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Ecology and Evolution May 2024Amphibians can obtain their colour from a combination of several different pigment and light reflecting cell types called chromatophores, with defects in one or several...
Amphibians can obtain their colour from a combination of several different pigment and light reflecting cell types called chromatophores, with defects in one or several of the cells leading to colour abnormalities. There is a need for better recording of colour abnormalities within wild amphibian populations, as this may provide baseline data that can be used to determine changes in environmental conditions and population dynamics, such as inbreeding. In this study, we provide records of several types of chromatophore deficiencies, including those involving iridophores, xanthophores and melanophores, among two Australian tree frog species; the green and golden bell frog, , and the eastern dwarf tree frog, . We explore these colour abnormalities in terms of the chromatophores that have likely been affected and associated with their expression, in combination with typical colour phenotypes, colour variations and colour changes for these species. We intend for our photographs to be used as a visual guide that addresses the need for more accessible information regarding the physical manifestation of different chromatophore defects among amphibians.
PubMed: 38779532
DOI: 10.1002/ece3.11438 -
Nature Communications May 2024Fossil feathers have transformed our understanding of integumentary evolution in vertebrates. The evolution of feathers is associated with novel skin ultrastructures,...
Fossil feathers have transformed our understanding of integumentary evolution in vertebrates. The evolution of feathers is associated with novel skin ultrastructures, but the fossil record of these changes is poor and thus the critical transition from scaled to feathered skin is poorly understood. Here we shed light on this issue using preserved skin in the non-avian feathered dinosaur Psittacosaurus. Skin in the non-feathered, scaled torso is three-dimensionally replicated in silica and preserves epidermal layers, corneocytes and melanosomes. The morphology of the preserved stratum corneum is consistent with an original composition rich in corneous beta proteins, rather than (alpha-) keratins as in the feathered skin of birds. The stratum corneum is relatively thin in the ventral torso compared to extant quadrupedal reptiles, reflecting a reduced demand for mechanical protection in an elevated bipedal stance. The distribution of the melanosomes in the fossil skin is consistent with melanin-based colouration in extant crocodilians. Collectively, the fossil evidence supports partitioning of skin development in Psittacosaurus: a reptile-type condition in non-feathered regions and an avian-like condition in feathered regions. Retention of reptile-type skin in non-feathered regions would have ensured essential skin functions during the early, experimental stages of feather evolution.
Topics: Animals; Feathers; Dinosaurs; Fossils; Biological Evolution; Skin; Reptiles; Melanosomes; Animal Scales; Epidermis; beta-Keratins
PubMed: 38773066
DOI: 10.1038/s41467-024-48400-3 -
Communications Biology May 2024Limited studies using animal models with a few natural mutations in melanophilin (Mlph) provided partial functions of Mlph in melanosome trafficking. To investigate...
Limited studies using animal models with a few natural mutations in melanophilin (Mlph) provided partial functions of Mlph in melanosome trafficking. To investigate cellular functions of Mlph, especially ZnF motif of Mlph, we analyzed all three Mlph knockout (KO) quail lines, one and two base pair (bp) deletions as models for total KO, and three bp deletion causing deletion of one Cysteine (C84del) in the ZnF motif. All quail lines had diluted feather pigmentation with impaired dendritogenesis and melanosome transport in melanocytes. In vitro studies revealed capability of binding of the ZnF motif to PIP3, and impairment of PI3P binding and mislocalization of MLPH proteins with ZnF motif mutations. The shortened melanocyte dendrites by the C84del mutation were rescued by introducing WT Mlph in vitro. These results revealed the diluted feather pigmentation by Mlph mutations resulted from congregation of melanosomes in the cell bodies with impairment of the dendritogenesis and the transport of melanosomes to the cell periphery.
Topics: Animals; Feathers; Melanocytes; Pigmentation; Melanosomes; Quail; Mutation; Adaptor Proteins, Signal Transducing
PubMed: 38760591
DOI: 10.1038/s42003-024-06284-5 -
Scientific Reports Apr 2024The Eocene Geiseltal Konservat-Lagerstätte (Germany) is famous for reports of three dimensionally preserved soft tissues with sub-cellular detail. The proposed mode of...
The Eocene Geiseltal Konservat-Lagerstätte (Germany) is famous for reports of three dimensionally preserved soft tissues with sub-cellular detail. The proposed mode of preservation, direct replication in silica, is not known in other fossils and has not been verified using modern approaches. Here, we investigated the taphonomy of the Geiseltal anurans using diverse microbeam imaging and chemical analytical techniques. Our analyses confirm the preservation of soft tissues in all body regions but fail to yield evidence for silicified soft tissues. Instead, the anuran soft tissues are preserved as two layers that differ in microstructure and composition. Layer 1 comprises sulfur-rich carbonaceous microbodies interpreted as melanosomes. Layer 2 comprises the mid-dermal Eberth-Katschenko layer, preserved in calcium phosphate. In addition, patches of original aragonite crystals define the former position of the endolymphatic sac. The primary modes of soft tissue preservation are therefore sulfurization of melanosomes and phosphatization of more labile soft tissues, i.e., skin. This is consistent with the taphonomy of vertebrates in many other Konservat-Lagerstätten. These findings emphasize an emerging model for pervasive preservation of vertebrate soft tissues via melanosome films, particularly in stagnation-type deposits, with phosphatization of more labile tissues where tissue biochemistry is favorable.
Topics: Fossils; Animals; Anura; Germany; Melanosomes
PubMed: 38654038
DOI: 10.1038/s41598-024-55822-y -
Proceedings of the National Academy of... Apr 2024Extracellular vesicles (EVs) facilitate the transfer of proteins, lipids, and genetic material between cells and are recognized as an additional mechanism for sustaining...
Extracellular vesicles (EVs) facilitate the transfer of proteins, lipids, and genetic material between cells and are recognized as an additional mechanism for sustaining intercellular communication. In the epidermis, the communication between melanocytes and keratinocytes is tightly regulated to warrant skin pigmentation. Melanocytes synthesize the melanin pigment in melanosomes that are transported along the dendrites prior to the transfer of melanin pigment to keratinocytes. EVs secreted by keratinocytes modulate pigmentation in melanocytes [(A. Lo Cicero , , 7506 (2015)]. However, whether EVs secreted by keratinocytes contribute to additional processes essential for melanocyte functions remains elusive. Here, we show that keratinocyte EVs enhance the ability of melanocytes to generate dendrites and mature melanosomes and promote their efficient transfer. Further, keratinocyte EVs carrying Rac1 induce important morphological changes, promote dendrite outgrowth, and potentiate melanin transfer to keratinocytes. Hence, in addition to modulating pigmentation, keratinocytes exploit EVs to control melanocyte plasticity and transfer capacity. These data demonstrate that keratinocyte-derived EVs, by regulating melanocyte functions, are major contributors to cutaneous pigmentation and expand our understanding of the mechanism underlying skin pigmentation via a paracrine EV-mediated communication.
Topics: Melanosomes; Melanins; Melanocytes; Keratinocytes; Extracellular Vesicles
PubMed: 38607931
DOI: 10.1073/pnas.2321323121 -
Communications Biology Mar 2024Transparent immunodeficient animal models not only enhance in vivo imaging investigations of visceral organ development but also facilitate in vivo tracking of...
Transparent immunodeficient animal models not only enhance in vivo imaging investigations of visceral organ development but also facilitate in vivo tracking of transplanted tumor cells. However, at present, transparent and immunodeficient animal models are confined to zebrafish, presenting substantial challenges for real-time, in vivo imaging studies addressing specific biological inquiries. Here, we employed a mitf/prkdc/il2rg triple-knockout strategy to establish a colorless and immunodeficient amphibian model of Xenopus tropicalis. By disrupting the mitf gene, we observed the loss of melanophores, xanthophores, and granular glands in Xenopus tropicalis. Through the endogenous mitf promoter to drive BRAF expression, we confirmed mitf expression in melanophores, xanthophores and granular glands. Moreover, the reconstruction of the disrupted site effectively reinstated melanophores, xanthophores, and granular glands, further highlighting the crucial role of mitf as a regulator in their development. By crossing mitf frogs with prkdc/il2rg frogs, we generated a mitf/prkdc/il2rg Xenopus tropicalis line, providing a colorless and immunodeficient amphibian model. Utilizing this model, we successfully observed intravital metastases of allotransplanted xanthophoromas and migrations of allotransplanted melanomas. Overall, colorless and immunodeficient Xenopus tropicalis holds great promise as a valuable platform for tumorous and developmental biology research.
Topics: Animals; Anura; Cytoplasm; Xenopus; Zebrafish; Microphthalmia-Associated Transcription Factor
PubMed: 38443437
DOI: 10.1038/s42003-024-05967-3 -
PloS One 2024Southern Amazonia is one of the less-explored regions by anuran taxonomists. We describe a small new species of snouted treefrog, genus Scinax, from this region, from a...
Southern Amazonia is one of the less-explored regions by anuran taxonomists. We describe a small new species of snouted treefrog, genus Scinax, from this region, from a fluvial archipelago in the Juruena River, state of Mato Grosso, Brazil. The description is based on external morphology of adults and tadpoles, advertisement call and molecular data. The species is phylogenetically related to other snouted treefrogs of the Scinax cruentomma species group and shows the most southeastern distribution in Amazonia among its close relatives. It is distinguished from congeners mainly by its larger adult body size and bilobate vocal sac that reaches the level of the pectoral fold, a reddish-brown horizontal stripe on the iris, dark melanophores or blotches on the vocal sac and the throat of females, and the uniformly brown posterior portion of the thigh. The advertisement call comprises one pulsed note emitted at regular intervals, with a duration of 189-227 ms, 30-35 pulses/note and a dominant frequency of 2,250-2,344 Hz. The type locality is suffering several environmental impacts, including illegal mining, overfishing, unsustainable agriculture, uncontrolled logging and degradation associated with the construction of new hydroelectric dams. Further study of the biology and regional distribution of the new species is required to propose mitigation measures needed for its conservation.
Topics: Animals; Female; Brazil; Anura; Rivers; Conservation of Natural Resources; Fisheries
PubMed: 38295055
DOI: 10.1371/journal.pone.0292441 -
Scientific Reports Jan 2024Tyrosinase (Tyr) is a key enzyme in the process of melanin synthesis that occurs exclusively within specialized organelles called melanosomes in melanocytes. Tyr is...
Tyrosinase (Tyr) is a key enzyme in the process of melanin synthesis that occurs exclusively within specialized organelles called melanosomes in melanocytes. Tyr is synthesized and post-translationally modified independently of the formation of melanosome precursors and then transported to immature melanosomes by a series of membrane trafficking events that includes endoplasmic reticulum (ER)-to-Golgi transport, post-Golgi trafficking, and endosomal transport. Although several important regulators of Tyr transport have been identified, their precise role in each Tyr transport event is not fully understood, because Tyr is present in several melanocyte organelles under steady-state conditions, thereby precluding the possibility of determining where Tyr is being transported at any given moment. In this study, we established a novel synchronized Tyr transport system in Tyr-knockout B16-F1 cells by using Tyr tagged with an artificial oligomerization domain FM4 (named Tyr-EGFP-FM4). Tyr-EGFP-FM4 was initially trapped at the ER under oligomerized conditions, but at 30 min after chemical dissociation into monomers, it was transported to the Golgi and at 9 h reached immature melanosomes. Melanin was then detected at 12 h after the ER exit of Tyr-EGFP-FM4. By using this synchronized Tyr transport system, we were able to demonstrate that Tyr-related protein 1 (Tyrp1), another melanogenic enzyme, is a positive regulator of efficient Tyr targeting to immature melanosomes. Thus, the synchronized Tyr transport system should serve as a useful tool for analyzing the molecular mechanism of each Tyr transport event in melanocytes as well as in the search for new drugs or cosmetics that artificially regulate Tyr transport.
Topics: Melanosomes; Monophenol Monooxygenase; Melanins; Melanogenesis; Melanocytes
PubMed: 38291221
DOI: 10.1038/s41598-024-53072-6 -
Proceedings of the National Academy of... Dec 2023Aldehydes fixation was accidentally discovered in the early 20th century and soon became a widely adopted practice in the histological field, due to an excellent...
Aldehydes fixation was accidentally discovered in the early 20th century and soon became a widely adopted practice in the histological field, due to an excellent staining enhancement in tissues imaging. However, the fixation process itself entails cell proteins denaturation and crosslinking. The possible presence of artifacts, that depends on the specific system under observation, must therefore be considered to avoid data misinterpretation. This contribution takes advantage of scanning electron assisted-dielectric microscopy (SE-ADM) and Raman 2D imaging to reveal the possible presence and the nature of artifacts in unstained, and paraformldehyde, PFA, fixed MNT-1 cells. The high resolution of the innovative SE-ADM technique allowed the identification of globular protein clusters in the cell cytoplasm, formed after protein denaturation and crosslinking. Concurrently, SE-ADM images showed a preferential melanosome adsorption on the cluster's outer surface. The micron-sized aggregates were discernible in Raman 2D images, as the melanosomes signal, extracted through 2D principal component analysis, unequivocally mapped their location and distribution within the cells, appearing randomly distributed in the cytoplasm. Protein clusters were not observed in living MNT-1 cells. In this case, mature melanosomes accumulate preferentially at the cell periphery and are more closely packed than in fixed cells. Our results show that, although PFA does not affect the melanin structure, it disrupts melanosome distribution within the cells. Proteins secondary structure, conversely, is partially lost, as shown by the Raman signals related to α-helix, β-sheets, and specific amino acids that significantly decrease after the PFA treatment.
Topics: Microscopy, Electron, Scanning; Melanosomes; Melanins
PubMed: 38091295
DOI: 10.1073/pnas.2308088120 -
PeerJ 2023The threespine stickleback () is an important model for studying the evolution of nuptial coloration, but histological analyses of color are largely lacking. Previous...
The threespine stickleback () is an important model for studying the evolution of nuptial coloration, but histological analyses of color are largely lacking. Previous analyses of one nuptial coloration trait, orange-red coloration along the body, have indicated carotenoids are the main pigment producing this color. In addition, recent gene expression studies found variation in the correlates of throat coloration between the sexes and between populations, raising the possibility of variation in the mechanisms underlying superficially similar coloration. We used transmission electron microscopy (TEM) to investigate the histological correlates of color in the throat dermal tissue of threespine stickleback from Western North America, within and between sexes, populations, and ecotypes. Ultrastructural analysis revealed carotenoid-containing erythrophores to be the main chromatophore component associated with orange-red coloration in both males and females across populations. In individuals where some darkening of the throat tissue was present, with no obvious orange-red coloration, erythrophores were not detected. Melanophore presence was more population-specific in expression, including being the only chromatophore component detected in a population of darker fish. We found no dermal chromatophore units within colorless throat tissue. This work confirms the importance of carotenoids and the erythrophore in producing orange-red coloration across sexes, as well as melanin within the melanophore in producing darkened coloration, but does not reveal broad histological differences among populations with similar coloration.
Topics: Female; Male; Animals; Pharynx; Smegmamorpha; Chromatophores; Fishes; Carotenoids
PubMed: 38077425
DOI: 10.7717/peerj.16248