Abstract
The fat body plays key roles in energy storage and utilization as well as biosynthetic and metabolic activities in insects. During metamorphosis from larva to pupa, the fat body undergoes dramatic changes in morphology and metabolic processes. However, the genetic basis underlying these changes has not been completely understood. In this study, the authors performed a time-course transcriptome analysis of the fat body during silkworm metamorphosis using RNA-sequencing. A total of 5217 differentially expressed genes (DEGs) were identified in the fat body at different developmental time points. DEGs involved in lipid synthesis and degradation were highly expressed at the third day of the last larval instar and during the prepupal-pupal transition, respectively. DEGs involved in the ecdysone signaling and bone morphogenetic protein (BMP) signaling pathways that modulate organ development exhibited a high expression level during the fat body remodeling process from prepupa to pupa. Intriguingly, the RNA interference-mediated knockdown of either decapentaplegic (Dpp) or protein 60A (Gbb), two DEGs involved in the BMP signaling pathway, inhibited fat body dissociation but promoted lipid mobilization, suggesting that the BMP signaling pathway not only is required for fat body remodeling, but also moderately inhibits lipid mobilization to ensure an appropriate lipid supply during the pupal-adult transition. In conclusion, the comparative transcriptome analysis provides novel insight into morphologic and metabolic changes in the fat body during silkworm metamorphosis.
Highlights
The fat body is regarded as the center of energy storage and utilization as well as biosynthetic and metabolic activities in insects [1]
To better understand the mechanism underlying the functional changes in the fat body that occur during silkworm metamorphosis, the authors first investigated the morphological diversity of the fat body and lipid droplets at seven time points during the larval-pupal transition, including the first day of the last larval instar (L5D1), the third day of the last larval instar (L5D3), the fifth day of the last larval instar (L5D5), just wandering (W0), the second day during wandering (W2), just pupation (P0), and the third day after pupation (P3)
The authors characterized the dramatic changes in morphology, lipid droplet size, and gene expression that occur in the fat body during silkworm metamorphosis from last larval instar to pupa
Summary
The fat body is regarded as the center of energy storage and utilization as well as biosynthetic and metabolic activities in insects [1]. During the metamorphotic period with the larval-pupal transition, the fat body provides the necessities for survival, including energy and amino acids [4]. The larval fat body undergoes tissue dissociation and separates into individual fat cells [6]. Several genes that respond to the steroid hormone ecdysone, which is involved in the initiation of larval molting and metamorphosis [7,8], have been demonstrated to play key roles in fat body remodeling [9,10,11]. The disruption of fat body remodeling leads to a failure of the larval-pupal transition [14]. Little is known about the genome-wide response to structural alterations of the fat body during insect metamorphosis
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