

Abstract

Neural induction is the first step in the formation of the vertebrate central nervous system. The emerging consensus of the mechanisms underling neural induction is the combined influences from inhibiting bone morphogenetic protein (BMP) signaling and activating fibroblast growth factor (FGF)/Erk signaling, which act extrinsically via either autocrine or paracrine fashions. However, do intrinsic forces (cues) exist and do they play decisive roles in neural induction? These questions remain to be answered. Here, we have identified a novel neural initiator, neuronatin (Nnat), which acts as an intrinsic factor to promote neural fate in mammals and Xenopus. ESCs lacking this intrinsic factor fail to undergo neural induction despite the inhibition of the BMP pathway. We show that Nnat initiates neural induction in ESCs through increasing intracellular Ca2+ ([Ca2+]i) by antagonizing Ca2+-ATPase isoform 2 (sarco/endoplasmic reticulum Ca2+-ATPase isoform 2) in the endoplasmic reticulum, which in turn increases the phosphorylation of Erk1/2 and inhibits the BMP4 pathway and leads to neural induction in conjunction with FGF/Erk pathway. STEM CELLS 2010;28:1950–1960

Neuronatin-mediated Aberrant Calcium Signaling and Endoplasmic Reticulum Stress Underlie Neuropathology in Lafora Disease

“…Existing literature suggests the involvement of neuronatin in the regulation of glycogen and lipid metabolism, and its mutation is associated with obesity (31,32,37,39). The primary and secondary structure of neuronatin is also strikingly similar with phospholamban (an ER-resident Ca 2ϩ regulator found in cardiac muscle), and recent reports have demonstrated that it is indeed involved in increasing the intracellular Ca 2ϩ by antagonizing SERCA2 pump in the ER (27,38). We have also detected a significant increase in intracellular Ca 2ϩ in neuronatin-transfected neuroblastoma cells.…”

“…Neuronatin is highly expressed in neonatal brain and possibly involved in neural induction and neuronal differentiation during brain development (27,38). In adult mice, it is also found to be selectively expressed in various limbic structures (31) of brain and several non-neural tissues including skin (33,34).…”

“…Although the physiological function of neuronatin is poorly understood, existing literature indicates its involvement in glucose-mediated insulin secretion from pancreas, in adipogenesis, and in metabolic regulation (31,32,(35)(36)(37). Interestingly, neuronatin has significant homology with phospholamban and PMP1 that function as regulatory subunit of ion channel and shown to promote neural lineage in embryonic stem cells through increasing the intracellular Ca 2ϩ by antagonizing serco/endoplasmic reticulum Ca 2ϩ -ATPase-2 (SERCA2) (27,38). Recently, we have reported that malin interacts with neuronatin and promotes its proteasomemediated degradation.…”

Regulation of neurogenesis by calcium signaling

“…In mammals, an increase in [Ca 2+ ] i also appears to be the key signal that controls neural fate determination [93]. However, while the main source of Ca 2+ increase in amphibian ectoderm is influx through voltage-operated Ca 2+ channels, mammalian embryonic stem cells do not express VOCCs and therefore must employ alternate pathways [94,95].…”

“…However, at the time of that study, the molecular identity of the SOC had not yet been determined and the potential role of the CRAC channel family in mediating these store-operated currents was not evaluated. More recently, a screen to identify neural induction genes in mammals identified neuronatin (Nnat), an ER membrane protein that physically antagonizes SERCA2 activity to regulate the intracellular Ca 2+ level [93]. Knocking down Nnat inhibits neural induction in ESCs by reducing the level of intracellular Ca 2+ .…”