Molecular basis of albinism in the rhesus monkey

Sequence analysis of the tyrosinase (TYR) coding region from one albino rhesus monkey (Macaca mulatta) family revealed that the two monkeys with phenotype similar to human TYR-negative oculocutaneous albinism (OCA) were homozygous for a missense mutation (S184TER) in exon 1 at codon 184. The offspring of one of the albino monkey (''Kangkang'') are all heterozygous for the S184TER mutation, but the S184TER mutation was not observed in 93 control individuals. We conclude that the point mutation is responsible and sufficient to generate the albino rhesus monkey phenotype. The rough age of the S184TER nonsense mutation may be about 0.8 million years using a rate of 0.16% per million years. (C) 2000 Elsevier Science B.V. All rights reserved.

Co-inheritance of two rare genodermatoses (Papillon Lefevre syndrome and Oculocutaneous Albinism Type 1) in two families

The co-occurrence of two rare recessive genetic conditions in apparently unrelated individuals or families is extremely rare. Two geographically distant and apparently unrelated families were identified in which individuals were simultaneously affected by two rare recessive mendelian syndromes, Papillon-Lefevre syndrome and type 1 oculocutaneous albinism. The families were tested for mutations in the causative genes, cathepsin C (CTSC) and tyrosinase (TYR), respectively, by direct sequencing. To assess the relationship of the two families, both families were tested for polymorphisms at eight microsatellite markers spanning both CTSC and TYR loci. Independent mutations (c.318-1G-->A and c.817G-->C/p.W272C) were identified in CTSC and TYR, respectively, that were shared by the affected individuals in both families. The two affected genes lie close together on chromosome bands 11q14.2-14.3, and studies with linked genetic markers suggested that the families shared a small chromosomal segment carrying both mutations that had been transmitted intact from a remote common ancestor. The co-occurrence of the two rare diseases in multiple families depends on their shared chromosomal location, but not on any shared pathogenic mechanism.

A nonsense mutation in the tyrosinase gene causes albinism in water buffalo

Background: Oculocutaneous albinism (OCA) is an autosomal recessive hereditary pigmentation disorder affecting humans and several other animal species. Oculocutaneous albinism was studied in a herd of Murrah buffalo to determine the clinical presentation and genetic basis of albinism in this species.Results: Clinical examinations and pedigree analysis were performed in an affected herd, and wild-type and OCA tyrosinase mRNA sequences were obtained. The main clinical findings were photophobia and a lack of pigmentation of the hair, skin, horns, hooves, mucosa, and iris. The results of segregation analysis suggest that this disease is acquired through recessive inheritance. In the OCA buffalo, a single-base substitution was detected at nucleotide 1,431 (G to A), which leads to the conversion of tryptophan into a stop codon at residue 477.Conclusion: This premature stop codon produces an inactive protein, which is responsible for the OCA buffalo phenotype. These findings will be useful for future studies of albinism in buffalo and as a possible model to study diseases caused by a premature stop codon.

A review of complete albinism in bats with five new cases from Brazil

Complete albinism is a rare phenomenon that occurs in all vertebrate groups. In bats, albinism has been recorded in several species but this information has not previously been reviewed in detail nor has there been an analysis of its importance. In this study, cases of albinism from the literature are checked and new cases are presented. Complete albinism in bats is documented in eight families, 38 species, and at least 64 individuals (47.4% female female and 52.6% males; n = 38). of these, 39 individuals were observed and/or captured in sheltered roosts, such as caves (51.3%), mines and galleries (20.5%), buildings (17.9%), and hollow-trees and bird boxes (7.7%). Only one albino bat (2.6%) was captured in an external roost (foliage). This individual is the fruit bat, Artibeus planirostris, which is recorded here for the first time. Information on four additional cases of albino individuals of the common vampire bat, Desmodus rotundus, is also presented. It is suggested that sheltered roosts favour survival of albino bars, offering protection against sunlight, water loss, and visually hunting predators.

Woakes' syndrome and albinism

Nasal polyposis is a very common and multifactorial disease. Whereas eosinophil-dominated polyps often are sensitive to anti-inflammatory treatment like corticosteroids, the therapy of polyps without eosinophils is more difficult and disappointing. We report the clinical course of a 29-year-old albino patient suffering from a extreme manifestation of Woakes' syndrome, which is characterized by severe recurrent nasal polyps, often without eosinophils on histological examination and with broadening of the nose. In this case, the recurrent fibrotic polyps without eosinophils were resistant to conventional medical and surgical treatment and required further treatment with radiotherapy with awareness of all possible future sequelae. The pathoetiology and treatment of Woakes' syndrome as well as of albinism were discussed.

Albinism in the American mink (Neovison vison) is associated with a tyrosinase nonsense mutation

Albino phenotypes are documented in various species including the American mink. In other species the albino phenotypes are associated with tyrosinase (TYR) gene mutations; therefore TYR was considered the candidate gene for albinism in mink. Four microsatellite markers were chosen in the predicted region of the TYR gene. Genotypes at the markers Mvi6025 and Mvi6034 were found to be associated with the albino phenotype within an extended half-sib family. A BAC clone containing Mvi6034 was mapped to chromosome 7q1.1-q1.3 by fluorescent in situ hybridization. Subsequent analysis of genomic TYR sequences from wild-type and albino mink samples identified a nonsense mutation in exon 1, which converts a TGT codon encoding cysteine to a TGA stop codon (c.138T>A, p.C46X; EU627590). The mutation truncates more than 90% of the normal gene product including the putative catalytic domains. The results indicate that the nonsense mutation is responsible for the albino phenotype in the American mink.

The ocular albinism type 1 gene product is a membrane glycoprotein localized to melanosomes.

Ocular albinism type 1 (OA1) is an inherited disorder characterized by severe reduction of visual acuity, photophobia, and retinal hypopigmentation. Ultrastructural examination of skin melanocytes and of the retinal pigment epithelium reveals the presence of macromelanosomes, suggesting a defect in melanosome biogenesis. The gene responsible for OA1 is exclusively expressed in pigment cells and encodes a predicted protein of 404 aa displaying several putative transmembrane domains and sharing no similarities with previously identified molecules. Using polyclonal antibodies we have identified the endogenous OA1 protein in retinal pigment epithelial cells, in normal human melanocytes and in various melanoma cell lines. Two forms of the OA1 protein were identified by Western analysis, a 60-kDa glycoprotein and a doublet of 48 and 45 kDa probably corresponding to unglycosylated precursor polypeptides. Upon subcellular fractionation and phase separation with the nonionic detergent Triton X-114, the OA1 protein segregated into the melanosome-rich fraction and behaved as an authentic integral membrane protein. Immunofluorescence and immunogold analyses on normal human melanocytes confirmed the melanosomal membrane localization of the endogenous OA1 protein, consistent with its possible involvement in melanosome biogenesis. The identification of a novel melanosomal membrane protein involved in a human disease will provide insights into the mechanisms that control the cell-specific pathways of subcellular morphogenesis.

Ophthalmic findings in albinism

Purpose: Albinism is a rare genetic disorder of melanin production, which can affect only eyes or simultaneously eyes and skin/hair, resulting respectively in ocular (OA) or oculocutaneous albinism (OCA). Through of a case report of a child with OCA we pretend review ophthalmological manifestations of albinism. Case Report: A girl of West African descent was referenced to our appointment for ophthalmological evaluation of oculocutaneous albinism. Visual acuity was 20/310 OD e 20/630 OS by teller cards. In biomicroscopy, iris hypopigmentation and transillumination was visible, allowing to see spiral vessels and other iris details. Fundoscopy showed a denser and complex choroidal circulation due to lack of pigment in retinal pigment epithelium. Foveal hypoplasia was assumed because foveal pit is not apparent and vessels become less respectful of normal arcade and transverse the macula. Results: Melanin plays an important role in the development of the optic system and it’s absence leads to diverse ocular manifestations, such as: iris hypopigmentation and transillumination , reducted pigmentation of retinal pigment epithelium cells, photoreceptor rod cell deficits, foveal hypoplasia, optic nerve hypoplasia and misrouting of optic nerve at the chiasm, with temporal retina fibers inappropriately routed contralaterally instead of ipsilaterally. Photophobia, nystagmus, reduced visual acuity, color impairment and strabismus are other manifestations usually seen in albinism. Conclusion: Ophthalmologists must be familiar with the specific visual manifestations and needs of these patients. It is essential to correct refractive error to optimize visual acuity. Patients should also be advised to wear tinted glasses and sunblock. In more severely affected children they may benefit of low vision consultation and specialized low vision aids like telescopes.

Membrane associated transporter protein gene (SLC45A2) and the genetic basis of normal human pigmentation variation

This work is concerned with the genetic basis of normal human pigmentation variation. Specifically, the role of polymorphisms within the solute carrier family 45 member 2 (SLC45A2 or membrane associated transporter protein; MATP) gene were investigated with respect to variation in hair, skin and eye colour ― both between and within populations. SLC45A2 is an important regulator of melanin production and mutations in the gene underly the most recently identified form of oculocutaneous albinism. There is evidence to suggest that non-synonymous polymorphisms in SLC45A2 are associated with normal pigmentation variation between populations. Therefore, the underlying hypothesis of this thesis is that polymorphisms in SLC45A2 will alter the function or regulation of the protein, thereby altering the important role it plays in melanogenesis and providing a mechanism for normal pigmentation variation. In order to investigate the role that SLC45A2 polymorphisms play in human pigmentation variation, a DNA database was established which collected pigmentation phenotypic information and blood samples of more than 700 individuals. This database was used as the foundation for two association studies outlined in this thesis, the first of which involved genotyping two previously-described non-synonymous polymorphisms, p.Glu272Lys and p.Phe374Leu, in four different population groups. For both polymorphisms, allele frequencies were significantly different between population groups and the 272Lys and 374Leu alleles were strongly associated with black hair, brown eyes and olive skin colour in Caucasians. This was the first report to show that SLC45A2 polymorphisms were associated with normal human intra-population pigmentation variation. The second association study involved genotyping several SLC45A2 promoter polymorphisms to determine if they also played a role in pigmentation variation. Firstly, the transcription start site (TSS), and hence putative proximal promoter region, was identified using 5' RNA ligase mediated rapid amplification of cDNA ends (RLM-RACE). Two alternate TSSs were identified and the putative promoter region was screened for novel polymorphisms using denaturing high performance liquid chromatography (dHPLC). A novel duplication (c.–1176_–1174dupAAT) was identified along with other previously described single nucleotide polymorphisms (c.–1721C>G and c.–1169G>A). Strong linkage disequilibrium ensured that all three polymorphisms were associated with skin colour such that the –1721G, +dup and –1169A alleles were associated with olive skin in Caucasians. No linkage disequilibrium was observed between the promoter and coding region polymorphisms, suggesting independent effects. The association analyses were complemented with functional data, showing that the –1721G, +dup and –1169A alleles significantly decreased SLC45A2 transcriptional activity. Based on in silico bioinformatic analysis that showed these alleles remove a microphthalmia-associated transcription factor (MITF) binding site, and that MITF is a known regulator of SLC45A2 (Baxter and Pavan, 2002; Du and Fisher, 2002), it was postulated that SLC45A2 promoter polymorphisms could contribute to the regulation of pigmentation by altering MITF binding affinity. Further characterisation of the SLC45A2 promoter was carried out using luciferase reporter assays to determine the transcriptional activity of different regions of the promoter. Five constructs were designed of increasing length and their promoter activity evaluated. Constitutive promoter activity was observed within the first ~200 bp and promoter activity increased as the construct size increased. The functional impact of the –1721G, +dup and –1169A alleles, which removed a MITF consensus binding site, were assessed using electrophoretic mobility shift assays (EMSA) and expression analysis of genotyped melanoblast and melanocyte cell lines. EMSA results confirmed that the promoter polymorphisms affected DNA-protein binding. Interestingly, however, the protein/s involved were not MITF, or at least MITF was not the protein directly binding to the DNA. In an effort to more thoroughly characterise the functional consequences of SLC45A2 promoter polymorphisms, the mRNA expression levels of SLC45A2 and MITF were determined in melanocyte/melanoblast cell lines. Based on SLC45A2’s role in processing and trafficking TYRP1 from the trans-Golgi network to stage 2 melanosmes, the mRNA expression of TYRP1 was also investigated. Expression results suggested a coordinated expression of pigmentation genes. This thesis has substantially contributed to the field of pigmentation by showing that SLC45A2 polymorphisms not only show allele frequency differences between population groups, but also contribute to normal pigmentation variation within a Caucasian population. In addition, promoter polymorphisms have been shown to have functional consequences for SLC45A2 transcription and the expression of other pigmentation genes. Combined, the data presented in this work supports the notion that SLC45A2 is an important contributor to normal pigmentation variation and should be the target of further research to elucidate its role in determining pigmentation phenotypes. Understanding SLC45A2’s function may lead to the development of therapeutic interventions for oculocutaneous albinism and other disorders of pigmentation. It may also help in our understanding of skin cancer susceptibility and evolutionary adaptation to different UV environments, and contribute to the forensic application of pigmentation phenotype prediction.

白化病的分子机制研究概况

　本文对白化病的症状及分类、白化病各类型的分子机制、人类白化病分子机制研究进展、 白化小鼠分子机制研究进行了综述。

猕猴白化病分子机制和灵长类的分子进化研究

酪氨酸酶是黑色素合成当中的关键酶。人酪氨酸酶基因包括5个外显子，在染色体11q14-q21位置上占据了约50kb长的区域。对人类眼皮肤型白化病（Oculocutaneous albinism, OCA)的许多研究表明，该病主要是由于酪氨酸酶基因的突变引起的。昆明动物研究所白化猴研究小组数十年来一直从事白化猕猴的培育和研究工作，目前饲养着2只白化猕猴和它们的后代，这提供了我们研究猕猴白化分子机制目的条件。为了弄清猕猴白化病的分子机制，我们根据人酪氨酸酶基因序列设计了5对PCR引物扩增相应的5个外显子，序列分析表明，白化猕猴珍珍酪氨酸酶基因第184个密码子第2位置（外显子1的核苷酸位置551）处发生一个C→A的无义突变，使编码丝氨酸（Ser)的密码子变成了一个终止密码，这样后面1038bp的核苷酸片段（346个氨基酸残基）被截断，导致酪氨酸酶翻译不完全，迄今为止，并没有发现合成黑色素的第二条生化途径，因此由于该酶不能行使正常功能而将导致黑色素不能正常表达。这可能是导致该例猕猴白化病的原因。为了解酪氨酸酶基因序列变异的规律及其与功能的关系，探讨该基因作为系统发育研究中遗传标记的有效性，我们测定了黑猩猩（Pan troglodytes)、倭黑猩猩（Pan paniscus)、大猩猩（Gorilla gorilla)、猩猩(Pongo pygmaeus)、长臂猿（Hylobates lar)、食蟹猴（Macaca fascicularis)、狒狒（Simia cynocephalus)、猕猴（Macaca mulatta)、熊猴（Macaca assamensis)、菲氏叶猴（Presbytis p. crepusculus)、白臀叶猴（Pygathrix nemaeus)、滇金丝猴（Rhinopithecus r. bieti）和蛛猴（Ateles paniscus)13个灵长类中代表种的酪氨酸酶基因全部5个外显子的DNA序列。基于这些序列，用简约法构建了分子系统树。结果表明，人猿超科与旧大陆猴各自形成一单系群。人猿超科各物种和旧大陆猴有明显分化，人与大猩猩的关系比人与黑猩猩的关系近。酪氨酸酶基因在解决灵长类系统发育关系上是一个较有用的基因。为了进一步了解中国猕猴（Macaca mulatta)的亚种分化和不同地理群体间的基因流状况，我们测定了来自中云南、广西、福建、海南、浙江、河南、湖南、湖北、安徽、四川、贵州和越南猕猴共96只个体和一只外群食蟹猴的线粒体DNA控制区576bp的DNA序列，基于这些序列，运用距离法对中国恒河猴的分子进行和遗传多样性进行了分析，我们的研究结果显示，云南、四川和湖南猕猴群体与其它群体存在显著分析，海南群体内遗传多样性最低、四川、广西、浙江、福建和越南群体内遗传多样性较丰富。中国猕猴的分化可能存在三条路线。中国猕猴的遗传多样性较丰富。

Brachypodium distachyon. A new model system for functional genomics in grasses

John Draper, Luis A.J. Mur, Glyn Jenkins, Gadab C. Ghosh-Biswas, Pauline Bablak, Robert Hasterok,and Andrew P.M. Routledge (2001). Brachypodium distachyon. A new model system for functional genomics in grasses. Plant Physiology, 127 (4), 1539-1555. Sponsorship: BBSRC / Gatsby Foundation RAE2008