Expressed sequence tag (EST) databases represent a large volume of information on expressed genes including tissue type, expression profile and exon structure. In this study we create an extensive data set of human alternative splicing. We report the analysis of 7867 non-redundant mRNAs, 3011 of which contained alternative splice forms (38% of all mRNAs analysed). From a total of 12 572 ESTs 4560 different possible alternative splice forms were detected. Interestingly, 70% of the alternative splice forms correspond to exon deletion events with only 30% exonic insertions. We experimentally verified 19 different splice forms from 16 genes in a total subset of 20 studied; all of the respective genes are of medical relevance.z 2000 Federation of European Biochemical Societies.

No abstract

The levels of pyruvate kinase (PYK1), alcohol dehydrogenase (ADH1), phosphoglycerate kinase (PGK1) and phosphoglycerate mutase (GPM1) mRNAs were measured during batch growth and during the yeast-to-hyphal transition in Candida albicans. The four mRNAs behaved in a similar fashion. PYK1, ADH1, PGK1 and GPM1 mRNA levels were shown to increase dramatically during the exponential growth phase of the yeast form, and then to decrease to relatively low levels in the stationary phase. The dimorphic transition was induced using two sets of conditions: (i) an increase in temperature (from 25 degrees C to 37 degrees C) combined with the addition of serum to the medium; and (ii) an increase in temperature (from 25 degrees C to 37 degrees C) and an increase in pH of the growth medium (from pH 4.5 to pH 6.5). Additional cultures were analysed to control for the addition of serum, and for changes in temperature or pH. Immediately following dilution of late-exponential cells into fresh media the levels of all four glycolytic mRNAs decreased rapidly in contrast to the ACT1 mRNA control, the level of which increased under most conditions. The recovery of glycolytic mRNA levels depended on the culture conditions, but there was no direct correlation with the formation of germ tubes, with the addition of serum to the medium, the increase in culture temperature, the medium pH, or the glucose concentration. This indicates that the changes in glycolytic gene expression that accompany the dimorphic transition in C. albicans reflect the underlying physiological status of the cells during morphogenesis and not alterations to cell shape.

The transcript level of the Candida albicans ACT1 gene (encoding actin) is strongly regulated during induction of hyphal morphogenesis. ACT1 mRNA declines rapidly during starvation pretreatment and quickly recovers in media inducing morphogenesis. The C. albicans URA3 and LEU2 mRNAs, as well as an ACT1 promoter/LAC4 fusion, are regulated similarly. The regulation of ACT1/LAC4 and unaltered mRNA stabilities suggest transcriptional regulation during morphogenesis. However, by individually testing morphogenesis induction parameters, it is shown that starvation and growth phase, but not hyphal formation, are responsible for ACT1 transcript regulation; this conclusion is confirmed by analyses of morphological mutants and by inhibition of hyphal development. Thus, the specific morphogenesis-induction conditions, but not morphogenesis per se, affect transcript levels in C. albicans.

No abstract