Identification and characterization of a doublesex gene which regulates the expression of insulin-like androgenic gland hormone in Fenneropenaeus chinensis

Genome-wide identification and expressional profile of the Dmrt gene family in the swimming crab (Portunus trituberculatus)

The swimming crab, Portunus trituberculatus is one of crucial aquaculture crabs with significant differences in growth and economic performance between male and female swimming crabs. Consequently, the culture of female populations presents higher economic value. The doublesex and mab-3 related transcription factor (Dmrt) gene family are known to play crucial role in gonad differentiation and development. However, there is limited information about this gene family in Portunus trituberculatus. In this study, we identified seven members of the Dmrt gene family in P. trituberculatus based on the published transcriptome and genome data and designated as Ptdmrt-1, Ptdoublesex (Ptdsx), Ptidmrt-1, Ptdmrt-11E, Ptidmrt-2, Ptdmrt-99B, and Ptdmrt-3 based on the homology analysis results, respectively. These Ptdmrt genes distributed across 6 chromosomes and were predicted to encode 283 aa, 288 aa, 529 aa, 436 aa, 523 aa, 224 aa, and 435 aa protein precursors, respectively. The expression patterns of these dmrt genes were characterized by qRT-PCR and gonad transcriptome data. The results showed that five members (Ptdmrt-99B, Ptdsx, Ptdmrt-1, Ptdmrt-3, and Ptdmrt-11E) were differentially expressed between the testis and ovary. In addition, their expression patterns from zoea 2 to juvenile 1 were characterized by published transcriptome data and the results showed that they were lowly expressed and did not exhibit notable difference except for Ptdsx during early development. Overall, majority of Ptdmrt genes were involved in gonad differentiation in the swimming crab. Current findings provide a solid foundation for further exploration of the roles of these genes in gonad development and differentiation in P. trituberculatus.

Doublesex is essential for masculinization but not feminization in Lygus hesperus

In most holometabolous insects, sex differentiation occurs via a hierarchical cascade of transcription factors, with doublesex (dsx) regulating genes that control sex-specific traits. Although less is known in hemimetabolous insects, early evidence suggests that substantial differences exist from more evolutionarily advanced insects. Here, we identified and characterized dsx in Lygus hesperus (western tarnished plant bug), a hemipteran pest of many agricultural crops in western North America. The full-length transcript for L. hesperus dsx (Lhdsx) and several variants encode proteins with conserved DNA binding and oligomerization domains. Transcript profiling revealed that Lhdsx is ubiquitously expressed, likely undergoes alternative pre-mRNA splicing, and, unlike several model insects, is sex-biased rather than sex-specific. Embryonic RNA interference (RNAi) of Lhdsx only impacted sex development in adult males, which lacked both internal reproductive organs and external genitalia. No discernible impacts on adult female development or reproductivity were observed. RNAi knockdown of Lhdsx in nymphs likewise only affected adult males, which lacked the characteristic dimorphic coloration but had dramatically elevated vitellogenin transcripts. Gene knockout of Lhdsx by CRISPR/Cas9 editing yielded only females in G0 and strongly biased heterozygous G1 offspring to females with the few surviving males showing severely impaired genital development. These results indicate that L. hesperus male development requires Lhdsx, whereas female development proceeds via a basal pathway that functions independently of dsx. A fundamental understanding of sex differentiation in L. hesperus could be important for future gene-based management strategies of this important agricultural pest.

Phenotypic sorting of individual male and female intersex Cherax quadricarinatus and analysis of molecular differences in the gonadal transcriptome

Cherax quadricarinatus exhibit sexual dimorphism, with males outpacing females in size specification and growth rate. However, there is limited understanding of the molecular mechanisms underlying sex determination and sex differentiation in crustaceans. To study the differences between intersex individuals and normal individuals, this study counted the proportion of intersex individuals in the natural population, collected the proportion of 7 different phenotypes in 200 intersex individuals, and observed the differences in tissue sections. RNA-seq was used to study the different changes in the transcriptome of normal and intersex gonads. The results showed that: the percentage of intersex in the natural population was 1.5 %, and the percentage of different types of intersex ranged from 0.5 % to 22.5 %; the sections revealed that the development of normal ovaries was stagnant at the primary oocyte stage when intersex individuals with ovaries were present; We screened for pathways and genes that may be associated with gonadal development and sex, including ovarian steroid synthesis, estrogen signaling pathway, oocyte meiosis, progesterone-mediated oocyte maturation, etc. Relevant genes including tra2a, dmrta2, ccnb2, foxl2, and smad4. This study provides an important molecular basis for sex determination, sex-controlled breeding, and unisex breeding in red crayfish.

Transcriptional regulation of IAG by dsx and foxl-2 in mud crab (Scylla paramamosain)

Scylla paramamosain is an important cultured crab species on the southeast coast of China. However, the molecular regulation mechanism of its gonadal development still has not been thoroughly studied. Dsx (doublesex) and foxl-2 (forkhead transcription factor gene 2) are important transcription factors involved in gonadal development. So far, studies on the functions of dsx and foxl-2 in crustaceans are very limited. Insulin-like androgenic gland hormone (IAG) is an effector molecule that regulates the differentiation, development and sex maintenance of testes in crustaceans. In this study, the promoter region of Sp-IAG was predicted, and several potential binding sites of dsx and foxl-2 were found. Site-directed mutagenesis was performed on the predicted potential binding sites, and their promoter activity was analyzed. The results showed that there was a dsx and a foxl-2 binding site, respectively, that could regulate the expression of Sp-IAG. In order to verify the regulatory effect of these two transcription factors on Sp-IAG, we constructed the expression plasmids of dsx and foxl-2 and co-transfected them into HEK293T cell lines with the promoter of Sp-IAG, respectively. The results showed that dsx could significantly promote the expression of Sp-IAG, while foxl-2 could inhibit its expression substantially. Then we carried out in vivo RNA interference experiment on mud crabs. The expression of dsx and foxl-2 in crabs was interfered respectively. The results of qRT-PCR showed that the expression of Sp-IAG was significantly inhibited after interfering with dsx, while significantly increased after interfering with foxl-2, which was consistent with the cell experiment. In conclusion, dsx and foxl-2 transcription factors play opposite roles in regulating the expression of Sp-IAG.

Monosex Populations of the Giant Freshwater Prawn Macrobrachium rosenbergii-From a Pre-Molecular Start to the Next Generation Era

Sexual manipulation in the giant freshwater prawn Macrobrachium rosenbergii has proven successful in generating monosex (both all-male and all-female) populations for aquaculture using a crustacean-specific endocrine gland, the androgenic gland (AG), which serves as a key masculinizing factor by producing and secreting an insulin-like AG hormone (IAG). Here, we provide a summary of the advancements from the discovery of the AG and IAG in decapods through to the development of monosex populations in M. rosenbergii. We discuss the broader sexual development pathway, which is highly divergent across decapods, and provide our future perspective on the utility of novel genetic and genomic tools in promoting refined approaches towards monosex biotechnology. Finally, the future potential benefits of deploying monosex prawn populations for environmental management are discussed.

Sexual dimorphic eyestalk transcriptome of kuruma prawn Marsupenaeus japonicus

Kuruma prawn (Marsupenaeus japonicus) is a benthic decapod crustacean that is widely distributed in the Indo-West Pacific region. It is one of the most important fishery resources in Japan, but its annual catches have declined sharply since the 1990s. To increase stocks, various approaches such as seed production and aquaculture were attempted. Since the demand for important fishery species, including kuruma prawn, is expected to increase worldwide in the future, there is a need to develop new technologies that will make aquaculture more efficient. Historically, the eyestalk endocrine organ is known to consist of the X-organ and sinus gland (XO/SG) complex that synthesizes and secrets various neuropeptide hormones that regulate growth, molt, sexual maturation, reproduction, and changes in body color. In the current study, eyestalk-derived neuropeptides were identified in the transcriptome. In addition, most orthologs of sex-determination genes were expressed in eyestalks. We identified two doublesex genes (MjapDsx1 and MjapDsx2) and found that MjapDsx1 showed male-biased expression in the eyestalk ganglion with no sex-specific splicing, unlike insect species. Therefore, this study will provide an opportunity to advance the research of neuropeptides and sex determination in the kuruma prawn.

Transcriptome profiling of banana shrimp (Fenneropenaeus merguiensis) ovaries and testes: Insights into FoxL2

The banana shrimp is found in the Pacific and Indian Oceans. Female shrimp are preferred for consumption because they are larger than males. Understanding the mechanism of sex differentiation is important for developing techniques to increase the number of female shrimp for economic benefits. This study investigates the reproductive development of F. merguiensis using transcriptome analysis. Sxl2, dsx, AGH, FEM-1, and Nrg-X2 were classified as essential genes for testes development during the juvenile stage. Several genes were required for both juvenile and adult male development. Additionally, the expression of several genes was shown to be required for juvenile and adult ovarian development, including SOP1, SOP2, Ptgr1, EST, Vgr, Vmol1, and TR-beta A. Interestingly, high levels of FoxL2 expression were observed in the testes, in contrast to previous studies in humans and other mammals. The binding of FoxL2 to the Vtg promoter was demonstrated in silico with the highest relative binding score (RS = 0.89) using the JASPAR program. Knock-down of the FoxL2 gene with dsRNA significantly suppressed FoxL2 at 2, 4, and 6 d. As a result, Vtg expression increased when compared with the control at 2, 4, and 6 d, indicating that FoxL2 plays an important role in Vtg expression in the ovary. Our findings highlight the role of FoxL2 in banana shrimp reproduction and provide valuable information on the genes associated with the F. merguiensis reproductive system.

Differentially expressed genes in the testes from early to mature development of banana shrimp (Fenneropenaeus merguiensis)

Banana shrimp (Fenneropenaeus merguiensis) is an economically important species in Thailand owing to the high value of globally exported frozen brine shrimps. However, the regulatory mechanisms governing spermatogenesis and testicular development in this species are poorly understood. High-throughput RNA sequencing was used to investigate the mechanisms and regulated genes involved in testis development using transcriptome profiling of juvenile and adult banana shrimp testes. Differentially expressed genes (DEGs) in these two libraries were identified and quantified to confirm gene expression. DEGs were found in 7,347 genes, with 4,465 upregulated and 2,882 downregulated. Some of these genes were designated as candidate genes, and six specific DEGs, including PRM1, SPATA20, Sry, SSRF, Sxl, and Tra-2c, were selected to confirm the reliability of the RNA-seq data using qPCR. Moreover, six non-DEGs were chosen based on testis-specific and regulatory genes that support a specific function in spermatogenesis and testis development in this species, including Dsx, Gfra2, IAG, Sox9, Sox13, and Sox14A. Furthermore, Sry, Sox14A, Sox14B and SPATA20 were identified in early stages (nauplius-postlarvae) of shrimp development to provide more information involving testes formation and development. The transcript data from this study could differentiate a group of genes required at the early and late stages of testis development and both sets of testis development. Therefore, this information would help in manipulating each stage of testicular development.

Isolation of an Insulin-Like Receptor Involved in the Testicular Development of the Mud Crab Scylla paramamosain

Insulin-like androgenic gland hormone (IAG) is a key regulator of male sexual differentiation in crustaceans that plays important roles in secondary sexual characteristics and testicular development. As a hormone, IAG interacts with its membrane receptor to initiate downstream signal pathways to exert its biological functions. In this study, we isolated a full-length cDNA of an insulin-like receptor (Sp-IR) from the mud crab Scylla paramamosain. Sequence analysis revealed that this receptor consists of a Fu domain, two L domains, three FN-III domains, a transmembrane domain, and a tyrosine kinase domain, classifying it as a member of the tyrosine kinase insulin-like receptors family. Our results also suggested that Sp-IR was highly expressed in the testis and AG in males. Its expression in the testis peaked in stage I but significantly decreased in stages II and III (p < 0.01). Next, both short- and long-term RNA interference (RNAi) experiments were performed on males in stage I to explore Sp-IR function in mud crabs. The results showed that Sp-vasa and Sp-Dsx expression levels in the testis were significantly down-regulated after the specific knockdown of Sp-IR by RNAi. Additionally, the long-term knockdown of Sp-IR led to a considerable decrease in the volume of seminiferous tubules, accompanied by large vacuoles and a reduced production of secondary spermatocytes and spermatids. In conclusion, our results indicated that Sp-IR is involved in testicular development and plays a crucial role in transitioning from primary to secondary spermatocytes. This study provided a molecular basis for the subsequent analysis of the mechanism on male sexual differentiation in Brachyuran crabs.

Identification of a Putative CFSH Receptor Inhibiting IAG Expression in Crabs

The crustacean female sex hormone (CFSH) is a neurohormone peculiar to crustaceans that plays a vital role in sexual differentiation. This includes the preservation and establishment of secondary female sexual traits, as well as the inhibition of insulin-like androgenic gland factor (IAG) expression in the androgenic gland (AG). There have been no reports of CFSH receptors in crustaceans up to this point. In this study, we identified a candidate CFSH receptor from the mud crab Scylla paramamosain (named Sp-SEFIR) via protein interaction experiments and biological function experiments. Results of GST pull-down assays indicated that Sp-SEFIR could combine with Sp-CFSH. Findings of in vitro and in vivo interference investigations exhibited that knockdown of Sp-SEFIR could significantly induce Sp-IAG and Sp-STAT expression in the AG. In brief, Sp-SEFIR is a potential CFSH receptor in S. paramamosain, and Sp-CFSH controls Sp-IAG production through the CFSH-SEFIR-STAT-IAG axis.

Analyses of the Dmrt family in a decapod crab, Eriocheir sinensis uncover new facets on the evolution of DM domain genes

DM domain genes are a group of transcription factors that are integral to sexual development and its evolution in metazoans. Their functions and regulatory mechanisms are not well understood in Malacostraca (crabs and crayfish) while these sex regulators have been widely identified in the past decade. In this study, the Dmrt family was investigated in the decapod crab, Eriocheir sinensis. We find that most members of the EsDmrt family begin to enrich around the juvenile 1 stage. In reproductive organs, EsDsx1, EsDsx2, EsiDMY and EsiDmrt1a highly express in the male-specific androgenic gland (AG), while EsDmrt-like, EsDsx-like, EsDmrt11E, and EsiDmrt1b show relatively high expression in testis. Also, we find the highly aberrant expression of EsiDMY and EsiDmrt1a in the chimeric AG, strongly indicating their function in AG development. Moreover, RNA interference of EsDsx1, EsiDMY, and EsiDmrt1a results in a significant decrease in transcription of the Insulin-like androgenic hormone (IAG), respectively. Our findings suggest that Dmrt genes in E. sinensis primarily function in male sexual differentiation, especially in AG development. Besides, this study identifies two unique groups of Dmrt genes in Malacostraca: Dsx and iDmrt1. In Malacostraca Dsx, we uncover a cryptic mutation in the eight zinc motif-specific residues, which were firmly believed to be invariant across the Dmrt family. This mutation sets the Malacostraca Dsx apart from all the other Dmrt genes and implies a different way of transcriptional regulation. Genes from the iDmrt1 group show phylogenetical limitation to the malacostracan species and underwent positive selection, suggesting their highly specialized gene function to this class. Based on these findings, we propose that Dsx and iDmrt1 in Malacostraca have developed unique transcriptional regulation mechanisms to facilitate AG development. We hope that this study would contribute to our understandings of sexual development in Malacostraca and provide new insights into the evolutionary history of the Dmrt family.

Identification and characterization of the Doublesex gene and its mRNA isoforms in the brine shrimp Artemia franciscana

Doublesex (DSX) proteins are members of the Doublesex/mab-3-related (DMRT) protein family and play crucial roles in sex determination and differentiation among the animal kingdom. In the present study, we identified two Doublesex (Dsx)-like mRNA isoforms in the brine shrimp Artemia franciscana (Kellogg 1906), which are generated by the combination of alternative promoters, alternative splicing and alternative polyadenylation. The two transcripts exhibited sex-biased enrichment, which we termed AfrDsxM and AfrDsxF. They share a common region which encodes an identical N-terminal DNA-binding (DM) domain. RT-qPCR analyses showed that AfrDsxM is dominantly expressed in male Artemia while AfrDsxF is specifically expressed in females. Expression levels of both isoforms increased along with the developmental stages of their respective sexes. RNA interference with dsRNA showed that the knockdown of AfrDsxM in male larvae led to the appearance of female traits including an ovary-like structure in the original male reproductive system and an elevated expression of vitellogenin. However, silencing of AfrDsxF induced no clear phenotypic change in female Artemia. These results indicated that the male AfrDSXM may act as inhibiting regulator upon the default female developmental mode in Artemia. Furthermore, electrophoretic mobility shift assay analyses revealed that the unique DM domain of AfrDSXs can specifically bind to promoter segments of potential downstream target genes like AfrVtg. These data show that AfrDSXs play crucial roles in regulating sexual development in Artemia, and further provide insight into the evolution of sex determination/differentiation in sexual organisms.

Comparative Transcriptome Reveals the Potential Modulation Mechanisms of Spdsx Affecting Ovarian Development of Scylla paramamosain

In previous study, we reported the identification, tissue distribution, and the roles of Spdsx played in the testis, androgenic gland, and ovary in Scylla paramamosain. Here, we primally identify its potential target genes in the ovary with RNAi and RNA-Seq technology. By comparing the transcriptome data of two groups (ovaries that injected with dsRNA for EGFP and Dsx), we found that 6520 Unigenes were differentially expressed, including a plenty of conserved crucial genes involved in ovarian development, such as vitellogenin (vtg), vtg receptor (vtgR), apolipoprotein D, adenylate cyclase 3, adenylate cyclase 5, cyclin A, cyclin B, and cell division cycle 2 (cdc2). In addition, these DEGs were also enriched in pathways related to ovary development, including PI3K-Akt signaling pathway, MAPK signaling pathway, insulin signaling pathway, Wnt signaling pathway, relaxin signaling pathway, estrogen signaling pathway, progesterone-mediated oocyte maturation, ovarian steroidogenesis, and oocyte meiosis. Moreover, several genes were selected for qRT-PCR to validate the accuracy of the bioinformatic result. According to current transcriptome result, we speculate that the Spdsx is a crucial regulator of ovary development in S. paramamosain. To the best of our knowledge, the current study was the first report about dsx function through comparative transcriptome analysis in crustacean species, which not only identified relevant genes and pathways involved in ovarian development of S. paramamosain, but also shed light on the regulatory mechanisms of dsx at the molecular level in crustacean.

The Sex-Specific Splicing of Doublesex in Brine Shrimp Artemia franciscana

The understanding of sex determination and differentiation in animals has recently made remarkable strides through the use of advanced research tools. At the gene level, the Mab-3-related transcription factor (Dmrt) gene family, which encodes for the typical DNA-binding doublesex/Mab-3 (DM) domain in their protein, is known for its contribution to sex determination and differentiation in insects. In this study, DNA-binding DM domain screening has identified eight transcripts from Artemia franciscana transcriptomic that encode proteins containing one conserved DNA-binding DM domain. The genome mapping confirmed that these eight transcripts are transcribed from six different loci on the A. franciscana genome assembly. One of those loci, the Af.dsx-4 locus, is closely related to Doublesex, a gene belonging to the Dmrt gene family. This locus could be transcribed into three alternative transcripts, namely Af.dsx⁴, Af.dsx^F and Af.dsx^M. While Af.dsx⁴ and Af.dsx^F could putatively be translated to form an identical Af.dsx^F protein of 186 aa long, Af.dsx^M translates for an Af.dsx^M protein of 289 aa long but shares a DNA-binding DM domain. Interestingly, Af.dsx^F and Af.dsx^M are confirmed as sex-specific transcripts, Af.dsx^F is only present in females, and Af.dsx^M is only present in male individuals. The results suggest that the sex-specific splicing mechanism of the doublesex described in insects is also present in A. franciscana. Af.dxs-4 locus can be used in further studies to clarify the sex determination pathways in A. fracnciscana.

Identification and Expression Analysis of Dsx and Its Positive Transcriptional Regulation of IAG in Black Tiger Shrimp (Penaeus monodon)

Doublesex (Dsx) is a polymorphic transcription factor of the DMRTs family, which is involved in male sex trait development and controls sexual dimorphism at different developmental stages in arthropods. However, the transcriptional regulation of the Dsx gene is largely unknown in decapods. In this study, we reported the cDNA sequence of PmDsx in Penaeus monodon, which encodes a 257 amino acid polypeptide. It shared many similarities with Dsx homologs and has a close relationship in the phylogeny of different species. We demonstrated that the expression of the male sex differentiation gene Dsx was predominantly expressed in the P. monodon testis, and that PmDsx dsRNA injection significantly decreased the expression of the insulin-like androgenic gland hormone (IAG) and male sex-determining gene while increasing the expression of the female sex-determining gene. We also identified a 5′-flanking region of PmIAG that had two potential cis-regulatory elements (CREs) for the PmDsx transcription. Further, the dual-luciferase reporter analysis and truncated mutagenesis revealed that PmDsx overexpression significantly promoted the transcriptional activity of the PmIAG promoter via a specific CRE. These results suggest that PmDsx is engaged in male reproductive development and positively regulates the transcription of the PmIAG by specifically binding upstream of the promoter of the PmIAG. It provides a theoretical basis for exploring the sexual regulation pathway and evolutionary dynamics of Dmrt family genes in P. monodon.

A novel Dmrt gene of crustacean: functional analysis of idmrt-2 gene in the male reproductive system from Scylla paramamosain

The Dmrt (double-sex and mab-3 related transcription factor) gene family is considered to be a highly conserved gene family related to sex determination and sexual differentiation across species. In order to better understand the role of the idmrt-2 gene in gonad development in Scylla paramamosain, the idmrt-2 gene was cloned and analyzed. The cDNA contains a 1659 bp ORF region encoding 552 amino acids. The qRT-PCR results showed that idmrt-2 was significantly more expressed in the testis than in other tissues (p<0.05). The expression of idmrt-2 was highest in the spermatids stage (T2 stage), followed by the mature sperms stage (T3 stage) and significantly higher than in the spermatocytes stage (T1 stage) (p<0.05) during testicular development and the expression difference was not significant in different stages of ovarian development. RNAi studies revealed that after idmrt-2 was knocked down, the expression of Dmrt-like and foxl-2 genes in the testis decreased, as well as IAG expression in the androgenic gland. The findings suggest that idmrt-2 may be an IAG regulator and involved in testicular development.

Molecular identification and putative role of insulin growth factor binding protein-related protein (IGFBP-rp) in the swimming crab Portunus trituberculatus

The insulin-like growth factor/insulin-like polypeptide (IGF/ILP) signaling is vital for growth, physiological metabolism, development, and reproduction. Insulin-like growth factor-binding protein (IGFBP) is involved in the insulin signaling pathway in both vertebrates and invertebrates and is critical for various physiology functions. Herein, we cloned and characterized the full-length cDNA of IGFBP-rp in the swimming crab, Portunus trituberculatus (PtIGFBP-rp). The deduced amino acid sequence of PtIGFBP-rp was found to contain three key domains (insulin-like binding (IB) domain, the kazale-type serine protease inhibitor (KAZAL) domain, and the immunoglobulin-like C2 (IGc2) domain). Results showed that PtIGFBP-rp shared the same expression pattern as P. trituberculatus insulin androgenic gland hormone (PtIAG) transcripts during the embryonic larval, juvenile crab stage and the androgenic gland (AG) developmental cycle. Moreover, PtIGFBP-rp transcripts were also present in high abundance in hepatopancreas, muscle, and androgenic glands. The regulatory relationship between PtIGFBP-rp and PtIAG was investigated by RNA interference and co-localization assays, which showed a co-localization relationship and feedback regulation between them. Bilateral eye stalk ablation (ESA) increased the expression of PtIGFBP-rp in the AG at 7 d after surgery. These results demonstrate the involvement of PtIGFBP-rp in the signaling regulatory network of IAG in P. trituberculatus.

DMRT Transcription Factors in the Control of Nervous System Sexual Differentiation

Sexual phenotypic differences in the nervous system are one of the most prevalent features across the animal kingdom. The molecular mechanisms responsible for sexual dimorphism throughout metazoan nervous systems are extremely diverse, ranging from intrinsic cell autonomous mechanisms to gonad-dependent endocrine control of sexual traits, or even extrinsic environmental cues. In recent years, the DMRT ancient family of transcription factors has emerged as being central in the development of sex-specific differentiation in all animals in which they have been studied. In this review, we provide an overview of the function of Dmrt genes in nervous system sexual regulation from an evolutionary perspective.

Evolutionary history of sexual differentiation mechanism in insects

Alternative splicing underpins functional diversity in proteins and the complexity and diversity of eukaryotes. An example is the doublesex gene, the key transcriptional factor in arthropod sexual differentiation. doublesex is controlled by sex-specific splicing and promotes both male and female differentiation in holometabolan insects, whereas in hemimetabolan species, doublesex has sex-specific isoforms but is not required for female differentiation. How doublesex evolved to be essential for female development remains largely unknown. Here, we investigate ancestral states of doublesex using Thermobia domestica belonging to Zygentoma, the sister group of Pterygota, that is, winged insects. We find that, in T. domestica, doublesex expresses sex-specific isoforms but is only necessary for male differentiation of sexual morphology. This result supports the hypothesis that doublesex initially promoted male differentiation during insect evolution. However, T. domestica doublesex has a short female-specific region and upregulates the expression of vitellogenin homologs in females, suggesting that doublesex may already play some role in female morphogenesis of the common ancestor of Pterygota. Reconstruction of the ancestral sequence and prediction of protein structures show that the female-specific isoform of doublesex has an extended C-terminal disordered region in holometabolan insects but not in nonholometabolan species. We propose that doublesex acquired its function in female morphogenesis through a change in the protein motif structure rather than the emergence of the female-specific exon.

Cloning, expression, and function of the Spdmrt-like gene in Scylla paramamosain

BACKGROUND

The mud crab Scylla paramamosain is an economically important species for aquaculture in China and has sexually dimorphic between females and males. Understanding sex differentiation in this species is essential for the development of monosex aquaculture. The Dmrt genes play a vital role in sex differentiation in animals.

METHODS AND RESULTS

In this study, two dmrt-like transcript variants, Spdmrt-like-tv1 and Spdmrt-like-v2, were cloned. SpDmrt-like-tv1 contained a DM domain, while SpDmrt-like-tv2 contained a DM and a DMA domain. Spdmrt-like-tv1 and Spdmrt-like-tv2 were both specifically expressed in testis. During testicular development, the expression level of Spdmrt-like-tv1 increased from stage I to stage II (P > 0.05) and then decreased from stage II to stage III (P < 0.05). The expression level of Spdmrt-like-tv2 in stages I and II was significantly higher than that in stage III (P < 0.05). During embryonic development, the expression level of Spdmrt-like-tv1 was higher in the mid-embryonic stage compared with the early and late stages, but the differences were not significant. Moreover, the expression level of Spdmrt-like-tv2 was stable and remained high throughout embryonic development. Furthermore, the expression level of Spdmrt-like-tv2 was significantly higher than that of Spdmrt-like-tv1. Knockdown of Spdmrt-like variants indicated that the regulative target gene of Spdmrt-like-tv1 was Spsox21, and the regulative target genes of Spdmrt-like-tv2 were Spfoxl2 and Spsox21. Combined with the results in our previously published peer-reviewed articles that the expression of Spfoxl2 in the testis was significantly higher than that in the ovary, and Spfoxl2 negatively regulated Spvtg expression. Spsox21 played a role in the development and maintenance of testis as well as in the process of neural development and regulation of body segmentation.

CONCLUSION

Therefore, we suggest that Spdmrt-like-tv1 and Spdmrt-like-tv2 might be involved in testicular development and embryonic development, and Spdmrt-like-tv2 might play more important roles in these two developmental processes by regulating the expression of Spfoxl2 and Spsox21 due to its high expression.

Identification and functional analysis of the doublesex gene in the mud crab Scylla paramamosain

Doublesex (Dsx) is a crucial member of the Dmrt gene family and plays a vital role in sex determination and differentiation among the animal kingdom. In the present study, a doublesex (designated as Spdsx) gene was identified and characterized for the first time in the mud crab, Scylla paramamosain. The Spdsx cDNA contains an 801 bp open reading frame (ORF) encoding 266 amino acids with a conserved DM domain. Meanwhile, to elucidate the conservation of Dsx, its orthologus were identified in several crustacean species as well. In addition, the expression pattern of Spdsx in various adult tissues and during embryo development was analyzed with qRT-PCR technology. Finally, the roles of Spdsx might play in the testis, androgenic gland, and ovary were analyzed by RNAi technology. The main results are as follows: (1) the Spdsx gene widely existed in analyzed crustacean species, and the multiple sequences alignment result indicated the conservation of Dsx was low except for the DM domain; (2) only one dsx gene was identified in analyzed crab and lobster, while 2 dsx genes (dsx-1 and dsx-2) were identified in shrimps; (3) the Spdsx gene was widely expressed in analyzed tissues, and the expression level in androgenic gland was obviously higher than that in other tissues. Interestingly, the expression level of Spdsx in the ovary was significantly higher than that in testis (p < 0.05); (4) The expression pattern of Spdsx during embryo development was divided into two groups: remained stable from blastula stage to 5 pairs of appendages stage; after 5 pairs of appendages stage, the expression level increased and remained stable from 7 pairs of appendages stage to hatching stage; (5) After the silencing of Spdsx, the expression level of marker genes in testis, ovary, and androgenic gland significantly changed, among which the expression level of vtg and vtgR in ovary down-regulated, the dmrt-like and dmrt-1a (exclusively expressed in testis) in testis up-regulated and the IAG in androgenic gland down-regulated. All the results above demonstrated that the Spdsx play crucial roles in regulating the reproduction system development of mud crab.

Molecular characterization and expression profiling of transformer 2 and fruitless-like homologs in the black tiger shrimp, Penaeus monodon

Transformer 2 (tra 2) and fruitless (fru) genes have been proven to play a key role in sex determination pathways in many Arthropods, including insects and crustaceans. In this study, a paralog of P. monodon tra 2 (Pmtra 2), P. monodon ovarian associated transformer 2 (PmOvtra 2) and 2 isoforms of P. monodon fruitless-like gene (Pmfru-1 and Pmfru-2) were identified and characterized. The full cDNA sequence of PmOvtra 2 consisted of 1,774 bp with the longest open reading frame (ORF) of 744 bp encoding for 247 amino acids. The PmOvtra 2 exhibited a predicted RNA-recognition motif (RRM) domain and two arginine-serine (RS) regions, suggesting its function in RNA splicing. The full cDNA sequence of Pmfru-1 consisted of 1,306 bp with 1,182 bp ORF encoding for 393 amino acids, whereas the full cDNA sequence of Pmfru-2 consisted of 1,858 bp with 1,437 bp ORF encoding 478 amino acids. The deduced amino acid sequences of Pmfru-1 and Pmfru-2 exhibited highly conserved domains of Fru proteins, including Broad-complex, Tramtrack and Bric-a-brac (BTB), and zinc finger (ZF) domains. In addition, Pmfru-1 and Pmfru-2 were suggestively originated from the same single genomic locus by genomic sequence analysis. Specifically, Pmfru pre-mRNA was alternatively spliced for Pmfru-1 and Pmfru-2 to include mutually exclusive exon 7 and exon 6, respectively. Temporal and spatial expression of PmOvtra 2, Pmfru-1, and Pmfru-2 were also investigated by qPCR. The results showed that all were expressed in early developmental stages with undifferentiated gonads starting from nauplius until postlarvae. The expression of PmOvtra 2 started at nauplius stage and gradually increased from mysis to postlarvae (PL) 1. However, the expression of Pmfru-1 was low at the nauplii stage and slightly increased from protozoea to PL5, whereas the expression of Pmfru-2 maintained a low level from nauplius to mysis and then gradually increased at the PL stages. Expressions of PmOvtra 2, Pmfru-1, and Pmfru-2 were detected in various tissues including nervous tissue, gill, heart, hepatopancreas, gut, and gonads. Interestingly, the sexually dimorphic expression of PmOvtra 2, Pmfru-1, and Pmfru-2 was demonstrated in fully developed gonads in which the ovary showed significantly higher expressions than the testis. The great difference in the expression pattern of PmOvtra 2, Pmfru-1, and Pmfru-2 in the ovary and testis suggested their roles in the female sex determination in P. monodon.

Cloning, functional and regulation analysis of a novel male reproduction-related protein gene from the oriental river prawn Macrobrachium nipponense

Gonadogenesis processes in crustaceans are complex. There, however, has been a large amount of research focused on regulation of female gonad (ovary) development in crustaceans, however, there has been little focus on the male gonad (testis). In the current study, a novel male reproduction-related protein gene (Mn-MRP) was identified from Macrobrachium nipponense. The relative abundance of Mn-MRP mRNA transcript in tissues and at different developmental stages were investigated. The relative abundance of Mn-MRP mRNA transcript was larger in the testis than other tissues, and during the testis maturation stage than at other developmental stages, suggesting Mn-MRP may have important functions in reproduction processes. The RNA interference (RNAi) was used to further investigate the Mn-MRP biological function. Silencing of the Mn-MRP gene effectively decreased the abundance of the sperm gelatinase (Mn-SG) mRNA transcript, implying the protein encoded by this gene may have functions in sperm activity during the fertilization process. Further studies with RNAi and eyestalk ablation confirmed that gonad inhibiting hormone gene (Mn-GIH) is a negative regulator of Mn-MRP, and that the insulin-like androgenic gland hormone gene (Mn-IAG) is a positive regulator. There, therefore, was cloning of the Mn-MRP gene, and investigation of its potential biological function, as well as elucidation of the positive/negative regulators in current study. The results from this study provide for a greater understanding of regulatory mechanisms of male reproduction in crustaceans.

Evolutionary transition of doublesex regulation from sex-specific splicing to male-specific transcription in termites

The sex determination gene doublesex (dsx) encodes a transcription factor with two domains, oligomerization domain 1 (OD1) and OD2, and is present throughout insects. Sex-specific Dsx splicing isoforms regulate the transcription of target genes and trigger sex differentiation in all Holometabola examined to date. However, in some hemimetabolous insects, dsx is not spliced sexually and its sequence is less conserved. Here, to elucidate evolutionary changes in dsx in domain organisation and regulation in termites, we searched genome and/or transcriptome databases for the dsx OD1 and OD2 in seven termite species and their sister group (Cryptocercus woodroaches). Molecular phylogenetic and synteny analyses identified OD1 sequences of termites and C. punctulatus that clustered with dsx of Holometabola and regarded them as dsx orthologues. The Cryptocercus dsx orthologue containing OD2 was spliced sexually, as previously shown in other insects. However, OD2 was not found in all termite dsx orthologues. These orthologues were encoded by a single exon in three termites for which genome information is available; they were not alternatively spliced but transcribed in a male-specific manner in two examined species. Evolution of dsx regulation from sex-specific splicing to male-specific transcription may have occurred at an early stage of social evolution in termites.

Evolution of sexual development and sexual dimorphism in insects

Most animal species consist of two distinct sexes. At the morphological, physiological, and behavioral levels the differences between males and females are numerous and dramatic, yet at the genomic level they are often slight or absent. This disconnect is overcome because simple genetic differences or environmental signals are able to direct the sex-specific expression of a shared genome. A canonical picture of how this process works in insects emerged from decades of work on Drosophila. But recent years have seen an explosion of molecular-genetic and developmental work on a broad range of insects. Drawing these studies together, we describe the evolution of sexual dimorphism from a comparative perspective and argue that insect sex determination and differentiation systems are composites of rapidly evolving and highly conserved elements.

Discovery of the Dmrt gene family members based on transcriptome analysis in mud crab Scylla paramamosain

Doublesex and mab-3 related transcription factors (Dmrts) play crucial roles in sex determination/differentiation and gonad development. The information on Dmrts and their functions are still scarce in mud crab Scylla paramamosain. In this study, 12 published transcriptome data of S. paramamosain were retrieved, pooled, and assembled. From the assembly, 7 Dmrt gene family members were identified and consisted of Spdmrt-like, Spdmrt-1a, Spdmrt-3, Spdmrt-11E, Spidmrt-1, Spdoublesex (Spdsx), and Spidmrt-2. These dmrt genes were predicted to encode 224 aa, 465 aa, 435 aa, 276 aa, 520 aa, 552 aa, and 266 aa protein precursors, respectively. The expression patterns of the dmrt genes were characterized by semi-quantitative PCR. The Spdmrt-like and Spdmrt-1a were exclusively detected in gonads, of which both expression levels in the testis were higher than that in the ovary. The Spdmrt-3, Spdmrt-11E, Spidmrt-1, Spdsx, and Spidmrt-2 were observed in various tissues; all these genes were sexually dimorphic except for dmrt-11E. Specifically, the expression level of Spdmrt-3 and Spidmrt-2 were higher in the testis than that in the ovary. On the contrary, the Spdsx and Spidmrt-1 expression level were higher in ovary than that in testis. The present study's findings provided a fundamental understanding of Dmrt gene family members involving sex determination/differentiation and gonad development in the S. paramamosain.

Insulin-like androgenic gland hormone 1 (IAG1) regulates sexual differentiation in a hermaphrodite shrimp through feedback to neuroendocrine factors

Insulin-like androgenic gland hormone (IAG) is regarded as a key sexual differentiation regulator in gonochoristic crustaceans. However, until now the knowledge concerning its functions in hermaphroditic crustaceans is scanty. Herein, we investigated the function of IAG (Lvit-IAG1) in peppermint shrimp Lysmata vittata, a species that possesses protandric simultaneous hermaphroditism (PSH) reproductive system, which is rare among crustaceans. Lvit-IAG1 was exclusively expressed in the androgenic gland. The qRT-PCR demonstrated that its mRNA expression level was relatively high at the functional male phase but decreased sharply in the subsequent euhermaphrodite phase. Both the short-term and long-term silencing experiments showed that Lvit-IAG1 negatively regulated both the gonad-inhibiting hormone (Lvit-GIH) and crustacean female sex hormone (Lvit-CFSH) expressions in the eyestalk ganglion. Besides, Lvit-IAG1 gene knockdown induced a retarded development of the appendices masculinae (AM) and male gonopores while suppressing the germ cells at the primary spermatocyte stage. Also, Lvit-IAG1 gene silencing hindered ovarian development. This in turn led to small vitellogenic oocytes and decreased expression of vitellogenin and vitellogenin receptor genes in hepatopancreas and ovarian region, respectively. Generally, this study's findings imply that Lvit-IAG1 modulated the male sexual differentiation in PSH species L. vittata, and exhibited negative feedback on Lvit-GIH and Lvit-CFSH genes expression in the species' eyestalk ganglion.

Sex-specific expression and DNA methylation in a species with extreme sexual dimorphism and paternal genome elimination

Phenotypic differences between sexes are often mediated by differential expression and alternative splicing of genes. However, the mechanisms that regulate these expression and splicing patterns remain poorly understood. The mealybug, Planococcus citri, displays extreme sexual dimorphism and exhibits an unusual instance of sex-specific genomic imprinting, paternal genome elimination (PGE), in which the paternal chromosomes in males are highly condensed and eliminated from the sperm. Planococcus citri has no sex chromosomes and both sexual dimorphism and PGE are predicted to be under epigenetic control. We recently showed that P. citri females display a highly unusual DNA methylation profile for an insect species, with the presence of promoter methylation associated with lower levels of gene expression. Here, we therefore decided to explore genome-wide differences in DNA methylation between male and female P. citri using whole-genome bisulphite sequencing. We identified extreme differences in genome-wide levels and patterns between the sexes. Males display overall higher levels of DNA methylation which manifest as more uniform low levels across the genome. Whereas females display more targeted high levels of methylation. We suggest these unique sex-specific differences are due to chromosomal differences caused by PGE and may be linked to possible ploidy compensation. Using RNA-Seq, we identify extensive sex-specific gene expression and alternative splicing, but we find no correlation with cis-acting DNA methylation.

Sex Determination and Differentiation in Decapod and Cladoceran Crustaceans: An Overview of Endocrine Regulation

Mechanisms underlying sex determination and differentiation in animals are known to encompass a diverse array of molecular clues. Recent innovations in high-throughput sequencing and mass spectrometry technologies have been widely applied in non-model organisms without reference genomes. Crustaceans are no exception. They are particularly diverse among the Arthropoda and contain a wide variety of commercially important fishery species such as shrimps, lobsters and crabs (Order Decapoda), and keystone species of aquatic ecosystems such as water fleas (Order Branchiopoda). In terms of decapod sex determination and differentiation, previous approaches have attempted to elucidate their molecular components, to establish mono-sex breeding technology. Here, we overview reports describing the physiological functions of sex hormones regulating masculinization and feminization, and gene discovery by transcriptomics in decapod species. Moreover, this review summarizes the recent progresses of studies on the juvenile hormone-driven sex determination system of the branchiopod genus Daphnia, and then compares sex determination and endocrine systems between decapods and branchiopods. This review provides not only substantial insights for aquaculture research, but also the opportunity to re-organize the current and future trends of this field.

Full Functional Sex Reversal Achieved Through Silencing of MroDmrt11E Gene in Macrobrachium rosenbergii: Production of All-Male Monosex Freshwater Prawn

The freshwater prawn Macrobrachium rosenbergii is one kind of important economic aquaculture species and displays remarkable sexual dimorphism. The molecular mechanism of sexual differentiation in M. rosenbergii has been primarily unraveled through the research efforts of the androgenic gland and its related genes. However, the understanding of conserved genes involved in the molecular mechanism underpinning sex determination and sexual differentiation of M. rosenbergii is still fragmentary. MroDmrt11E is a member of the doublesex and mab-3-related transcription factor (Dmrt) gene family and is prominently expressed in the testis. In the present study, in vivo knockdown of MroDmrt11E at the postlarva stage in male prawn induced a complete and functional sex reversal and achieved the production of an all-male monosex population. Furthermore, a great deal of new information of upregulated and downregulated transcriptions involved in sexual differentiation of MroDmrt11E knockdown was enriched by comparative transcriptomic analysis. The effects of RNAi-mediated gene knockdown of MroDmrt11E on the differentially expressed and sex-related candidate genes, such as transformer, fruitless, feminization, insulin-like androgenic gland gene, Dmrt gene family, were primarily focused on, and their possible molecular regulatory relationships in sexual differentiation were analyzed. Meanwhile, the response of primary Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathways was investigated to expound the potential roles of MroDmrt11E in male sexual differentiation, which provided a deeper understanding of the molecular regulatory network underlying sexual differentiation of M. rosenbergii. The finding provided a novel sexual manipulation technique through silencing of Dmrt gene family for achieving a complete and functional sex reversal and offered a new insight regarding the mechanism of the Dmrt gene family in the sexual differentiation of crustaceans.

Multi-Tissue Transcriptome Analysis Identifies Key Sexual Development-Related Genes of the Ornate Spiny Lobster (Panulirus ornatus)

Sexual development involves the successive and overlapping processes of sex determination, sexual differentiation, and ultimately sexual maturation, enabling animals to reproduce. This provides a mechanism for enriched genetic variation which enables populations to withstand ever-changing environments, selecting for adapted individuals and driving speciation. The molecular mechanisms of sexual development display a bewildering diversity, even in closely related taxa. Many sex determination mechanisms across animals include the key family of "doublesex- and male abnormal3-related transcription factors" (Dmrts). In a few exceptional species, a single Dmrt residing on a sex chromosome acts as the master sex regulator. In this study, we provide compelling evidence for this model of sex determination in the ornate spiny lobster Panulius ornatus, concurrent with recent reports in the eastern spiny lobster Sagmariasus verreauxi. Using a multi-tissue transcriptomic database established for P. ornatus, we screened for the key factors associated with sexual development (by homology search and using previous knowledge of these factors from related species), providing an in-depth understanding of sexual development in decapods. Further research has the potential to close significant gaps in our understanding of reproductive development in this ecologically and commercially significant order.

Identification and functional analysis of the doublesex gene in the redclaw crayfish, Cherax quadricarinatus

DM-domain (Zn-finger motif domain) genes play an important role in the sex determination and differentiation among animal kingdom. In the present study, the gene of Doublesex (Cqdsx) was identified and characterized for the first time in the redclaw crayfish, Cherax quadricarinatus. The full-length cDNA was 1271 bp, comprising a 155 bp 5'-untranslated region (5'-UTR), an 885 bp predicted open reading frame (ORF) encoding 294 amino acid polypeptides, and a 231 bp 3'-UTR. The deduced amino acid sequence of Cqdsx was predicted to contain a highly conserved DM domain and shared nearly 50% identity to DM-peptides from other species. The results of quantitative Real-time PCR in various tissues revealed that Cqdsx was strongly expressed in gonads, while was almost undetectable in gill, heart, hepatopancreas, muscle and intestine. Comparing expression level in different embryonic stages found that Cqdsx was gradually increased with the development of the embryos. In situ hybridization to gonad sections showed that intensive hybridization signals were mainly observed in oocytes and ovarian lamellae and weak signals were detected in spermatocyte. Additionally, Cqdsx gene exhibited higher transcript levels in the early stage of ovarian development. Furthermore, RNAi-targeting Cqdsx silencing induced a decrease of Cq-IAG trascripts, which regulate the male sexual differentiation in crustaceans. Taken together, these findings strongly suggest an essential role for Cqdsx in the female ovarian development/differentiation of the redclaw crayfish.

Molecular Characterization and Expression Profiling of Three Transformer-2 Splice Isoforms in the Redclaw Crayfish, Cherax quadricarinatus

Sex determination/sex differentiation is determined by genetics, environmental factors, or the interactions of the two. The Transformer-2 (Tra-2) gene plays an important role in the sex determination cascade signal pathway in insects. In this study, the Tra-2 gene was isolated and characterized from the cDNA library of gonad tissues in the redclaw crayfish, Cherax quadricarinatus. Three splice variants were identified, designated as CqTra-2A, CqTra-2B, and CqTra-2C, and sequence analysis showed that they had a highly conserved RRM domain. Phylogenetic analysis was performed by the NJ method, and the results revealed that the Tra-2 protein of the redclaw crayfish was very closely related to those of Macrobrachium rosenbergii, Fenneropenaeus chinensis, and Macrobrachium nipponense. Real-time PCR analysis showed that the three isoforms were predominantly expressed in the ovary and gradually increased with embryonic development. Additionally, the expression pattern of CqTra-2 at different developmental stages was analyzed by qPCR and revealed that the phase of having a body length of 3 cm may be the key period for the sex differentiation of C. quadricarinatus. RNAi-targeting gene silencing further confirmed the function of CqTra-2 in sexual differentiation in redclaw crayfish. Our experimental data will contribute to understanding the mechanism of sex determination in crustaceans.

Sex-Specific Transcriptome Sequencing of Zoea I Larvae and Identification of Sex-Linked Genes Using Bulked Segregant Analysis in Pacific White Shrimp Litopenaeus vannamei

In order to learn the sex determination and differentiation process in shrimp, we performed sex-specific transcriptome sequencing of the Zoea I larvae in Litopenaeus vannamei (L. vannamei) using a DNA/RNA co-extraction method. The sex-specific genes and the sex-linked SNPs were identified. De novo assembly of all the clean reads generated 41,270 unigenes with an average length of 1026 bp and an N50 of 1922 bp. A total of 60 differentially expressed genes (DEGs) between females and males at Zoea I stage were obtained, in which 41 unigenes had annotations. DEGs that might be related to sex development in L. vannamei were analyzed. Besides, paralogous genes of some known sex-related genes in model organisms such as sex-lethal (Sxl) showed no sex-biased difference, which indicated they may not play roles in sex development at Zoea I stage. Candidate sex-linked SNPs were validated in six populations of L. vannamei, and SNPs in Unigene0020898 and Unigene0020336 were fully linked to genders, suggesting the two genes located in the sex-determining region of L. vannamei. Our report provided the sex-specific gene expression in early developmental stage of L. vannamei, and found some sex-biased genes that may participate in the sex development process. We also detected two sex-linked genes which may be located in the sex determination region of L. vannamei through bulked segregant analysis, and the SNPs on these genes also provided a method for genetic sex identification at transcriptional level. Our findings will facilitate further researches on molecular mechanism of sex determination and differentiation in shrimps.

Mutation of doublesex in Hyphantria cunea results in sex-specific sterility

BACKGROUND

The gene doublesex (dsx) plays pivotal roles in sex determination and controls sexually dimorphic development in certain insects. Importantly, it also displays a potential candidate target for pest management due to its sex-specific splicing. Therefore, we used CRISPR/Cas9-mediated gene disruption to investigate the function of dsx in Hyphantria cunea, an invasive forest pest.

RESULT

In the present study, we identified the dsx gene from H. cunea which showed a sex-biased expression pattern that was different from other lepidopteran insects. Referring to sex-specific functional analyses in Bombyx mori, we performed a site-specific knockout of the Hcdsx gene by using a CRISPR/Cas9 system, which induced severe abnormalities in external genitalia and some incomplete sex reversal phenotypes, which in turn led to reduced sex-specific fecundity. An alternative splicing pattern of Hcdsx was altered by CRISPR/Cas9-induced mutation, and alterations in splicing affected expression of downstream genes encoding pheromone binding protein 1, vg1 and vg2 (encoding vitellogenin), which contributed to the sex-specific sterility phenotypes in the Hcdsx mutants.

CONCLUSION

The Hcdsx gene plays important roles in sexual differentiation in H. cunea. Disruption of Hcdsx induced sex-specific sterility, demonstrating a potential application in control of this pest. © 2019 Society of Chemical Industry.

Hemimetabolous insects elucidate the origin of sexual development via alternative splicing

Insects are the only known animals in which sexual differentiation is controlled by sex-specific splicing. The doublesex transcription factor produces distinct male and female isoforms, which are both essential for sex-specific development. dsx splicing depends on transformer, which is also alternatively spliced such that functional Tra is only present in females. This pathway has evolved from an ancestral mechanism where dsx was independent of tra and expressed and required only in males. To reconstruct this transition, we examined three basal, hemimetabolous insect orders: Hemiptera, Phthiraptera, and Blattodea. We show that tra and dsx have distinct functions in these insects, reflecting different stages in the changeover from a transcription-based to a splicing-based mode of sexual differentiation. We propose that the canonical insect tra-dsx pathway evolved via merger between expanding dsx function (from males to both sexes) and narrowing tra function (from a general splicing factor to dedicated regulator of dsx).

Molecular Characterization and Functional Study of Insulin-Like Androgenic Gland Hormone Gene in the Red Swamp Crayfish, Procambarus clarkii

The androgenic gland (AG) is a male-specific endocrine organ that controls the primary and secondary sexual characteristics in male crustaceans. More evidence indicates that the insulin-like androgenic gland hormone gene (IAG) is the key male sexual differentiation factor, particularly the application of RNA interference (RNAi) technology on IAG. In this study, the full-length cDNA of IAG (termed PcIAG) was isolated from the red swamp crayfish, Procambarusclarkii. Tissue distribution analysis showed that in addition to its expression in the AG of male P. clarkii, PcIAG was widely expressed in female tissues and other male tissues. The PcIAG protein was detected in the reproductive and nervous systems of adult male P. clarkii. Additionally, RNAi results showed that the PcIAG expression could be silenced efficiently, and the male sperm maturation and release possibly present a transient adverse interference at lower doses (0.1 μg/g and 1 μg/g) of PcIAG–dsRNA (PcIAG double-stranded RNA). Dramatically, the expression level of PcIAG increased sharply shortly after the injection of higher doses (5 μg/g and 10 μg/g) of PcIAG–dsRNA, which might accelerate the maturation and release of sperm. Moreover, the expression of PcSxl (P. clarkii Sex-lethal) was detected by Quantitative Real-Time PCR (qPCR) after the injection of PcIAG–dsRNA to explore whether the PcIAG gene regulates the PcSxl gene, and we found that the PcIAG did not directly regulate PcSxl in P. clarkii. The study could help accelerate the progress of PcIAG functional research and provide a useful reference for the single-sex selective breeding of P. clarkii.

Modular tissue-specific regulation of doublesex underpins sexually dimorphic development in Drosophila

The ability of a single genome to produce distinct and often dramatically different male and female forms is one of the wonders of animal development. In Drosophila melanogaster, most sexually dimorphic traits are controlled by sex-specific isoforms of the doublesex (dsx) transcription factor, and dsx expression is mostly limited to cells that give rise to sexually dimorphic traits. However, it is unknown how this mosaic of sexually dimorphic and monomorphic organs arises. Here, we characterize the cis-regulatory sequences that control dsx expression in the foreleg, which contains multiple types of sex-specific sensory organs. We find that separate modular enhancers are responsible for dsx expression in each sexually dimorphic organ. Expression of dsx in the sex comb is co-regulated by two enhancers with distinct spatial and temporal specificities that are separated by a genitalia-specific enhancer. The sex comb-specific enhancer from D. willistoni, a species that primitively lacks sex combs, is not active in the foreleg. Thus, the mosaic of sexually dimorphic and monomorphic organs depends on modular regulation of dsx transcription by dedicated cell type-specific enhancers.