Delaying Sexual Maturation in Female Olive Flounders Using Exemestane and Tamoxifen

Greg Howard
28th May, 2024

Delaying Sexual Maturation in Female Olive Flounders Using Exemestane and Tamoxifen

Treatment with the aromatase inhibitor exemestane induced the development of male cells (intersex) in the ovaries of female olive flounder, Paralichthys olivaceus (a), an effect not observed with tamoxifen treatment (b).

Image adapted from: Kim et al. / CC BY (Source)

Key Findings

  • The study was conducted by researchers at Jeju National University on female olive flounder
  • Exemestane treatment led to intersex characteristics in olive flounder, showing both male and female reproductive tissues
  • Tamoxifen treatment did not result in intersex characteristics, indicating different effects on sex differentiation compared to exemestane
Sex determination in various reptiles, amphibians, and fishes can be influenced by environmental factors, including temperature and the presence of specific hormones. A recent study conducted by researchers at Jeju National University delves into the role of estrogen-related compounds in sex determination in olive flounder (Paralichthys olivaceous)[1]. This study provides new insights into the impact of exemestane and tamoxifen on sex differentiation, potentially offering novel approaches to understanding and manipulating reproductive processes in fish. In mammals, reproductive function is regulated by pituitary gonadotropins such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are controlled by the hypothalamic hormone gonadotropin-releasing hormone (GnRH)[2]. Estrogens, acting through estrogen receptors (ESRs), play crucial roles in reproductive activities across vertebrates. Previous studies have highlighted the differential roles of various estrogen receptors in fish, particularly in tilapia, where mutations in esr1, esr2a, and esr2b genes showed distinct impacts on reproductive development and function[3]. In the study by Jeju National University, researchers focused on the effects of exemestane and tamoxifen on female olive flounder. Exemestane is known as an estrogen agonist non-steroid hormone, while tamoxifen is widely used in human cancer therapy as an anti-estrogen agent (estrogen receptor antagonist). The researchers injected these compounds intraperitoneally into the bodies of female olive flounder to observe their effects on sex differentiation. The results showed that the expression levels of estrogen receptor mRNA and vitellogenin mRNA in the liver were almost identical in both exemestane and tamoxifen treatments. However, histological analysis revealed intersex characteristics in the exemestane-treated flounder, a condition where both male and female reproductive tissues are present. This phenomenon was not observed in the tamoxifen-treated group. These findings suggest that exemestane may induce intersex conditions by influencing estrogen synthesis or signaling pathways, while tamoxifen does not appear to have the same effect. The study's results align with earlier research on the role of aromatase (Cyp19a1a), the enzyme responsible for estrogen synthesis, in fish gonadal sex differentiation. Previous studies have proposed that up-regulation of cyp19a1a is crucial for ovarian differentiation, while its down-regulation is necessary for testicular differentiation[4]. The findings from the Jeju National University study support the idea that manipulating estrogen pathways can significantly impact sex differentiation in fish. The researchers noted that the underlying mechanisms by which tamoxifen influences estrogen synthesis or signaling are not yet fully understood, necessitating further examinations to confirm its direct involvement. This study opens new avenues for exploring how estrogen-related compounds can be used to control sex differentiation in fish, which could have significant implications for aquaculture and conservation efforts. In conclusion, the study by Jeju National University highlights the complex interplay between estrogen-related compounds and sex differentiation in olive flounder. By demonstrating the distinct effects of exemestane and tamoxifen on sex differentiation, this research contributes to a deeper understanding of the hormonal regulation of reproductive processes in fish. The findings underscore the importance of further investigations into the mechanisms of estrogen signaling and synthesis to develop targeted approaches for managing sex differentiation in aquatic species.

MedicineAnimal ScienceMarine Biology

References

Main Study

1) Sexual maturation inhibition using exemestane and tamoxifen in female olive flounder (Paralichthys olivaceous)

Published 27th May, 2024

https://doi.org/10.1007/s44338-024-00007-0

Related Studies

2) Regulation of gonadotropin subunit gene transcription.

Journal: Journal of molecular endocrinology, Issue: Vol 33, Issue 3, Dec 2004

3) Establishment of three estrogen receptors (esr1, esr2a, esr2b) knockout lines for functional study in Nile tilapia.

https://doi.org/10.1016/j.jsbmb.2019.105379

4) Ovarian aromatase and estrogens: a pivotal role for gonadal sex differentiation and sex change in fish.

https://doi.org/10.1016/j.ygcen.2009.03.002


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