Roughly 25% of human B-cell chronic lymphocytic leukaemias (CLL) are characterized by a chromosomal lesion involving 13q14. This region contains the retinoblastoma gene (RB1). We have used a variety of techniques to determine whether RB1 or some other locus is the critical region in 11 cases of low grade B-cell malignancy (mainly CLL), all with deletions or translocations involving 13q14. In all cases, except the one with minimal disease, there was deletion or a structural lesion in the region of D13S25, with at least 4 cases showing homozygous disruption. We conclude that D13S25 lies close to a tumour suppressor locus whose inactivation contributes to the initiation or progression of low grade B-cell malignancy. This locus is located at least 530 kilobases telomeric to RB1.

During Saccharomyces cerevisiae sporulation distinct changes in translatable mRNA species have been detected by two-dimensional gel electrophoresis of the polypeptides produced in a messenger-dependent, cell-free rabbit reticulocyte lysate primed with RNA prepared from a/a, a/a, and a/a isogenic diploids at different stages of sporulation. The availability of functional mRNA increased by about 25% during the first 4 h after transfer of either sporulating (a/a.), or nonsporulating (a/a and a/a) diploids to sporulation medium. Thereafter functional mRNA decreased such that in the a/a strain after 24 h there was only about 50% of the amount in vegetative cells; a less marked decrease was observed in the a/a and a/a strains. Of 750 mRNA species detected, 43 underwent alterations only during sporulation in the a/a strain, whereas 36 changes were common to all three strains and one mRNA specific to a/a vegetative cells was detected. Only four of the sporulation-specific changes were due to the de novo appearance of translatable species, and two of these became predominant species of the total population. The majority of the specific changes were due to either permanent or transient increases in the concentration of individual mRNA species; 11 decreases were found. Changes were found at most stages of sporulation, although many occurred in either of two stages, one early (before 2 h) and the other later (between 6 and 8 h) when commitment to meiotic segregation was beginning. The results provide evidence for both quantitative and, to a lesser extent, qualitative transcriptional control of gene expression during sporulation.Sporulation in the yeast Saccharomyces cerevisiae is a useful system for studying development for several reasons: the genetics of S. cerei'isiae has been extensively studied, and many mutants with known physiological and biochemical characteristics are available; sporulation is readily initiated, and relatively synchronous populations of cells in various stages of sporulation can be obtained; only heterozygous MATa/MATa diploid cells can complete ascus formation under sporulation conditions, the haploid and homozygous diploids being unable to sporulate; and under the nitrogen starvation conditions utilized for the induction of synchronous sporulation, mitotic cell division does not occur, even in cells that do not sporulate. Therefore, this development process is not complicated by concomitant cell cycle events. This also allows one to establish which events during this regimen are due solely to step-down by looking at the behavior of nonsporulating strains.To understand how gene expression is regulated during development, it is first necessary to identify biochemical changes specifically associated with the process. Genetic analyses have implicated at least 50 loci to code for functions indispensible to the process of meiosis and sporulation (16), and it has been established that sporulation in S. cerevisiae is dependent upon certain vegetative gene products (29,30). However, only a very few bioche...

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During Saccharomyces cerevisiae sporulation distinct changes in translatable mRNA species have been detected by two-dimensional gel electrophoresis of the polypeptides produced in a messenger-dependent, cell-free rabbit reticulocyte lysate primed with RNA prepared from a/alpha, a/a, and alpha/alpha isogenic diploids at different stages of sporulation. The availability of functional mRNA increased by about 25% during the first 4 h after transfer of either sporulating (a/alpha), or nonsporulating (a/a and alpha/alpha) diploids to sporulation medium. Thereafter functional mRNA decreased such that in the a/alpha strain after 24 h there was only about 50% of the amount in vegetative cells; a less marked decrease was observed in the a/a and alpha/alpha strains. Of 750 mRNA species detected, 43 underwent alterations only during sporulation in the a/alpha strain, whereas 36 changes were common to all three strains and one mRNA specific to alpha/alpha vegetative cells was detected. Only four of the sporulation-specific changes were due to the de novo appearance of translatable species, and two of these became predominant species of the total population. The majority of the specific changes were due to either permanent or transient increases in the concentration of individual mRNA species; 11 decreases were found. Changes were found at most stages of sporulation, although many occurred in either of two stages, one early (before 2 h) and the other later (between 6 and 8 h) when commitment to meiotic segregation was beginning. The results provide evidence for both quantitative and, to a lesser extent, qualitative transcriptional control of gene expression during sporulation.

Transfection of mouse C127 cells with mitotic chromosomes isolated from a human EJ bladder carcinoma cell line gave rise, at high frequency, to foci of transformed cells. Independent, HRAS1-selected chromosome-mediated transformants displayed distinctive cellular morphologies in monolayer culture and colony-forming abilities in low-melting-point agarose. Subcutaneous inoculation of neonatally thymectomized, Ara-C-protected, total-body-irradiated CBA mice was used to compare the tumorigenic potential of each transformant. Significant quantitative and qualitative differences in tumorigenicity were found between transformants which correlated with differences in malignant phenotype observed in vitro. The sensitivity of the tumorigenicity assay is such that rare transformation events can be selected directly in vivo.