Scanning transmission X-ray microscopic analysis of purified melanosomes of the mouse iris
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Published on: February 12, 2022
Michael G Anderson1, Tamás Haraszti, Greg E Petersen
1Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, United States. michael-g-anderson@uiowa.edu
Abstract:
Melanosomes are specialized intracellular membrane bound organelles that produce and store melanin pigment. The composition of melanin and distribution of melanosomes determine the color of many mammalian tissues, including the hair, skin, and iris. However, the presence of melanosomes within a tissue carries potentially detrimental risks related to the cytotoxic indole-quinone intermediates produced during melanin synthesis. In order to study melanosomal molecules, including melanin and melanin-related intermediates, we have refined methods allowing spectromicroscopic analysis of purified melanosomes using scanning transmission X-ray microscopy. Here, we present for the first time absorption data for melanosomes at the carbon absorption edge ranging from 284 to 290 eV. High-resolution images of melanosomes at discrete energies demonstrate that fully melanized mature melanosomes are internally non-homogeneous, suggesting the presence of an organized internal sub-structure. Spectra of purified melanosomes are complex, partially described by a predominating absorption band at 288.4 eV with additional contributions from several minor bands. Differences in these spectra were detectable between samples from two strains of inbred mice known to harbor genetically determined melanosomal differences, DBA/2J and C57BL/6J, and are likely to represent signatures arising from biologically relevant and tractable phenomena.
Insights
Researchers developed new spectromicroscopic methods to analyze melanosomes, revealing their internal non-homogeneous structure and unique spectral signatures. These findings offer insights into melanin synthesis and melanosome biology.
Area of Science:
- Cell Biology
- Biophysics
- Spectroscopy
Background:
- Melanosomes are organelles producing melanin, determining mammalian tissue color.
- Melanin synthesis involves cytotoxic intermediates, posing potential risks.
- Understanding melanosome composition is crucial for biological and medical research.
Purpose of the Study:
- To refine methods for analyzing melanosomal molecules using spectromicroscopy.
- To investigate the internal structure and spectral properties of purified melanosomes.
- To identify spectral differences between melanosomes from distinct mouse strains.
Main Methods:
- Purification of melanosomes from mouse strains (DBA/2J and C57BL/6J).
- Scanning transmission X-ray microscopy (STXM) for spectromicroscopic analysis.
- Acquisition of absorption data at the carbon absorption edge (284–290 eV).
Main Results:
- First reported absorption data for melanosomes at the carbon edge.
- High-resolution images revealed internal non-homogeneity in mature melanosomes.
- Complex spectra with a predominant band at 288.4 eV were observed.
- Distinct spectral differences were detected between DBA/2J and C57BL/6J mouse melanosomes.
Conclusions:
- Mature melanosomes possess an organized internal sub-structure.
- Melanosome spectra provide signatures of biologically relevant phenomena.
- STXM is a powerful tool for studying melanosome composition and internal organization.
