# The Role of Twist2 in Myoblast Proliferation, Fusion, and Its Impact on Muscle Structure During the Growth of Chinese Perch (Siniperca chuatsi)

## TL;DR

This study shows that the Twist2 gene helps muscle growth in Chinese perch by promoting myoblast proliferation and fusion during muscle repair.

## Contribution

The novel finding is that Twist2 specifically regulates fast muscle growth in juvenile Chinese perch through myoblast proliferation and fusion.

## Key findings

- Twist2 expression increases during muscle repair in Chinese perch.
- Knockdown of Twist2 reduces myoblast proliferation and fusion markers.
- Muscle fiber diameter and nuclei count decrease with Twist2 knockdown.

## Abstract

Twist2 is crucial for the growth of skeletal muscle in organisms. However, the role of the Twist2 gene in the growth of skeletal muscle of economically important fish during the post-embryonic stage remains unclear. This study showed that in the muscle injury model of Chinese perch, Twist2 expression increased during the rapid muscle repair phase. After in vivo knockdown of Twist2 in fast muscle, the expression of myogenic regulatory factors (MRFs) and Myomaker was significantly reduced, while there was no difference in the expression of Pax3 and Pax7. In addition, the diameter of muscle fibers, the number of nuclei in single muscle fibers, and the number of BrdU-labeled myoblasts were all significantly reduced. These findings indicate that Twist2 can promote the proliferation and fusion of myoblasts, thereby facilitating the growth of fast muscle in juvenile Chinese perch.

Twist2 plays a pivotal regulatory role in the growth of skeletal muscle across various organisms. Nonetheless, the specific mechanism by which Twist2 governs skeletal muscle function in fish, particularly in the economically significant Chinese perch (Siniperca chuatsi), remains unclear. Within the muscle injury model in Chinese perch, we observed that Twist2 expression was upregulated during the repair phase of fast muscle tissue, exhibiting an expression pattern analogous to that of Pax7. Following the knockdown of Twist2 using Twist2-specific in vivo-siRNA in fast muscle tissues, the expression of myogenic regulatory factors (MRFs) and Myomaker was significantly reduced in the Twist2-siRNA-treated group compared with the control group, whereas no significant differences were observed for Pax3 and Pax7. Furthermore, the diameter of myofibers and the number of nuclei in single myofibers were reduced, and concurrently, the number of BrdU-positive cells (proliferating cells) was significantly reduced in the Twist2-siRNA-treated group. Taken together, this study demonstrates that Twist2 promotes myoblast proliferation and fusion, thereby regulating fast muscle growth in juvenile Chinese perch. These findings provide a clear direction for further exploration of molecular mechanisms underlying skeletal muscle growth in economic fish species.