This observation suggests that cohesin levels are maintained at least in part by an epigenetic mechanism

male-specific pattern observed in the C. capitata mAb104 immunoblots is due to male-specific phosphorylation for at least some of the SR proteins. The absent mAb104 signal in females could be due to absence of protein phosphorylation or to a lower expression of these SR proteins and corresponding genes. As a first step to investigate this question, we investigated by digital differential expression analysis in adult C. capitata males and females using available RNA-seq data sets. The male and female reads were combined together and de novo assembled using Trinity software. We obtained 188,625 assembled transcripts with an N50 value of 1693 bp. Using this data set six C. capitata SR orthologous proteins were identified by TBLASTN analysis and found to be highly conserved with the respect of the six Drosophila SR EW-7197 biological activity polypeptides:S6 http://www.biomedcentral.com/1471-2156/15/S2/S6 Page 3 of 6 respectively 88%, 95%, 98%, 92%, 74% and 84% amino acid identity when compared to Drosophila). Male and female reads were then used separately to compute gene expression levels in both sexes. We used the male-specific beta-tubulin and the female-specific fst genes of Ceratitis as a preliminary DGE controls and found that the former is exclusively expressed in the male sex while the latter gene is only expressed in females. Although we have no replicates for this DGE analysis and, hence, we cannot measure the sex bias, this first control data is consistent with what was expected, suggesting that we could answer to the question whether SR-encoding mRNAs are present or not in females. When we used the six Ceratitis SR genes for DGE, no one showed absence of expression in females. We have choosen CcB52 for further analysis, we performed an RT-PCR, using two pair of primers and we got cDNA fragments in both sexes of adult flies. These data suggests that the observed male-specific phosphorylation patterns are likely due to increased phosphorylation rather than to higher transcription in males or reduced transcription in females. In metazoans SR phosphorylation is mainly controlled by a serine-threonine kinase specific for the SR domain, which is therefore named SR protein-specific kinase 1 or SRPK1. In addition, the Cdc2-like kinase family has also been implicated in SR protein phosphorylation events. We therefore investigated whether SR-specific kinases are expressed only in C. capitata males. We identified two putative Ceratitis SRPK1related kinases and expression was observed in the two sexes by DGE analysis. A similar result was obtained for the Drosophila CLK kinase darkener of apricot ortholog in C. capitata which seems to produce mRNAs also in the adult females. The Drosophila doa gene expresses female-specific isoforms which may be involved in sex-specific SR phosphorylation events. Further investigations would be needed to clarify if there are also alternative isoforms for some of Saccone et al. BMC Genetics 2014, 15:S6 http://www.biomedcentral.com/1471-2156/15/S2/S6 Page 4 of 6 these genes in C. capitata, which could have been differentially expressed in the two sexes. Conclusions In conclusion, we show that in two distantly related dipteran species, such as Drosophila and the housefly, the phosphorylation pattern of SR proteins detected by the mAb104 in adult flies seems to be non sex-specific. In contrast in C. capitata adult flies the SR phosphorylation mAb104 pattern of six proteins PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19793655 is almost exclusively male-specific or strongly enriched in this