Microcells were prepared by enucleation of micronucleated normal human diploid cells and these microcells were purified by using bovine serum albumin gradient. SV40-transformed xeroderma pigmentosum (XP) cells were fused with the purified microcells and UV resistant clones were obtained. Analysis of UV sensitivity and chromosome numbers of the transferred clones indicated that a part of genome of normal human cells were transferred and the gene(s) controlling excision repair of UV damage should have been introduced into the XP cells. Identification of chromosome(s) responsible for the DNA repair was not possible because of aberrent chromosome constitution of the recipient cells.
The correlation between dominant-lethal mutations and chromosome aberrations in first cleavage and the relative sensitivities of germ cells and zygotes to the induction of chromosome aberrations by methyl methanesulfonate (MMS), iso-propyl methanesulfonate (iPMS) and Mitomycin C (MC) were studied in copulated females. All chemicals tested induced dose-dependent dominant-lethal erects. The incidence of dominant lethals induced by postcopulation treatment with MMS was about half of that induced in spermatozoa and late spermatids in males at same dose, whereas the incidence obtained by iPMS or MC treatment was about 7 and 14 times, respectively. The relationship between dominant lethals and chromosome aberrations at first cleavage was not necessarily direct, which was suggestive of the involvement of some non-genetic erects. Chromosome aberrations observed in first cleavage were very high in preovulatory oocytes and sperm in oviducts (immediately after copulation) by MMS or MC treatment. iPMS, on the other hand, did not induce so many aberrations as MMS or MC did. In the case of MMS, the number of structural aberrations in the paternal chromosomes was greater than in maternals, but the extent of aberrations induced by MC or iPMS could not be distinguished because of the chemical-induced delay of pronuclei to develop.
A temperature-sensitive cell clone has been isolated from Chinese hamster ovary cells (CHO-KI) after mutagenesis with MNNG and BrdU-light suicide selection. The clone, ts-123, has a tetraploid chromosome complement and grows well at the permissive temperature (33°C). However, when incubated at the non-permissive temperature (39°C), the cell number increases only to a limited extent (2-fold increase) within three days. After this period the majority of cells reach higher degree of polyploidy and cells become multinucleated. The temperature effect is irreversible. Cell cycling analysis with a technique of differential staining of sister chromatids with BrdU-Hoechst reveales that at 39°C, ts-123 cells can replicate chromosomal DNA at least 3-rounds before they cease to grow. The processes of polyploidization and multinucleation in synchronized cells were further examined by autoradiography and time-lapse photomicroscopy. Based on the results of such experiments and findings of continued DNA replication, nuclear division, successive polyploidization or multinucleation, it is concluded that the defective function is associated exclusively with the process of cytokinesis. Polyploidization and multinucleation in ts-123 appear to be due to the incomplete cytokinesis and subsequent fusion of daughter nuclei.
Drosophila spermatozoa treated with triethylene melamine (TEM) or ethyl methanesulfonate (EMS) were stored in untreated females, and changes in the frequency of sex-chromosome losses were determined. In some experiments, an enhancing effect of storage on sex-chromosome losses was observed, while in other experiments the effect disappeared. The effect of storage was found to be dependent on the strains used. In the case of TEM, the effect was dose-dependent. At low doses the yield of sex-chromosome losses increased markedly after storage, while at high doses the enhancing effect disappeared. When enhancing effects were observed, the increase in yield after storage was marked for double marker losses (loss of both terminal markers on the doubly marked Y) than for single marker losses (loss of one of the two markers). These results suggest that sex-chromosome losses potentially respond to storage treatment, but the effect can be modified by some factors. The present findings are discussed in terms of potential break hypothesis.
Using two different kinds of experiment, spontaneous mutation at two esterase loci in D. virilis was investigated with special reference to heterozygosity and sex. Twelve newly-arisen variants at the two loci have been obtained among approximately 800, 000 genes examined in cross experiments, and eight variants from cage experiments. The experiments have revealed the following features which appear to be unique to the present study. (1) In the cross experiments only female heterozygotes produced new variants, at a rate of 0.5-1.0×10-4/α-locus/generation. (2) The α-esterase alleles appear to mutate in a particular direction. (3) New variants (α8+ and βD+) which have not been observed previously have been obtained. (4) The Est-α locus coding for a monomer esterase appears to be more mutable than the Est-β locus coding for a dimer enzyme. (5) In the cage experiments, the gene frequencies of newly arisen variants, except for α8+, remained nearly constant. Intracistronic recombination has been suggested as the mechanism responsible for these phenomena.
Alleles of Px2A and Px4A at the Px-1 locus in wild and cultivated rice strains code dimeric peroxidase isozymes, which were detected zymographically with lemmata and paleae at higher intensity as well as with leaf blade and leaf sheath at lower intensity. In a heterozygote, Px2APx4A, three isozyme bands 2A, 3A and 4A appear. Distinct differences in the intensity ratio of the bandmorphs were observed, and they were classified into types I to V. A cross between Japonica sativa and Asian perennis showed type I only. Another cross between two strains of Asian perennis showed type II only, but a cross between Japonica sativa and African perennis showed types I to III. A receptor mutant gene adjacent to the Px-1 locus and two regulator gene loci independent from the Px-1 locus were assumed to account for the inheritance.
Of seven expected allotrisomics with AA genome and an extra chromosome from genome B six were found in the progenies of triploid hybrids Avenabarbata Pott. (AABB) crossed with A, strigosa Schreb. (AA) or A. wiestii Steud. (AA). The primary allotrisomics further produced six derived types such as autotrisomic with AA and a chromosome from A, long arm telotriso-mic and long arm isotrisomic. Most of trisomic types were easily distinguished from disomic sibs by dwarf ness, low seed fertility and some morphological characteristics governed by genes located on the trisome from genome B though the former two seem to be mainly due to the genic unbalance caused by aneuploidy. In self ed progenies of the various trisomics, transmission rate of the trisome ranged from 6 to 28 per cent and their fertility varied 30 to 78 per cent. Most of allotrisomic types indicated 7//+1/, but sometimes 6//+1/// at MI. In two allotrisomic types, the extra chromosomes were highly homologous with their homoeologues of genome A. Then, substitution between them, only in a single dose, was sometimes observed in disomic and trisomic progenies.
Cytological observations were made on spike primordia as well as root and leaf meristems of hybrids between Hordeum vulgare and H, bulbosum (2x) to elucidate mechanism of chromosome elimination. High frequencies of cells with micronuclei were observed in spike primordia of the hybrids examined. The average percentages of cells with micronuclei in three different hybrids were 16.8% (R25788), 12.9% (S92-201) and 7.9% (S130-200). About 40% of spike primordium cells of R25788 had fewer chromosomes than the 14 expected in a diploid hybrid. On the other hand, in root and leaf meristems of R25788, percentages of cells with micronuclei were 2.3% and 2.4%, respectively. Also, 94.6% of root meristem cells of R25788 had the expected hybrid chromosome number. Thus, chromosome elimination in hybrids between H. vulgare and H. bulbosum appears to be a tissue-dependent phenomenon, perhaps related to the extent of differentiation required. Disturbances in nuclear division were also examined. Percentages of cells with non-congressed chromosomes at metaphase and lagging chromosomes at anaphase were 15.2% and 20.7%, respectively in spike primordia of R25788. These percentages are similar to those of cells with micronuclei in spike primordia of R25788. It is suggested that failure of congression of some chromosomes during prometaphase is the main mitotic disturbance leading to chromosome elimination.