The boule gene is essential for spermatogenesis of haploid insect male

boule (bol), a member of the Deleted in Azoospermia (DAZ) gene family plays an important role in meiosis (reductional maturation divisions) in a spermatogenesis-specific manner in animals by regulating translation of the downstream cell division cycle 25 (cdc25) phosphatase mRNA. Orthologues of bol are conserved among animals and found in the genomes of hymenopteran insects, in which the general mode of reproduction is haplodiploidy: female is diploid and male is haploid. In this mode of reproduction, haploid males produce haploid sperm through non-reductional maturation divisions. The question thus arises of whether the bol gene actually functions during spermatogenesis in these haploid males. In this study, we identified two transcriptional isoforms of bol orthologue (Ar bol and Ar bol-2), and one cdc25 orthologue (Ar cdc25) in the hymenopteran sawfly, Athalia rosae. Ar bol was expressed exclusively in the testis when maturation divisions occurred, while Ar bol-2 was expressed ubiquitously. Knockdown of all bol transcripts (both Ar bol and Ar bol-2) resulted in a lack of mature sperm, whereas males with sole knockdown of Ar bol-2 were able to produce a small number of mature sperm. The cell cycle was arrested before maturation divisions in the testis in which all bol transcripts were knocked down, as revealed by flow cytometry. Although no mature sperm was produced, sperm elongation was partially observed when Ar cdc25 alone was knocked down. These results indicate that Ar bol is essential for the entry and progression of maturation divisions and sperm differentiation in haploid males. •The functions of boule (bol) in haplodiploid organisms were investigated.•Two isoforms, with testis-specific and ubiquitous expression, were identified.•bol functions exclusively in spermatogenesis of haploid males.•bol gene is essential for entry of maturation divisions and sperm differentiation.