Involvement of glucose transporter 4 in ovarian development and reproductive maturation of Harmonia axyridis (Coleoptera: Coccinellidae)

Glucose is vital to embryogenesis, as are glucose transporters. Glucose transporter 4 (Glut4) is one of the glucose transporters, which is involved in rapid uptake of glucose by various cells and promotes glucose homeostasis. Although energy metabolism in insect reproduction is well known, the molecular mechanism of Glut4 in insect reproduction is poorly understood. We suspect that Glut4 is involved in maintaining glucose concentrations in the ovaries and affecting vitellogenesis, which is critical for subsequent oocyte maturation and insect fertility. Harmonia axyridis (Pallas) is a model organism for genetic research and a natural enemy of insect pests. We studied the influence of the Glut4 gene on the reproduction and development of H. axyridis using RNA interference technology. Reverse transcription quantitative polymerase chain reaction analysis revealed that HaGlut4 was most highly expressed in adults. Knockdown of the HaGlut4 gene reduced the transcript levels of HaGlut4, and the weight and number of eggs produced significantly decreased. In addition, the transcript levels of vitellogenin receptor and vitellogenin in the fat bodies and the ovaries of H. axyridis decreased after the interference of Glut4, and decreased the triglyceride, fatty acid, total amino acid and adenosine triphosphate content of H. axyridis. This resulted in severe blockage of ovary development and reduction of yolk formation; there was no development of ovarioles in the developing oocytes. These changes indicate that a lack of HaGlut4 can impair ovarian development and oocyte maturation and result in decreased fecundity. Bioinformatics analysis of Glut4 and assembly chaperone genes. (A) Phylogenetic analysis of insect HaGlut4 and assembly chaperones. The phylogenetic tree was constructed based on the deduced amino acid sequences of HaGlut4 and assembly chaperones from 18 insect species by the maximum‐likelihood method using Mega X (http://www.megasoftware.net/). Bootstrap analysis was set for values of 100 trials and bootstrap values greater than 50% are shown on each node of the tree. (B) Domain structures of HaGlut4 protein. Conserved domains in the deduced amino acid sequences of HaGlut4 were determined using SMART (http://smart.embl.de/) and NCBI (http://www.ncbi.nlm.nih.gov/). Grey bars represent the number of amino acid residues and colored boxes represent the characteristic domains.