Regulation of vertebrate eye development by Rx genes

The paired-like homeobox-containing gene Rx has a critical role in the eye development of several vertebrate species including Xenopus, mouse, chicken, medaka, zebrafish and human. Rx is initially expressed in the anterior neural region of developing embryos, and later in the retina and ventral hypothalamus. Abnormal regulation or function of Rx results in severe abnormalities of eye formation. Overexpression of Rx in Xenopus and zebrafish embryos leads to overproliferation of retinal cells. A targeted elimination of Rx in mice results in a lack of eye formation. Mutations in Rx genes are the cause of the mouse mutation eyeless (ey1), the medaka temperature sensitive mutation eyeless (el) and the zebrafish mutation chokh. In humans, mutations in Rx lead to anophthalmia. All of these studies indicate that Rx genes are key factors in vertebrate eye formation. Because these results cannot be easily reconciled with the most popular dogmas of the field, we offer our interpretation of eye development and evolution.     

<Emphasis Type="Italic">CHX10</Emphasis> mutations cause non-syndromic microphthalmia/anophthalmia in Arab and Jewish kindreds

Microphthalmia/anophthalmia is a clinically heterogeneous disorder of eye formation, ranging from small size of a single eye to complete bilateral absence of ocular tissues. The genetic defect underlying isolated autosomal recessive microphthalmia/anophthalmia is yet unclear. We studied four families (two of Arab origin, one of Bedouin origin, and one of Persian-Jewish origin) with autosomal recessive microphthalmia/anophthalmia and no associated eye anomalies, and one Syrian–Jewish family with associated colobomas. Assuming a founder effect in each of the families, we performed homozygosity mapping using polymorphic markers adjacent to human homologues of genes known to be associated with eye absence in various species, namely EYA1, EYA2, EYA3, SIX4, SIX6, PAX6 and CHX10. No association was found with EYA1, EYA2, EYA3, SIX6 or PAX6. In two families, linkage analysis was consistent with possible association with SIX4, but no mutations were found in the coding region of the gene or its flanking intron sequences. In three of the five families, linkage analysis followed by sequencing demonstrated that affected individuals in each family were homozygous for a different CHX10 aberration: a mutation in the CVC domain and a deletion of the homeobox domain were found in two Arab families, and a mutation in the donor-acceptor site in the first intron in the Syrian-Jewish family. There was phenotypic variation between families having different mutations, but no significant phenotypic variation within each family. It has been previously shown that mutations in a particular nucleotide in CHX10 are associated with an autosomal recessive syndrome of microphthalmia/anophthalmia with iris colobomas and cataracts in two families. We now show that different mutations in other domains of the same gene underlie isolated microphthalmia/anophthalmia.     

Semidominant Effect of the l(1)ts403 (sbr 10) Mutation on Sex Chromosome Nondsjunction in Meiosis in Drosophila melanogaster Females Exposed to Heat

The sbrgene of Drosophila melanogasterbelongs to the NXF(nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37°C, 1 h) females, the l(1)ts403(sbr ¹⁰) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr ¹⁰ mutation is observed. At the same time, the sbr ¹⁰ mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)v ^L4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr ¹⁰ mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr ¹⁰ allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has an active effect on sex chromosome disjunction in meiosis.     

A new inbred strain JF1 established from Japanese fancy mouse carrying the classic piebald allele

A new inbred strain JF1 (Japanese Fancy Mouse 1) was established from a strain of fancy mouse. Morphological and genetical analysis indicated that the mouse originated from the Japanese wild mouse, Mus musculus molossinus. JF1 has characteristic coat color, black spots on the white coat, with black eyes. The mutation appeared to be linked to an old mutation piebald (s). Characterization of the causative gene for piebald, endothelin receptor type B (ednrb), demonstrated that the allele in JF1 is same as that of classic piebald allele, suggesting an identical origin of these two mutants. Possibly, classic piebald mutation was introduced from the Japanese tame mouse, which was already reported at the end of the 1700s. We showed that JF1 is a useful strain for mapping of mutant genes on laboratory strains owing to a high level of polymorphisms in microsatellite markers between JF1 and laboratory strains. The clarified genotypes of JF1 for coat color are ``aa BB CC DD ss'. Received: 30 May 1997 / Accepted: 26 August 1997     

Mutations in the SPARC-related modular calcium-binding protein 1 gene, SMOC1, cause waardenburg anophthalmia syndrome

Waardenburg anophthalmia syndrome, also known as microphthalmia with limb anomalies, ophthalmoacromelic syndrome, and anophthalmia-syndactyly, is a rare autosomal-recessive developmental disorder that has been mapped to 10p11.23. Here we show that this disease is heterogeneous by reporting on a consanguineous family, not linked to the 10p11.23 locus, whose two affected children have a homozygous mutation in SMOC1. Knockdown experiments of the zebrafish smoc1 revealed that smoc1 is important in eye development and that it is expressed in many organs, including brain and somites.     

Identification of a new allele of Es-1 segregating in an inbred strain of mice

A new allele of Es-1, designated Es-1 ^e, has been identified in the mouse. This allele was discovered segregating among the progeny of a strain DBA/2J male and is apparently the result of a spontaneous mutation within this strain. Genetic analyses have shown that this mutation is heritable and, further, that both heterozygous and homozygous progeny are viable and fertile. To date, no discernible deleterious effects have been identified as associated with this mutation.     

rim2 (recombination-induced mutation 2) is a new allele of pearl and a mouse model of human Hermansky-Pudlak Syndrome (HPS): genetic and physical mapping

A mouse mutation, rim2, is one of a series of spontaneous mutations that arose from the intra-MHC recombinants between Japanese wild mouse-derived wm7 and laboratory MHC haplotypes. This mutation is single recessive and characterized by diluted coat color and hypo-pigmentation of the eyes. We mapped the rim2 gene close to an old coat color mutation, pearl (pe), on Chromosome (Chr) 13 by the high-density linkage analysis. The pearl mutant is known to have abnormalities similar to Hermansky-Pudlak syndrome (HPS), a human hemorrhagic disorder, characterized by albinism and storage pool deficiency (SPD) of dense granules in platelets. A mating cross of C57BL10/Slc-rim2/rim2 and C57BL/6J-pe/pe showed no complementation of coat color. Additionally, characteristics similar to SPD were also observed in rim2. Thus, rim2 appeared to be a new allele of the pe locus and serves as a mouse model for human HPS. We have made a YAC contig covering the rim2/pe locus toward positional cloning of the causative gene. Received: 23 July 1997 / Accepted: 26 August 1997     

The insertion/deletion polymorphisms in the waxy gene of barley genetic resources from East Asia

The length polymorphism in the waxy gene, which encodes a granule-bound ADP-glucose-glucosyl transferase [granule-bound starch synthase I (GBSS I), E.C. 2.4.1.11] in barley (Hordeum vulgare), was found. The 5′ leader sequence of the waxy gene of barley germplasm from Japan and Korea was analyzed by the polymerase chain reaction (PCR). The waxy gene of these genetic stocks had three types of length polymorphisms, suggesting that there are insertion/deletion mutations at the 5′ leader sequence of the waxy gene. DNA sequence analysis of the polymorphic PCR products showed that: (1) a 403-bp deletion mutation, which included a complete exon I, was found in the wax allele and a 193-bp insertion sequence was located in the intron I, and (2) the insertion sequence was also located in intron I of the Wax allele. The identity of the insertion sequence was completely conserved between the wax allele and the novel Wax allele. These finding s implying that the wax allele, which was found in indigenous waxy barley, originated in non-waxy barley with the novel Wax allele. Received: 12 January 2001 / Accepted: 17 April 2001     

A novel heterozygous SOX2 mutation causing congenital bilateral anophthalmia,hypogonadotropic hypogonadism and growth hormone deficiency

Heterozygous de novo mutations in SOX2 have been reported in approximately 10–20% of patients with unilateral or bilateral anophthalmia or microphthalmia. An additional phenotype of hypopituitarism, with anterior pituitary hypoplasia and hypogonadotropic hypogonadism, has been reported in patients carrying SOX2 alterations. We report a novel heterozygous mutation in the SOX2 gene in a male affected with congenital bilateral anophthalmia, hypogonadotrophic hypogonadism and growth hormone deficiency. The mutation we describe is a cytosine deletion in position 905 (c905delC) which causes frameshift and an aberrant C-terminal domain. Our report highlights the fact that subjects affected with eye anomalies and harboring SOX2 mutations are at high risk for gonadotropin deficiency, which has important implications for their clinical management.     

Canine TCOF1; cloning, chromosome assignment and genetic analysis in dogs with different head types

We describe the construction of a dog embryonic head/neck cDNA library and the isolation of the dog homolog of the Treacher Collins Syndrome gene, TCOF1. The protein shows a similar three-domain structure to that described for human TCOF1, but the dog gene lacks exon 10 and contains two exons not present in the human sequence. In addition, exon 19 is differentially spliced in the dog. How these structural differences relate to TCOF1 phosphorylation is discussed. Isolation of a genomic clone allowed the exon/intron boundaries to be characterized and the dog TCOF1 gene to be mapped to CF Chr 4q31, a region syntenic to human Chr 5. Genetic analysis of DNA of dogs from 13 different breeds identified nine DNA sequence variants, three of which gave rise to amino acid substitutions. Grouping dogs according to head type showed that a C396T variant, leading to a Pro117Ser substitution, is associated with skull/face shape in our dog panel. The numbers are small, but the association between the T allele and brachycephaly, broad skull/short face, was highly significant (p= 0.000024). The short period of time during which the domestic dog breeds have been established suggests that this mutation has arisen only once in the history of dog domestication. Received: 12 January 2001 / Accepted: 1 April 2001     

Molecular analysis of the loss of somatic instability in the bz2::mu1 allele of maize

Summary Multiple genetic and epigenetic changes were detected within one plant generation at the bz2:: mu1 mutable allele in a population of 118 plants. Loss of somatic instability in bz2::mu1 was usually correlated with methylation of the Mu1 transposable element; in 6 plants, somatic instability was lost as a result of mutations in bz2::mu1. This is a surprisingly high frequency of mutation per allele (2.5%) for the Mutator family, for which germinal revertants occur at a frequency of about 10^–4 per gamete. One germinal excision event was found that contained an 8 by deletion, frameshift mutation in Bronze-2. The three other mutants described occurred as a result of abortive transposition, in which 75–77 by deletions were generated at the junction between Bronze-2 and Mu1. We discuss the possible mechanisms, and the role of host factors in abortive transposition in maize.     

Ocular defects associated with a null mutation in the mouse arylamine <Emphasis Type="Italic">N</Emphasis>-acetyltransferase 2 gene

The xenobiotic metabolizing enzyme, mouse arylamine N-acetyltransferase type 2 (Nat2), is expressed during embryogenesis from the blastocyst stage and in the developing neural tube and eye. Mouse Nat2 is widely believed to have an endogenous role distinct from xenobiotic metabolism, and polymorphisms in the human ortholog have been implicated in susceptibility to spina bifida and orofacial clefting. The developmental role of Nat2 was investigated using transgenic Nat2 knockout/lacZ knockin (Nat2 ^tm1Esim) mice. The transgene was bred onto an A/J background and offspring were scored for developmental defects at weaning. After backcross generation eight, an ocular defect, ranging from cataract to microphthalmia and anophthalmia, was recorded among offspring of backcross and intercross pairs. Histologic analysis of cataract cases revealed a failure of the lens to separate from the cornea and plaques within the lens tissue. While Nat2 ^−/− mice have been described as overtly aphenotypic, the presence of a Nat2 null allele in one or both parents can result in ocular defects. These ocular phenotypes and their association with Nat2 genotype indicate that the Nat2 locus may be responsible for the previously described microphthalmic Cat4 phenotype and implicate the orthologous human NAT as a phenotypic modifier of microphthalmia and anophthalmia.     

Conditional ancestral times and related properties of an extant mutant at a locus A given the number of segregating sites observed at a linked locus B

 It is shown how the mean ancestral times at one locus are affected in a two- locus model with recombination when information is given regarding the number of segregating sites at another locus. For samples of n genes, recursive equations are derived that describe precisely the evolution of the time-depth of such a linked genealogy. Exact numerical solutions and Markov chain Monte Carlo simulations are discussed and compared. The dependence of some properties of a singleton mutation on waiting times between events in the two-locus genealogy is quantified and illustrates the effect of recombination on these properties. The following cases are presented: (1) the distribution of the number of mutant genes in a sample arising from a singleton mutation; (2) the probability that an allele observed in a genes of a sample of size n is the ancestral type (the oldest); (3) the expectation and variance of the age of a mutant having b copies in a sample of n genes. Received: 1 September 2000 / Revised version: 1 October 2001 / Published online: 8 May 2002     

Distribution of an allele associated with blond hair color across northern island melanesia

Pigmentation of the skin, hair, and eyes is a complex trait controlled by multiple genetic loci. Recently a non‐synonymous mutation in the pigmentation candidate gene TYRP1 was shown to be significantly associated with a blond‐hair phenotype in populations from the Solomon Islands. The distribution of this mutation in the islands of Northern Island Melanesia, where the blondism phenotype is also prevalent, was unknown. Here, we present data describing the distribution of this allele in 550 individuals sampled from across this region, and test for associations between genotype at this locus and quantitatively measured skin and hair pigmentation phenotype. We report that the frequency of the 93C allele is notably lower than observed in the Solomons (0.12 vs. 0.26). The allele exhibits significant geographic heterogeneity across the islands sampled (χ² = 108.4, P < 0.0001). It is observed at its highest frequencies on the islands of New Ireland and New Hanover, while being almost completely absent from the large island of New Britain. Using linear regression with age, sex, and island as covariates we report that, as in the Solomons, the 93C allele is significantly associated with a decrease in hair pigmentation but not skin pigmentation. We discuss the distribution of the 93C allele across the Southwest Pacific in light of its possible place of origin and dispersal. Am J Phys Anthropol 153:653–662, 2014. © 2014 Wiley Periodicals, Inc.     

Phenotypic consequences and genetic interactions of a null mutation in the Drosophila posterior Sex Combs gene

The Posterior Sex Combs (Psc) gene of Drosophila is a member of the Polycomb (Pc) group of transregulatory genes. Previous analyses of the function of this gene in Drosophila em-bryogenesis have been hampered by the lack of a null mutation. We recently isolated a mutation that deletes the 5′ end of the Psc gene. This allele appears to be a null mutation, and we have used it to determine the Psc zygotic null phenotype and to look at the interactions of a null allele of Psc with five other Pc group mutations. We find evidence for transformations along both the anterior-posterior and dorsal-ventral axes in embryos of a variety of genotypes that include a null mutation in Psc. The phenotypes of embryos that are doubly mutant for a null allele of Psc and a mutation in a second Pc group gene show dramatic synergistic effects, but in their specifics they are dependent on the identify of the second Pc group gene. This is different from the relatively uniform phenotypes seen among double mutants that contained the allele Psc¹, which has both gain and loss of function properties. The differences in the phenotypes of the doubly mutant embryos allow us to eliminate one class of molecular models to explain the dramatic synergism seen with mutations in this group of genes.     

Mutation rate and pattern of microsatellites in common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

Microsatellites are popular molecular markers in genetic and evolutionary studies. Their mutational dynamics have been extensively studied in humans and fruit flies, but few data were available in fish. By genotyping 55 individuals of a F1 pedigree, we investigated the mutation rates and patterns of 49 microsatellites in one of the most important fresh water fish species, the common carp (Cyprinus carpio L.). The overall mutation rate of the 49 loci was 5.56×10⁻⁴/locus/generation (95% confidence interval 1.52×10⁻⁴ and 1.63×10⁻³). The change of allele size was between +2 to −5 repeat units, assuming that the mutation allele arose from the parental allele most similar in size to the mutant.     

Male sterility associated with APRT deficiency in Arabidopsis thaliana results from a mutation in the gene APT1

Four mutants of Arabidopsis thaliana that are deficient in adenine phosphoribosyl transferase (APRT) activity have been isolated by selecting for germination of seeds and growth of the plantlets on a medium containing 2,6-diaminopurine (DAP), a toxic analog of adenine. In all mutants, DAP resistance is due to a recessive nuclear mutation at a locus designated apt. The mutants are male sterile due to pollen abortion after meiosis. Furthermore, it has been shown that metabolism of cytokinins is impaired in the mutant BM3, which has the lowest level of APRT activity among the mutants tested. However, three different cDNAs encoding APRT have been isolated in A. thaliana and this raised the question of the nature of the mutation which results in low APRT activity. The mutation was genetically mapped to chromosome I and lies within 6 cM of the phenotypic marker dis2, indicating that the mutation affects the APT1 gene, a result confirmed by sequencing of mutant alleles. The mutation in the allele apt1-3 is located at the 5′ splicing site of the third intron, and eliminates a BstNI restriction site, as verified by Southern blotting and PCR fragment length analysis. Received: 20 February 1997 / Accepted: 28 August 1997