Transcriptome profiling of the spermatheca identifies genes potentially involved in the long-term sperm storage of ant queens

Abstract

Females of social Hymenoptera only mate at the beginning of their adult lives and produce offspring until their death. In most ant species, queens live for over a decade, indicating that ant queens can store large numbers of spermatozoa throughout their long lives. To reveal the prolonged sperm storage mechanisms, we identified enriched genes in the sperm-storage organ (spermatheca) relative to those in body samples in Crematogaster osakensis queens using the RNA-sequencing method. The genes encoding antioxidant enzymes, proteases, and extracellular matrix-related genes, and novel genes that have no similar sequences in the public databases were identified. We also performed differential expression analyses between the virgin and mated spermathecae or between the spermathecae at 1-week and 1-year after mating, to identify genes altered by the mating status or by the sperm storage period, respectively. Gene Ontology enrichment analyses suggested that antioxidant function is enhanced in the spermatheca at 1-week after mating compared with the virgin spermatheca and the spermatheca at 1-year after mating. In situ hybridization analyses of 128 selected contigs revealed that 12 contigs were particular to the spermatheca. These genes have never been reported in the reproductive organs of insect females, suggesting specialized roles in ant spermatheca.

Transcriptome characterization of male accessory glands in ants to identify molecules involved in their reproductive success

“… *NS shows that the expression is not significantly different between samples (false discovery rate ≥ 0.01, Gotoh et al ., ). ERAP1, Endoplasmic reticulum aminopeptidase‐1; DHR, Disc‐large homologous regions.…”

“…Of 2292 contigs of the accessory glands that were highly expressed relative to the bodies in males, 559, 356 and 320 contigs were the same as contigs of the spermatheca in queens that were highly expressed relative to their bodies 1 week after mating, 1 year after mating, and both time frames, respectively (FDR < 0.01 and |log 2 fold change| ≥ 1; Fig. ), including comp71039_c3_seq1.m.351761 (thyrotropin‐releasing hormone‐degrading ectoenzyme‐like) and comp68199_c1_seq1.m.135927 (angiotensin‐converting enzyme, Tables and Supporting Information Table S1; Gotoh et al ., ). Whole‐mount in situ hybridization analyses revealed that comp71039_c3_seq1.m.351761 (thyrotropin‐releasing hormone‐degrading ectoenzyme‐like) was expressed not only in the accessory glands but also strongly expressed in the seminal vesicles of males (Fig.…”

“…In the present study, contigs thought to be proteolysis regulators, including serine proteases and serine protease inhibitors, were enriched in the accessory glands relative to the bodies (Table ). These have also been identified in the male accessory glands or seminal fluid of other taxa such as honeybees, mosquitoes, beetles and field crickets (Dottorini et al ., ; Baer et al ., ; Simmons et al ., ; Xu et al ., ), and have also been detected in female sperm storage organs of C. osakensis (Gotoh et al ., ) and D. melanogaster (Allen & Spradling, ; Prokupek et al ., ). In males of some insect species, serine proteases induce sperm motility and maturation (Osanai et al ., ; Friedländer et al ., ; Miyata et al ., ; Nagaoka et al ., ).…”

“…Highly expressed genes of the queen spermatheca were identified using nextgeneration sequencing in our previous study. As we also prepared and sequenced male accessory glands and bodies during that study, the sequencing data are available for further analysis of gene expression in the accessory glands of this species (Gotoh et al, 2017b). Furthermore, gene expression profiles of the reproductive organs of both sexes will be useful in understanding the molecular basis for reproductive strategies in this ant species.…”

Genes and genomic processes underpinning the social lives of ants

“…Because queens are long lived but mate shortly after emergence from the pupae, the longterm storage of viable sperm in the queen's specialized organ (spermatheca) is another conundrum that is only now being investigated. Recent comparative transcriptomic analysis of spermatheca in virgin and mated Crematogaster queens identified a number of differentially expressed genes including some associated with antioxidizing function [45 ].…”