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Regulation of melanosome number, shape and movement in the zebrafish retinal pigment epithelium by OA1 and PMEL.

Burgoyne T, O'Connor MN, Seabra MC, Cutler DF, Futter CE - J. Cell. Sci. (2015)

Bottom Line: We further show that PMEL, a key component of mammalian melanosome biogenesis, is required for the generation of cylindrical melanosomes in zebrafish, which in turn is required for melanosome movement into the apical processes and maintenance of photoreceptor integrity.Spherical and cylindrical melanosomes containing similar melanin volumes co-exist in the cell body but only cylindrical melanosomes enter the apical processes.Taken together, our findings indicate that melanosome number and shape are independently regulated and that melanosome shape controls a function in the RPE that depends on localisation in the apical processes.

View Article: PubMed Central - PubMed

Affiliation: UCL Institute of Ophthalmology, London EC1V 9EL, UK.

No MeSH data available.


Related in: MedlinePlus

OA1 MOs reduce melanosome number at 2 dpf without affecting melanosome size. (A–D) Contrast-enhanced images of zebrafish eye cross-sections highlighting only electron-dense melanin. Images are shown from (A,B) control and (C,D) OA1 MO-treated zebrafish. KD, knockdown. Scale bars: 20 µm. (E) At 2 dpf there is a significant reduction in melanin area between controls and OA1 MO-treated zebrafish. By 5 dpf, the OA1 MO appears to be less effective, resulting in no significant difference in melanin area between controls and OA1 MO-treated animals. (F) The OA1 MO had no apparent effect on melanosome diameter at 2 and 5 dpf. Results show the mean±s.e.m.; *P<0.05 (Student's t-test).
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f01: OA1 MOs reduce melanosome number at 2 dpf without affecting melanosome size. (A–D) Contrast-enhanced images of zebrafish eye cross-sections highlighting only electron-dense melanin. Images are shown from (A,B) control and (C,D) OA1 MO-treated zebrafish. KD, knockdown. Scale bars: 20 µm. (E) At 2 dpf there is a significant reduction in melanin area between controls and OA1 MO-treated zebrafish. By 5 dpf, the OA1 MO appears to be less effective, resulting in no significant difference in melanin area between controls and OA1 MO-treated animals. (F) The OA1 MO had no apparent effect on melanosome diameter at 2 and 5 dpf. Results show the mean±s.e.m.; *P<0.05 (Student's t-test).

Mentions: To compare the regulation of melanosome biogenesis in zebrafish with that in mammalian cells and to evaluate zebrafish as a model to study human disease, the transcript for zebrafish OA1 was targeted with antisense morpholinos (MOs). At 2 and 5 days post-fertilisation (dpf) larvae were fixed and processed for transmission electron microscopy (TEM). It was immediately apparent from ultrathin sections through the entire retina of zebrafish embryos that there is a huge increase in melanin production between 2 and 5 dpf. Image thresholding allowed the area of melanin in the RPE at 2 and 5 dpf to be quantified. Correcting for a small increase in melanosome size between these two ages, the area of melanin indicates that there is a large (greater than fivefold) increase in melanosome number between 2 and 5 dpf (Fig. 1). Embryos depleted of OA1 could be identified by their reduced pigmentation at 2 dpf but the difference between OA1 targeting and control-morpholino-treated embryos was less clear at 5 dpf (supplementary material Fig. S1). TEM analysis of OA1 MO-treated zebrafish larvae showed no difference in melanosome size or distribution compared with that of controls, but there was a significant reduction in melanosome area and, therefore, number at 2 dpf (Fig. 1). This corroborates mammalian studies where OA1-knockout mice have been found to show reduced melanosome numbers at birth prior to a latent defect in melanosome size and distribution. By 5 dpf, melanosome numbers had largely recovered in larvae treated with OA1 MOs, presumably owing to the loss of MO efficacy due to dilution as the larvae increase in size.


Regulation of melanosome number, shape and movement in the zebrafish retinal pigment epithelium by OA1 and PMEL.

Burgoyne T, O'Connor MN, Seabra MC, Cutler DF, Futter CE - J. Cell. Sci. (2015)

OA1 MOs reduce melanosome number at 2 dpf without affecting melanosome size. (A–D) Contrast-enhanced images of zebrafish eye cross-sections highlighting only electron-dense melanin. Images are shown from (A,B) control and (C,D) OA1 MO-treated zebrafish. KD, knockdown. Scale bars: 20 µm. (E) At 2 dpf there is a significant reduction in melanin area between controls and OA1 MO-treated zebrafish. By 5 dpf, the OA1 MO appears to be less effective, resulting in no significant difference in melanin area between controls and OA1 MO-treated animals. (F) The OA1 MO had no apparent effect on melanosome diameter at 2 and 5 dpf. Results show the mean±s.e.m.; *P<0.05 (Student's t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4379728&req=5

f01: OA1 MOs reduce melanosome number at 2 dpf without affecting melanosome size. (A–D) Contrast-enhanced images of zebrafish eye cross-sections highlighting only electron-dense melanin. Images are shown from (A,B) control and (C,D) OA1 MO-treated zebrafish. KD, knockdown. Scale bars: 20 µm. (E) At 2 dpf there is a significant reduction in melanin area between controls and OA1 MO-treated zebrafish. By 5 dpf, the OA1 MO appears to be less effective, resulting in no significant difference in melanin area between controls and OA1 MO-treated animals. (F) The OA1 MO had no apparent effect on melanosome diameter at 2 and 5 dpf. Results show the mean±s.e.m.; *P<0.05 (Student's t-test).
Mentions: To compare the regulation of melanosome biogenesis in zebrafish with that in mammalian cells and to evaluate zebrafish as a model to study human disease, the transcript for zebrafish OA1 was targeted with antisense morpholinos (MOs). At 2 and 5 days post-fertilisation (dpf) larvae were fixed and processed for transmission electron microscopy (TEM). It was immediately apparent from ultrathin sections through the entire retina of zebrafish embryos that there is a huge increase in melanin production between 2 and 5 dpf. Image thresholding allowed the area of melanin in the RPE at 2 and 5 dpf to be quantified. Correcting for a small increase in melanosome size between these two ages, the area of melanin indicates that there is a large (greater than fivefold) increase in melanosome number between 2 and 5 dpf (Fig. 1). Embryos depleted of OA1 could be identified by their reduced pigmentation at 2 dpf but the difference between OA1 targeting and control-morpholino-treated embryos was less clear at 5 dpf (supplementary material Fig. S1). TEM analysis of OA1 MO-treated zebrafish larvae showed no difference in melanosome size or distribution compared with that of controls, but there was a significant reduction in melanosome area and, therefore, number at 2 dpf (Fig. 1). This corroborates mammalian studies where OA1-knockout mice have been found to show reduced melanosome numbers at birth prior to a latent defect in melanosome size and distribution. By 5 dpf, melanosome numbers had largely recovered in larvae treated with OA1 MOs, presumably owing to the loss of MO efficacy due to dilution as the larvae increase in size.

Bottom Line: We further show that PMEL, a key component of mammalian melanosome biogenesis, is required for the generation of cylindrical melanosomes in zebrafish, which in turn is required for melanosome movement into the apical processes and maintenance of photoreceptor integrity.Spherical and cylindrical melanosomes containing similar melanin volumes co-exist in the cell body but only cylindrical melanosomes enter the apical processes.Taken together, our findings indicate that melanosome number and shape are independently regulated and that melanosome shape controls a function in the RPE that depends on localisation in the apical processes.

View Article: PubMed Central - PubMed

Affiliation: UCL Institute of Ophthalmology, London EC1V 9EL, UK.

No MeSH data available.


Related in: MedlinePlus