Description:
<jats:title>Abstract</jats:title>
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<jats:title>Background</jats:title>
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<jats:italic>Park2-co-regulated gene</jats:italic> (<jats:italic>PACRG</jats:italic>) is evolutionarily highly conserved from green algae to mammals. In <jats:italic>Chlamydomonas</jats:italic> and trypanosomes, the PACRG protein associates with flagella. Loss of <jats:italic>PACRG</jats:italic> results in shortened or absent flagella. In mouse the PACRG protein is required for spermatogenesis. The purpose of the present study was to analyze (1) the expression patterns of <jats:italic>PACRG</jats:italic> during vertebrate embryogenesis, and (2) whether the PACRG protein was required for left-right (LR) axis specification through cilia-driven leftward flow in <jats:italic>Xenopus laevis</jats:italic>.</jats:p>
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<jats:title>Methods</jats:title>
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<jats:italic>PACRG</jats:italic> cDNAs were cloned and expression was analyzed during early embryonic development of <jats:italic>Xenopus</jats:italic>, mouse, rabbit and zebrafish. Antisense morpholino oligonucleotide (MO) mediated gene knockdown was applied in <jats:italic>Xenopus</jats:italic> to investigate LR development at the level of tissue morphology, leftward flow and asymmetric marker gene expression, using timelapse videography, scanning electron microscopy (SEM) and whole-mount <jats:italic>in situ</jats:italic> hybridization. Results were statistically evaluated using Wilcoxon paired and χ<jats:sup>2</jats:sup> tests.</jats:p>
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<jats:title>Results</jats:title>
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<jats:italic>PACRG</jats:italic> mRNA expression was found in cells and tissues harboring cilia throughout the vertebrates. Highly localized expression was also detected in the brain. During early development, <jats:italic>PACRG</jats:italic> was specifically localized to epithelia where leftward flow arises, that is, the gastrocoel roof plate (GRP) in <jats:italic>Xenopus</jats:italic>, the posterior notochord (PNC) in mammals and Kupffer’s vesicle (KV) in zebrafish. Besides its association with ciliary axonemes, subcellular localization of PACRG protein was found around the nucleus and in a spotty pattern in the cytoplasm. A green fluorescent protein (GFP) fusion construct preferentially labeled cilia, rendering PACRG a versatile marker for live imaging. Loss-of-function in the frog resulted dose dependently in LR, neural tube closure and gastrulation defects, representing ciliary and non-ciliary functions of PACRG.</jats:p>
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<jats:title>Conclusions</jats:title>
<jats:p>The PACRG protein is a novel essential factor of cilia in <jats:italic>Xenopus</jats:italic>.</jats:p>
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