The tyrosinase gene and oculocutaneous albinism type 1 (OCA1): A model for understanding the molecular biology of melanin formation

Gene-knockout by iSTOP enables rapid reproductive disease modeling and phenotyping in germ cells of the founder generation

Cytosine base editing achieves C•G-to-T•A substitutions and can convert four codons (CAA/CAG/CGA/TGG) into STOP-codons (induction of STOP-codons, iSTOP) to knock out genes with reduced mosaicism. iSTOP enables direct phenotyping in founders' somatic cells, but it remains unknown whether this works in founders' germ cells so as to rapidly reveal novel genes for fertility. Here, we initially establish that iSTOP in mouse zygotes enables functional characterization of known genes in founders' germ cells: Cfap43-iSTOP male founders manifest expected sperm features resembling human "multiple morphological abnormalities of the flagella" syndrome (i.e., MMAF-like features), while oocytes of Zp3-iSTOP female founders have no zona pellucida. We further illustrate iSTOP's utility for dissecting the functions of unknown genes with Ccdc183, observing MMAF-like features and male infertility in Ccdc183-iSTOP founders, phenotypes concordant with those of Ccdc183-KO offspring. We ultimately establish that CCDC183 is essential for sperm morphogenesis through regulating the assembly of outer dynein arms and participating in the intra-flagellar transport. Our study demonstrates iSTOP as an efficient tool for direct reproductive disease modeling and phenotyping in germ cells of the founder generation, and rapidly reveals the essentiality of Ccdc183 in fertility, thus providing a time-saving approach for validating genetic defects (like nonsense mutations) for human infertility.

The bridge towards a more stable and active side-on-peroxido (Cu2II(µ-η2:η2-O2)) complex as a tyrosinase model system

A novel dinucleating bis(pyrazolyl)methane ligand was developed for tyrosinase model systems. After ligand synthesis, the corresponding Cu(I) complex was synthesized and upon oxygenation, formation of a µ-η2:η2 peroxido complex could be observed and monitored using UV/Vis-spectroscopy. Due to the high stability of this species even at room temperature, a molecular structure of the complex could be characterized via single-crystal XRD. Additional to its promising stability, the peroxido complex showed catalytic tyrosinase activity which was investigated via UV/Vis-spectroscopy. Products of the catalytic conversion could be isolated and characterized and the ligand could be successfully recycled after catalysis experiments. Furthermore, the peroxido complex was reduced by reductants with different reduction potentials. The characteristics of the electron transfer reactions were investigated with the help of the Marcus relation. The combination of the high stability and catalytic activity of the peroxido complex with the new dinucleating ligand, enables the shift of oxygenation reactions for selected substrates towards green chemistry, which is furthered by the efficient ligand recycling capability.

Abnormal foveal morphology in carriers of oculocutaneous albinism

BACKGROUND/AIMS

To investigate the foveal morphology in carriers of oculocutaneous albinism (OCA) using spectral domain optical coherence tomography (SD-OCT). A cross-sectional, observational study.

METHODS

Handheld SD-OCT (Envisu C2300) was used to acquire horizontal scans through the centre of the fovea in biological parents of patients with OCA (n=28; mean age±SD=40.43±8.07 years) and age-matched and ethnicity-matched controls (n=28; mean age±SD=38.04±10.27 years). Sequence analysis was performed for variants in known genes associated with OCA. Best-corrected visual acuity (BCVA), presence of foveal hypoplasia and grade, foveal, parafoveal and perifoveal thickness measurements of total retinal layers (TRL), inner retinal layers (IRL) and outer retinal layers (ORL) thickness were measured.

RESULTS

Foveal hypoplasia was identified in 32.14% of OCA carriers; grade 1 in all cases. OCA carriers demonstrated significant thicker TRL thickness (median difference: 13.46 µm, p=0.009) and IRL thickness (mean difference: 8.98 µm, p<0.001) at the central fovea compared with controls. BCVA of carriers was between -0.16 and 0.18 logMAR (mean: 0.0 logMAR). No significant differences in BCVA was noted between OCA carriers or controls (p=0.83). In the OCA carriers, we identified previously reported pathogenic variants in TYR, OCA2 and SLC45A2, novel OCA2 variants (n=3) and heterozygosity of the pathogenic TYR haplotype.

CONCLUSION

We have, for the first time, identified foveal abnormalities in OCA carriers. This provides clinical value, particularly in cases where limited phenotype data are available. Our findings raise the possibility that previously reported mild cases of foveal hypoplasia or isolated foveal hypoplasia could correspond to OCA carrier status.

Chemical Characterization of Different Extracts from Artemisia annua and Their Antioxidant, Enzyme Inhibitory and Anti-Inflammatory Properties

Artemisia annua L. (Asteraceae Family) is an important plant in Asia that has been used for treating different diseases, including fever due to malaria, wounds, tubercolisis, scabues, pain, convulsions, diabetes, and inflammation. In this study we aimed to evaluate the effects of different polarity extracts (hexane, dichloromethane, ethyl acetate, ethanol, ethanol/water (70 %) and water) from A. annua against the burden of inflammation and oxidative stress occurring in colon tissue exposed to LPS. In parallel, chemical composition, antiradical, and enzyme inhibition effects against α-amylase, α-glucosidase, tyrosinase, and cholinesterases were evaluated. The water extract contained the highest content of the total phenolic with 34.59 mg gallic acid equivalent (GAE)/g extract, while the hexane had the highest content of the total flavonoid (20.06 mg rutin equivalent (RE)/g extract). In antioxidant assays, the polar extracts (ethanol, ethanol/water and water) exhibited stronger radical scavenging and reducing power abilities when compared to non-polar extracts. The hexane extract showed the best AChE, tyrosinase and glucosidase inhibitory effects. All extracts revealed effective anti-inflammatory agents, as demonstrated by the blunting effects on COX-2 and TNFα gene expression. These effects seemed to be not related to the only phenolic content. However, it is worthy of interest to highlight how the higher potency against LPS-induced gene expression was shown by the water extract ; thus suggesting a potential phytotherapy application in the management of clinical symptoms related to inflammatory colon diseases, although future in vivo studies are needed to confirm such in vitro and ex vivo observations.

A Multi-Approach Study of Phytochemicals and Their Effects on Oxidative Stress and Enzymatic Activity of Essential Oil and Crude Extracts of Rosmarinus officinalis

Rosmarinus officinalis or Rosemary is a highly valued medicinal vegetal, owing to its notable antispasmodic, anti-inflammatory, and antibacterial properties. In the current work, we aimed to identify the chemical components of the essential oil (EO) of R. officinalis and evaluate its biological properties using an in vitro approach. High performance liquid chromatography time-of-flight mass spectrometry (HPLC-TOF-MS) was utilized to analyze of the hydro-methanolic extract (HME), while gas chromatography–mass spectrometry (GC/MS) was considered during the analysis of the EO’s chemical composition. The antioxidant abilities of HME and the EO were assessed using diverse tests (DPPH, ABTS, GOR, CUPRAC, and FRAP). The anti-enzymatic properties were tested by the inhibition of cholinesterases, α-glucosidase, and tyrosinase enzyme. The HPLC-TOF-MS displayed the existence of flavonoids like luteolin glucuronide I and II, and a few known hydroxycinnamic acids. The EO contained three major components, namely, eucalyptol (28.7%), camphor (16.7%), and borneol (13.5%). The HME had a high total polyphenol content, as determined by the Folin–Ciocalteau method (335.37 ± 9.33 µg of gallic acid eq·mg−1). Notably, the analysis of the bioactivities of the HME and EO revealed comparatively that they possessed higher radical scavenging capacity in the DPPH, ABTS, and galvinoxyl assays, while EO exhibited a higher capacity for enzyme inhibition. Overall, our findings suggest that both the EO and HME extract of Algerian’s R. officinalis holds great usefulness in the pharmaceutical and nutraceutical fields due to its elevated polyphenol content and potent bioactivities.

A frame-shift mutation in COMTD1 is associated with impaired pheomelanin pigmentation in chicken

The biochemical pathway regulating the synthesis of yellow/red pheomelanin is less well characterized than the synthesis of black/brown eumelanin. Inhibitor of gold (IG phenotype) is a plumage colour variant in chicken that provides an opportunity to further explore this pathway since the recessive allele (IG) at this locus is associated with a defect in the production of pheomelanin. IG/IG homozygotes display a marked dilution of red pheomelanin pigmentation, whilst black pigmentation (eumelanin) is only slightly affected. Here we show that a 2-base pair insertion (frame-shift mutation) in the 5th exon of the Catechol-O-methyltransferase containing domain 1 gene (COMTD1), expected to cause a complete or partial loss-of-function of the COMTD1 enzyme, shows complete concordance with the IG phenotype within and across breeds. We show that the COMTD1 protein is localized to mitochondria in pigment cells. Knockout of Comtd1 in a mouse melanocytic cell line results in a reduction in pheomelanin metabolites and significant alterations in metabolites of glutamate/glutathione, riboflavin, and the tricarboxylic acid cycle. Furthermore, COMTD1 overexpression enhanced cellular proliferation following chemical-induced transfection, a potential inducer of oxidative stress. These observations suggest that COMTD1 plays a protective role for melanocytes against oxidative stress and that this supports their ability to produce pheomelanin.

A single-cell transcriptomic atlas of the human ciliary body

The ciliary body critically contributes to the ocular physiology with multiple responsibilities in the production of aqueous humor, vision accommodation and intraocular immunity. Comparatively little work, however, has revealed the single-cell molecular taxonomy of the human ciliary body required for studying these functionalities. In this study, we report a comprehensive atlas of the cellular and molecular components of human ciliary body as well as their interactions using single-cell RNA sequencing (scRNAseq). Cluster analysis of the transcriptome of 14,563 individual ciliary cells from the eyes of 3 human donors identified 14 distinct cell types, including the ciliary epithelium, smooth muscle, vascular endothelial cell, immune cell and other stromal cell populations. Cell-type discriminative gene markers were also revealed. Unique gene expression patterns essential for ciliary epithelium-mediated aqueous humor inflow and ciliary smooth muscle contractility were identified. Importantly, we discovered the transitional states that probably contribute to the transition of ciliary macrophage into retina microglia and verified no lymphatics in the ciliary body. Moreover, the utilization of CellPhoneDB allowed us to systemically infer cell–cell interactions among diverse ciliary cells including those that potentially participate in the pathogenesis of glaucoma and uveitis. Altogether, these new findings provide insights into the regulation of intraocular pressure, accommodation reflex and immune homeostasis under physiological and pathological conditions.

Design, synthesis, spectroscopic characterization, in vitro tyrosinase inhibition, antioxidant evaluation, in silico and kinetic studies of substituted indole-carbohydrazides

In the current study, twenty-five indole-carbohydrazide derivatives linked to different aryl substitutions were rationally designed and synthesized. The structures of all derivatives were confirmed using different spectroscopic techniques including ¹H NMR, ¹³C NMR, Mass spectrometry, and elemental analysis. The tyrosinase inhibitory activities of all synthetic compounds exhibited IC₅₀ values in the range of 0.070 to > 100 μM. Structure-activity relationships showed that compounds 4f (R = 4-OH, IC₅₀ = 0.070 μM), 8f (R = 4-OH, IC₅₀ = 0.072 μM), and 19e (IC₅₀ = 0.19 μM) with para-OH substituent at the R position was found to be the most active members of all three tested series. Kinetic studies exhibited that compounds 4f, 8f, and 19e are mixed-type inhibitors. Furthermore, toxicity and cell-based anti-melanogenesis assessments were performed on the most potent derivatives and it was shown that 4f, 8f, and 19e had no toxicity at 8 µM and reduced the percent of melanin content to 68.43, 72.61, 73.47 at 8 μM, respectively. In silico analyses of absorption, distribution, metabolism, and excretion (ADME) profile of synthesized compounds showed that these molecules followed drug-likeness rules and acceptable predictive ADMET features. Results of the docking study were almost in line with biological results with ChemPLP values of 53.56 to 79.33. Also, the docking study showed the critical interactions of potent inhibitors with the active site of the enzyme which affects the potency of the synthesized hybrids. Based on molecular dynamic simulations, compound 4f exhibited pronounced interaction with the critical residues of the tyrosinase active site so that the indole ring participated in H-bond interaction with Gly281 and 4-hydroxy benzylidene recorded another H-bond interaction with Asp289 plus hydrophobic interactions with Phe292. Hydrazide linker also exhibited three H-bond interactions with His263 and Gly281.

Stressful Daylight: Differences in Diel Rhythmicity Between Albino and Pigmented Fish

In laboratory experiments, variously colored strains of animals, including those with albino phenotypes, are commonly used. The melanocortin theory suggests, however, that coloration phenotypes alter animal physiology and behavior. Animals with the albino phenotype show photoreceptor degradation associated with lowered visual accuracy, escape reactions, etc., presumably accompanied by prevailing nocturnal activity and lowered aggressiveness. This assumption was tested in small groups of albino and pigmented European catfish, Silurus glanis, during the diel cycle. The frequency of agonistic interactions was observed during mutual contests for shelters, and subsequently, blood plasma, brain, gill, and liver samples were collected to evaluate stress parameters. In an experimental arena with shelters, the light/dark rhythmicity of locomotor activity and aggressiveness of the two phenotypes were comparable; the peak was observed at night, and a lower peak was observed at dawn. In an experimental stream without shelters, the peak of locomotor activity occurred at night for only the pigmented phenotype. In the evaluation of 4 antioxidants and 1 oxidative stress indicator, representing a total of 15 indices, albino fish showed significant rhythmicity for 8 indices, whereas pigmented catfish showed significant rhythmicity for 5 indices. The production of blood stress parameters with the peak during the day occurred only in albino fish. A complex model was fitted with the aim of evaluating the links between behavioral and biochemical indices. Time periodicity was modeled using a sine wave and confirmed parallel courses of agonistic interactions in the catfish groups; the peak at dawn was associated with a 4.08-fold (conf. int. 3.53–4.7) increase in such interactions. The changes in glucose and superoxide dismutase concentrations varied with phenotype, while the effects of cortisol, lactate and catalase did not. In summary, the rhythmicity of locomotor activity and changes in the aggressiveness of catfish were influenced by shelter availability, and the effect of light-induced stress was more apparent in albino fish than in pigmented conspecific fish. The results suggested that laboratory-raised animals with pigmentation patterns naturally occurring in the wild show more reasonable values during experiments than those with an albino phenotype.

Clinical and Mutation Spectrum of Autosomal Recessive Non-Syndromic Oculocutaneous Albinism (nsOCA) in Pakistan: A Review

Oculocutaneous albinism (OCA) is an autosomal recessive syndromic and non-syndromic defect with deficient or a complete lack of the melanin pigment. The characteristics of OCA appears in skin, hair, and eyes with variable degree of pigmentation. Clinical manifestations of OCA include nystagmus, photophobia, reduced visual acuity, hypo-plastic macula, and iris trans-illumination. There are eight OCA types (OCA1–8) documented with non-syndromic characteristics. Molecular studies identified seven genes linked to the OCA phenotype (TYR, OCA2, TYRP1, SLC45A2, SLC24A5, C10orf11, and DCT) and one locus (OCA5) in consanguineous and sporadic albinism. The complications of OCA result in skin cancer and variable syndromes such as Hermansky–Pudlak syndrome (HPS) Chediak–Higashi syndrome (CHS). In the Pakistani population, autosomal recessive non-syndromic OCA is common and is associated with a large number of consanguineous families, and mutations in genes of non-syndromic types are reported. This review highlights the updates on the genetic mutation of OCA genes reported from Pakistani families. Several studies reported the genetic mutations in OCA1, OCA2, OCA3, OCA4, and OCA6 albinism in Pakistani families. A locus, OCA5, was also reported from the Pakistani population, but the gene has not been identified. A new type of OCA8 was identified due to the DCT gene mutation, and it is also reviewed here.

Efficient C-to-G Base Editing with Improved Target Compatibility Using Engineered Deaminase-nCas9 Fusions

CRISPR-guided DNA base editors (BEs) are potent genome editing tools in biotechnology and medicine. However, conventional cytosine and adenine BEs can only induce base transitions (C-to-T and A-to-G) and cannot induce base transversions. Recently, several C-to-G base editors (CGBEs) were generated and applied in human cells. By comparing them, we found that engineered deaminases rather than additional base excision repair proteins significantly improved the C-to-G efficiency. In addition, significant increase in C-to-G transversions in the GC context were determined by using rationally engineered eAID deaminase. The genome-targeting scope of CGBEs were further expanded by using SpRY Cas9 variant, which then successfully induced stop codon (TAC to TAG) to disrupt Tyr gene in mouse embryos. Taken together, these new CGBEs with engineered deaminase-nCas9 fusions broaden the BE toolsets for efficient gene modification and therapeutic applications.

Comparative study of stress responses, laterality and familiarity recognition between albino and pigmented fish

Oculocutaneous albinism is the result of a combination of homozygous recessive mutations that block the synthesis of the tyrosine and melatonin hormones. This disability is associated with physiological limitations, e.g., visual impairment expressed by lower visual acuity and movement perception, and eventually leads to acrophobia and/or photophobia, suggesting a potentially higher stress level associated with the behavioral responses of individuals with albinism to external stimuli compared to their pigmented conspecifics. However, in fish, differences in behavioral and/or physiological responses and stress levels between these phenotypes have been poorly documented. While acoustic perception of albino individuals is well known, the use of olfactory sensors for social communication, e.g., for the preference for familiar conspecifics, remains poorly understood. We performed two laboratory experiments with albino and pigmented European catfish Silurus glanis to observe: i) their behavioral and physiological responses to short-term stress induced by a combination of air exposure and novel environmental stressors and ii) their ability to use odor keys to recognize of familiar conspecifics and the influence of lateralization on this preference. In response to stress stimuli, albino fish showed higher movement activities and ventilatory frequencies and more often changed their swimming directions compared to their pigmented conspecifics. Blood plasma analysis showed significantly higher values of stress-, deprivation-, and emotional arousal-associated substances, e.g., glucose and lactate, as well as of substances released during intensive muscle activity of hyperventilation and tissue hypoxia, e.g., hemoglobin, mean corpuscular hemoglobin, erythrocytes, and neutrophil granulocytes. A preference test between environments with and without scented water showed the preference by both albino and pigmented catfish for environments with scent of familiar conspecifics, and both groups of fish displayed left-side lateralization associated with the observation of conspecifics and group coordination. The results tended to show higher physiological and behavioral responses of albinos to stress stimuli compared to the responses of their pigmented conspecifics, but the uses of olfactory sensors and lateralization were not differentiated between the two groups.

Recent advances in the design and discovery of synthetic tyrosinase inhibitors

Tyrosinase is a copper-containing metalloenzyme that is responsible for the rate-limiting catalytic step in the melanin biosynthesis and enzymatic browning. As a promising target, tyrosinase inhibitors can be used as skin whitening agents and food preservatives, thus having broad potential in the fields of food, cosmetics, agriculture and medicine. From 2015 to 2020, numerous synthetic inhibitors of tyrosinase have been developed to overcome the challenges of low efficacy and side effects. This review summarizes the enzyme structure and biological functions of tyrosinase and demonstrates the recent advances of synthetic tyrosinase inhibitors from the perspective of medicinal chemistry, providing a better understanding of the catalytic mechanisms and more effective tyrosinase inhibitors.

Characterization of Temperature-Dependent Kinetics of Oculocutaneous Albinism-Causing Mutants of Tyrosinase

Human tyrosinase (Tyr) is a glycoenzyme that catalyzes the first and rate-limiting step in melanin production, and its gene (TYR) is mutated in many cases of oculocutaneous albinism type 1 (OCA1). The mechanisms by which individual mutations contribute to the diverse pigmentation phenotype in patients with OCA1 have only began to be examined and remain to be delineated. Here, we analyze the temperature-dependent kinetics of wild-type Tyr (WT) and two OCA1B mutant variants (R422Q and P406L) using Michaelis–Menten and Van’t Hoff analyses. Recombinant truncated human Tyr proteins (residues 19–469) were produced in the whole insect Trichoplusia Ni larvae. Proteins were purified by a combination of affinity and size-exclusion chromatography. The temperature dependence of diphenol oxidase protein activities and kinetic parameters were measured by dopachrome absorption. Using the same experimental conditions, computational simulations were performed to assess the temperature-dependent association of L-DOPA and Tyr. Our results revealed, for the first time, that the association of L-DOPA with R422Q and P406L followed by dopachrome formation is a complex reaction supported by enthalpy and entropy forces. We show that the WT has a higher turnover number as compared with both R422Q and P406L. Elucidating the kinetics and thermodynamics of mutant variants of Tyr in OCA1B helps to understand the mechanisms by which they lower Tyr catalytic activity and to discover novel therapies for patients.

Pharmacologic manipulation of skin pigmentation

Skin complexion is among the most recognizable phenotypes between individuals and is mainly determined by the amount and type of melanin pigment deposited in the epidermis. Persons with dark skin complexion have more of a brown/black pigment known as eumelanin in their epidermis whereas those with fair skin complexions have less. Epidermal eumelanin acts as a natural sunblock by preventing incoming UV photons from penetrating into the skin and therefore protects against UV mutagenesis. By understanding the signaling pathways and regulation of pigmentation, strategies can be developed to manipulate skin pigmentation to improve UV resistance and to diminish skin cancer risk.

Enhancing Catecholase Activity of a Recombinant Human Tyrosinase Through Multiple Strategies

Background:

Tyrosinases are copper-containing enzymes that initiate the melanin synthesis. They catalyze the direct oxidation of L-tyrosine or L-DOPA into L-DOPAquinone.

Objectives:

In present study, we aimed to obtain a recombinant tyrosinase with enhanced catecholase activity through site-directed mutagenesis.

Materials and Methods:

The coding sequence of human tyrosinase along with native signal sequence was cloned into pET-28a (+). BL-21 was used as expression host and recombinant protein was purified by Ni-NTA resins. Site-directed mutagenesis was performed on M374 residue to achieve four mutants: M374D, M374T, M374K and M374R. Chloride ions (Cl^-) were removed from all solutions, and an extra amount of Cu²⁺ ions was added to recombinant tyrosinases by a novel technique during the purification process. Removal of Cl^- ions and addition of extra Cu²⁺ ions tripled catecholase activity of the recombinant protein. Therefore, all mutants were obtained under similar conditions.

Results:

Although all the mutants presented higher catecholase activity in comparison to the wild-type enzyme, a significant increase in catecholase activity of the M374D mutant was observed ‒ 13.2-fold. In silico modeling suggested that a de novo hydrogen bond occurs between side chain carboxyl oxygens of D374 and H367 in M374D. In the wild-type tyrosinase, the peptide oxygen atom of M374 is responsible for hydrogen bonding with H367.

Conclusions:

Our data suggests that M374D mutational variant has applications in different areas such as agriculture, industry, and medicine.

Identification of a candidate genetic variant for the Himalayan color pattern in dogs

Acromelanism is a temperature-dependent hypopigmentation pattern commonly manifested as the Himalayan coat color found in rabbits, rats, mice, minks, and gerbils, wherein the extreme "points" are dark and the torso is pale. It is known as the Siamese pattern in cats. Himalayan color is genetically determined by the allelic variant c^h of the locus C, later identified as the tyrosinase gene TYR. The tyrosinase functions at the initial steps of melanin production, and alteration of its activity by sequence changes results in pigmentation defects in vertebrates. The presence of acromelanism in dogs has not been described until now. We analyzed a DNA sample of a dachshund with a unique coat color resembling the Himalayan type. Sequencing of the coding part of the TYR gene from the proband revealed a homozygous variant (c.230G > A) in exon 1, leading to an amino acid substitution (p.R77Q) in a conserved region of the protein. The proband's mother, which is black-and-tan, is a heterozygous carrier of the c.230A allele, while none of the 210 dogs of different breeds, unrelated to the proband, carried the c.230A allele. These results suggest that the identified sequence variant is likely the cause of the Himalayan coloration of the proband.

Microwave enhanced synthesis of halogenated derivatives of L-tyrosine labeled with deuterium in aromatic ring

Three halogenated derivatives of L-tyrosine, selectively labeled with deuterium in aromatic ring, i.e., 3′-fluoro-[5′-2H]-, 3′-chloro-[5′-2H]-, and 3′-iodo-[2′,5′-2H2]-L-tyrosine, were synthesized using microwave assisted acid-catalyzed isotope exchange between 3′-fluoro-, 3′-chloro- and 3′-iodo-L-tyrosine and heavy water. The degree of deuterium incorporation was confirmed by 1H NMR spectroscopy. The spectroscopic data indicate that isotope exchange depends on the method of heating and the power of microwaves. The deuterium enrichment of 3′-fluoro-[5′-2H]- and 3′-chloro-[5′-2H]-L-tyrosine amounted to 70% and 60%, respectively, while for 3′-iodo-[2′,5′-2H2]-L-tyrosine this value was about 50% and 95% for the 2′- and 5′-position. The isotopomers were obtained in good chemical yields of 50–70%.

The metabolic profile of Asinara (albino) and Sardo donkeys (pigmented) (Equus asinus L., 1758) points to unequivocal breed assignment of individuals

This study pointed to explore if variations in circulating levels of metabolites in the blood stream of no. 25 feral donkeys occur in view of the different coat color between specimens of Asinara (albino, no. 8) vs. Sardo (dun-grey, no. 17) breed. All individuals involved in this investigation are living in the nature, at Mediterranean latitudes and roam in the same areas all over the National Park of Capo Caccia, where they feed on spontaneous vegetation sources. The study was conducted during the positive photoperiod of the boreal hemisphere (peak in the month of June, 2019) to maximize the effect of exposure to the natural sun radiation and thus elicit the coping ability of albino (Asinara) in comparison with pigmented donkeys (Sardo). The biochemical profile of all donkeys was used in a Discriminant Analysis (DA) to explore if circulating levels of metabolites could point to metabolic markers for breed assignment of individuals following a canonical discriminant analysis (CANDISC). The biochemical investigation included also the determination of the circulating Vitamin E (alpha tocopherol, α-TOH), as an essential biologically active compound involved in antioxidant mechanisms, and its respective status (circulating α-TOH to total triglycerides and total cholesterol ratio). In the CANDISC, the distance between the two breeds was not significant. However, it pointed to different metabolites (UREA, total protein, total triglycerides, Zn) capable of describing biochemical patterns on each respective breed (Asinara vs. Sardo). The multivariate analysis DA carried out using 22 metabolites correctly assigned individuals to the two breeds in the 100% of cases. In view of such metabolic background, circulating α-TOH found in the bloodstream of Asinara vs. Sardo donkeys under free grazing conditions turned out to reach similar values (2.114 vs. 1.872 µg/ml, respectively, p = 0.676). It is worth noting that significant differences were observed as to circulating lactate dehydrogenase (LDH, p = 0.022) levels, in association with increased creatine phosphokinase (CPK, p = 0.076), both above the upper limit of the physiological range reported in other donkey breeds, and found in the totality of Asinara (albino) donkeys solely, still apparently clinically healthy.

De novo assembly transcriptome analysis reveals the preliminary molecular mechanism of pigmentation in juveniles of the hard clam Mercenaria mercenaria

Color plays a vital function in camouflage, sexual selection, immunity, and evolution. Mollusca possess vivid shell colors and pigmentation starts at the juvenile stage. The hard clam Mercenaria mercenaria is a widely cultivated bivalve of high economic value. To explore the molecular mechanism of pigmentation in juvenile clams, here, we performed RNA-Seq analysis on non-pigmented, white, and red M. mercenaria specimens. Clean reads were assembled into 358,285 transcripts and 149,234 unigenes, whose N50 lengths were 2107 bp and 1567 bp, respectively. Differentially expressed genes were identified and analyzed for KEGG enrichment. "Melanoma/Melanogenesis", "ABC transporters", and "Porphyrin and chlorophyll metabolism" pathways appeared to be associated with pigmentation. Pathways related to carotenoid metabolism seemed to also play a vital role in pigmentation in juveniles. Our results provide new insights into the formation of shell color in juvenile hard clams.

The expression of miR-129-5p and its target genes in the skin of goats

Coat color is one of the major quality traits of animals, and miR-129-5p acts as an important regulator for melanin biosynthesis in mammals. In this study, real-time PCR and western blotting were used to examine the expression of miR-129-5p and its targets genes in the skin of different coat color goats. The results showed that the expression of miR-129-5p in the skin samples of Inner Mongolia cashmere goats (IMCG) was higher than that of Dazu black goat (DBG). Also, the target genes (tyrosinase (TYR), frizzled 6 (FZD6) and glycogen synthase kinase 3β (GSK3β)) of miR-129-5p was highly expressed in the skin samples of DBG. The expression of miR-129-5p firstly increased and then decreased with age in F1 hybrid generation of DBG and IMCG. In addition, the expression of TYR decreased with age, while the expression of MITF increased with age but then decreased. The expression of FZD6 and GSK3β in the skin samples of F1 of different ages were irregular. Our results indicated that miR-129-5p mainly affects the formation of coat color of goats by decreasing the expression of TYR. This study suggests that miR-129-5p can act as a suppressor in the formation of coat color to lay the foundation for studying the effect of miR-129-5p on melanin synthesis.

A genome-wide scan study identifies a single nucleotide substitution in the tyrosinase gene associated with white coat colour in a red deer (Cervus elaphus) population

Background

Red deer with very pale coat colour are observed sporadically. In the red deer (Cervus elaphus) population of Reinhardswald in Germany, about 5% of animals have a white coat colour that is not associated with albinism. In order to facilitate the conservation of the animals, it should be determined whether and to what extent brown animals carry the white gene. For this purpose, samples of one white hind and her brown calf were available for whole genome sequencing to identify the single nucleotide polymorphism(s) responsible for the white phenotype. Subsequently, samples from 194 brown and 11 white animals were genotyped.

Results

Based on a list of colour genes of the International Federation of Pigment Cell Societies, a non-synonymous mutation with exchange of a glycine residue at position 291 of the tyrosinase protein by arginine was identified as the cause of dilution of the coat colour. A gene test led to exactly matching genotypes in all examined animals. The study showed that 14% of the brown animals carry the white gene. This provides a simple and reliable way of conservation for the white animals. However, results could not be transferred to another, unrelated red deer population with white animals. Although no brown animals with a white tyrosinase genotype were detected, the cause for the white colouring in this population was different.

Conclusions

A gene test for the conservation of white red deer is available for the population of the Reinhardswald. While mutations in the tyrosinase are commonly associated with oculocutaneous albinism type 1, the amino acid exchange at position 291 was found to be associated with coat colour dilution in Cervus elaphus.

Potential adverse effect of tyrosinase inhibitors on teleosts:A review

Coloration plays a crucial role in the social communication and survival of organisms. Multidisciplinary studies have been conducted to elucidate the correlation between coloration and melanin biosynthesis (referred as melanogenesis). The multi-copper enzyme tyrosinase catalyzes the first two steps of melanogenesis for coloration in teleosts. Due to the increasing demand of tyrosinase inhibitors for the production of skin whitening cosmetics, hypopigmentation pharmaceuticals, and anti-browning agents, a large number of natural and synthetic inhibitors have been developed over the past few decades. Although a number of previous studies have focused on human use and toxicity, such as the increased cytotoxic effects of ROS-generating compounds, their ecotoxicological impacts on aquatic organisms are still poorly understood. Hence, the focus of the present review is to describe the role of coloration in teleosts as well as potential ecotoxicological effects elicited by exposure to tyrosinase inhibitors. Furthermore, this review introduces our recently registered adverse outcome pathway (AOP) related to tyrosinase inhibition and population decline in teleosts.

Linking Genes to Molecules in Eukaryotic Sources: An Endeavor to Expand Our Biosynthetic Repertoire

The discovery of natural products continues to interest chemists and biologists for their utility in medicine as well as facilitating our understanding of signaling, pathogenesis, and evolution. Despite an attenuation in the discovery rate of new molecules, the current genomics and transcriptomics revolution has illuminated the untapped biosynthetic potential of many diverse organisms. Today, natural product discovery can be driven by biosynthetic gene cluster (BGC) analysis, which is capable of predicting enzymes that catalyze novel reactions and organisms that synthesize new chemical structures. This approach has been particularly effective in mining bacterial and fungal genomes where it has facilitated the discovery of new molecules, increased the understanding of metabolite assembly, and in some instances uncovered enzymes with intriguing synthetic utility. While relatively less is known about the biosynthetic potential of non-fungal eukaryotes, there is compelling evidence to suggest many encode biosynthetic enzymes that produce molecules with unique bioactivities. In this review, we highlight how the advances in genomics and transcriptomics have aided natural product discovery in sources from eukaryotic lineages. We summarize work that has successfully connected genes to previously identified molecules and how advancing these techniques can lead to genetics-guided discovery of novel chemical structures and reactions distributed throughout the tree of life. Ultimately, we discuss the advantage of increasing the known biosynthetic space to ease access to complex natural and non-natural small molecules.

Human Tyrosinase: Temperature-Dependent Kinetics of Oxidase Activity

Human tyrosinase (Tyr) is involved in pigment biosynthesis, where mutations in its corresponding gene TYR have been linked to oculocutaneous albinism 1, an autosomal recessive disorder. Although the enzymatic capabilities of Tyr have been well-characterized, the thermodynamic driving forces underlying melanogenesis remain unknown. Here, we analyze protein binding using the diphenol oxidase behavior of Tyr and van ’t Hoff temperature-dependent analysis. Recombinant Tyr was expressed and purified using a combination of affinity and size-exclusion chromatography. Michaelis-Menten constants were measured spectrophotometrically from diphenol oxidase reactions of Tyr, using L-3,4-dihydroxyphenylalanine (L-DOPA) as a substrate, at temperatures: 25, 31, 37, and 43 °C. Under the same conditions, the Tyr structure and the L-DOPA binding activity were simulated using 3 ns molecular dynamics and docking. The thermal Michaelis-Menten kinetics data were subjected to the van ‘t Hoff analysis and fitted with the computational model. The temperature-dependent analysis suggests that the association of L-DOPA with Tyr is a spontaneous enthalpy-driven reaction, which becomes unfavorable at the final step of dopachrome formation.

Efficient base editing with high precision in rabbits using YFE-BE4max

Cytidine base editors, composed of a cytidine deaminase fused to Cas9 nickase, enable efficient C-to-T conversion in various organisms. However, current base editors suffer from severe trade-off between editing efficiency and precision. Here, based on rationally mutated cytidine deaminase domain, we develop a new base editor, YFE-BE4max, effectively narrow the editing width to as little as approximately three nucleotides while maintaining high efficiency in rabbits. Moreover, YFE-BE4max successfully mediated the Tyr p. Q68Stop and Lmna p. G607G mutation in F0 rabbit with high efficiency and precision, which precisely recapitulates the pathological features of human OCA1 and HGPS, respectively. Collectively, YFE-BE4max system provide promising tools to perform efficient base editing with high precision in rabbits and enhances its capacity to precisely model human diseases.

Insights Into the Explication of Potent Tyrosinase Inhibitors with Reference to Computational Studies

Background:

Pigment melanin has primarily a photo defensive role in human skin, its unnecessary production and irregular distribution can cause uneven skin tone ultimately results in hyper pigmentation. Melanin biosynthesis is initiated by tyrosine oxidation through tyrosinase, the key enzyme for melanogenesis. Not only in humans, tyrosinase is also widely distributed in plants and liable for browning of vegetables and fruits. Search for the inhibitors of tyrosinase have been an important target to facilitate development of therapies for the prevention of hyperpigmentary disorders and an undesired browning of vegetables and fruits.

Methods:

Different natural and synthetic chemical compounds have been tested as potential tyrosinase inhibitors, but the mechanism of inhibition is not known, and the quest for information regarding interaction between tyrosinase and its inhibitors is one of the recent areas of research. Computer based methods hence are useful to overcome such issues. Successful utilization of in silico tools like molecular docking simulations make it possible to interpret the tyrosinase and its inhibitor’s intermolecular interactions and helps in identification and development of new and potent tyrosinase inhibitors.

Results:

The present review has pointed out the prominent role of computer aided approaches for the explication of promising tyrosinase inhibitors with a focus on molecular docking approach. Highlighting certain examples of natural compounds whose antityrosinase effects has been evaluated using computational simulations.

Conclusion:

The investigation of new and potent inhibitors of tyrosinase using computational chemistry and bioinformatics will ultimately help millions of peoples to get rid of hyperpigmentary disorders as well as browning of fruits and vegetables.

Expanded targeting scope and enhanced base editing efficiency in rabbit using optimized xCas9(3.7)

Evolved xCas9(3.7) variant with broad PAM compatibility has been reported in cell lines, while its editing efficiency was site-specific. Here, we show that xCas9(3.7) can recognize a broad PAMs including NGG, NGA, and NGT, in both embryos and Founder (F0) rabbits. Furthermore, the codon-optimized xCas9-derived base editors, exBE4 and exABE, can dramatically improve the base editing efficiencies in rabbit embryos. Our results demonstrated that the optimized xCas9 with expanded PAM compatibility and enhanced base editing efficiency could be used for precise gene modifications in organisms.

The physiology of melanin deposition in health and disease

Eumelanin is the major pigment responsible for human skin color. This black/brown pigment is localized in membrane-bound organelles (melanosomes) found in specialized cells (melanocytes) in the basal layer of the epidermis. This review highlights the steps involved in melanogenesis in the epidermis and the disorders in skin pigmentation that occur when specific steps critical for this process are defective. Melanosomes, which contain tyrosinase, a major enzyme involved in melanin synthesis, develop through a series of steps in the melanocyte. They are donated from the melanocyte dendrites to the surrounding keratinocytes in the epidermis. In the keratinocytes, the melanosomes are found singly or packaged into groups, and as the keratinocytes move upward in the epidermis, the melanosomes start to degrade. This sequence of events is critical for melanin pigmentation in the skin and can be influenced by genetic, hormonal, and environmental factors, which all play a role in levels of melanization of the epidermis. The effects these factors have on skin pigmentation can be due to different underlying mechanisms involved in the melanization process leading to either hypo- or hyperpigmentary disorders. These disorders highlight the importance of mechanistic studies on the specific steps involved in the melanization process.

TYR Gene in Llamas: Polymorphisms and Expression Study in Different Color Phenotypes

Tyrosinase, encoded by TYR gene, is an enzyme that plays a major role in mammalian pigmentation. It catalyzes the oxidation of L-dihydroxy-phenylalanine (DOPA) to DOPA quinone, a precursor of both types of melanin: eumelanin and pheomelanin. TYR is commonly known as the albino locus since mutations in this gene result in albinism in several species. However, many other TYR mutations have been found to cause diluted phenotypes, like the Himalayan or chinchilla phenotypes in mice. The llama (Lama glama) presents a wide variety of coat colors ranging from non-diluted phenotypes (eumelanic and pheomelanic), through different degrees of dilution, to white. To investigate the possible contribution of TYR gene to coat color variation in llamas, we sequenced TYR exons and their flanking regions and genotyped animals with diluted, non-diluted, and white coat, including three blue-eyed white individuals. Moreover, we analyzed mRNA expression levels in skin biopsies by qPCR. TYR coding region presented nine SNPs, of which three were non-synonymous, c.428A > G, c.859G > T, and c.1490G > T. We also identified seven polymorphisms in non-coding regions, including two microsatellites, an homopolymeric repeat, and five SNPs: one in the promoter region (c.1-26C > T), two in the 3'-UTR, and two flanking the exons. Although no complete association was found between coat color and SNPs, c.1-26C > T was partially associated to diluted phenotypes. Additionally, the frequency of the G allele from c.428A > G was significantly higher in white compared to non-diluted. Results from qPCR showed that expression levels of TYR in white llamas were significantly lower (p < 0.05) than those in diluted and non-diluted phenotypes. Screening for variation in regulatory regions of TYR did not reveal polymorphisms that explain such differences. However, data from this study showed that TYR expression levels play a role in llama pigmentation.

Improved base editor for efficient editing in GC contexts in rabbits with an optimized AID-Cas9 fusion

Cytidine base editors, which are composed of a cytidine deaminase fused to clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (Cas9) nickase, enable the efficient conversion of the C·G base pair to T·A in various organisms. However, the currently used rat apolipoprotein B mRNA-editing enzyme, catalytic polypeptide 1(rA1)-based BE3 is often inefficient in target Cs that are immediately downstream of a G (GC context). Here, we observed that, with an 11-nt editing window, an optimized activation-induced cytidine deaminase (AID)-Cas9 fusion can efficiently convert C to T in a variety of sequence contexts in rabbits. Strikingly, the enhanced AID-Cas9 fusion (eAID-BE4max) has significant effectiveness of inducing Tyr p.R299H mutation in GC contexts (from 16.67 to 83.33%) in comparison with BE3 in founder rabbits. Furthermore, the engineered AID-Cas9 variants were produced with reduced bystander activity [eAID (N51G)-BE4max] and increased genome-targeting scope (eAID-NG-BE4max). Overall, this work provides a series of improved tools that were generated using optimized AID-Cas9 fusions and associated engineered variants that can be used for efficient and versatile C-to-T base editing, especially in GC contexts.-Liu, Z., Shan, H., Chen, S., Chen, M., Zhang, Q., Lai, L., Li, Z. Improved base editor for efficient editing in GC contexts in rabbits with an optimized AID-Cas9 fusion.

Polymorphism in MC1R, TYR and ASIP genes in different colored feather chickens

Coat color genetics successfully adapted and applied to different animal species, which provides a good demonstration of the concept of comparative genetics. In this study, we sequenced 945 bp fragments of melanocortin 1 receptor (MC1R) gene, 421 bp fragments of exon 1 of tyrosinase (TYR) gene and 266 bp fragments of exon 3 of agouti signaling protein (ASIP) gene for 250 individuals with five plumage color patterns. We detected a total of three SNPs (T398A, T637C, and G920C) in MC1R and built six haplotypes (H1-H6) based on the three SNPs. H5 and H6 haplotypes were mainly concentrated in white and grey chicken. And diplotypes H2H3 occurred in white feather and black-speckle feather with the same frequency. Moreover, a total of three SNPs (C47G, T120C, and T172C) in TYR were found and built six haplotypes (P1-P6) based on the three SNPs. Among them, haplotype P2, P3 and P6 were not occurred in black chicken, the diplotypes P1P6 and P4P6 were only distributed in white, gray and black-speckled feather. We only detected one SNP (T168C) in ASIP gene and found that genotype TT was advantage genotype in the different plumage color groups of chickens. Collectively, our study suggested an association between plumage color and genetic variation of MC1R, TYR and ASIP in chicken.

Conversations with Ray Guillery on albinism: linking Siamese cat visual pathway connectivity to mouse retinal development

In albinism of all species, perturbed melanin biosynthesis in the eye leads to foveal hypoplasia, retinal ganglion cell misrouting, and, consequently, altered binocular vision. Here, written before he died, Ray Guillery chronicles his discovery of the aberrant circuitry from eye to brain in the Siamese cat. Ray's characterization of visual pathway anomalies in this temperature sensitive mutation of tyrosinase and thus melanin synthesis in domestic cats opened the exploration of albinism and simultaneously, a genetic approach to the organization of neural circuitry. I follow this account with a remembrance of Ray's influence on my work. Beginning with my postdoc research with Ray on the cat visual pathway, through my own work on the mechanisms of retinal axon guidance in the developing mouse, Ray and I had a continuous and rich dialogue about the albino visual pathway. I will present the questions Ray posed and clues we have to date on the still-elusive link between eye pigment and the proper balance of ipsilateral and contralateral retinal ganglion cell projections to the brain.

Comprehensive Review of the Genetics of Albinism

Introduction

It is important to understand albinism, since it is a disorder associated with visual impairment, predisposition to malignant melanomas, and social stigma. The main objective of this article is to review the genetics and biologic mechanisms of the non-syndromic albinism subtypes and to describe associated clinical manifestations. We also discuss research on its treatments.

Methods

A review of the published literature on albinism subtypes was performed, spanning basic laboratory research, published case reports, and experiences of people with albinism.

Results

Clear progress has been made in comprehending the causes of albinism; research has shed light on the complexity of the disorder and has led to the molecular classification of subtypes.

Discussion

Despite the increase in knowledge with regards to albinism, gaps still exist. It is important to continue the pursuit of unraveling the mechanism of the disorder and to monitor the frequency of the subtypes worldwide in order to aid in the development of treatments. Furthermore, disseminating knowledge of albinism is crucial for future progress.

Implications for practitioners

Albinism is a disorder characterized by hypopigmentation of the hair, skin, and eyes, with accompanying ocular abnormalities that remain relatively stable throughout life. The disorder is defined by a spectrum of pigmentation where albinism is more evident among individuals of dark complexion than their lighter-pigmented peers. Patients with albinism require protection against sun exposure and special resources to address visual impairments. When albinism patients are diagnosed and properly accommodated, they generally report a positive quality of life.

Isotope effects in the tyrosinase catalysed hydroxylation of l-tyrosine methyl derivatives

To investigate isotope effects in the hydroxylation of [3',5'-²H₂]-α-methyl- and [3',5'-²H₂]-N-methyl-l-tyrosine, they were synthesised using acid catalysed isotope exchange at high temperature. The kinetic and solvent deuterium isotope effects on V_max and V_max/K_m parameters of tyrosinase in its action on methylated derivatives of l-tyrosine were determined using the non-competitive spectrophotometric method. Lineweaver-Burk plots were used to consider the inhibition type of O-methyl-l-tyrosine, revealing that it is an uncompetitive inhibitor of tyrosinase.

Highly efficient RNA-guided base editing in rabbit

Cytidine base editors (CBEs) and adenine base editors (ABEs), composed of a cytidine deaminase or an evolved adenine deaminase fused to Cas9 nickase, enable the conversion of C·G to T·A or A·T to G·C base pair in organisms, respectively. Here, we show that BE3 and ABE7.10 systems can achieve a targeted mutation efficiency of 53-88% and 44-100%, respectively, in both blastocysts and Founder (F0) rabbits. Meanwhile, this strategy can be used to precisely mimic human pathologies by efficiently inducing nonsense or missense mutations as well as RNA mis-splicing in rabbit. In addition, the reduced frequencies of indels with higher product purity are also determined in rabbit blastocysts by BE4-Gam, which is an updated version of the BE3 system. Collectively, this work provides a simple and efficient method for targeted point mutations and generation of disease models in rabbit.

Downregulation of α-Melanocyte-Stimulating Hormone-Induced Activation of the Pax3-MITF-Tyrosinase Axis by Sorghum Ethanolic Extract in B16F10 Melanoma Cells

Ultraviolet irradiation-induced hyperpigmentation of the skin is associated with excessive melanin production in melanocytes. Tyrosinase (TYR) is a key enzyme catalyzing the rate-limiting step in melanogenesis. TYR expression is controlled by microphthalmia-associated transcription factor (MITF) expression. Sorghum is a cereal crop widely used in a variety of foods worldwide. Sorghum contains many bioactive compounds and is beneficial to human health. However, the effects of sorghum in anti-melanogenesis have not been well characterized. In this study, the biological activity of sorghum ethanolic extract (SEE) on α-melanocyte-stimulating hormone (α-MSH)-induced TYR expression was evaluated in B16F10 melanoma cells. SEE attenuated α-MSH-induced TYR gene promoter activity through the downregulation of the transcription factor MITF. We found that paired box gene 3 (Pax3) contributes to the maximal induction of MITF gene promoter activity. Further analysis demonstrated that SEE inhibited α-MSH-induced Pax3 expression. The collective results indicate that SEE attenuates α-MSH-induced TYR expression through the suppression of Pax3-mediated MITF gene promoter activity. Targeting the Pax3-MITF axis pathway could be considered a potential strategy to increase the efficacy of anti-melanogenesis.

Molecular cloning and expression analysis of tyr and tyrp1 genes in normal and albino yellow catfish Tachysurus fulvidraco

The full-length complementary DNA of two genes related to vertebrate albinism, the tyrosinase gene tyr and tyrosinase-related protein 1 gene tyrp1, were cloned and analysed from normal and albino yellow catfish Tachysurus fulvidraco. The open reading frames (ORF) of tyr and tyrp1 encode putative peptides of 533 and 526 amino acids (amino-acid), both of which possess two conserved copper binding sites. The homologous identities of deduced amino-acid sequences showed that both Tyr and Tyrp1 of T. fulvidraco share considerable similarity with that of channel catfish Ictalurus punctatus. Both tyr and tyrp1 were expressed in a wide range of adult tissues. Tyr gene had the highest expression level in the brain of both normal and albino T. fulvidraco. Tyrp1 had the highest expression level in the skin of normal groups, and the fin of albino groups. The messenger (m)RNA expressions of tyr and tyrp1 were detectable at different early developmental stages and varied with embryonic and larval growth. Tyr and tyrp1 mRNA have obvious tissue specificity both in normal and albino T. fulvidraco and higher expression levels were detected in the normal group revealing that tyr and tyrp1 may have an important role in pigmentation. These results will provide useful data for understanding the molecular mechanism of melanin formation and the occurrence of albinism in T. fulvidraco.

Oculocutaneous albinism type 1: link between mutations, tyrosinase conformational stability, and enzymatic activity

Oculocutaneous albinism type 1 (OCA1) is an autosomal recessive disorder caused by mutations in the tyrosinase gene. Two subtypes of OCA1 have been described: severe OCA1A with complete absence of tyrosinase activity and less severe OCA1B with residual tyrosinase activity. Here, we characterize the recombinant human tyrosinase intramelanosomal domain and mutant variants, which mimic genetic changes in both subtypes of OCA1 patients. Proteins were prepared using site-directed mutagenesis, expressed in insect larvae, purified by chromatography, and characterized by enzymatic activities, tryptophan fluorescence, and Gibbs free energy changes. The OCA1A mutants showed very low protein expression and protein yield and are enzymatically inactive. Mutants mimicking OCA1B were biochemically similar to the wild type, but exhibited lower specific activities and protein stabilities. The results are consistent with clinical data, which indicates that OCA1A mutations inactivate tyrosinase and result in severe phenotype, while OCA1B mutations partially inactivate tyrosinase and result in OCA1B albinism.

Isotope effects in mechanistic studies of l-tyrosine halogen derivatives hydroxylation catalyzed by tyrosinase

The kinetic (KIE) and solvent (SIE) isotope effect methods were used to investigate the mechanism of enzymatic hydroxylation of halogenated derivatives of l-tyrosine to l-DOPA catalyzed by the enzyme tyrosinase (EC 1.14.18.1). The values of deuterium KIE and SIE were obtained using the non-competitive method with spectrophotometric measurements. The Lineweaver–Burk plots were used for determination of the inhibition mode of 3′-iodo-l-tyrosine. Based upon kinetic effects values the mechanism of action of enzyme tyrosinase was proposed.

Candidate Gene Identification of Feed Efficiency and Coat Color Traits in a C57BL/6J × Kunming F2 Mice Population Using Genome-Wide Association Study

Feed efficiency (FE) is a very important trait in livestock industry. Identification of the candidate genes could be of benefit for the improvement of FE trait. Mouse is used as the model for many studies in mammals. In this study, the candidate genes related to FE and coat color were identified using C57BL/6J (C57) × Kunming (KM) F2 mouse population. GWAS results showed that 61 and 2 SNPs were genome-wise suggestive significantly associated with feed conversion ratio (FCR) and feed intake (FI) traits, respectively. Moreover, the Erbin, Msrb2, Ptf1a, and Fgf10 were considered as the candidate genes of FE. The Lpl was considered as the candidate gene of FI. Further, the coat color trait was studied. KM mice are white and C57 ones are black. The GWAS results showed that the most significant SNP was located at chromosome 7, and the closely linked gene was Tyr. Therefore, our study offered useful target genes related to FE in mice; these genes may play similar roles in FE of livestock. Also, we identified the major gene of coat color in mice, which would be useful for better understanding of natural mutation of the coat color in mice.

Identification and characterization of the tyrosinase gene (TYR) and its transcript variants (TYR_1 and TYR_2) in the crab-eating macaque (Macaca fascicularis)

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis and is encoded by the tyrosinase (TYR) gene. Previous studies demonstrated that mutations in TYR could lead to oculocutaneous albinism type 1 (OCA1) owing to the failure of melanin formation. Although a previous study found that albinism in the rhesus monkey was derived from a mutation in TYR, the identification and characterization of this gene in non-human primates has not been achieved thus far. Thus, using the rapid amplification of cDNA ends (RACE) and internal reverse transcription PCR (RT-PCR) we identified the full-length sequence of TYR in the crab-eating macaque, and two different transcript variants (TYR_1 and TYR_2). While TYR_1 comprised five exons and its coding sequence was highly similar to that of humans, TYR_2 comprised four exons and was generated by a third-exon-skipping event. Interestingly, these two transcripts were also present in the African green monkey (Old World monkey) and the common marmoset (New World monkey). Deduced amino acid sequence analyses revealed that TYR_2 had a shorter C-terminal region than TYR_1 owing to the exon-skipping event. Thus, the present study is the first to identify and characterize a full-length TYR gene in a non-human primate, while the further validation of the third-exon-skipping in TYR indicates that this event is well conserved in the primate lineage. Therefore, this study provides useful and important information for the study of albinism using non-human primate models.