CDK9 and its repressor LARP7 modulate cardiomyocyte proliferation and response to injury in the zebrafish heart

Gianfranco Matrone,John J Mullins,Kathryn S Wilson,Carl S Tucker,Martin A Denvir,Sana Maqsood

doi:10.1242/dev.134148

Abstract

Cyclin dependent kinase (Cdk)9 acts through the positive transcription elongation factor-b (P-TEFb) complex to activate and expand transcription through RNA polymerase II. It has also been shown to regulate cardiomyocyte hypertrophy, with recent evidence linking it to cardiomyocyte proliferation. We hypothesised that modification of CDK9 activity could both impair and enhance the cardiac response to injury by modifying cardiomyocyte proliferation. Cdk9 expression and activity were inhibited in the zebrafish (Danio rerio) embryo. We show that dephosphorylation of residue Ser2 on the C-terminal domain of RNA polymerase II is associated with impaired cardiac structure and function, and cardiomyocyte proliferation and also results in impaired functional recovery following cardiac laser injury. In contrast, de-repression of Cdk9 activity, through knockdown of La-related protein (Larp7) increases phosphorylation of Ser2 in RNA polymerase II and increases cardiomyocyte proliferation. Larp7 knockdown rescued the structural and functional phenotype associated with knockdown of Cdk9. The balance of Cdk9 and Larp7 plays a key role in cardiomyocyte proliferation and response to injury. Larp7 represents a potentially novel therapeutic target to promote cardiomyocyte proliferation and recovery from injury.

Highlights

Cyclin Dependent Kinase 9 (CDK9) has emerged from the wider family of CDKs as an important signaling mechanism in the initiation and progression of cardiac hypertrophy (Krystof et al, 2012, Krystof et al, 2010)
CDK9 and Larelated protein 7 (LARP7) expression display a distinct pattern in whole larvae and in isolated larval hearts during normal development CDK9 was detected in normal whole larvae from 24 hours post fertilization and showed a distinctive pattern of expression during the course of development increasing between 24 and 72 hpf (p
We provide evidence that CDK9 plays a key role in early cardiac development and in cardiomyocyte proliferation

Summary

Introduction

Cyclin Dependent Kinase 9 (CDK9) has emerged from the wider family of CDKs as an important signaling mechanism in the initiation and progression of cardiac hypertrophy (Krystof et al, 2012, Krystof et al, 2010). CDK9 has been shown to act as a binding partner of GATA4, an important regulator of cardiomyocyte proliferation in mammals and zebrafish (Kikuchi et al, 2010). Knockdown of endogenous CDK inhibitors by small interfering RNA was found to induce neonatal and adult cardiomyocytes to re-enter the cell cycle resulting in active proliferation of previously quiescent cells (Di Stefano et al, 2011). This intriguing finding suggests a key role for CDKs in controlling the proliferative behaviour of cardiomyocytes and points to a potential mechanism by which cardiomyocytes could be induced to divide

Methods

Results

Conclusion