Orphan G-protein coupled receptor 22 (Gpr22) regulates cilia length and structure in the zebrafish Kupffer's vesicle

PLoS One. 2014 Oct 21;9(10):e110484. doi: 10.1371/journal.pone.0110484. eCollection 2014.

Abstract

GPR22 is an orphan G protein-coupled receptor (GPCR). Since the ligand of the receptor is currently unknown, its biological function has not been investigated in depth. Many GPCRs and their intracellular effectors are targeted to cilia. Cilia are highly conserved eukaryotic microtubule-based organelles that protrude from the membrane of most mammalian cells. They are involved in a large variety of physiological processes and diseases. However, the details of the downstream pathways and mechanisms that maintain cilia length and structure are poorly understood. We show that morpholino knock down or overexpression of gpr22 led to defective left-right (LR) axis formation in the zebrafish embryo. Specifically, defective LR patterning included randomization of the left-specific lateral plate mesodermal genes (LPM) (lefty1, lefty2, southpaw and pitx2a), resulting in randomized cardiac looping. Furthermore, gpr22 inactivation in the Kupffer's vesicle (KV) alone was still able to generate the phenotype, indicating that Gpr22 mainly regulates LR asymmetry through the KV. Analysis of the KV cilia by immunofluorescence and transmission electron microscopy (TEM), revealed that gpr22 knock down or overexpression resulted in changes of cilia length and structure. Further, we found that Gpr22 does not act upstream of the two cilia master regulators, Foxj1a and Rfx2. To conclude, our study characterized a novel player in the field of ciliogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Body Patterning
  • Cilia / chemistry
  • Cilia / physiology*
  • Embryo, Nonmammalian / metabolism
  • Embryonic Development / physiology
  • Forkhead Transcription Factors / metabolism
  • Microscopy, Electron, Transmission
  • Oligonucleotides, Antisense / metabolism
  • Phenotype
  • RNA Interference
  • RNA, Messenger / metabolism
  • Receptors, G-Protein-Coupled / antagonists & inhibitors
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Transcription Factors / metabolism
  • Zebrafish / growth & development
  • Zebrafish Proteins / antagonists & inhibitors
  • Zebrafish Proteins / genetics
  • Zebrafish Proteins / metabolism*

Substances

  • Forkhead Transcription Factors
  • Foxj1a protein, zebrafish
  • Oligonucleotides, Antisense
  • RNA, Messenger
  • Receptors, G-Protein-Coupled
  • Transcription Factors
  • Zebrafish Proteins

Grants and funding

This study was supported by the “TREAT-OA”- (Translational Research in Europe Applied Technologies for OsteoArthritis) consortium, funded by the Framework 7 European Research Program (FP7) (http://www.treatoa.eu/) and a IWT (Agency for Innovation by Science and 21 Technology) Strategic Basic Research grant (http://www.iwt.be/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.