Zebrafish Parla‐ and Parlb‐deficiency affects dopaminergic neuron patterning and embryonic survival

Abstract

Many genes associated with familial Parkinson's disease contribute to mitochondrial morphology and function. Some of these genes, for example, Pink1 and Parkin, are part of a common pathway. The presenilin-associated rhomboid-like (PARL) gene was recently linked to familial Parkinson's disease. The PARL gene product is found in the inner mitochondrial membrane and cleaves the optic atrophy 1 protein, involved in mitochondrial morphology and apoptosis. In Drosophila, the PARL-related rhomboid-7 gene acts upstream of pink1 and parkin. However, such a genetic relationship is still unknown in vertebrates. Here, we show that the zebrafish genome comprises two parl paralogs: parla and parlb. Morpholino-mediated loss of parla and/or parlb function resulted in mild neurodegeneration, as evidenced by a lower density of dopaminergic neurons. Patterning of dopaminergic neurons was also perturbed in the ventral diencephalon. Morphants exhibited extensive cell death throughout the entire body as well as increased larval mortality. The morphant phenotype could be rescued by injection of human PARL mRNA, but not catalytically inactive PARL, suggesting functional conservation between the human and zebrafish proteins. More importantly, the zebrafish pink1 mRNA as well as the human PINK1 mRNA, but not kinase-dead nor Parkinson's disease-linked mutant PINK1 mRNA, also rescued the morphant phenotype, providing evidence that Parl genes may function upstream of Pink1, as part of a conserved pathway in vertebrates.

Zebrafish as an Animal Model for Drug Discovery in Parkinson’s Disease and Other Movement Disorders: A Systematic Review

“…PARL is a component of the mitochondrial membrane involved in mitochondrial morphology and apoptosis. Morpholino knockdown of both zebrafish paralogs, parla and parlb , results in high mortality, whereas loss of PARLb leads to the mildest phenotype ( 94 ). Loss of one of the PARL’s results in mild neurodegeneration and disarranged dopaminergic neurons.…”

Fishing in the Cell Powerhouse: Zebrafish as A Tool for Exploration of Mitochondrial Defects Affecting the Nervous System

“…Moreover, PARL cleaves the optic atrophy 1 protein (OPA1) [94] that is a crucial protein involved in the fusion of inner mitochondrial membranes and in the formation of cristae , crucial for proper mitochondrial metabolism in early development [71]. Bioinformatics analyses revealed that in zebrafish there are two paralogues, parla and parlb , whose transcripts are both ubiquitously expressed during embryogenesis [63]. The PD-phenotype caused by the KD of both parl genes can be rescued by the overexpression of human PARL mRNA.…”

PARL: The mitochondrial rhomboid protease

“…Two PARL orthologues have been identified in the zebrafish: parla and parlb [15]. Both parl transcripts are expressed during embryonic development and in adult tissues.…”

“…Both parl transcripts are expressed during embryonic development and in adult tissues. Morpholinomediated knockdown of parla and parlb simultaneously causes embryonic lethality, increased acridine orange staining, and altered expression of tyrosin hydroxylase mRNA and dopamine transporter [15], which were used as markers of dopaminergic neurons. Interestingly, overexpression of zebrafish pink1, but not kinase dead pink1 or pink1 containing Parkinson' s disease causing mutations, rescues larval lethality or dopaminergic neurons abnormalities, indicating that parl is genetically upstream of pink1, confirming this pathway in vertebrates.…”