Alternative cleavage and polyadenylation (APA) is a widespread phenomenon that generates transcript isoforms with alternative 3’UTR. Through alteration of 3’UTRs, APA potentially regulates the stability, cellular localization, and/or translation efficiency of target mRNAs. Previous work in our lab demonstrated that Tut, Bam, and Bgcn can form a physical complex to promote germ cell differentiation in Drosophila. Surprisingly, mei-P26 has alternative 3’ UTR in fly testes, longer in tut, bam or bgcn mutant while shorter in wild type. We aim to explore the relationship between the change of 3’UTR length and germline differentiation and how differentiation-related 3’UTR is regulated. At the first step, we analyzed the 3’UTR profiles of wild type, tut, bam, or bgcn mutant testes by Poly(A) Site Sequencing (PAS-Seq). We found that hundreds of genes’ 3’UTR were lengthened in tut, bam, or bgcn mutant testes. Our data indicate that 3’UTR length is mis-regulated in spermatogonia-enriched mutant testes, suggesting that APA may be involved in germ cell differentiation. Due to the different cell types between the wild type control and these mutant testes in PAS-Seq, we will clarify whether the change of 3’UTR in tut, bam, or bgcn mutant testes is caused by germ cell differentiating stages. Meanwhile, we will examine the 3’UTR profiles at different stage of germline differentiation to further survey the relationship between the change of 3’UTR length and germline differentiation. In order to elucidate how differentiation-related 3’UTR is regulated, the mRNA target(s) of the Tut-Bam-Bgcn complex will be identified to clarify how the Tut-Bam-Bgcn complex regulates 3’UTR.