Environmental stresses inhibit splicing in the aquatic fungus Blastocladiella emersonii.
BACKGROUND
Exposure of cells to environmental stress conditions can lead to the interruption of several intracellular processes, in particular those performed by macromolecular complexes such as the spliceosome.


RESULTS
During nucleotide sequencing of cDNA libraries constructed using RNA isolated from B. emersonii cells submitted to heat shock and cadmium stress, a large number of ESTs with retained introns was observed. Among the 6,350 ESTs obtained through sequencing of stress cDNA libraries, 181 ESTs presented putative introns (2.9%), while sequencing of cDNA libraries from unstressed B. emersonii cells revealed only 0.2% of ESTs containing introns. These data indicate an enrichment of ESTs with introns in B. emersonii stress cDNA libraries. Among the 85 genes corresponding to the ESTs that retained introns, 19 showed more than one intron and three showed three introns, with intron length ranging from 55 to 333 nucleotides. Canonical splicing junctions were observed in most of these introns, junction sequences being very similar to those found in introns from genes previously characterized in B. emersonii, suggesting that inhibition of splicing during stress is apparently a random process. Confirming our observations, analyses of gpx3 and hsp70 mRNAs by Northern blot and S1 protection assays revealed a strong inhibition of intron splicing in cells submitted to cadmium stress.


CONCLUSIONS
In conclusion, data indicate that environmental stresses, particularly cadmium treatment, inhibit intron processing in B. emersonii, revealing a new adaptive response to cellular exposure to this heavy metal.
Georg
Raphaela Castro
RC
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Brazil. raphaela@iq.usp.br
Stefani
Rosane M P
RM
Gomes
Suely Lopes
SL
D000222:Adaptation, Physiological; D001754:Blastocladiella / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology*; D020224:Expressed Sequence Tags; D015966:Gene Expression Regulation, Fungal; D015723:Gene Library; D005800:Genes, Fungal; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006358:Hot Temperature; D007438:Introns; D012326:RNA Splicing; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017381:Spliceosomes / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological
D050884:HSP72 Heat-Shock Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D002104:Cadmium