The Hox gene Abdominal‐B regulates the appendage development during the embryogenesis of scorpionflies

Abstract

The Homeotic Complex (Hox) genes encode conserved homeodomain transcription factors that specify segment identity and appendage morphology along the antero‐posterior axis in bilaterian animals. The Hox gene Abdominal‐B (Abd‐B) is mainly expressed in the posterior segments of the abdomen and plays an important role in insect organogenesis. In Mecoptera, the potential function of this gene remains unclear yet. Here, we performed a de novo transcriptome assembly and identified an Abd‐B ortholog in the scorpionfly Panorpa liui. Quantitative real‐time reverse transcription PCR showed that Abd‐B expression increased gradually in embryos 76 h post oviposition, and was mainly present in the more posterior abdominal segments. Embryonic RNA interference of Abd‐B resulted in a set of abnormalities, including developmental arrest, malformed suckers and misspecification of posterior segment identity. These results suggest that Abd‐B is required for the proper development of the posterior abdomen. Furthermore, in Abd‐B RNAi embryos, the expression of the appendage marker Distal‐less (Dll) was up‐regulated and was additionally present on abdominal segments IX and X compared with wild embryos, suggesting that scorpionfly Abd‐B may act to suppress proleg development and has gained the ability to repress Dll expression on the more posterior abdominal segments. This study provides additional information on both the functional and evolutionary roles of Abd‐B across different insects.

Functional characterization of developmentally critical genes in the white‐backed planthopper: Efficacy of nanoparticle‐based dsRNA sprays for pest control

“…Abd‐A is mainly expressed in abdominal segments 1–7 (A1–A7) in D. melanogaster , whereas Abd‐B have been described in A4–A9 59 . Similar expression patterns for the two genes have been reported for many insects 60–62 . Furthermore, the distinct characteristics of the segments located the abdomen and the genitalia region are specified by Ubx and Abd‐A , 63,64 with abdominal morphology regulated by Abd‐B 65–67 .…”

“…59 Similar expression patterns for the two genes have been reported for many insects. [60][61][62] Furthermore, the distinct characteristics of the segments located the abdomen and the genitalia region are specified by Ubx and Abd-A, 63,64 with abdominal morphology regulated by Abd-B. [65][66][67] Mutations in Abd-A resulted in developmental defects of the head, thorax, and genitalia in D. melanogaster, 56,68,69 and led to the emergence of extra legs in the A1-A2 segments for the silkworm Bombyx mori.…”

Distinct roles of the Hox genes Ultrabithorax and abdominal‐A in scorpionfly embryonic proleg development

“…For SEM, the scorpionfly embryos were dissected out from different developmental stages as previously described in Liu et al (2022). After dehydration in a graded methanol series, the samples were treated with tertiary butanol twice for 30 min, critical point dried in liquid CO 2 for 3 h, sputter coated with gold and imaged using a Hitachi S-3400 N SEM at 15 kV.…”

“…Embryo collection, fixation, dissection and ISH followed Liu et al (2022). The controls were performed with 10 specimens for each gene and stage.…”

“…These studies imply that abdominal appendages have a complex evolutionary history of gain and loss in the Mecoptera. Although many advances have been made on the origin of ventral prolegs in Panorpidae (Bitsch, 2012; Kou & Hua, 2016; Yue & Hua, 2010), the regulatory mechanisms underlying varied proleg patterns remain largely unclear in Mecoptera (Liu et al, 2022).…”