Genes involved in melanin production directly impact insect pigmentation and can affect diverse physiology and behaviours. The role these genes have on sex behaviour, however, is unclear. In the present study, the crucial melanin pigment gene black was functionally characterised in an urban pest, the German cockroach, Blattella germanica. RNAi knockdown of B. germanica black (Bgblack) had no effect on survival, but did result in black pigmentation of the thoraxes, abdomens, heads, wings, legs, antennae, and cerci due to cuticular accumulation of melanin. Sex-specific variation in the pigmentation pattern was apparent, with females exhibiting darker coloration on the abdomen and thorax than males. Bgblack knockdown also resulted in wing deformation and negatively impacted the contact sex pheromone-based courtship behaviour of males. This study provides evidence for black function in multiple aspects of B. germanica biology and opens new avenues of exploration for novel pest control strategies.

Some lichenized ascomycetes synthesize melanic pigments in their upper cortices when exposed to ultraviolet light and high solar radiation. Our previous work showed that melanized chloro- and cyanolichens from both high light and more shaded habitats were less photoinhibited than pale ones during controlled exposure to high light. However, protection from high light might not necessarily be the consequence of just sun-screening by melanins in upper cortices. An inherent problem with earlier experiments was that the photobionts of melanized thalli might have received more light than those beneath pale cortices. The photobionts may therefore have possessed other light-induced tolerance mechanisms that gave protection from photoinhibition. Here, we aimed to test directly the inherent tolerance of lichen photobionts to photoinhibition. The method involved removing the lower cortices and medullas of three lichen species, Cetraria islandica, Crocodia aurata and Lobaria pulmonaria, and exposing the photobionts to light from below. Results confirmed that most of the improvement in tolerance to photoinhibition in melanized lichens derives from fungal melanization in the upper cortex. However, in C. islandica, the most heavily melanized species, algae from melanized thalli possessed a significantly higher tolerance to photoinhibition than those from pale thalli, suggesting that photobionts can also adapt themselves to high light.

Hair colouration in animals is controlled primarily by inherited factors, with a complex set of genes and genetic variants determining phenotypic expression. The colours in the hair shaft are created initially by the melanocyte cells within the hair bulb which produce and secrete two types of melanin into the hair cortex, black eumelanin and brown pheomelanin. Together these two pigments are responsible for creating the considerable diversity of colour seen in hair across the animal kingdom. In the absence of melanins the hair remains translucent, appearing white to the eye. Colour, or absence thereof, can only be imparted on a hair during its ‘anagen’ or growing phase. During the telogen (resting) phase the colour of the hair is relatively constant, notwithstanding effects of environmental influences such as UV in sunlight, or staining agents. A further environmental factor is nutrition. The intensity of black in the hair of both cats and dogs is known to be influenced by the dietary intake of certain amino acids such as phenylalanine (Phe) and tyrosine (Tyr). However the role of nutrition in hair pigmentation is generally poorly understood. This trial investigated the impact of diet on the commonly observed red discolouration of white coat in dogs. Two panels of 13 Swiss White Shepherd dogs were fed diets containing different concentrations of Phe + Tyr (test diet containing 3.02 g/Mcal versus control 4.82 g/Mcal) and copper (test diet containing 8.93 ppm versus control 13.28 ppm) for four months. Coat colouration was assessed via spectrophotometry using the CIE Lab colour space system (International Commission on Illumination). Dogs fed the reduced Phe + Tyr and copper showed significantly less red coat pigmentation (a* parameter) by the end of the feeding study (P < 0.02). It was concluded that the level of Phe + Tyr not only affects black but also white coat in dogs. Diet can therefore exert an influence on multiple aspects of coat pigmentation.

It has been demonstrated that microRNAs (miRNAs) play important roles in the control of melanogenesis and hair color in mammals. By comparing miRNA expression profiles between brown and white alpaca skin, we previously identified miR508-3p as a differentially expressed miRNA suggesting its potential role in melanogenesis and hair color formation. The present study was conducted to determine the role of miR508-3p in melanogenesis in alpaca melanocytes. In situ hybridization showed that miR508-3p is abundantly present in the cytoplasma of alpaca melanocytes. miR508-3p was predicted to target the gene encoding microphthalmia transcription factor (MITF) and a luciferase reporter assay indicated that miR508-3p regulates MITF expression by directly targeting its 3′UTR. Overexpression of miR508-3p in alpaca melanocytes down-regulated MITF expression both at the messenger RNA and protein level and resulted in decreased expression of key melanogenic genes including tyrosinase and tyrosinase-related protein 2. Overexpression of miR508-3p in melanocytes also resulted in decreased melanin production including total alkali-soluble melanogenesis, eumelanogenesis and pheomelanogenesis. Results support a functional role of miR508-3p in regulating melanogenesis in alpaca melanocytes by directly targeting MITF.

The appearance of a red hue to the hair in black coated cats and dogs has previously been reported as a “red hair syndrome”. Such changes in hair colour are related to an alteration in the proportions of two types of pigments produced by melanocytes; black eumelanin and brown pheomelanin. In black cats, it has been demonstrated that higher levels of phenylalanine + tyrosine (Phe+Tyr) than those recommended for growth are required to support eumelanin synthesis. The purpose of this study was to evaluate if a similar observation could be made in dogs. Twelve black coated puppies (Black Labrador retrievers and Newfoundlands) were divided into 3 groups of 4 and fed 3 diets with increasing concentrations of Phe+Tyr (A: 4 g/Mcal; B: 5.8 g/Mcal; C: 7 g/Mcal) for a period of 6 months. Quantification of plasma amino acids (Phe, Tyr, Cys) and spectrocolourimetry of hair samples from the Labrador retrievers (as the a* dimension of CIE Lab system) were performed at the beginning, during and at the end of the study. There was a significant negative linear relationship between plasma Tyr levels and a* values of hair in Labrador dogs on diets A and B, suggesting that a diet with total Phe+Tyr content of 6 g/Mcal (higher than the growth recommended allowance) was necessary to ensure an optimal black coat colour in these puppies and that levels up to 7 g/Mcal can lead to a more intense black coat colour. Moreover, similar to what was found in kittens, plasma levels of Tyr up to 54 μmol/l did not guarantee an optimal black colour coat and led to the “reddish hair” appearance in black coated puppies.

The tachinid fly Exorista larvarum (L.) (Diptera: Tachinidae) is a polyphagous larval endoparasitoid that deposits its eggs on the host exoskeleton of lepidopteran and tenthredinid larvae. The attachment of larval E. larvarum and the formation of the respiratory funnel were studied during infestation in the last larval instar of the wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae). The tachinid larvae burrow through the host integument after hatching, using their robust cephalopharyngeal skeleton, leaving a dark spot at the point of their penetration as a result of host cuticle melanization. Endoparasitoid penetration induces the host cellular defence, resulting in the formation of a haemocyte capsule consisting of multi-cellular sheaths. This enveloping capsule later undergoes melanization, which is mostly obvious towards the posterior part of the endoparasitoid. The endoparasitoid uses the host encapsulation response to build a respiratory funnel from the modified host integument, leading to the host surface. The encapsulated larva remains attached to the respiratory funnel via an anal hook and cuticular spines until fully developed. Additional immunohistochemical analyses were used to study host–parasitoid interactions. Indirect immunofluorescence showed no labelling of potential tachinid antigens and confirmed no effect on the surrounding host tissues. A simulated parasitization with coated polybead microspheres revealed the mortal impact of tachinid antigens to the host. Hosts injected with antigen-coated polybeads died as a consequence of an acute and extensive immunological response to the tachinid antigens and not due to the trauma caused by foreign objects inside their body.

In our earlier work, we demonstrated the presence of the multicopper oxidases tyrosinase and laccase in the cell walls of lichens from the Peltigerales, while these enzymes appeared to be absent in lichens from other orders. Likely roles for tyrosinase in lichens include melanin synthesis, the generation of quinones needed for laccase-mediated redox cycling, and the removal of harmful reactive molecules formed by this cycling. Non-Peltigeralean lichens will not need tyrosinase to detoxify laccase-generated radicals. However, many non-Peltigeralean lichens are often heavily melanized. Apparent absence of tyrosinase activity in these species prompted us to suggest that, in these lichens, melanins are probably synthesized by the polyketide pathway, which does not involve tyrosinase. Here, we surveyed intracellular tyrosinase activity in thallus homogenates from a range of lichens. Results showed that Peltigeralean species generally have much higher activities than species from other orders. However, the non-Peltigeralean lichen Dermatocarpon miniatum displays significant tyrosinase activity. In D. miniatum, tyrosinase differs from the corresponding enzyme from Peltigeralean lichens with respect to cellular location, substratum specificity, stability and pH optimum. Furthermore, unlike Peltigeralean lichens, in D. miniatum tyrosinase activity increased strongly following the rehydration of dry thalli. These differences are possibly a consequence of the role of tyrosinase in melanin synthesis rather than laccase-mediated redox cycling.

Ocular hypopigmentation is associated with neurological defects in structure and function. This paper investigates the ab/Fute visual thresholds in dark-adapted hypopigmented animals compared to their normally pigmented controls. Here we asked (1) whether the threshold elevation found in hypopigmented animals is a general consequence of the reduction in melanin content; (2) if so, which melanin components in the eye are likely to influence visual thresholds; and (3) whether similar threshold defects can be detected in orders other than rodents. By single-unit recordings from the superior colliculus, we compared incremental thresholds of normal black mice of the C57BL/6J strain to hypopigmented mutants: beige (bg/bg), pale ear (ep/ep), and albino (c2J/c2J) mice, three mutants in which melanin pigment throughout the body is affected; and Steel (Sl/Sld) and dorninant-spotting/W-mice (W/Wν), two mutants with normal pigmentation in the retinal pigment epithelium (RPE) but without any melanin in the choroid or the rest of the body. We found that all mutants had elevated thresholds that varied with the reduction in melanin. The albinos were 25 times less sensitive than black mice, pale ear mice 20 times, beige mice 11 times, and Steel and W-mice 5 times. The mean thresholds of dark-adapted black mice were 0.008 cd/m2. Recordings from rabbits showed a similar impairment of visual sensitivity: incremental thresholds were elevated 40 times in New Zealand-White albino rabbits (0.0008 cd/m2) compared to Dutch-Belted pigmented controls (0.00002 cd/m2). Previously, it has been shown that hypopigmented rats have elevated dark-adapted thresholds compared to pigmented controls (Balkema, 1988); here we show that the difference between hypopigmented rats and pigmented controls is not caused by insufficient dark adaptation or excessive variability in the results from albino mutant compared to its control.

Mutations that cause a reduction of ocular melanin pigmentation, regardless of the gene mutated or the mechanism underlying the hypopigmentation, are accompanied by an elevation in visual thresholds which is roughly proportional to the reduction in melanin. Melanin both in the RPE and choroid exert an effect on visual thresholds. Like the defects in optic nerve crossing and eye movements, the effect of melanin on visual thresholds is not restricted to rodents, but is seen in other orders. The threshold impairment in hypopigmented animals cannot be explained by impaired photoprotection, but it points to another physiological action of melanin.

In albinos, the retinofugal projections to the ipsilateral side of the brain are reduced (e.g., see Guillery, 1969; LaVail et al., 1978; Lund, 1965). Although all ganglion cell types are affected, in mice the displaced ganglion cell population is the main target of the albino mutation (Dräger & Olsen, 1980). Here we tested whether this preferential effect on displaced ganglion cells is a general consequence of the melanin reduction or a pleiotropic effect unique to the albino locus, retrogradely tracing tracing retinal ganglion cells in normal C57BL/6J mice and in several non-allelic hypopigmentation mutants on the same background: albino (C57BL/6J-c2J), beige (C57BL/6J-bg), pale ear (C57BL/6J-ep), ruby-eye/haze (C57BL/6J-ru-2hz), and pearl (C57BL/6J-pe). All mutants have lower overall cell counts in the ipsilateral projection, but the displaced population is disproportionately affected: the albinos contain 42% of the normal number of displaced ganglion cells, and the other mutants have an average 57% of normal counts.

The reduction in uncrossed retinofugal projections in albinos affects the inputs to the lateral geniculate nucleus and the superior colliculus, but not to the suprachiasmatic nucleus (Dräger, 1974). To address the question in which way the susceptible uncrossed projections differ from the nonsusceptible one, we compared ganglion cells backfilled from the suprachiasmatic nucleus to ganglion cells backfilled from the optic tract at geniculate level. Whereas the uncrossed optic tract projection originates from the binocular region in the ventro-temporal retina and contains a high fraction of large and displaced ganglion cells (Dräger & Olsen, 1980), both the crossed and uncrossed inputs to the suprachiasmatic nucleus originate from the entire retina with a relative preference for the lower nasal region that corresponds to part of the monocular visual field; all ganglion cells projecting to the suprachiasmatic nucleus are of medium size, and they are located in the ganglion cell layer.

These observations allow the following conclusions: (1) All genetic mutants which cause a reduction in ocular melanin, regardless of the molecular or cell-biological mechanism underlying the pigment reduction, result in decreased uncrossed projections; this confirms previous reports (LaVail et al., 1978, Sanderson et al., 1974). (2) The decrease affects only projections involved in binocular vision. (3) In mice, the ganglion cells displaced to the inner nuclear layer, and hence located closer to the retinal pigment epithelium, are disproportionately affected by the melanin reductions. These observations may provide cues to the spatio-temporal mechanism of the melanin action in the embryonic visual system.

We used synchrotron light to determine VUV-UV absorption spectra (125–340 nm) of thin films of substances associated with UV resistance in specific groups of organisms or across limited phylogenetic boundaries: scytonemin, mycosporine-like amino acids, dipicolinic acid, β-carotene, melanin and flavonoids (quercitrin, isoquercitrin, robinin and catechin). The objective was to extend known UV absorption spectra into the vacuum UV, and to evaluate the likely effectiveness of these molecules in shielding DNA from the unfiltered solar UV found in space, using similarity with DNA absorption spectra as the primary criterion. The spectroscopy indicated that plant flavonoids would be ideal UV screens in space. We suggest that flavonoids represent primitive UV screens, and offer explanations (including horizontal gene transfer) for their presence in plants. We also discuss the possibility of improving UV resistance by increasing flavonoid accumulation through metabolic engineering, in the hope of better adapting life for space travel, i.e. for its dissemination away from the Earth (exospermia). Finally, we propose using plant seeds as exospermia vehicles for sending life (including artificial life) into space.

Induction of secondary compounds in three reindeer lichens (Cladonia arbuscula, C. rangiferina and C. stellaris) was studied under controlled conditions in a growth chamber. Acetone rinsed (secondary compounds removed) lichen mats were subjected to three light regimes (PAR, PAR+UV-A and PAR+UV-A+UV-B), each combined with simulated herbivory (clipping). After 4 weeks, lichen extracts were analyzed by HPLC for any synthesized secondary compounds. UV-B induced the synthesis of usnic acid in C. arbuscula and C. stellaris and melanic pigments in C. rangiferina. Atranorin, fumarprotocetraric acid and perlatolic acid were not influenced by light quality. None of the identified compounds were significantly influenced by clipping. In conclusion, all three lichen species responded to UV-B radiation by developing cortical UV-B absorbing pigments that might function as protective screens. However, the experiment did not produce evidence for a herbivore-deterrent role of compounds studied.

The amount/distribution of liver melanin in 3 amphibian species (Rana esculenta, Triturus a. apuanus, Triturus carnifex) was studied during 2 periods of the annual cycle (summer activity–winter hibernation) by light and electron microscopy, image analysis and microspectrofluorometry. The increase in liver pigmentation (melanin content) during winter appeared to be correlated with morphological and functional modifications in the hepatocytes, which at this period were characterised by a decrease in metabolic activity. These findings were interpreted according to the functional role (e.g. phagocytosis, cytotoxic substance inactivation) played by the pigment cell component in the general physiology of the heterothermic vertebrate liver and, in particular, in relation to a compensatory engagement of these cells against hepatocellular hypoactivity during the winter period.