Single choroideremia gene in non-mammalian vertebrates explains early embryonic lethality of the zebrafish model of choroideremia
Mariya Moosajee 1,
Merrin Tulloch 2,
Rudi A Baron 2,
Cheryl Y. Gregory-Evans 1,
Jose B. Pereira-Leal 3,
and
Miguel C. Seabra 4*
1 Neuroscience and Mental Health, Imperial College London, London, United Kingdom
2 NHLI, Imperial College London, London, United Kingdom
3 Instituto Gulbenkian de Ciencia, Oeiras, Portugal
4 NHLI , Imperial College London, Molecular Medicine, London, SW7 2AZ, United Kingdom
* To whom correspondence should be addressed. E-mail: m.seabra{at}imperial.ac.uk.
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Abstract |
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PURPOSE : Mutations of the CHM gene underlie the X-linked chorioretinal degeneration, choroideremia (CHM). The affected gene product, Rab Escort Protein-1 (REP1) mediates the post-translational prenyl modification of Rab GTPases. In CHM patients, the related REP2 partly compensates for the loss-of-function of REP1. The objective was to study the natural history of disease in a zebrafish model of CHM.
METHODS : Zebrafish chm-/- were bred and subjected to extensive histological analysis and TUNEL assays, and cellular extracts used for immunoblot and in vitro prenylation assays. A detailed evolutionary analysis was performed on the REP family.
RESULTS : We report that the retina of chm-/- zebrafish develops normally for the first 4 days post-fertilisation (dpf) followed by a catastrophic multi-layer degeneration, synchronously with severe multisystemic disease. The mean survival is 4.8 dpf. At the onset of generalized disease, we demonstrate a significant reduction in rep expression levels and activity, with unprenylated rabs accumulating in the cytosol. Extensive bioinformatic analysis of the REP family of proteins revealed a single rep isoform in fish, other non-mammalian vertebrates and invertebrates, which is more similar to mammalian REP1.
CONCLUSIONS : REP1 appears to be the ancestral gene in the family whilst the intronless REP2 gene is restricted to the mammalian lineage. We propose that in chm-/- zebrafish, maternally-derived rep allows initial successful development of the embryo, but its gradual loss leads to the multisystemic disease and invariable lethality observed. In its current form, the chm-/- zebrafish has limited utility.
Key Words:
retinal degeneration, genetic diseases, development, ocular, photoreceptor dystrophy, retinal pigment epithelium
