Abstract
Eicosanoids are crucial downstream signals in the insect immune responses. Phospholipase A2 (PLA2) catalyzes phospholipids, the initial step in eicosanoid biosynthesis. In mammals, the biological roles of Ca2+-independent Phospholipase A2 (iPLA2) have been extensively studied; however, only a few studies have attempted to explore iPLA2 functions in insects. In this study, we identified two iPLA2 genes (designated as BmiPLA2A and BmiPLA2B) in the silkworm, Bombyx mori. BmiPLA2A had a 2427 base pair (bp) open reading frame (ORF) that coded for a protein with 808 amino acids. In contrast, BmiPLA2B had a 1731 bp ORF that coded for a protein with 576 amino acids. Domain analysis revealed that BmiPLA2A had six ankyrin repeat domains, but BmiPLA2B lacks these domains. BmiPLA2A and BmiPLA2B were transcribed widely in various tissues and developmental stages with different expression patterns. The administration of 20-hydroxyecdysone increased their expression levels in the epidermis and hemocytes. Furthermore, challenged with virus, fungus, Gram-negative bacteria, and Gram-positive bacteria induced the expression of BmiPLA2A and BmiPLA2B with variable degrees along with different time points. Our findings imply that BmiPLA2A and BmiPLA2B may have important biological roles in the development and innate immunity of B. mori.
Highlights
In living organisms, the Phospholipase A2 (PLA2) superfamily is divided into 16 groups [1], which were further classified into three types based on their properties: Ca2+-dependent cellular PLA2, secretory PLA2, and Ca2+-independent cellular PLA2 [2]
BmiPLA2A is located on chromosome 11 in the silkworm genome, with 15 exons and 14 introns, whereas BmiPLA2B is located on chromosome 28, with 11 exons and 10 introns (Figure 1)
PLA2s are an important group of a gene family, serving as a crucial regulator of diverse physiological processes, including development and immunity [24]. secretory PLA2 (sPLA2) have been described in a variety of insect species [10,11,12,14,16]
Summary
The PLA2 superfamily is divided into 16 groups [1], which were further classified into three types based on their properties: Ca2+-dependent cellular PLA2 (cPLA2), secretory PLA2 (sPLA2), and Ca2+-independent cellular PLA2 (iPLA2) [2]. Among PLA2, iPLA2s have only been found in a few insects. There is little research on iPLA2s in insects despite their relevance in various physiological processes. Insect iPLA2s, such as SeiPLA2A and SeiPLA2B, were first discovered in Spodoptera exigua, and have been demonstrated to play crucial physiological roles in insect immunity and larval growth [7,8]. PLA2-VIA mutation in Drosophila caused increased sensitivity to oxidative stress, progressive neurodegeneration, and a severely reduced lifespan [10]. These studies show that insect iPLA2 may play crucial biological roles in development and immunity
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