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K Mikamo

Publications and source records attributed to K Mikamo.

At least 37 records · Page 2Linked to original sources
PubMed1986

A quantitative study of synaptic ribbons in pinealocytes of adult Chinese hamsters (Cricetulus griseus) under different photoperiodic conditions.

Synaptic ribbons (SR) in pinealocytes of adult (120-130 day-old) male Chinese hamsters (Cricetulus griseus) were classified into types 1, 2 and 3; these have a central dense structure showing rod-like, various and ring-like profiles, respectively. The central structure of the type-2 SR usually appeared as round, oval or comma-like bodies, and occasionally as plates showing various profiles or club-shaped bodies. The quantity of each type of SR, expressed as the SR index, was determined over a 24-h period under a light/dark regime (LD) 12:12 or LD 14:10. On comparing the results obtained from adults with previously published data from young (60-70-days-old) animals under LD 12:12, it was found that, in both young and adult animals, the type-1 and type-3 SR indices exhibited different 24-h variations, whereas the type-2 SR index remained constant over a 24-h period. In addition, the indices of the type-2 SR, but not those of the other SR types, were found to be significantly larger in adult than in young animals. In adult animals, the effects of the photoperiod were different between the three types of SR. A nocturnal increase in the type-1 SR index was observed under both LD 12:12 and LD 14:10, its time course being different for each of these photoperiods. Under LD 14:10, the type-2 SR index showed a significant 24-h rhythm with larger values during the dark period; this was not observed under LD 12:12. The type-3 SR index was almost the same under LD 12:12 and LD 14:10.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1986

Maternal ageing and nondisjunction: a comparative study of two chromosomal techniques on the formation of univalents in first meiotic metaphase oocytes of the mouse.

The incidence of univalents was compared between slides prepared according to two clearly different chromosomal methods, i.e. Tarkowski's method and ours, in order to examine whether a univalent pair could be formed artifactually at the first meiotic metaphase (MI). The oocytes used were obtained from young (2-3 months) and old (12-15 months) age groups of both C57BL/6 and dd mice. In Tarkowski's method only a single fixative was used, while in our method three different fixatives were used successively in order to fix oocytes without their being ruptured. Despiralized, fuzzy and loosely associated chromatids were seen frequently in the slides prepared by Tarkowski's method, while such features were seen less frequently in the slides prepared by our method. The incidence of oocytes with univalents in the slides made by Tarkowski's method was much higher than in those made by ours in both age and strain groups (P less than 0.05-0.001). Thus, it was confirmed that the so-called univalents could be produced artifactually. The results did not support the production line hypothesis of Henderson and Edwards (1968) which was based on their observation of an increased incidence of univalents in MI oocytes from aged female mice.

Aging↗
PubMed1986

Absence of late effects on survival and developmental abilities of pachytene oocytes X-irradiated during neonatal stages in the Chinese hamster.

In neonatal Chinese hamsters, all oocytes on day 0 after birth are at pachytene and ovarian X-irradiation with 1 Gy causes no acute oocyte killing. The same treatment on day 4, however, kills all diplotene-dictyate oocytes within 48 h, and consequently only a small number of pachytene oocytes survives. We investigated late effects of X-rays on the pachytene oocytes in relation to the reproductive capacity of irradiated females. There was no difference between the 0-day irradiated females and the controls with respect to the age of sexual maturation, fertility span and the rate of age-dependent reduction in the number of oocytes due to follicular atresia. On the other hand, the 4-day irradiated females showed a marked delay in sexual maturation and a very precocious cessation of oestrous cycles. However, the degeneration of the surviving oocytes was not accelerated. Fertility tests on day 18.5 of gestation revealed that there was no difference between both irradiated groups and the controls with respect to the mean number of corpora lutea and to the occurrence of dead and abnormal conceptuses. These results indicate clearly that pachytene oocytes were not affected at all by either acute or late effects of X-rays although the dose was high enough to kill diplotene-dictyate oocytes completely.

Aging↗
PubMed1986

An improved, efficient method for analyzing human sperm chromosomes using zona-free hamster ova.

We have developed an improved method for analyzing human sperm chromosome, using zona-free hamster ova. Our main improvements of methodology are as follows: (1) Fertilization rate of hamster oocytes by human spermatozoa was markedly raised by successive treatments of the spermatozoa with 5-15 microM ionophore A23187 solutions and a capacitation medium (BWW medium) containing 3.5% HSA. The HSA most effective in inducing capacitation was selected from several kinds of HSA products commercially available. (2) Monospermic fertilization was ensured by inseminating oocytes with highly capacitated spermatozoa at a low concentration for a short time. (3) TC medium 199 was used for postinsemination culture of the eggs. (4) A medium containing podophyllotoxin and vinblastine (0.04 micrograms/ml each) was used to block karyogamy and first-cleavage spindle formation. (5) Chromosome slides were prepared with our gradual fixation-air-dry method instead of Tarkowski's method. Ninety-two to 177 spermatozoa corresponding in number to 43%-79% (mean: 62%) of the inseminated oocytes were successfully karyotyped in each experiment. In spite of above-mentioned quantitative improvements, quality of Q-banding was not necessarily satisfactory in our slides. Improvement of banding technique is an important problem to be solved in our method. Spontaneous incidence of chromosome aberrations was studied in a total of 1,091 spermatozoa obtained from nine semen samples from four donors. Incidences of aneuploidy and structural anomaly were 0.9% (hyperhaploidy, 0.45%; hypohaploidy, 0.45%) and 13.0%, respectively. Structural aberrations included breaks (45.1%), fragments (32.4%), exchanges (21.8%), and deletions (0.7%). Ratio of X-sperm to Y-sperm was 53% to 47%. These results were discussed in comparison with those reported previously.

Animals↗
PubMed1985

Maturation of spermatozoa in the epididymis of the Chinese hamster.

Chinese hamster spermatozoa gain their ability to move when they descend from the testis to the distal part of the caput epididymis, but it is not until they enter the corpus epididymis that they become capable of fertilizing eggs. The maturation of the spermatozoa proceeds as they further descend the tract and perhaps continues even in the vas deferens. During transit between the distal caput and proximal cauda epididymides, small membrane-limited vesicles (and tubules) appear on the plasma membrane over the acrosomes of the spermatozoa. The number of vesicles appearing on the sperm brane reaches a maximum when the spermatozoa are in the proximal cauda epididymis. It declines sharply in the distal cauda epididymis. Spermatozoa in the vas deferens are free of the vesicles. The origin, chemical nature, and functional role of the vesicles that appear on the sperm surface during epididymal transit must be the subject of further investigation.

Animals↗
PubMed1984

Neonatal oocyte development and selective oocyte-killing by X-rays in the Chinese hamster, Cricetulus griseus.

The process of ovarian development in neonatal Chinese hamsters aged between 0 and 16 days was studied histologically and quantitatively in both a non-irradiated group and an irradiated group. In the latter, ovaries were exposed to a single dose of 1 Gy X-rays on days 0, 2, 4, 6, 8, 10, 12 and 14 after birth. All oocytes on day 0 were at pachytene, and nearly all of them seemed to develop to dictyate by day 10. A quantitative analysis of age-dependent changes in the distribution of oocytes showed that a marked spontaneous degeneration of oocytes took place twice, i.e. during pachytene (day 0 to day 4) and dictyate (day 12 to day 14). Oocytes of this species were found to be very radioresistant at pachytene, but to become sharply sensitive during the phases between diplotene and early dictyate, suffering an almost complete oocyte-killing after 1 Gy. However, they recovered radioresistance after the onset of the resting stage. The changing aspects of radiosensitivity in the Chinese hamster were shown to be far more marked than in the mouse and the rat, which have been observed by previous investigators.

Animals↗
PubMed1983

Absence of correlation between univalent formation and meiotic nondisjunction in aged female Chinese hamsters.

The effects of maternal aging on the configuration of chiasmata, formation of univalents, and segregation of first meiotic (MI) chromosomes were investigated in young (5-8 mo) and old (16-19 mo) Chinese hamsters. Primary oocytes were collected only from mature follicles approximately 10 h before ovulation, and secondary oocytes were obtained from the oviducts 5 h after spontaneous ovulation. The average number of chiasmata per oocyte was significantly smaller in aged hamsters than in the young hamsters (P less than 0.001). Terminal chiasmata were found more frequently in the former group than in the latter one (P less than 0.001). These results coincided well with findings in the mouse. Since the 11 meiotic chromosomes could be divided into four morphologically distinguishable subgroups, it was possible to determine whether the same bivalent forming univalents at MI actually underwent nondisjunction in the following meiotic division. The incidence of both MI oocytes with a univalent pair and aneuploid MII oocytes due to first meiotic nondisjunction was significantly higher in the aged group than in the young group (P less than 0.01) and P less than 0.05, respectively). However, univalents occurred almost exclusively in the smallest metacentric chromosome group (96%), whereas nondisjunction took place nearly equally in each chromosomal subgroup. These results clearly showed that there was no correlation between the univalents seen at MI and nondisjunction during the first meiotic division.

Aging↗
PubMed1983

Developmental-stage-dependent teratogenic effects of maternal spontaneous diabetes in the chinese hamster.

The effect of maternal diabetes on teratogenesis was examined utilizing female Chinese hamsters with typical diabetic symptoms from our closed colony (CHA) and F13-F19 of the brother-sister mating generations of a diabetic strain (CHAD). Both groups were mated with nondiabetic males from CHA. Embryologic studies on day 2.5, 4.5, and 18.5 of gestation were performed with 30, 31, 71 diabetic females that were impregnated during a normal 4-day estrous cycle. The preimplantation embryos of day 2.5 and 4.5 were also karyotyped. The results indicated that: (1) There was no decrease in the number of ovulated ova, of collected embryos, and of implantation sites in the diabetic females. (2) As far as the preimplantation stages were concerned, there was no decrease in the cleavage activity and no increase in the incidence of developmental anomalies. (3) There was no increase of chromosomal aberrations in the preimplantation embryos. (4) With respect to the postimplantation development, however, there were significant increases in embryonic death (P less than 0.001), gross malformation (P less than 0.001), and fetal hypoplasia (P less than 0.001). Results (1), (2), and (3) indicated that in diabetic females capable of conceiving during a normal estrous cycle, the maternal diabetic milieu did not affect oogenesis, ovulation, fertilization, cleavage division, implantation, and chromosomal behavior. Result (4), however, showed definitely that maternal diabetes exerted deleterious effects on fetal development during the stage of organogenesis, and also markedly reduced fetal growth during later developmental stages.

Animals↗
PubMed1982

Establishment of Chinese hamster stocks homozygous for a reciprocal translocation originally induced by testicular X-irradiation.

Following testicular X-irradiation of Chinese hamster (Cricetulus griseus) males eight progeny (five males and three females) with reciprocal translocatons (heterozygotes) were obtained. They were all phenotypically normal but semi-sterile. Homozygotes were produced successfully with CHAT3 (2p-;9q+) and CHAT5 (2q-;8q+). They were proven to be fertile. Thus, two homozygous stocks with distinct marker chromosomes were established. CHAT3 homozygotes have shown a high incidence of diabetes, while CHAT5 nomozygotes had no genetic burden. Progeny tests of outcrosses and intercrosses with the heterozygotes and homozygotes were performed in both stocks. Karyological analysis of the first cleavage division showed the marker chromosomes of both stocks to be useful in distinguishing the paternal chromosome complements from the maternal ones.

Animals↗
PubMed1980

Giant diploid oocytes as a cause of digynic triploidy in mammals.

Giant oocytes and zygotes twice the normal size from the Chinese hamster were studied embryologically and cytogenetically in order to clarify their significance as a cause of digynic triploidy. There were 6 (0.62%) giant eggs among 973 primary oocytes, 5 (1.37%) among 365 secondary oocytes from mature follicles missing ovulation, 3 (0.44%) among 677 secondary oocytes from oviducts, 4 (0.45%) among 886 one-cell zygotes, and 3 (0.49%) among 608 two-cell zygotes. The results indicated that follicles containing a giant oocyte might have a tendency to miss ovulation. But once ovulated, the giant eggs were fertilized normally and developed normally. Nuclear and chromosomal aspects were studied in 6 primary and 18 secondary oocytes, and 6 one-cell and 5 two-cells zygotes. There were mononuclear and binuclear giant oocytes, but the latter state was rarely maintained to metaphase II. The primary oocytes showed a diploid number of bivalents (22 tetrads) with normal chiasma configuration, and the secondary oocytes had 22 dyads with normal features, indicating normal segregation. The one-cell zygotes exhibited one set of diploid female pronuclear chromosomes and one set of haploid male pronuclear chromosomes in the late prophase. The two-cell zygotes were all digynic triploids; the tail of a fertilizing spermatozoon was attached. There were five XXX and six XXY giant triploids, giving a ratio of 1:1, as expected. It was suggested that the nuclear-cytoplasmic ratio of giant triploid eggs may be more favorable at least for preimplantation development than that of any other type of triploidy. Giant diploid oocytes may be an important source of human digynic triploids, in spite of the prevailing view from studies of marker chromosomes that suppression of first polar body extrusion is the predominant cause.

Aneuploidy↗
PubMed1980

An experimental approach to the analysis of mechanisms of meiotic nondisjunction and anaphase lagging in primary oocytes.

The in vivo genomic mutagenicity of colchicine in Chinese hamster primary oocytes was analyzed at a carefully chosen dose that did not completely arrest the formation of the first meiotic spindle but exhibited a remarkable ability to induce nondisjunction, very possibly as a result of inhibition of tubulin polymerization. A single dose of 3 microgram of colchicine per gram body weight was administered intraperitoneally at the onset of formation of the first meiotic spindle in females with a normal estrous cycle. Morphologically abnormal secondary oocytes with one or two extremely large first polar bodies occurred frequently, namely, in 47 (11.3%) of 416 oocytes. Chromosome analysis of a total of 2,124 secondary oocytes revealed that the overall incidence of aneuploids increased significantly (P less than 0.001) in the experimental group (25.9%, or 99/382) as compared with the control group (2.0%, or 35/1,742). The minimum genomic mutagenicity of colchicine caused non-disjunction in one or two bivalents and eventually induced the formation of aneuploid secondary oocytes with chromosome numbers within the haploid range. The maximum genomic mutagenicity at the selected dose caused the elimination of a large number of chromosomes from the egg body, in association with the formation of a giant polar body or bodies. Three types, each with two subdivisions, of abnormal chromosome segregation between the oocytes and their giant polar body or bodies were studied, revealing part of the process resulting in aneuploid production due to either nondisjunction or anaphase lagging. The fate of the lagging chromosomes was also observed; they were included in neither the oocytes nor the polar body but eventually degenerated within the perivitelline space. The conditions of the spindle in oocytes aged by pre- and postovulatory over-ripeness, both of which have been known to induce meiotic chromosomal nondisjunction, are discussed in relation to tubulin polymerization.

Aneuploidy↗
PubMed1978

Anatomic and chromosomal anomalies in 944 induced abortuses.

A total of 944 induced abortuses, 922 of which apparently were anatomically normal and 22 of which were anatomically abnormal, were set up in culture. Of these abortuses, 910 (96.4%) were successfully karyotyped. The study can be divided into two periods. In the initial period, specimens without recovered fetal tissues were excluded, and no chromosome anomalies were found among the 182 abortuses karyotyped. In the later period of study, abortion specimens both with and without recovered fetal tissues were included, and 23 chromosomally abnormal abortuses, 9 of which were without recovered fetal tissues, were found among the 728 abortuses karyotyped. This gives a chromosome abnormality rate of 3.2%. The mean ovulation age for the 728 abortuses was 63.4 days (range 33--109 days). The mean maternal age was 28.4 years (range 15--48 years). The chromosomally abnormal abortuses included 13 (10 nonmosaic and 3 mosaic) trisomics, 7 triploids, 2 abortuses with balanced D/D translocations and an abortus with an XXq- karyotype. Among the 616 abortuses in which both amniotic and fetal tissues were karyotyped, there was complete karyotypic agreement between the two tissues. Among the 339 abortuses in which tissue samples from both sides of the body were analyzed, complete agreement was also found. Factors that may influence the prevalence of abnormal karyotypes in induced abortuses are discussed.

Abortion, Induced↗