Morphological studies on the mechanisms of pigmentary organelle transport in fish xanthophores and melanophores

Abstract

Pigmentary organelle translocations within fish chromatophores undergo physiological color changes when exposed to external signals. Chromatophores can be isolated in high yields, and their pigmentary organelles can be tracked readily by microscopy. The combined efforts of morphology and biomolecular chemistry have led to the identification of and determination of the interrelationships between cytoskeletal elements and accessory proteins, motor molecules, cytomatrix, and pigmentary organelles of various sizes. Fish chromatophores have been classified as fast, intermediate, and slow translocators, based on the relative numbers of microtubules. Studies on cultured goldfish (Carassius auratus L.) xanthophores for over 20 years have demonstrated that in this slow translocator, tubulovesicular structures of the smooth endoplasmic reticular (SER) cisternae are involved in the disperson and aggregation of associated carotenoid droplets (CD) with some involvement of cytoskeletal elements. Killifish (Fundulus heteroclitus L.) melanophore, a fast translocator, was also examined. Recent work demonstrates a bright fluorescent "starburst"-like spot that we call an actin filament-organizing center (AFOC) with radiating microfilaments, akin to the microtubule-organizing center (MTOC) with radiating microtubules. Melanosomes translocate single-file on microtubules and are not associated with SER cisternae. Slower CD dispersion or aggregation in goldfish xanthophores seems to be predominantly microfilament-based transport, or microfilament- and microtubule-based transport, respectively. Faster melanosome translocations in killifish melanophores are based on microtubules, with our evidence indicating microfilament involvement. Neural crest-derived chromatophores are models for vesicular transport in axons, and immunocytochemical and imaging technologies may help to elucidate the cellular transport mechanisms.

Provitamin A conversion to retinal via theβ,β-carotene-15,15′-oxygenase (bcox) is essential for pattern formation and differentiation during zebrafish embryogenesis

“…Our data indicate that bcox itself is expressed in cranial and trunk neural crest. So far, carotenoids and neural crest have been discussed solely with respect to neural crestderived pigmentation (Kimler and Taylor, 2002). Our analyses suggest an additional role of carotenoids as precursors for retinoids for subsequent RA generation and signaling in neural crest contributing to the craniofacial skeleton.…”

Morphological Studies on Microfilaments and their Organizing Center in Killifish (Fundulus heteroclitus L.) Melanophores

“…The overall purpose of our studies in Fundulus melanophores is to establish the identity of microfilament organization and microfilament‐based melanosome translocations from an actin‐filament organizing center (AFOC), a central bright spot seen by fluorescence labeling for microfilaments. This investigation is supported, in part, by microtubule‐based pigmentary organelle translocations from the MTOC in melanophores of fishes by different microscopic means (6, 12–17). The interaction between microfilaments and microtubules in melanosome transport has been well established in the melanophores of fishes (7, 9, 12, 13, 18, 19).…”

“…Furthermore, mechanisms of cytoskeleton‐based translocations of melanosomes within detergent‐permeabilized melanophores (4) and the energy cycling for retrograde translocations of pigment into the aggregate (5), were also investigated in this fish species. Our recent review describes the translocation of melanosomes by microtubules from a dispersed state to an aggregated state around the microtubule‐organizing center (MTOC) was demonstrated by immunofluorescence microscopy (6). Furthermore, it is now well established that both dispersion and aggregation of melanosomes in vertebrate melanophores requires both microtubules and microfilaments (7–9).…”

“…WCTEM permits high‐resolution viewing of different pigment distributions and describes the interaction of pigmentary organelles and cytoskeletal elements. With the identification of and the interaction with the MTOC in melanosome translocations (6, 12, 14), we proceeded to determine the presence of an AFOC as suggested earlier (10, 26). We also determined the significance of radially arranged microfilaments which follow the patterns of microtubules.…”

The effect of male colouration on reproductive success in Nile tilapia (Oreochromis niloticus)

“…To name a few, Kelsh et al (2000) used the embryo of the zebrafish to investigate the genetics behind melanophore development, Quigley and Parichy (2002) also used zebrafish to look at the formation of pigment patterns, Sugimoto (2002) studied morphological colour changes in fish, Kimler and Taylor (2002) et al (2005) at pigment pattern in medaka embryo and Logan et al (2006) at the regulation of melanophores in zebrafish. The number of articles published on pigmentation in fish over the last few years shows the continuing importance of this topic.…”