Kanikah Mehndiratta, MSc, University of Glasgow
Insects secrete pheromones to attract the opposite gender. The nature, activity and sex-specific differences in such pheromones is usually attributed to different regulatory mechanisms at the genetic level. Cuticular hydrocarbons in arthropods act as a crucial signalling chemical for intra-specie communication. Their primary role is to prevent drying of the outer layer of arthropod skin due to dehydration. The molecular basis of production and the significance of sexually dimorphic hydrocarbons (SDHCs) isn’t very well understood. A recent study published in the PLOS Biology journal uses RNA interference (RNAi) screening and heterologous expression of 2 genes involved in female-specific HC profile of Blattella germanica.
Sexual dimorphism in Cockroaches:
Sexual dimorphism is a highly existent phenomenon in the kingdom Animalia. Male and female species continuously evolve in their traits through natural selection. This has been increasing survival rate and reproduction under a continuously changing environment pressure and resulting in sexual dimorphism. This could also be due to an asymmetric inter or intra-sexual selection of dimorphic traits. We do not know much about the genetic basis of such traits that are specific to individual sexes. Pre-existing genetic mechanisms are supporting such sex-specific adaptations.
Adult female cockroaches have more C29 CHCs, particularly the precursor 3,11- DimeC29. A lot of research is going into understanding the regulatory networks behind production of such CHCs in a dimorphic scenario. The fruit fly D. melanogaster’s females produce more C27 and C29 dienes which play role as contact-sex pheromones while their male counterparts have the C23 and C25 monoenes. The gene Transformer is responsible for feminizing the CHC profile in males. Other studies indicated a female-specific desatF gene for imparting specific nature to female SDHCs.
The Research Strategy adopted:
B. germanica is an indoor pest that is acting as a model insect in this research. The SDHCs characterization, the description of their temporal development and a comparison between treated females and wild-type male SDHC profiles has been done. Two genes, BgElo12 and BgElo24 that are majorly responsible for SDHC production have been identified in the study. RNAi in females of the BgElo12 gene reduced courtship behaviour in males. The repression of the BgElo24 gene also down-regulated the C28 and C32 SDHCs which was confirmed via a 2nd RNAi target. The internal HCs were analysed for any changes they exhibit. The RNAi also indicated a deficiency of de novo HC biosynthesis.
Conclusions drawn from the study:
Two genes, BgElo12 and BgElo24 are showing involvement in HC production. Repression of the BgElo12 gene is resulting in a more masculinized CHC profile and thus, resulting in reduced sexual attractiveness of the female cockroaches. This could be due to a reduction in contact sex pheromone levels in the female body. The study also reveals a sex differentiation cascade that asymmetrically modulates the expression of the BgElo12 gene. The BgDsx represses transcription of BgElo12 gene only in males while the BgTra nullifies this effect in females leading to a higher number of SDHCs.
References:
1. Pei, X. J., Fan, Y. L., Bai, Y., Bai, T. T., Schal, C., Zhang, Z. F., … & Liu, T. X. (2021). Modulation of fatty acid elongation sustains sexually dimorphic hydrocarbons and female attractiveness in Blattella germanica (L.). bioRxiv. https://doi.org/10.1101/2021.03.04.434003
2. Stökl, J., & Steiger, S. (017). Evolutionary origin of insect pheromones. Current opinion in insect science, 24, 36-42. https://doi.org/10.1016/j.cois.2017.09.004
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Author info:
Kanikah Mehndiratta is an avid researcher in the field of Genetics with a background in Biotechnology. She is a postgraduate from the University of Glasgow in their Medical Genetics and Genomics program. Currently, based in Chandigarh as a scientific writer, she involves herself mainly in projects related to neurological disorders. Apart from academics, she likes to read novels, travel. and involves herself in volunteer work mostly.
LinkedIn profile- https://www.linkedin.com/in/kanikah-mehndiratta-301830171
Other articles-
1. https://bioxone.in/news/worldnews/pre-exposure-prophylaxis-trajectories-for-targeting-aids/
2. https://bioxone.in/news/worldnews/crispr-cas9-for-disease-resistance-in-salmon/
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