# Characterization of Maturation-Associated Genes in Ovary–Hepatopancreas Transcriptome and Vitellogenin Expression in Pacific Blue Swimming Crab Callinectes arcuatus During Gonadal Maturity Stages

## TL;DR

This study identifies genes and proteins involved in reproduction in the Pacific blue swimming crab, focusing on vitellogenin, a key protein for crab reproduction, and finds that it is mainly produced in the hepatopancreas.

## Contribution

The study reports 33 previously unreported reproduction-related genes, including the complete vitellogenin sequence, in the Pacific blue swimming crab.

## Key findings

- Vitellogenin is synthesized primarily in the hepatopancreas, not the ovaries, of the Pacific blue swimming crab.
- Vitellogenin expression in the hepatopancreas increases exponentially with gonadal maturity stages.
- The study identified 196 reproduction-related proteins, with 33 being novel to this species.

## Abstract

Swimming crabs, which belong to the genus Callinectes, are highly valued species and considered a delicacy worldwide, underscoring their importance to both fisheries and aquaculture. Along the Mexican Pacific coast, the blue crab C. arcuatus is present year-round. Despite its culinary appeal and commercial value, molecular studies on this species are limited, particularly those related to its reproduction. In this study, next-generation sequencing was used to investigate the genes and proteins involved in vitellogenesis (the synthesis and accumulation of yolk in the ovaries) in female crabs, a process closely linked to maturation. A total of 196 different reproduction-related proteins were identified, 33 of which have not been previously reported in this species, and are now available to the scientific community. For example, vitellogenin, a key protein essential for crab reproduction, was found in both the ovaries and hepatopancreas (a nutrient storage organ). Interestingly, the hepatopancreas was identified as the primary site of vitellogenin synthesis.

The swimming crab is a commercially and nutritionally important marine resource with the highest catch volumes in Mexico occurring along the East Pacific coast. Among the Pacific species of the genus Callinectes, the blue crab C. arcuatus has the widest distribution and is found throughout the year. Its close resemblance to the well-studied Atlantic blue swimming crab (C. sapidus) makes it an excellent model for molecular reproductive studies in the Mexican Pacific. Using next-generation sequencing, this study aimed to characterize maturation-associated genes in an ovary–hepatopancreas transcriptome of C. arcuatus, with a particular focus on vitellogenin (Vtg) and its expression in the ovaries and hepatopancreas across different gonadal maturity stages. The transcriptome library generated from pooled samples produced 27,729 unigenes, of which, 196 (1.81%) were identified as reproduction-related genes. Notably, 33 of these genes, including the complete Vtg sequence, have not been previously reported in this species. Vtg expression was found to be tissue-specific, with levels in the hepatopancreas up to 13 orders of magnitude higher than in the ovary. In the hepatopancreas, Vtg expression increased exponentially from stage I to stage V of gonadal maturity, whereas in the ovaries, its expression showed the opposite trend. These findings highlight that the hepatopancreas, with its abundant nutrient reserves, serves as the primary site of Vtg expression and synthesis.