Deletion of the WD40 domain of LRRK2 in Zebrafish causes Parkinsonism-like loss of neurons and locomotive defect.

LRRK2 plays an important role in Parkinson's disease (PD), but its biological functions are largely unknown. Here, we cloned the homolog of human LRRK2, characterized its expression, and investigated its biological functions in zebrafish. The blockage of zebrafish LRRK2 (zLRRK2) protein by morpholinos caused embryonic lethality and severe developmental defects such as growth retardation and loss of neurons. In contrast, the deletion of the WD40 domain of zLRRK2 by morpholinos targeting splicing did not induce severe embryonic developmental defects; rather it caused Parkinsonism-like phenotypes, including loss of dopaminergic neurons in diencephalon and locomotion defects. These neurodegenerative and locomotion defects could be rescued by over-expressing zLRRK2 or hLRRK2 mRNA. The administration of L-dopa could also rescue the locomotion defects, but not the neurodegeneration. Taken together, our results demonstrate that zLRRK2 is an ortholog of hLRRK2 and that the deletion of WD40 domain of zLRRK2 provides a disease model for PD.

Depletion of Bhmt elevates sonic hedgehog transcript level and increases ß-cell number in zebrafish.

Betaine homocysteine S-methyltransferase (BHMT, EC 2.1.1.5) is a key enzyme in the methionine cycle and is highly expressed in the liver. Despite its important biochemical function, it is not known whether BHMT plays a role during organ development. In this report, we showed that early in development of zebrafish before endoderm organogenesis, bhmt is first expressed in the yolk syncytial layer and then after liver formation becomes a liver-enriched gene. By using the anti-bhmt morpholinos that deplete the Bhmt, we found that in morphant embryos, several endoderm-derived organs, including liver, exocrine pancreas, and intestine are hypoplastic. Strikingly, the number of ß-cells in the pancreatic islet was increased rather than reduced in the morphant. Additional studies showed that Bhmt depletion elevates the sonic hedgehog (shh) transcript level in the morphant, whereas Bhmt-depletion in the Shh-deficient mutant syu failed to rescue the isletless phenotype. These molecular and genetic data strongly suggest that Shh functions downstream of Bhmt to promote ß-cell development. Therefore, although there are still many intriguing questions to be answered, our finding may identify a novel function for Bhmt involving modulation of Shh signaling to control ß-cell development.