Functional dissection of the ash2 and ash1 transcriptomes provides insights into the transcriptional basis of wing phenotypes and reveals conserved protein interactions.
BACKGROUND
The trithorax group (trxG) genes absent, small or homeotic discs 1 (ash1) and 2 (ash2) were isolated in a screen for mutants with abnormal imaginal discs. Mutations in either gene cause homeotic transformations but Hox genes are not their only targets. Although analysis of double mutants revealed that ash2 and ash1 mutations enhance each other's phenotypes, suggesting they are functionally related, it was shown that these proteins are subunits of distinct complexes.


RESULTS
The analysis of wing imaginal disc transcriptomes from ash2 and ash1 mutants showed that they are highly similar. Functional annotation of regulated genes using Gene Ontology allowed identification of severely affected groups of genes that could be correlated to the wing phenotypes observed. Comparison of the differentially expressed genes with those from other genome-wide analyses revealed similarities between ASH2 and Sin3A, suggesting a putative functional relationship. Coimmunoprecipitation studies and immunolocalization on polytene chromosomes demonstrated that ASH2 and Sin3A interact with HCF (host-cell factor). The results of nucleosome western blots and clonal analysis indicated that ASH2 is necessary for trimethylation of the Lys4 on histone 3 (H3K4).


CONCLUSIONS
The similarity between the transcriptomes of ash2 and ash1 mutants supports a model in which the two genes act together to maintain stable states of transcription. Like in humans, both ASH2 and Sin3A bind HCF. Finally, the reduction of H3K4 trimethylation in ash2 mutants is the first evidence in Drosophila regarding the molecular function of this trxG gene.
Beltran
Sergi
S
Departament de Genètica, Universitat de Barcelona, Diagonal 645, Barcelona, Spain. beltran@ub.edu
Angulo
Mireia
M
Pignatelli
Miguel
M
Serras
Florenci
F
Corominas
Montserrat
M
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D019521:Body Patterning / Q000235:genetics; D049109:Cell Proliferation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004330:Drosophila / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020869:Gene Expression Profiling; D006657:Histones / Q000378:metabolism; D008745:Methylation; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D056264:Sin3 Histone Deacetylase and Corepressor Complex; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014921:Wings, Animal / Q000033:anatomy & histology / Q000254:growth & development* / Q000378:metabolism
C490910:ASH1 protein, Drosophila; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006657:Histones; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D012269:Ribosomal Proteins; C099683:SIN3A transcription factor; D014157:Transcription Factors; C103604:ash2 protein, Drosophila; C473147:host cell factor, Drosophila; D056264:Sin3 Histone Deacetylase and Corepressor Complex