DLK1 Is a Somato-Dendritic Protein Expressed in Hypothalamic Arginine-Vasopressin and Oxytocin Neurons

Delta-Like 1 Homolog, Dlk1, is a paternally imprinted gene encoding a transmembrane protein involved in the differentiation of several cell types. After birth, Dlk1 expression decreases substantially in all tissues except endocrine glands. Dlk1 deletion in mice results in pre-natal and post-natal growth deficiency, mild obesity, facial abnormalities, and abnormal skeletal development, suggesting involvement of Dlk1 in perinatal survival, normal growth and homeostasis of fat deposition. A neuroendocrine function has also been suggested for DLK1 but never characterised. To evaluate the neuroendocrine function of DLK1, we first characterised Dlk1 expression in mouse hypothalamus and then studied post-natal variations of the hypothalamic expression. Western Blot analysis of adult mouse hypothalamus protein extracts showed that Dlk1 was expressed almost exclusively as a soluble protein produced by cleavage of the extracellular domain. Immunohistochemistry showed neuronal DLK1 expression in the suprachiasmatic (SCN), supraoptic (SON), paraventricular (PVN), arcuate (ARC), dorsomedial (DMN) and lateral hypothalamic (LH) nuclei. DLK1 was expressed in the dendrites and perikarya of arginine-vasopressin neurons in PVN, SCN and SON and in oxytocin neurons in PVN and SON. These findings suggest a role for DLK1 in the post-natal development of hypothalamic functions, most notably those regulated by the arginine-vasopressin and oxytocin systems.Delta样1同源物（Delta-Like 1 Homolog, Dlk1）是一种父本印记基因，编码一种跨膜蛋白，参与多种细胞类型的分化。出生后，除内分泌腺体外，Dlk1在所有组织中的表达水平均显著下调。小鼠体内Dlk1基因敲除会导致产前及产后生长缺陷、轻度肥胖、面部畸形及骨骼发育异常，提示Dlk1参与围产期存活、正常生长及脂肪沉积稳态调控。此前有研究提出DLK1具备神经内分泌功能，但尚未得到证实。为探究DLK1的神经内分泌功能，我们首先对小鼠下丘脑组织中的Dlk1表达特征进行了分析，随后研究了其产后下丘脑表达的动态变化。对成年小鼠下丘脑蛋白提取物的蛋白质印迹（Western Blot）分析显示，Dlk1几乎仅以细胞外结构域剪切产生的可溶性蛋白形式存在。免疫组织化学（Immunohistochemistry）结果显示，DLK1在视交叉上核（suprachiasmatic nucleus, SCN）、视上核（supraoptic nucleus, SON）、室旁核（paraventricular nucleus, PVN）、弓状核（arcuate nucleus, ARC）、背内侧下丘脑核（dorsomedial nucleus, DMN）及外侧下丘脑核（lateral hypothalamic nucleus, LH）的神经元中均有表达。DLK1在室旁核、视交叉上核及视上核内的精氨酸加压素神经元的树突和胞体中，以及室旁核与视上核内的催产素神经元中均有表达。上述研究结果提示，DLK1可能参与下丘脑功能的产后发育调控，尤其是精氨酸加压素与催产素系统所调控的生理过程。