# The Period (per) Gene Plays an Important Role in Regulating Circadian Oscillation and Ovarian Development in the Ridgetail White Prawn, Exopalaemon carinicauda

## TL;DR

This study shows that the period gene in ridgetail white prawns regulates circadian rhythms and ovarian development, offering insights into crustacean reproduction.

## Contribution

The study identifies Ec-per as a key regulator of circadian rhythms and ovarian development in crustaceans through gene expression and functional analysis.

## Key findings

- Ec-per exhibits rhythmic expression under various light-dark cycles, indicating its role as an endogenous oscillator.
- RNA interference of Ec-per reduces expression of circadian genes and ecdysone receptors, affecting ovarian development.
- In situ hybridization shows Ec-per involvement in oocyte proliferation and nutrient accumulation.

## Abstract

This study elucidates the characteristics of the circadian clock gene (period) in the ridgetail white prawn, Exopalaemon carinicauda (Ec-per). Ec-per exhibited rhythmic expression under multiple light–dark (L–D) cycles, including constant darkness, confirming its role as an endogenous oscillator. Functional analysis using RNA interference indicated that Ec-per, as an important component of the circadian feedback loop, influenced reproductive physiology by synergistically regulating circadian genes (timeless and cryptochrome1) and upregulating ecdysone receptors. In situ hybridization results further suggested Ec-per is involved in oogenesis. Together, these findings highlight the important role of Ec-per in circadian rhythm regulation and ovarian development, offering new insights into photoperiod-mediated reproductive regulation mechanisms in crustaceans.

To explore the function of the period gene (Ec-per) in Exopalaemon carinicauda, we cloned the gene of 4611 bp with a 5′UTR of 201 bp, a 3′UTR of 813 bp, and an ORF of 3597 bp encoding 1198 amino acids. The predicted protein includes two PAS and one PERIOD domain. qPCR analysis revealed that Ec-per was expressed across all tissues tested at different developmental stages and during both embryonic and larval stages. Moreover, Ec-per oscillated rhythmically under different conditions of light-to-dark (L:D) ratios, including continuous darkness (0 L:24 D), where changes in the photoperiod influenced amplitude and phase shifts. The knockdown of Ec-per mRNA significantly reduced the expression of the circadian-related genes timeless (tim) and cryptochrome 1 (cry1) (p < 0.05). This suggests that Ec-per is an endogenous clock gene that may participate in molecular feedback loops and synergistically regulate the circadian rhythms through interacting with tim and cry1. RNA interference of Ec-per also markedly downregulated ecdysone receptor mRNA (p < 0.05), suggesting a positive role in the ovarian development of E. carinicauda. In situ hybridization further demonstrated that Ec-per is involved in oocyte proliferation and the accumulation of exogenous nutrients. This study provides new insights for promoting ovarian development and artificial breeding in crustaceans through optimized light-cycle management.