Immunoglobulin Production in Cloned Sublines of a Human Lymphocytoid Cell Line

In the present study we obtained seven sublines (five diploid and two tetraploid) by cloning LK1D cell line and found that all the sublines contained individual cells which synthesized both α and γ heavy chains along with a single type of light chains, kappa chains. Six of these sublines showed homogeneous karyotypes which were characteristic of each subline, indicating that each subline was most likely to have been derived from a single ancestor cell. Our results show that cells which do not react with anti-immunoglobulin antibodies at a particular time of harvest have the potential to produce immunoglobulins. Moreover, two different heavy chains detected in individual cells are actually synthesized in the same cell and are not due to the transfer of immunoglobulins among the cells.

Chronology and pattern of human chromosome replication. 8. Behavior of the X and Y in early S-phase

The pattern of initiation of DNA replication in normal male and female human cells was studied by a modified method of Mukherjee and Sinha (1965). One of the X chromosomes of female and the Y chromosome of male cells were found to begin DNA replication definitely later than other chromosomes. The possible cause of the discrepancy among reported studies was discussed.

Chronology and pattern of human chromosome replication. VII. Cellular and chromosomal DNA behavior

DNA synthesis in diploid human cells was studied at the cellular and chromosomal levels by means of ³H-thymidine labeling and autoradiography. It was observed that the rate of DNA synthesis increased slowly at the beginning and decreased rapidly at the end of the S period, with a peak midway in the period. The rate and duration of DNA synthesis in individual chromosomes were found to be characteristic for each chromosome pair. Even though there is a certain tendency for the longer chromosomes to have a longer S period, enough variation existed to indicate that the structural make-up of the chromosomes may play an important role in the rate and length of time during which chromosomal DNA synthesis occurs.

Chronology and pattern of human chromosome replication. IX. Metasynchronous DNA replication in homologs

The chronology of DNA synthesis in homologous chromosomes was investigated autoradiographically and statistically. The statistical approach addressed itself toward establishing rigorously the occurrence of synchrony or antisynchrony in the autosomal pairs of groups A and E. In order to evaluate DNA synthesis more intimately, chromosome No. 2, whose short and long arms can be readily identified morphologically, was divided into five arbitrarily defined segments, and the autoradiographic behavior of these was determined. Neither consistent synchrony nor antisynchrony was found to characterize the group A homologs and the segments of No. 2. In contrast to the above findings, chromosomal pair 16 apparently replicated much of its DNA antisynchronously, and a suggestion of similar behavior was obtained for pairs 17 and 18. Nevertheless, exceptions for certain chromosomes at certain times in the S period were found, indicating synchrony or antisynchrony to be present under the conditions of the experiments. Even though no one simple and universal explanation appears to be compatible with the complex data presented, the results are compatible with metasynchronous replication of DNA in homologous chromosomes. This method of replication postulates a time gap of varying length between two homologous DNA loci on chromosomes, this time gap varying from locus to locus, from chromosome to chromosome and from time to time in the S period. Thus, the time length of exposure of cells to labeled thymidine plays a crucial and all-important factor in the type of data obtained autoradiographically and accounts for the diverse statements made in the literature regarding homolog replication.

Autoradiographic investigations of centric fragments and rings in patients with stigmata of gonadal dysgenesis

Four patients with various phenotypic stigmata of gonadal dysgenesis are presented. Cytogenetic investigation revealed each to be mosaic for 45 XO and 46 XO+ minute element stemlines. In two patients the additional element proved to be a small ring, and in the remaining two the supernumerary chromosome was a minute centric fragment. Autoradiographic studies indicated that the ring chromosomes were late replicating, while the metacentric fragments were not. The correlation of the autoradiographic behavior of these abnormal chromosomes with their possible origin is discussed, and a new hypothesis concerning the evolution of the XO karyotype is proposed.

Chronology and pattern of human chromosome replication, IV. Autoradiographic studies of binucleate cells

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