To clone the Bombyx xanthine dehydrogenase (XDH) gene as a dominant marker for silkworm transgenesis, we performed nested reverse transcriptase–polymerase chain reaction (RT-PCR) using embryonic mRNA and primers designed from the conserved region of Drosophila and rat XDH genes. Sequencing of amplified 180 bp fragments showed that two different sequences were present in the fragments. Since both possessed striking similarity to XDH genes of other organisms, we considered these to be portions of silkworm XDH genes and designated them BmXDH1 and BmXDH2. Subsequently we cloned separately the entire region of the two cDNAs by PCR using phage DNA of an embryonic cDNA library and sequenced them. The two cDNAs were around 4 kb in size and possessed complete open reading frames. The deduced amino acid sequences of the two BmXDHs were very similar to each other and to those of other organisms. The expression pattern of wild-type larvae basically followed the tissue specificity of the enzyme and no significant difference was observed between the two XDH genes. The expression of both genes was detected in the XDH-deficient mutants, oq and og, but non-synonymous substitutions were specifically detected in the BmXDH1 of the oq mutant. In addition, a length polymorphism of the second intron of the BmXDH1 co-segregated with the oq translucent phenotype, suggesting that deficiency in BmXDH1 is the cause of the oq translucent phenotype.

Oculocutaneous albinism (OCA) is a heterogeneous autosomal recessive genetic disorder that affects melanin synthesis. OCA results in reduced or absent pigmentation in the hair, skin and eyes. Type 1 OCA (OCA1) is the result of tyrosinase (TYR) gene mutations and is a severe disease type. This study investigated TYR mutations in a Chinese cohort with OCA1. This study included two parts: patient genetic study and prenatal genetic diagnosis. A total of 30 OCA1 patients were subjected to TYR gene mutation analysis. Ten pedigrees were included for prenatal genetic diagnosis. A total of 100 unrelated healthy Chinese individuals were genotyped for controls. The coding sequence and the intron/exon junctions of TYR were analysed by bidirectional DNA sequencing. In this study, 20 mutations were identified, four of which were novel. Of these 30 OCA1 patients, 25 patients were TYR compound heterozygous; two patients carried homozygous TYR mutations; and three were heterozygous. Among the ten prenatally genotyped fetuses, three fetuses carried compound heterozygous mutations and seven carried no mutation or only one mutant allele of TYR and appeared normal at birth. In conclusion, we identified four novel TYR mutations and showed that molecular-based prenatal screening to detect TYR mutations in a fetus at risk for OCA1 provided essential information for genetic counselling of couples at risk.

1. A form of syndactylism (jt) involving two or three digits on one or more feet has been found in the descendants of Swiss-albino mice treated with HN2. The fusions are in a proximo-distal direction and usually involve only the skin and soft tissues; digits 1 and 5 are unaffected.

2. This type of syndactylism is apparently due to a single recessive gene, jt, whose penetrance is influenced by ‘genetic background’. Apparently the identical mutation has occurred independently in stock maintained at Bar Harbor and Stanford. Linkage tests indicate that jt is not linked with c or lu.

3. Embryological studies of the developing footplate reveal a loss in both preaxial and postaxial footplate tissue, primarily the latter, prior to and during the condensation of mesenchyme into the precartilage of the digital elements in the jt/jt limb.

4. The importance of the shape and amount of footplate tissue to the resultant morphology of the foot is apparent. It is evident that genes such as jt are responsible for changes in footplate development, but the immediate underlying factors which cause these alterations remain an unsolved problem.

By means of grafting skin in which the epidermis of one genotype was combined with dermis of another to a nude host, we have shown that the effect of the mutant at the tabby (Ta) locus on follicle initiation in tail skin was not confined to either the epidermis or the dermis, that the effect of Ta on the morphology of body hairs was determined by the epidermis but that the close proximity of epidermis of a different genotype also affected body hair morphology.

Young mice of the strains A/Y and B10.D2 were repeatedly treated with diethylsulphate (DES) in different doses (36 to 1100 mg/kg). At the age of 9 weeks they were mated to females of the strains A. CA (‘A’ group) and C57BL/10Eg (‘D’ group) respectively. 2101 progeny of these matings were tested for histocompatibility by skin grafting. The spontaneous H-mutation rates were 6·96 × 10−4 per gamete in the A group and 9·6 × 10−4 per gamete in D group. In progeny of treated males the H-mutation rates were 0 in A group and 5·79 × 10−3 per gamete in D group, showing apparent effect of paternal DES treatment on mutation frequency in the last group. Two mutations of the H-2 locus were found, which together with the other three H-2 mutations published so far yielded a mutation rate of 5·18 × 10−4 per gamete. The mutation rate of the H-2 locus is higher than the expected rate per H-locus, indicating a great genetic complexity of H-2.

Mice homozygous for the asebia mutation (ab/ab) are char1acterized by defective sebaceous glands, a short sparse hair coat from 7 days and progressive alopecia. In addition, we have found that the initial hair follicle rudiments in the skin of these mice are able to differentiate into relatively normal anagen follicles which are often excessive in length and have minor abnormalities of the inner and outer root sheath components. The inner root sheath fails to form the typical transverse corrugations at the level of the sebaceous glands and its cells apparently remain, partially undegraded, plugging the hair canal and adhering to emerging hair shafts. Defects noted in the outer root sheath may be responsible for the failure of inner root sheath degradation. With increasing age, irregularities in hair cycle duration, loss of the originally parallel arrangement of hair follicles and further abnormalities of the individual follicular components are increasingly evident. Follicles in asebic mice have a tendency to form buds and branches which occasionally begin typical follicular differentiation. The consistent failure of the asebic follicles to pass normally through the catagen stage to the telogen stage results in long twisted follicles with abnormal and often loosely anchored hair clubs. The dermal papillae are often abnormal or absent from telogen follicles, while typical germ cells are not formed. Thus the lack of multiple hair follicles, the disorganization of follicles and the progressive alopecia observed in the asebic mice are accounted for. It is suggested that the altered dermal environment and outer root sheath abnormalities may be responsible for many of the follicular defects.

Hair follicle initiation and development was examined in tabby mutants and compared with a previous study of this sequence in normal mice. Initiation commenced at about the 17th embryonic day and continued for 1 and possibly 2 days after birth. Although central primary follicle initiation was of shorter than normal duration, it was more rapid, with the result that the central primaries achieved a greater maximum density, and their total numbers were greater in tabby than in normal mice.

In general structural terms, follicle group development proceeded normally except that no secondary follicles appeared, and for this reason, the mature grouping pattern of follicles was comparatively simple. Central primary follicles, the first to be initiated, were evenly spaced in the skin but the later association of lateral primaries with them was unusually close, and the resulting groups of primary follicles were relatively more compact in the mutants than they were in normal mice.

No simple explanation in terms of the altered timing of follicle initiation or the reduced complexity of the follicle group could be given for the abnormalities of the tabby coat.

Selection for high and low numbers of secondary vibrissae in tabby mice produced some correlated changes in the maincoat follicle population, but there was no apparent alteration to the time of onset of initiation. Evidently selection did not simply modify the effects of the Ta gene.

To investigate the cellular action of the Miωh allele in the mouse with regard to its effects upon coat color patterns, we generated a series of aggregation chimeras, using embryos that differ in their mi locus genotype. We have obtained 11 chimeras Miωh/ + C/C↔ + / + c/c and 8 chimeras + / + C/C↔ + / + c/c. Chimerism was determined by coat and retinal pigment epithelium mosaicism and by the electrophoretic analysis of GPI-1 isoenzymes. In Miωh/+ C/C↔, +/+ c/c mice white coat color prevailed due to the higher percentage of unpigmented areas and the higher percentage of unpigmented hairs in pigmented areas. Our data indicate that a single Miωh gene dose decreases the melanoblast proliferative activity, causing the lightening of coat pigmentation. In Miωh/ + C/C↔+/+ c/c mice a few pigmented hairs were often detected on the belly where Miωh / + mice always had a white spot. This suggests that in the chimeras the presence of some non-Miωh cells in the skin of the belly allows pigment cells to develop. Using embryos of two substrains of Miωh/Miωh mice that differ in their Gpi-1 locus genotype we have produced 8 Miωh/ + ↔ Miωh/Miωh chimeras. In all these chimeras coat color patterns resembled those of Miωh/ + heterozygotes despite the higher percentage of the Miwh/Miωh component in three chimeras. Mosaic hairs were absent in the chimeras. This shows that the chimeras have only one Miωh/ + melanoblast population which actively proliferates and colonizes almost all hair follicles. Thus the Miωh/Miωh dermis and epidermis do not suppress proliferation and differentiation of the Miωh/ + melanoblasts except the certain area on the belly.

In mice homozygous for the asebia mutation (abJ/abJ) the sebaceous glands were small and the sebaceous cells abnormal, the fully grown hair follicles were twice as long as those in wild-type (+ / +) mice, the catagen and telogen follicles were abnormal and, because the active phase of the hair cycle was longer than in + / + mice, the initiation of the second hair cycle was delayed. The abnormalities in the sebaceous glands and in catagen and telogen follicles were also present in abJ/abJ embryonic skin grown on a nude host but anagen of the second hair cycle commenced at about the same time in abJ / abJ and + / + grafts. When recombinants incorporating mutant or wild-type epidermis and dermis were grown on a nude host, the abnormalities in the sebaceous glands and the catagen and telogen follicles were only observed in the recombinants incorporating abJ / abJ epidermis. It was concluded that mutant activity in the epidermis was responsible for the abnormalities in the sebaceous glands and in catagen and telogen follicles and that mutant activity at some site distant from the skin was responsible for the abnormalities in the timing of the hair cycles.

Aggregation chimaeras were constructed by fusing embryos homozygous for sash (Wsh) with fuzzy, leaden beige (fz, ln, bg) homozygotes to investigate the site of action of the beige and leaden loci. The genotype of the hair follicle was identified by fuzzy alleles (+ +fz or fzfz). All melanocytes were derived from the fuzzy leaden beige population, as sash homozygotes do not produce functional melanocytes. Reciprocal recombinant epidermal/ /dermal skin grafts were constructed from 14-day embryonic skin of homozygous fzln bg and either albino (aa cc) or pink-eyed dilution (pp) embryos to test for any dermal expression of leaden or beige, since the epidermal and dermal genotype of the chimaeric hair follicles could differ.

Patches of fuzzy and non-fuzzy hairs were distributed throughout the coats of two of the three chimaeras obtained. The pigmented regions were blue grey, typical of the leaden beige interactive phenotype. Large abnormal beige granules were found in fuzzy and non-fuzzy hairs. Melanocytes in both classes of growing follicles were nucleopetal, typical of leaden. Similarly, the results of the 14-day skin grafts showed that the beige and leaden loci are melanocyte-autonomous.

The chimaeras showed a pigment distribution resembling the heterozygous sash phenotype. Thus the 1:1 gene dosage of sash: wild type in heterozygotes and chimaeras has an overall effect on pigment pattern that overrides the predicted random distribution of the melanocyte precursors.

1. The earliest manifestations of the gene for syndactylism discovered include hyperplasia of the apical ectodermal ridge of the limbs and hyperplasia of parts of the limb epidermis (10–10½-day stage). Somewhat later, a similar hyperplasia of the epidermis in the distal parts of the tail is found in some sm/sm embryos.

2. Enlargement and deformation of the foot plates in both fore and hind limbs is present in the 12-day stage; in the fore limbs it probably starts on the preceding day. The foot plates are bent over in a palmar or plantar direction respectively; the crowding together of the middle digits thus produced is the mechanical cause of syndactylism.

3. It is suggested that the enlargement of the foot plates with the ensuing deformities is due to increased stimulation of mesenchymal growth by the hyperplastic apical ectodermal ridge. On this interpretation, all the skeletal effects (including those in the tail) are secondary to a systemic tendency to epidermal hyperplasia.

4. The hyperplastic regions of the apical ectodermal ridge and of the limb epidermis start to keratinize (parakeratosis) in the 13-day stage whereas in normal development keratinization of the skin does not start until some 3 days later.

A pair of mutant mice with a first sparse coat appeared spontaneously in the production stock of BALB/c mice with a normal coat. After being sib-mated, they produced three phenotypes in their progeny: mice with normal hair, mice with a first sparse coat and then a fuzzy coat, and uncovered mice. Genetic studies revealed the mutants had inherited an autosomal monogene that was semi-dominant. By using 11 biochemical loci – Idh, Car2, Mup1, Pgm1, Hbb, Es1, Es10, Gdc, Ce2, Mod1 and Es3 – as genetic markers, two-point linkage tests were made. The results showed the gene was assigned to chromosome 11. The result of a three-point test with Es3 and D11Mit8 (microsatellite DNA) as markers showed that the mutation was linked to Es3 with the recombination fraction 7·89±2·19%, and linked to D11Mit8 with the recombination fraction 26·30±3·57%. The recombination fraction between Es3 and D11Mit8 was 32·90±3·81%. It is suggested that the mutation is a new genetic locus that affected the skin and hair structure of the mouse. The mutation was named uncovered, with the symbol Uncv. Further studies showed the mutation affected not only the histology of skin and hair but also the growth and reproductive performance of the mice. The molecular characterization of the Uncv locus needs to be further studied.

Two mosaic birds are described, from a sex-linked F1 cross (Rhode Island Red ♂ × Light Sussex ♀). They are sexually normal males and full brothers. Each has the following abnormalities on one side of the body: absence of the maternal dominants S (silver, sex-linked), W (white skin) and Co (Columbian restriction of black), and reduction in size. In one case all the melanocytes appear to be derived from the smaller side, so that the plumage pattern is identical on the two sides; in the other there is a minor deviation (modified expression of Co) from normal F1 plumage pattern on the larger side. Mated to Brown Leghorn hens, both mosaics bred as normal F1 males, with no evidence of germinal mosaicism. Over thirty full sibs were all found to be normal.

A purely paternal origin of the smaller side appears to be excluded in both cases by the lack of striping in the down, and by minor deviations from normal Brown Leghorn phenotype in adult plumage pattern. Origin by some kind of maldistribution of chromosomes at first cleavage division would require the X-chromosome and possibly as many as three autosomes to be affected simultaneously.

Two further unrelated crossbred mosaic males are described. Each has yellow skin (w) on one side of the body. In one case this is accompanied by a slight difference in plumage pattern, reduction in size and abnormal proportions in the limb bones; in the other merely by a slight reduction in size. Loss or non-disjunction of a single chromosome at first cleavage division is a possible explanation of these.

1. Nude is a new recessive gene causing hairlessness in the mouse. It is linked to rex and trembler in linkage group VII. The order of the three loci and the recombination frequencies are as follows:

2. In addition to hairlessness the new gene causes reduced body growth rate, very low fertility and a liver disease causing death. Nude mice may be classified at birth by the absence of vibrissae.

3. The hairlessness is due to abnormal keratinization of hair in the follicles. The skin histology resembles that of naked mice. The hair follicles were found to be deficient in free sulphydryl groups.

4. The majority of nude mice die of general body weakness within 2 weeks of birth. The survivors grow slowly and may live for a considerable period. But all nude mice eventually die, usually between 3 and 14 weeks of age.

5. The livers of dead or moribund nude mice are covered with lesions and scars. The defect has been traced histologically to its initial stage, namely, necrosis of small areas of tissue.

6. Attempts to relate the deficiency of sulphydryl groups in the hair follicles to abnormal sulphur metabolism in the liver were unsuccessful.

7. Pseudo-cysts of a parasitic protozoan, Toxoplasma gondii, were identified in the liver and brain of nude mice. In one case the free form of the organism was found.

8. The possible relationship between the liver disease and the pathogenic organism is discussed.

A form of the human skin disease, ichthyosis, results from a mutation at the steroid sulphatase locus (STS) on the X chromosome. This locus appears to escape inactivation in the XX female, resulting in the expression of two doses of the STS gene (Shapiro et al. 1978; Crawfurd, 1982). The scurfy mutation in the mouse is thought to be homologous to the human disease (McKusick, 1978), and so should also be due to a steroid sulphatase (STS) deficiency. Our findings in male and female mice suggest that, in contrast to the human, the murine ‘STS’ locus is subject to X chromosome inactivation. However, another interpretation of the results is possible, namely that STS may be coded for by an autosomal gene.

(1) F1-hybrid mice derived from a cross of the highly inbred strains: C57BL/6 and BALB/c, were tested for inherited changes of histocompatibility by an orthotopic inter-exchange of tail-skin grafts. The fathers of tested mice received either 522 rads of gonadal X-irradiation, or received no irradiation 2 months prior to mating.

(2) Thirty-two mice with altered histocompatibilities were found in a total of 2572 complete tests. All of those mutant mice (twenty-one) that produced an adequate number of offspring were shown to pass the incompatibility on to their progeny.

(3) Mutants were classified as to whether they effected a gain, a loss or both a gain and a loss in antigen specificity as determined by whether they rejected skin of donor mice or their skin was rejected by host mice. Twenty-six were clearly of the gain type, five were most likely gain type and only one showed both a loss and a gain effect. There was no clearcut evidence that loss types had occurred. The preponderance of gain types was tentatively explained as an artifact of the system used for the assay.

(4) Several of the detected mutants were probably from parents carrying mutations that originated in past generations, for some mutant mice occurred in clusters.

(5) There was no apparent effect of paternal irradiation (522 rads) on mutation frequency. The induced mutation rate was estimated to be less than 2·6 × 10−5/ gamete/rad.

(6) Independent data on isografts from F1 hybrids of proven non-carrier pedigreed parents provided an estimate of spontaneous mutation rate of 6·75 × 10−3/ gamete.

(7) The estimate of doubling dose (greater than 260 rads) was consistent with the estimates for recessive lethals and visibles in mice.

In the present study, skin fibroblasts and leukocyte cultures from patients with acute infectious mononucleosis were examined to determine if any in vitro marker chromosomes could be detected. No alterations in chromosomes could be found in fibroblasts either from the region of the typical rash or from other areas of skin. This would tend to suggest but does not necessarily prove that this tissue was not extensively involved in the disease process.

Mi-spotted (misp) is a new mutation in the mouse at the microphthalmia (mi) locus. It has no obvious visible effect in either the heterozygote (misp/+) or homozygote (misp/misp) and was discovered by virtue of its interaction with white (miwh). Mice of genotype miwh/misp are pale yellow with white spots; yellow areas later become ‘sooty’ at the first moult.

Though mice of genotypes a/a; misp/+ and a/a; misp/misp cannot be visibly distinguished from those of a/a; +/+, the amount of tyrosine-2-C14 incorporated in melanin in skins of 5-day-old mice of these genotypes differed. Assays of tyrosine incorporation were extended to include other non-agouti genotypes differing only at the microphthalmia locus. The amount of tyrosine incorporated was greatest in +/+ followed in order by misp/+, misp/+, misp/misp, miwh/+, miwh/misp, and miwh/miwh.

Pigment granules were examined in club hairs of these same genotypes for different regions of the hair shaft. Hairs of misp/+, misp/misp, and mi/+ could not be distinguished from +/+ either in number, kind or arrangement of granules. Hairs of miwh/+ showed reduced cortical and medullary pigment, especially distally, which was even more pronounced in hairs of miwh/misp. Medullary granules of miwh/misp varied greatly in size with a few large yellow-brown granules.