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Biomedical subjects

M Kessel

Publications and source records attributed to M Kessel.

At least 163 records · Page 9Linked to original sources
PubMed1968

Regulation and timing of deoxyribonucleic acid synthesis in hyphae of Aspergillus nidulans.

Pulse labeling of deoxyribonucleic acid (DNA) and radioautography have been used to study the effect of growth rate on nuclear replication in Aspergillus nidulans. When conidia were germinated in media supporting a fast growth rate, the radioactive pulse labeled either all of the nuclei in a cell or none of them. At slower growth rates, hyphae contained both labeled and unlabeled nuclei. Altering the growth rate thus changed nuclear replication from simultaneous to sequential. The time taken to duplicate the DNA in a nucleus, estimated from the ratio of labeled to total nuclei, remained constant at the different doubling times. The distribution of label showed that nuclei in the same hypha spent unequal times in both the postmitotic gap (G1) and the premitotic gap (G2) periods when grown at slow rates. These unequal G1 and G2 periods are considered to cause asynchrony. Once DNA synthesis was out of phase through growth on a poor medium, transferring the hypha to a rich medium did not resynchronize the nuclei. To interpret the data, two initiator mechanisms, one starting DNA synthesis and the other mitosis, are postulated to control nuclear replication in A. nidulans.

Adenine↗
PubMed1968

Nonrandom sister chromatid segregation and nuclear migration in hyphae of Aspergillus nidulans.

Radioactive conidiospores of Aspergillus nidulans were prepared by growing a purine-requiring mutant with tritiated adenine. When these spores germinated in a nonradioactive medium, the dispersion of the original chromosome set could be followed by treating the hyphae with ribonuclease and preparing radioautograms. Germinating spores with four or eight nuclei contained two highly labeled nuclei and two or six nuclei with much less or no radioactivity. Successive mitotic divisions thus distributed the deoxyribonucleic acid (DNA) of the eight spore chromosomes among only two of the progeny nuclei. The two nuclei containing the original chromosome set were not dispersed at random along the linear hypha but were usually located near the growing tip. These results are compatible with the view that chromatids containing DNA strands of identical age segregate as a unit during mitosis. They further indicate that the mechanism which disperses newly formed nuclei in the growing hypha can distinguish between nuclei containing DNA strands of different ages.

Adenine↗
PubMed1967

Synchrony of nuclear replication in individual hyphae of Aspergillus nidulans.

The synchrony of nuclear replication in individual, multinucleate hyphae of Aspergillus nidulans has been investigated. Samples were taken from cultures of germinating conidiospores, and the relative frequency of hyphae containing two to eight nuclei was determined. Because the conidiospores are mononucleate, complete synchrony will yield populations of hyphae containing only 2(n) nuclei, n being the number of doublings after germination. The appearance of hyphae with total numbers of nuclei other than 2(n) will indicate lack of synchrony. The relative frequency of hyphae not having 2(n) nuclei will depend on the degree of synchrony in the individual hyphae; numerical aspects of this relation are discussed. In two different strains, replication of the nuclei in any one hypha was highly synchronized when the dry weight doubling time was 1.4 to 1.8 hr. As the doubling time was made longer by changing the nitrogen or carbon source, synchrony was progressively lost. At the slowest growth rate tested, the interval between the division of the fastest and the slowest nucleus equaled 48% of the dry weight doubling time. The active replication of some nuclei in a hypha where other nuclei were resting suggested that nuclear duplication in this eukaryotic organism may be controlled by specific initiators.

Arabinose↗