Noboru Wakasugi

Endoplasmic reticulum is missing in dendritic spines of Purkinje cells of the ataxic mutant rat.

Dilute-opisthotonus (dop) is a spontaneous ataxic mutation in the rat, regulated by an autosomal recessive gene. Immunohistochemical staining with anti-inositol 1,4,5-trisphosphate receptor antibody and electron microscopic examinations revealed that the endoplasmic reticulum in dendritic spines of Purkinje cell was missing in the ataxic rat. This could impair the intracellular signal transduction in the parallel fiber-Purkinje cell synapse, and be a cause of the severe ataxic movement.

Gracile Axonal Dystrophy (GAD), a New Neurological Mutant in the Mouse

Abstract A new neurological mutant has been found in the F2 offspring of CBA/Nga and RFM/Nga mice. Affected mice exhibited ataxia beginning at about 80 days of age, followed by tremor, difficulty in moving, and muscular atrophy of the hind limbs. The neurological signs became progressively severe, and death occurred by 5 to 6 months of age. Since the animals could be distinguished from normal mice by the abnormal positions of the hind limbs when the mouse was hung by the tail after 1 month of age, they could be bred until onset of the signs. Pathological examination revealed neuroaxonal dystrophy and degeneration in the gracile nucleus of the medulla oblongata and the gracile fascicules of the spinal cord, which could be the main cause of the clinical signs. The mutation is inherited as an autosomal recessive trait. It was, therefore, named gracile axonal dystrophy (GAD) with the gene symbol gad. The mice could be a new pathological model for the study of neuroaxonal dystrophy.

Transdifferentiation from Retinal Pigment Epithelium (RPE) into Neural Retina Due to Silver Plumage Mutant Gene in Japanese Quail

Homozygotes for silver plumage gene (BIB) of Japanese quail have an abnormal retina, i.e. there is a circular pigment lacking area on the center of retina, therefore, the pigmented part takes a doughnut or ring shape and the character is called a ring retina for convenience sake. This abnormality was studied light-microscopically in comparison with the wild-type (+/ +) and silver heterozygote (Bl +). Transdifferentiation from retinal pigment epithelium (RPE) into neural retina was found to occur at the pigment lacking abnormal area of BIB retina. The abnormality was first observed as a partial thickening at the fundus of RPE in 5-day embryos. It gave rise to the structure of neural retina at about 7-days of incubation and hence, double layer retinas were formed at the fundus. Both original and transdifferentiated neural retinas began to degenerate at about 10 days of incubation. In both B I B and BI + retinas, melanin synthesis was retarded and melanin granules were less abundant as compared with the +/ + retina. In addition, no melanin granules were observed in the choroid of BIB and BI + embryos. Thus, it has been clarified that the silver gene partially suppresses melanin synthesis in the eyes as well as in the feather follicles. These observations suggest that the transdifferentiation of RPE into a neural retina would occur following partial suppression of melanin synthesis in the B I B RPE cells.

Female mice of DDK strain are fully fertile in the intersubspecific crosses with Mus musculus molossinus and M. m. castaneus

The female mice of DDK strain are almost infertile when mated with males from other strains. This phenomenon is caused by the early death of F1 embryos owing to the incompatibility system attributed to the ovum mutant (Om) locus on Chromosome (Chr) 11 and known as DDK syndrome. In the present study, DDK females were found to be fully fertile in the intersubspecific matings with the males of two wild mouse-derived strains, MOM (originated from Japanese wild mice, Mus musculus molossinus) and Cas (originated from Philippine wild mice, M. m. castaneus), indicating that no incompatibility exists between DDK oocytes and spermatozoa of MOM and Cas strains. Furthermore, this compatibility has been confirmed by the following two findings: (1) Normal fertility was shown by the two types of backcrosses, DDK females x F(1) (DDK female x MOM male) males and DDK females x F(1) (DDK female x Cas male) males; and (2) the offspring from these backcrosses segregated equally into the homozygotes and heterozygotes as genotyped by the microsatellite markers closely linked to Om locus. MOM and Cas strains would be useful for further investigations on the Om locus. On the other hand, the litter size of F(1) [C57BL/6Cr (B6) female x Cas male] females mated with B6 males was about half that of the mating with DDK males. It would be interesting to investigate whether this reduction in fertility is related to the Om locus or not.

Modification of Survival Rate of Mouse Embryos Developing in Heterozygous Females for Ovum Mutant Gene

Abstract The DDK syndrome (polar infertility) is caused by an incompatibility system due to the ovum mutant (Om) locus. For brevity, the following gene symbols are used in the present report: DDK allele, Om; C57BL/6Cr allele, +. In this investigation, we first attempted to introduce the Om allele of DDK strain into the genetic background of C57BL/6Cr strain. The attempt resulted in the production of no young at the third generation of successive backcrosses. Secondly, mating experiments were performed with heterozygous (Om/+) females having background genes of C57BL/6Cr and DDK strains in the ratios 1:1(B1D), 3:1(B3D), 7:1(B7D), and 15:1(B15D). The survival rate of the embryos as judged by the percentage number of live fetuses/number of corpora lutea at Day 12 of pregnancy was 41.3 ± 3.2%, 27.3 ± 3.2%, 16.4 ± 3.3%, and 11.3 ± 3.2% (mean ± SEM) in the B1D, B3D, B7D, and B15D females, respectively, when they were mated with C57BL/6Cr males. Furthermore, the increased embryonic mortality in the heterozygous (Om/+) females with more background genes of C57BL/6Cr strain was found to be due to a failure in blastocyst formation, as in the DDK syndrome. The parallelism between the proportion of C57BL/6Cr background genes and embryonic mortality has led to a hypothesis proposing the participation of a modifier gene, namely that a mechanism similar to allelic exclusion may be working in the synthesis of cytoplasmic factor of eggs and that only the Om allele is activated during oogenesis to produce DDK-type cytoplasmic factor in heterozygous (Om/+) females having a modifier gene in the homozygous state.

Studies on Blood Groups in the Japanese Quail: The Common Antigens Possessed by Red Blood Cells and Leukocytes, and Their Inheritance

Two alloantigens, Ly1 and Ly2, were detected with alloantisera made by immunization with leukocytes. These antigens were present on red blood cells, peripheral leukocytes and spleen cells and found to be controlled by the autosomal codominant alleles. The phenotypic frequencies of Ly1 antigen in the three quail stocks, 1, 2, and 3, were 6.7, 0, and 100 percent, respectively, and those of Ly2 antigen were 0 percent in stocks 1 and 2, and 7.1 percent in stock 3. It was suggested that Ly1 and Ly2 antigens might be associated with the system controlling A(QN1) antigen which was originally detected by the natural alloantibody. However, it remains to be investigated whether these antigens are associated with the major histocompatibility complex (MHC) of the Japanese quail.

Embryologic, cytobiologic and genetic interpretations of DDK syndrome in mice.

DDK syndrome is known as embryonic death at the morula‐blastocyst stage in female mice of the DDK strain mated with males from other strains (alien males). The embryonic death is interpreted to be caused by incompatibility between oocyte factors and the product from male pronucleus, both of which are under the control of alleles at the same locus on Chromosome 11. This review explains the hypothesis proposing that the embryonic death may be caused primarily by failure in de novo regeneration of centrosomes containing centrioles in the trophectodermal cells. Centrioles disintegrate during gametogenesis in mice, and new centrioles are formed after the cleavage stage during which cell division proceeds with the microtubule organizing center having no centrioles. The failure in de novo regeneration of the centrosomes may arrest cell division and consequently result in embryonic death. Another aspect of DDK syndrome is distortion of the second polar body extrusion in the semi‐incompatible cross. In the heterozygous (DDK/alien) oocytes fertilized with alien spermatozoa, DDK allele is more frequently retained in the oocyte nucleus, and alien allele tends to be carried into the polar body. This distortion may possibly be caused by derangement in the spindle system. Therefore, both aspects of DDK syndrome can be regarded as being derived from the abnormality in the centrosome‐spindle system according to this hypothesis.

Studies on the blood groups in the Japanese quail: Detection of three antigens and their inheritance

Attempts were made to prepare antisera that could be used for the blood typing of the Japanese quail (Coturnix coturnix japonica). Three type specific antisera were obtained; (1) natural alloantiserum, (2) natural heteroantiserum from the domesticated rabbit, (3) natural heteroantiserum from a Holstein cow. Alloimmunization and heteroimmunization resulted in the production of antisera that had the same specificity as those described above. Genetical studies demonstrated that the three antigens detected by the above antisera were controlled by three separate autosomal dominant genes and the possibility was suggested that the suitable strains of the Japanese quail for the studies of immunogenetics could be established.

A novel partial t haplotype with a Brachyury-independent effect on tail phenotype

The btm (brachyury-interacting tail length modifier) mutation was discovered in strain MOL-NIS derived from Japanese wild mice (Mus musculus molossinus) as an autosomal recessive mutation. Homozygotes for this mutation show a short tail phenotype and, moreover, this mutation causes the tailless character by interacting with the T (brachyury) gene on Chromosome (Chr) 17. Our linkage tests and RFLP analyses suggest that btm is located within the t complex on Chr 17 and represents a new partial t haplotype.

The Developmental and Morphological Studies on the Neural and Skeletal Abnormalities in the T/btm Tailless Mice

The crosses, T/+ or T/tw2×btm/btm, give rise to 50% incidence of the tailless mice, development of which was investigated. No difference was seen in external appearance of the embryos at 9 days of gestation. However, some embryos showed fusion of the notochord and the neural tube at the posterior part of the body on the histological examination. The prospective tailless individuals were distinguishable from the normal littermates by the constriction of the root of the tail at 10 days of gestation. Thereafter, they showed several abnormalities such as the poor growth of the posterior part of the body, thinning of the tail and a blood blister at the tail tip or in the lumbosacral region. The abnormal embryos of 11–12 days showed severer abnormalities in the medio‐dorsal area, i.e., the notochord was branched or degenerated at several places and the neural tube was distorted, duplicated or fused with the mesenchyme. All the tailless newborn young had blood blisters or red scars on the dorsal skin at the middle of the lumbosacral region.