Leucine-rich repeat-containing G-protein-coupled receptors (LGRs) form a subfamily of the large superfamily of G-protein-coupled receptors. LGRs can be divided into three groups. LGR2 from Drosophila melanogaster is involved in cuticle tanning (melanization and sclerotization). In this study, one LGR2 (MnLGR2) was identified from Macrobrachium nipponense. MnLGR2 has an open reading frame of 4515 bp encoding a protein with 1504 amino acids. MnLGR2 is comprised of a 7-transmembrane domain, 12 leucine-rich repeats, and 5 low-complexity regions. The highest expression level of MnLGR2 was observed in gills. The expression levels of MnLGR2 in gills and stomach could be regulated by bacterial challenge. Knockdown of MnLGR2 upregulated the expression of anti-microbial peptide (AMP) genes. Further study indicated that inhibition of AMP expression by MnLGR2 was through inhibition of relish-mediated AMP expression. In addition to the negative regulation of AMP expression, MnLGR2 participated in positive regulation of phenol oxidase (PO) activity and expression of proPO activating pathway-related genes (proPO-activating factor and proPO-activating enzymes). Therefore, MnLGR2 plays an important role in prawn innate immunity.

富含亮氨酸的重复序列包含的G蛋白偶联受体（LGR）形成了G蛋白偶联受体超家族的一个亚家族。LGR可以分为三类。果蝇的LGR2参与角质层鞣制（黑色素化和硬化）。在这项研究中，从日本沼虾中鉴定出一种LGR2（MnLGR2）。MnLGR2具有4515 bp的开放阅读框，编码具有1504个氨基酸的蛋白质。MnLGR2由7个跨膜结构域，12个富含亮氨酸的重复序列和5个低复杂度区域组成。在g中观察到最高的MnLGR2表达水平。MnLGR2的表达水平bacterial和胃中的细菌可以通过细菌攻击来调节。敲低MnLGR2上调了抗微生物肽（AMP）基因的表达。进一步的研究表明，抑制AMP通过表达MnLGR2是通过抑制津津有味介导的AMP表达。除AMP表达的负调控外，MnLGR2还参与酚氧化酶（PO）活性和proPO激活途径相关基因（proPO激活因子和proPO激活酶）的表达的正调控。因此，MnLGR2 在虾固有免疫中起重要作用。