Circadian rhythms in the growth and reproduction of the brown alga Undaria pinnatifida and gametogenesis under different photoperiods

Circadian growth rhythm of the juvenile sporophyte of the brown alga Undaria pinnatifida was measured with the computer-aided image analysis system in constant florescent white light under constant temperature （ 10 ℃ ）. The growth rhythm persisted for 4 d in constant light with a free-running period of 25.6 h. Egg release from filamentous gametophytes pre-cultured in the light - dark regime was evaluated for six consecutive days at fixed time intervals in constant white light and 12 h light per day. Egg release rhythm persisted for 3 d in both regimes, indicating the endogenous nature. Temporal scale of egg release and gametogenesis in 18, 16, 12 and 8 h light per day were evaluated respectively using vegetatively propagated filamentous gametophytes. Egg release occurred 2 h after the onset of dark phase and peaked at midnight. Evaluation of the rates of oogonium formation, egg release or fertilization revealed no significant differences in four light-dark regimes, indicating the great plasticity of sexual reproduction. No photoperiodic effect in gametogenesis in terms of oogonium formation and egg release was found, but fertilization in short days was significantly higher than in long days. Results of this investigation further confirmed the general occurrence of circadian rhythms in intertidal seaweed species.

Characterization, Expression and Function Analysis of DAX1 Gene of Scallop(Chlamys farreri Jones and Preston 1904) During Its Gametogenesis

DAX1, a member of nuclear receptor superfamily, has a function in the sex determination and gonadal differentiation of several vertebrate species. However, little information about DAX1 of invertebrates is available. Here we cloned a homolog of scallop(Chlamys farreri Jones and Preston 1904) dax1, Cf-dax1, and determined its expression characteristics at m RNA and protein levels. The c DNA sequence of Cf-dax1 was 2093 bp in length, including 1404 bp open reading frame(ORF) encoding 467 amino acids. Unlike those of vertebrates, no conserved LXXLL-related motif was found in the putative DNA binding region of Cf-DAX1. Fluorescence in situ hybridization showed that Cf-dax1 located on the short arm of a pair of subtelocentric chromosomes. Tissue distribution analysis using semi-quantitative RT-PCR revealed that Cf-dax1 expressed widely in adult scallop tissues, with the highest expression level found in adductor muscle, moderate level in mantle, gill and testis, and low level in kidney, ovary and hepatopancreas. The result of quantitative real-time PCR indicated that the expression of Cf-dax1 was significantly higher(P<0.05) in testis than in ovary at the same stage, showing a sex-dimorphic expression pattern. Furthermore, immunohistochemical detection found that Cf-DAX1 mainly located in spermatogonia and spermatocytes of testis and in oogonia and oocytes of ovary, implying that DAX1 may involve in gametogenesis of bivalves.

Hypothalamic-Pituitary-Gonadal(HPG)Axis and Transcriptional Regulatory Elements Regulate piwil2 Gene Expression During Gametogenesis and Gonadal Development in Japanese Flounder(Paralichthys olivaceus)

The P-element induced wimpy testis(Piwi)proteins,which are associated with PIWI-interacting RNAs(piRNAs),play important roles in meiosis,germ cell division,and germline maintenance.In this study,we identified and characterized the Paralichthys olivaceus piwil2 gene,a constituent factor of the piRNA pathways involved in the biogenesis of reproductive development.The biological analysis indicated that piwil2,which contains PAZ and PIWI domains,was highly conserved between teleosts and tetrapods.The piwil2 distribution profile in different tissues confirmed a sexually dimorphic expression pattern,with a higher expression level in testis.In situ hybridization demonstrated that piwil2 was expressed in the oogonia and oocytes of the ovaries as well as in the Sertoli cells and spermatocytes of the testes.Gene piwil2 showed a maternally inherited expression pattern during embryonic development,and was highly expressed during the early embryonic development.Different luciferase reporters were constructed to determine the transcriptional regulatory mechanisms of piwil2.The piwil2 core promoter region was located at−360 bp to−60 bp.Furthermore,some representative sex hormones,including human chorionic gonadotropin,17α-methyltestosterone,and estradiol-17βhad distinct regulatory effects on piwil2.In a summery,these results indicate that piwil2,regulated by sex hormones and transcriptional elements,has vital functions in the reproductive cycle and gonadal development.

CYTOLOGICAL COMPARISON OF GAMETOGENESIS OF SCALLOPS,ARGOPECTEN IRRADIANS AND CHLAMYS FARRERI

Histological characteristics of gametogenesis of two kinds of scallops, gonochoric Chinese scallop, Chlamys farreri and hermaphroditic bay scallop, Argopecten irradians were investigated in this study. Spermatogenesis in C. farreri has different developmental stages: spermatogonia, primary spermatocyte, second spermatocyte, spermatid and spermatozoon. A large number of same developmental stage spermatic cells converge at a definite area of the testis. Premeiotic, previtellogenic and vitellogenic oocytes can be found during oogenesis in C. farreri , where oocyte distribution is obviously irregular. The A. irradians gonad consists of two different parts in one individual: one part functions as testis, the other as ovary. Between these two parts is a special appearance area, where a large number of spermatic cells are bound with two layers of acellular substance with many oocytes in it.

GametesOmics:A Comprehensive Multi-omics Database for Exploring the Gametogenesis in Humans and Mice

Gametogenesis plays an important role in the reproduction and evolution of species.The transcriptomic and epigenetic alterations in this process can influence the reproductive capacity,fertilization,and embryonic development.The rapidly increasing single-cell studies have provided valuable multi-omics resources.However,data from different layers and sequencing platforms have not been uniformed and integrated,which greatly limits their use for exploring the molecular mechanisms that underlie oogenesis and spermatogenesis.Here,we develop GametesOmics,a comprehensive database that integrates the data of gene expression,DNA methylation,and chromatin accessibility during oogenesis and spermatogenesis in humans and mice.GametesOmics provides a user-friendly website and various tools,including Search and Advanced Search for querying the expression and epigenetic modification(s)of each gene;Tools with Differentially expressed gene(DEG)analysis for identifying DEGs,Correlation analysis for demonstrating the genetic and epigenetic changes,Visualization for displaying single-cell clusters and screening marker genes as well as master transcription factors(TFs),and MethylView for studying the genomic distribution of epigenetic modifications.GametesOmics also provides Genome Browser and Ortholog for tracking and comparing gene expression,DNA methylation,and chromatin accessibility between humans and mice.GametesOmics offers a comprehensive resource for biologists and clinicians to decipher the cell fate transition in germ cell development,and can be accessed at http://gametesomics.cn/.

RebL1 is required for macronuclear structure stability and gametogenesis in Tetrahymena thermophila

Histone modification and nucleosome assembly play important roles in chromatin-related processes.Histone chaperones form different complexes and coordinate histone transportation and assembly.Various histone chaperone complexes have been identified in different organisms.The ciliate protozoa(ciliates)have various chromatin structures and different nuclear morphology.However,histone chaperone components and functions of different subunits remain unclear in ciliates.Tet-rahymema thermophila contains a transcriptionally active macronucleus(MAC)and a transcriptionally inactive micronu-cleus(MIC)which exhibit multiple replication and various chromatin remodeling progresses during vegetative growth and sexual developmental stages.Here,we found histone chaperone RebL1 not only localized evenly in the transcriptionally active MAC but also dynamically changed in the MIC during vegetative growth and sexual developmental stages.REBL1 knockdown inhibited cellular proliferation.The macronuclear morphology became bigger in growing mutants.The abnormal macronuclear structure also occurred in the starvation stage.Furthermore,micronuclear meiosis was disturbed during sexual development,leading to a failure to generate new gametic nuclei.RebL1 potentially interacted with various factors involved in histone-modifying complexes and chromatin remodeling complexes in different developmental stages.REBL1 knockdown affected expression levels of the genes involved in chromatin organization and transcription.Taken together,RebL1 plays a vital role in maintaining macronuclear structure stability and gametogenesis in T.thermophila.

Spindle-E is essential for gametogenesis in the silkworm, Bombyx mori

As a defense mechanism against transposable elements,the PIWI-interacting RNA(piRNA)pathway maintains genomic integrity and ensures proper gametogenesis in gonads.Numerous factors are orchestrated to ensure normal operation of the piRNA pathway.Spindle-E(Spn-E)gene was one of the first genes shown to participate in the piRNA pathway.In this study,we performed functional analysis of Spn-E in the model lepidopteran insect,Bombyx mori.Unlike the germline-specific expression pattern observed in Drosophila and mouse,BmSpn-E was ubiquitously expressed in all tissues tested,and it was highly expressed in gonads.Immunofluorescent staining showed that BmSpn-E was localized in both germ cells and somatic cells in ovary and was expressed in spermatocytes in testis.We used a binary transgenic CRISPR/Cas9 system to construct BmSpn-E mutants.Loss of BmSpn-E expression caused derepression of transposons in gonads.We also found that mutant gonads were much smaller than wild-type gonads and that the number of germ cells was considerably lower in mutant gonads.Quantitative real-time PCR analysis and TUNEL staining revealed that apoptosis was greatly enhanced in mutant gonads.Further,we found that the BmSpn-E mutation impacted gonadal development and gametogenesis at the early larval stage.In summary,our data provided the first evidence that BmSpn-E plays vital roles in gonadal development and gametogenesis in B.mori.

Modelling in vitro gametogenesis using induced pluripotent stem cells:a review

In vitro gametogenesis(IVG)has been a topic of great interest in recent years not only because it allows for further exploration of mechanisms of germ cell development,but also because of its prospect for innovative medical applications especially for the treatment of infertility.Elucidation of the mechanisms underlying gamete development in vivo has inspired scientists to attempt to recapitulate the entire process of gametogenesis in vitro.While earlier studies have established IVG methods largely using pluripotent stem cells of embryonic origin,the scarcity of sources for these cells and the ethical issues involved in their use are serious limitations to the progress of IVG research especially in humans.However,with the emergence of induced pluripotent stem cells(iPSCs)due to the revolutionary discovery of dedifferentiation and reprogramming factors,IVG research has progressed remarkably in the last decade.This paper extensively reviews developments in IVG using iPSCs.First,the paper presents key concepts from groundwork studies on IVG including earlier researches demonstrating that IVG methods using embryonic stem cells(ESCs)also apply when using iPSCs.Techniques for the derivation of iPSCs are briefly discussed,highlighting the importance of generating transgene-free iPSCs with a high capacity for germline transmission to improve efficacy when used for IVG.The main part of the paper discusses recent advances in IVG research using iPSCs in various stages of gametogenesis.In addition,current clinical applications of IVG are presented,and potential future applications are discussed.Although IVG is still faced with many challenges in terms of technical issues,as well as efficacy and safety,novel IVG methodologies are emerging,and IVG using iPSCs may usher in the next era of reproductive medicine sooner than expected.This raises both ethical and social concerns and calls for the scientific community to cautiously develop IVG technology to ensure it is not only efficacious but also safe and adheres to social and ethical norms.

Arabidopsis Transcription Factor Genes NF-YA 1, 5, 6, and 9 Play Redundant Roles in Male Gametogenesis, Embryogenesis, and Seed Development

Nuclear factor Y （NF-Y） is a highly conserved transcription factor presented in all eukaryotic organisms, and is a heterotrimer consisting of three subunits： NF-YA, NF-YB, and NF-YC. In Arabidopsis, these three subunits are encoded by multigene families. The best-studied member of the NF-Y transcription factors is LEAFY COTYLEDON1 （LEC1）, a NF-YB family member, which plays a critical role in embryogenesis and seed maturation. However, the function of most NF-Y genes remains elusive. Here, we report the characterization of four genes in the NF-YA family. We found that a gain- of-function mutant of NF-YA1 showed defects in male gametogenesis and embryogenesis. Consistently, overexpression of NF-YA1, 5, 6, and 9 affects male gametogenesis, embryogenesis, seed morphology, and seed germination, with a stronger phenotype when overexpressing NF-YA1 and NF-YA9. Moreover, overexpression of these NF-YA genes also causes hypersensitivity to abscisic acid （ABA） during seed germination, retarded seedling growth, and late flowering at different degrees. Intriguingly, overexpression of NF-YA1, 5, 6, and 9 is sufficient to induce the formation of somatic embryos from the vegetative tissues. However, single or double mutants of these NF-YA genes do not have detectable phenotype. Collectively, these results provide evidence that NF-YA1, 5, 6, and 9 play redundant roles in male gameto- phyte development, embryogenesis, seed development, and post-germinative growth.

The Arabidopsis Anaphase-Promoting Complex/Cyclosome Subunit 1 is Critical for Both Female Gametogenesis and Embryogenesis

Anaphase-promoting complex/cyclosome （APC/C）, a multisubunit E3 ligase, plays a critical role in cell cycle control, but the functional characterization of each subunit has not yet been completed. To investigate the function of APC1 in Arabidopsis, we analyzed four mutant alleles of APC1, and found that mutation in APC1 resulted in significantly reduced plant fertility, accumulation of cyclin B, and disrupted auxin distribution in embryos. The three mutant alleles apcl-1, apcl-2 and apcl-3 shared variable defects in female gametogenesis including degradation, abnormal nuclear number, and disrupted polarity of nuclei in the embryo sac as well as in embryogenesis, in which embryos were arrested at multiple stages. All of these defects are similar to those previously identified in apc4. The mutant apcl-4, in which the T-DNA was inserted after the transmembrane domain at the C-terminus, showed much more severe phenotypes; that is, most of the ovules were arrested at the one-nucleate female gametophyte stage （stage FG1）. In the apcl apc4 double mutants, the fertility was further reduced by one-third in apcl-ll＋ apc4-1/＋, and in some cases no ovules even survived in siliques of apcl-4/＋ apc4-1/＋. Our data thus suggest that APC1, an essential component of APC/C, plays a synergistic role with APC4 both in female gametogenesis and in embryogenesis.

Reconstitution of Gametogenesis In Vitro:Meiosis Is the Biggest Obstacle

Germ-line cells are responsible for transmitting genetic and epigenetic information across generations, and ensuring the creation of new individuals from one generation to the next. Gametogenesis process requires several rigorous steps, including primordial germ cell （PGC） specification, proliferation, migration to the gonadal ridges and differentiation into mature gametes such as sperms and oocytes. But this process is not clearly explored because a small number of PGCs are deeply embedded in the developing embryo. In the attempt to establish an in vitro model for understanding gametogenesis process well, several groups have made considerable progress in differen- tiating embryonic stem cells （ESCs） and adult stem cells （ASCs） into germ-like cells over the past ten years. These stem cell-derived germ cells appear to he capable of undergoing meiosis and generating both male and female gametes. But most of gametes turn out to be not fully functional due to their abnormal meiosis process compared to endogenous germ cells. Therefore, a robust system of differentiating stem cells into germ cells would enable us to investigate the genetic, epigenetic and environmental factors associated with germ cell development. Here, we review the stem cell-derived germ cell development, and discuss the potential and challenges in the differentiation of functional germ cells from stem cells.

SNAIL1 is essential for female gametogenesis in Arabidopsis thaliana

Two yeast Brix family members Ssfl and Ssf2, involved in large ribosomal subunit synthesis, are essential for yeast cell viability and mating efficiency. Their putative homologs exist in the Arabidopsis genome; however, their role in plant development is unknown. Here, we show that Arabidopsis thaliana SNAIL1 （AtSNAIL1）, a protein sharing high sequence identity with yeast Ssfl and Ssf2, is critical to mitosis progression of female gametophyte development. The snail1 homozygous mutant was nonviable and its heterozygous mutant was semi-sterile with shorter siliques. The mutation in SNAIL1 led to absence of female transmission and reduced male transmission. Further phenotypic analysis showed that the synchronic development of female gametophyte in the snail1 heterozygous mutant was greatly impaired and the snaih pollen tube growth, in vivo, was also compromised. Furthermore, SNAIL1 was a nucleolar- localized protein with a putative role in protein synthesis. Our data suggest that SNAIL1 may function in ribosome biogenesis like Ssf1 and Ssf2 and plays an important role during megagametogenesis in Arabidopsis.

Somatostatin 4 regulates growth and modulates gametogenesis in zebrafish

Somatostatin(SST)plays important roles in growth and development.In teleost fishes six SST encoding genes(sst1 to sst6)have been identified although few studies have addressed their function.Here we aim to determine the function of the teleost specific sst4 in the zebrafish.A CRISPR/Cas9 sst4 zebrafish mutant with loss of function(sst4−/−)was produced which grew significantly faster and was heavier at the onset of gonadal maturation than the wild type(WT).Consistent with their faster growth,liver igf1,igf2a and igf2b expression was significantly upregulated in the sst4−/−fish compared to the WT.Histological examination of the ovaries and testis indicated that sst4−/−fish had slightly delayed testicular gametogenesis compared to the WT.Significantly lower expression of igf3,amh,insl3,hsd17b3,hsd11b2,hsd20b,cyp11b and cyp17 was consistently observed in the sst4−/−testis.In contrast,the ovaries had lower expression of igf1,igf2a and cyp19a1a but increased expression of igf2b and hsd20b.The gonadotrophin beta subunits(fshb and lhb)in the brain were downregulated indicating the brain-pituitary-gonadal axis was downregulated in the sst4−/−fish and suggesting that the steroid production is compromised in the maturing gonads.In addition,analysis of sst1 and sst3 mRNA levels in sst4−/−fish suggests a dosage compensation effect of sst1 in the brain and liver.Altogether,the results from the zebrafish sst4−/−line support the idea that sst4 is involved in the regulation of igf signalling,somatic growth and reproduction since steroidogenesis and gametogenesis at pubertal onset were compromised.

ABORTED GAMETOPHYTE 1 is required for gametogenesis in Arabidopsis

In flowering plants, the male and female gameto- genesis is a crucial step of sexual reproduction. Although many genes have been identified as being involved in the gametogenesis process, the genetic mechanisms underlying gametogenesis remains poorly understood. We reported here characterization of the gene, ABORTED GAMETOPHYTE 1 （AOGI） that is newly identified as essential for gametogenesis in Arabidopsis thaliana. AOG1 is expressed predominantly in reproductive tissues including the developing pollen grains and ovules. The AOG1 protein shares no significant amino acid sequence similarity with other documented proteins and is located mainly in nuclei of the cells. Mutation in AOG~ caused degeneration of pollen at the uninucleate microspore stage and severe defect in embryo sacs, leading to a significant reduction in male and female fertility.Furthermore, the molecular analyses showed that the aogl mutant significantly affected the expression of several genes, which are required for gametogenesis. Our results suggest that AOG1 plays important roles in gameto- genesis at the stage prior to pollen mitosis 1 （PMI） in Arabidopsis, possibly through collaboration with other genes.

Regulation of Reproduction in Delayed Gametophyte of Saccharina japonica (Laminariales, Phaeophyceae): Effects of Light Intensity, Quality and Photoperiod

Saccharina japonica gametophytes can survive a long period under unfavorable environmental conditions,while they also delay in growth and/or reproduction.Although the reproduction in delayed gametophyte of S.japonica was known to be strongly influenced by light intensity,light quality,and photoperiod,no previous studies have evaluated their interactive effects on gametogenesis.To evaluate these effects,we used an orthogonal experiment to expose delayed gametophytes of S.japonica to different light intensities,light qualities,and photoperiods for 12 days.The results showed that changes in light intensity rather than light quality and photoperiod significantly affected the relative growth rates of the delayed gametophytes.Blue light had the greatest promotion on reproduction rate.The optimal light conditions in the early vegetative growth phase in gametogenesis induction for the delayed gametophytes were at 60–80μmol photons m^(−2) s^(−1) with daylength of 12 or 16 hours under white or blue light.When the delayed gametophytes were maintained in a constant light condition from delayed state to gametogenesis,the beneficial photoperiods for vegetative growth and reproductive rate were both 16L(16 hours of light):8D(8 hours of dark).However,when the delayed S.japonica gametophytes achieve the optimal growth state during the first 6 days and then they were cultured at different light conditions for the following 6 days,the reproduction rate increased as the daylength decreased and attained a peak value in group of 8L:16D photoperiod,indicating that photoperiod adjustment at the transition period is crucial in the gametogenesis induction process of delayed gametophyte of S.japonica.

Advances in Small RNAs and Sexual Reproduction in Plants

Small RNAs are non-coding RNA molecules with 20-30 nucleotides （nt） in length that mainly play regulatory roles in gene expression at the post-transcription level by directly cutting target mRNA or inhibiting its translation. Small RNAs play regulatory roles in the growth and development process of plants at the core of gene regulatory networks, which has been widely studied and confirmed in sporophyte generation of plants. However, few researches have been conducted on small RNAs and gametophyte generation. It is reported that small RNAs play important roles in floral organ development, gametogenesis, fertilization, and early zygotic development of plants. In addition, various small RNAs also play roles in controlling genetic integrity, cell differentiation and functions during the sexual reproduction process of plants. However, most of the specific functions of small RNAs in the sexual reproduction process are unknown yet. This study mainly aimed to introduce small RNAs in plants, summarize the latest advances in researches of small RNAs and plant sexual reproduction, and make prospect on its future.

Protective effect of ascorbic acid on cyclophosphamide induced testicular gametogenic and androgenic disorders in male rats

Aim:To study the detrimental effects of cyclophosphamide on the testicular androgenic and gametogenic activities through endocrine inhibition and/or induction of oxidative stress in male albino rats and to evaluate the protective effect of ascorbic acid.Methods:The testicular△^(5),3β-hydroxysteroid dehydrogenase(HSD),17β-HSD,peroxidase and catalase activities along with the levels of malondialdehyde(MDA)and conjugated dienes in testicular tissue were measured for the evaluation of testicular oxidative stress.The plasma testosterone(T)level was measured by immunoassay.Various germ cells at stageⅦof spermatogenic cycle were quantified from testicular stained sections.Results:Cyclophosphamide treatment results in a significant inhibition in the testicular△^(5),3β-HSD and 17β-HSD activities,a decrease in plasma T level and a diminution in the counts of various germ cells.Moreover,this treatment was also associated with a significant inhibition of the peroxidase and catalase activities along with high levels of MDA and conjugated dienes in the testis.All these changes were reversed by ascorbic acid co-administration.Conclusion:Cyclophosphamide treatment at the dosage used caused testicular gametogenic and androgenic disorders as well as induced testicular oxidative stress that can be reversed by ascorbic acid co-administration.

STUDY ON GAMETOPHYTE VEGETATIVE GROWTH OF UNDARIA PINNATIFIDA AND ITS APPLICATIONS

When cultured under certain environmental coriditions (25℃, light intensity 80 μmol/m2 ·s, LD12/12, in enriched seawater medium with 7 × 10-4mol/L NO3,-N, 1.56× 10-4mol/L, PO4-P and supplementsof other elements like Mn, Fe, I, etc.), mate and female gametophytes of U pinnatifida keptgrowing vegetatively and propagated fast at average daily fresh weight increase rate of about 20%. Theempirical formula Gm=Go. 3m was established to estimate the output of vegeative gametophytes. Vigorousvegetative gametophyte cells began to form reproductive structures (oogonium and spermatangium, whenthe tmperature was lower than 25℃ and other environmental factors wrre kept optimal. The sufficientsupply of gametophyte cells provided enough seeds for raising Undaria sporelings on prodiction scale.Controlled cross-breeding experiments using selcted male and female gametophyte clones which increasetheir cell number by mitosis instead of meiosis were also carried out in vitro. Juvenile sporophytes fromthe

Seasonal Variation of Biochemical Components in Clam (Saxidomuspurpuratus Sowerby 1852) in Relation to Its Reproductive Cycle and the Environmental Condition of Sanggou Bay, China

Seasonal variation of biochemical components in clam(Saxidomus purpuratus Sowerby 1852) was investigated from March 2012 to February 2013 in relation to environmental condition of Sanggou Bay and the reproductive cycle of clam.According to the histological analysis,the reproductive cycle of S.purpuratus includes two distinctive phases:a total spent and inactive stage from November to January,and a gametogenesis stage,including ripeness and spawning,during the rest of the year.Gametes were generated at a low temperature(2.1℃) in February.Spawning took place once a year from June to October.The massive spawning occurred in August when the highest water temperature and chlorophyll a level could be observed.The key biochemical components(glycogen,protein and lipid) in five tissues(gonad,foot,mantle,siphon and adductor muscle) were analyzed.The glycogen content was high before gametogenesis,and decreased significantly during the gonad development in the gonad,mantle and foot of both females and males,suggesting that glycogen was an important energy source for gonad development.The protein and lipid contents increased in the ovary during the gonad development,demonstrating that they are the major organic components of oocytes.The lipid and protein contents decreased in the testis,implying that they can provide energy and material for spermatogenesis.The results also showed that protein stored in the mantle and foot could support the reproduction after the glycogen was depleted.

Reproductive polyphenism and its advantages in aphids:Switching between sexual and asexual reproduction

Reproductive polyphenism,which allows one genotype to produce sexual and asexual morphs,is an extreme case of phenotypic plasticity and is commonly observed in aphids.Aphids are typical species that switch these reproductive modes,and the pathway orientation is triggered by the environmental conditions(mainly photoperiod and temperature).The typical arm ual life of aphids in eludes a successi on of parthenogenetic gen erations duri ng the spri ng and summer and a single sexual generation in autumn.In this review,we describe how the environmental cues orientate the reproductive mode of aphids from photoperiodic perception to endocrine regulation,and how juvenile hormones may act on the target cells(oocytes)to initiate the gametogenesis and embryogenesis in sexual and asexual reproduction.We also discuss the paradox of sex,especially the advantages of sexual reproduction in aphids.With the recent development of genomic resources in aphids,many potential genes involved in the reproductive polyphenism will enter the public's awareness.In particular,we describe a novel RNAi method in aphids,which may provide a molecular technique for determining the developmental fate and multiple reproductive strategies.