Sex-specific expression profiles of ecdysteroid biosynthesis and ecdysone response genes in extreme sexual dimorphism of the mealybug Planococcus kraunhiae (Kuwana)

Abstract

Insect molting hormone (ecdysteroids) and juvenile hormone regulate molting and metamorphic events in a variety of insect species. Mealybugs undergo sexually dimorphic metamorphosis: males develop into winged adults through non-feeding, pupa-like stages called prepupa and pupa, while females emerge as neotenic wingless adults. We previously demonstrated, in the Japanese mealybug Planococcus kraunhiae (Kuwana), that the juvenile hormone titer is higher in males than in females at the end of the juvenile stage, which suggests that juvenile hormone may regulate male-specific adult morphogenesis. Here, we examined the involvement of ecdysteroids in sexually dimorphic metamorphosis. To estimate ecdysteroid titers, quantitative RT-PCR analyses of four Halloween genes encoding for cytochrome P450 monooxygenases in ecdysteroid biosynthesis, i.e., spook, disembodied, shadow and shade, were performed. Overall, their expression levels peaked before each nymphal molt. Transcript levels of spook, disembodied and shadow, genes that catalyze the steps in ecdysteroid biosynthesis in the prothoracic gland, were higher in males from the middle of the second nymphal instar to adult emergence. In contrast, the expression of shade, which was reported to be involved in the conversion of ecdysone into 20-hydroxyecdysone in peripheral tissues, was similar between males and females. These results suggest that ecdysteroid biosynthesis in the prothoracic gland is more active in males than in females, although the final conversion into 20-hydroxyecdysone occurs at similar levels in both sexes. Moreover, expression profiles of ecdysone response genes, ecdysone receptor and ecdysone-induced protein 75B, were also analyzed. Based on these expression profiles, we propose that the changes in ecdysteroid titer differ between males and females, and that high ecdysteroid titer is essential for directing male adult development.

Sex‐specific expression and DNA methylation in a species with extreme sexual dimorphism and paternal genome elimination

“…It is important to bear in mind that the differences we describe in this study are found in adult whole‐body samples and thus do not capture expression and DNA methylation biases between tissues and developmental stages, which are known to vary greatly (Grath & Parsch, 2016; Harrison et al, 2015). Recently, both sex‐specific and developmental stage‐specific expression has been identified in other mealybug species: Phenacoccus solenopsis (Omar et al, 2019), Planococcus kraunhiae (Muramatsu et al, 2020) and Maconellicoccus hirsutus (Kohli et al, 2020). With Kohli et al (2020) identifying sex‐specific expression of numerous epigenetic regulators, including the genes SMYDA ‐ 4 and SDS3 which are up‐regulated in males and SMYD5 and nucleoplasmin which are up‐regulated in females.…”

“…Planococcus kraunhiae (Muramatsu et al, 2020) and Maconellicoccus hirsutus (Kohli et al, 2020). With Kohli et al (2020) identifying sexspecific expression of numerous epigenetic regulators, including the genes SMYDA-4 and SDS3 which are up-regulated in males and SMYD5 and nucleoplasmin which are up-regulated in females.…”

Sex-Biased Gene Expression and Isoform Profile of Brine Shrimp Artemia franciscana by Transcriptome Analysis

“…Ecdysteroid signaling, including the Sad gene, is associated with sexual dimorphism in addition to molting and metamorphosis in insects. For example, ecdysteroids contribute to extreme sexual dimorphisms in mealybugs, whose mRNA expression levels from the second nymphal instar to adult stages were higher in males than in females [ 69 ]. In beetles, ecdysteroids have been reported to control horn length dimorphisms in male heads [ 70 ], and Halloween genes, including Shade ( Shd ) and Phm , have been suggested as candidate target genes that are downregulated by the Dsx gene [ 71 ].…”

Knockdown of ecdysone receptor in male desert locusts affects relative weight of accessory glands and mating behavior

“…In adult male insects ecdysteroids have been shown to be crucial for male fertility and development of the reproductive system (Dalton et al, 2009;Ganter et al, 2011;Herndon et al, 1997;Ishimoto et al, 2009;Leiblich et al, 2019;Muramatsu et al, 2020;Sharma et al, 2017;Shinbo and Happ, 1989;Xu et al, 2020). In insects, spermatozoa produced by the testes are stored in paired seminal vesicles, which are surrounded by the male accessory glands (MAG).…”

“…MAG protein synthesis and sperm production were affected in the red flour beetle, Tribolium castaneum, after an RNAi-induced knockdown of several nuclear receptors that play a role in the 20E-induced signaling cascade (E75 or HR38 and E78 or HR39, respectively) (Xu et al, 2020). Muramatsu et al (2020) suggested that higher ecdysteroid titers in males of the Japanese mealybug, Planococcus kraunhiae, drive male development and cause extreme sexual dimorphism. These studies contributed to the increasing evidence supporting an important role of ecdysteroids in male reproductive physiology, and more specifically MAG development and activity.…”