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Monarch butterflies (Danaus plexippus) use bright orange coloration to warn off predators as well as for sexual selection. Surprisingly the underlying pigment compounds have not been previously characterized. We used LCMS and fragmentation MS (including MSMS and MSn) of extracted pigments from nonmigratory summer-generation female monarch forewings to identify and provide relative quantitation of various orange pigments from D. plexippus. We observed seven ommochrome pigments, with xanthommatin and decarboxylated xanthommatin being the most abundant followed by xanthommatin methyl ester. Among the seven pigments, we also observed molecules that correspond to deaminated forms of these three amine-containing pigments. To the best of our knowledge, these deaminated compounds have not been previously discovered. A seventh pigment that we observed was α-hydroxyxanthommatin methyl ester, previously described in other nymphalid butterflies. We also show that chemical reduction of pigment extracts results in a change of their color from yellow to red, concomitant with the appearance of dihydro-xanthommatin and similarly reduced forms of the other pigment compounds. These findings indicate that monarchs may employ differences in the redox states of these pigments in order to achieve different hues of orange., (© The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America.)

Tissue proteomics has relied heavily on two-dimensional gel electrophoresis, for protein separation and quantification, then single protein isolation, trypsin digestion, and mass spectrometric protein identification. Such methods are predominantly used for study of high-abundance, full-length proteins. Tissue peptidomics has recently been developed but is still used to study the most highly abundant species, often resulting in observation and identification of dozens of peptides only. Tissue lipidomics is likewise new, and reported studies are limited. We have developed an "omics" approach that enables over 7,000 low-molecular-weight, low-abundance species to be surveyed and have applied this to human placental tissue. Because the placenta is believed to be involved in complications of pregnancy, its proteomic evaluation is of substantial interest. In previous research on the placental proteome, abundant, high-molecular-weight proteins have been studied. Application of large-scale, global proteomics or peptidomics to the placenta have been limited, and would be challenging owing to the anatomic complexity and broad concentration range of proteins in this tissue. In our approach, involving protein depletion, capillary liquid chromatography, and tandem mass spectrometry, we attempted to identify molecular differences between two regions of the same placenta with only slightly different cellular composition. Our analysis revealed 16 species with statistically significant differences between the two regions. Tandem mass spectrometry enabled successful sequencing, or otherwise enabled chemical characterization, of twelve of these. The successful discovery and identification of regional differences between the expression of low-abundance, low-molecular weight biomolecules reveals the potential of our approach.