Temporal and spatial SOX9 expression patterns in the course of gonad development of the caudate amphibian Pleurodeles waltl

Regulation mechanism of endochondral ossification in Rana zhenhaiensis during metamorphosis based on histomorphology and transcriptome analyses

Endochondral ossification plays a crucial role in the limb development of amphibians. This study explored the ossification sequence in the hindlimb of Rana zhenhaiensis tadpoles and the correlation between thyroid hormones (THs) and endochondral ossification via histomorphology and transcriptional analyses. Our results suggest that ossification of the femur and tibiofibula was initiated during the period of high THs activity (metamorphosis climax). In addition, the results of differentially expressed gene analyses in the hindlimb and tail showed that systemic factors, transcription factors, and locally secreted factors interacted with each other during the metamorphosis climax to regulate the occurrence of endochondral ossification. These results will enrich the morphological data of anurans and provide scientific reference for the evolutionary history of vertebrates.

gjSOX9 Cloning, Expression, and Comparison with gjSOXs Family Members in Gekko japonicus

SOX9 plays a crucial role in the male reproductive system, brain, and kidneys. In this study, we firstly analyzed the complete cDNA sequence and expression patterns for SOX9 from Gekko japonicus SOX9 (gjSOX9), carried out bioinformatic analyses of physiochemical properties, structure, and phylogenetic evolution, and compared these with other members of the gjSOX family. The results indicate that gjSOX9 cDNA comprises 1895 bp with a 1482 bp ORF encoding 494aa. gjSOX9 was not only expressed in various adult tissues but also exhibited a special spatiotemporal expression pattern in gonad tissues. gjSOX9 was predicted to be a hydrophilic nucleoprotein with a characteristic HMG-Box harboring a newly identified unique sequence, "YKYQPRRR", only present in SOXE members. Among the 20 SOX9 orthologs, gjSOX9 shares the closest genetic relationships with Eublepharis macularius SOX9, Sphacrodactylus townsendi SOX9, and Hemicordylus capensis SOX9. gjSOX9 and gjSOX10 possessed identical physicochemical properties and subcellular locations and were tightly clustered with gjSOX8 in the SOXE group. Sixteen gjSOX family members were divided into six groups: SOXB, C, D, E, F, and H with gjSOX8, 9, and 10 in SOXE among 150 SOX homologs. Collectively, the available data in this study not only facilitate a deep exploration of the functions and molecular regulation mechanisms of the gjSOX9 and gjSOX families in G. japonicus but also contribute to basic research regarding the origin and evolution of SOX9 homologs or even sex-determination mode in reptiles.

Harderian SOX9: Molecular characterization and its dimorphic expression in hamster

The molecular action of SOX9 can promote lipogenesis. Because the hamster Harderian gland (HG) synthesizes lipids and exhibits sexual dimorphism, this study aimed to identify and characterize Harderian SOX9. We examined the tissue distribution and expression profiles of SOX9 in hamster Mesocricetus auratus HGs. The full-length SOX9 cDNA sequence [3649-base pairs (bp)] contains an 81-bp 5' untranslated region (UTR), a 3' UTR of 2044-bp, an open reading frame (ORF) of 1524-bp, and a polyadenylation signal (AATAAA) at 19-bp upstream of poly(A) tail. The cDNA encodes a 507 amino acid protein containing the potential DNA-binding domain known as the HMG box. BLAST analysis revealed 99%, 99%, and 97% identity with the SOX9 of mouse, rat, and human, respectively. High expression levels were also observed in the testis, cerebellum, and hypothalamus. qPCR analysis demonstrated that SOX9 is expressed more abundantly in the HGs of males than in females. Sexually dimorphic expression of SOX9 suggests that differential expression between male and female HGs could be under the regulation of sex steroids. SOX9 might play a similar role in regulating exocrine secretions of lipids; these could occur downstream of FGF signaling - as found during embryogenesis - and/or androgen signaling.

Testis Development and Differentiation in Amphibians

Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity of the sex-determining mechanisms, or the existence of polyploids, may hinder the design of experiments when studying how the gonads can differentiate. Even so, other features, like their external development or the possibility of inducing sex reversal by external treatments, can be helpful. This review summarizes the current knowledge on amphibian sex determination, gonadal development, and testis differentiation. The analysis of this information, compared with the information available for other vertebrate groups, allows us to identify the evolutionarily conserved and divergent pathways involved in testis differentiation. Overall, the data confirm the previous observations in other vertebrates-the morphology of the adult testis is similar across different groups; however, the male-determining signal and the genetic networks involved in testis differentiation are not evolutionarily conserved.

Molecular cloning, characterization, mRNA expression changes and nucleocytoplasmic shuttling during kidney embryonic development of SOX9 in Alligator sinensis

SOX9 plays a crucial, extensive and conservative role in the process of somatic tissue development and adult regeneration through the positive self-regulation mediated by SOM across all vertebrates. In this study, we have cloned SOX9 from the kidney of hatchling Alligator sinensis. The full-length of SOX9 cDNA is 3878 bp with an open reading frame encoding 494 amino acids. Amino acid alignment analyses indicated that the SOX9 exhibit highly conserved functional domains. Using the droplet digital PCR, the mRNA abundances of SOX9 during nephrogenesis in A. sinensis showed prominent changes in the embryonic development, suggesting that SOX9 might combines a vital role in the regulation of complex renal development. Interestingly, we detected the nucleocytoplasmic shuttling of SOX9 protein using immunofluorescence, implying that nucleocytoplasmic shuttling is critical to the regulation of SOX9 in the renal embryonic development. Collectively, these data provide an important foundation for further studies on renal developmental biology and molecular biology of non-mammalian SOX9. Furthermore, it provides new insights into the phenomenon of SOX9 nucleocytoplasmic shuttling in Alligator sinensis, which is probably of great significance to the development of kidney metanephros embryo.

A role for SOX9 in post-transcriptional processes: insights from the amphibian oocyte

Sox9 is a member of the gene family of SOX transcription factors, which is highly conserved among vertebrates. It is involved in different developmental processes including gonadogenesis. In all amniote species examined thus far, Sox9 is expressed in the Sertoli cells of the male gonad, suggesting an evolutionarily conserved role in testis development. However, in the anamniotes, fishes and amphibians, it is also expressed in the oocyte but the significance of such an expression remains to be elucidated. Here, we have investigated the nuclear localization of the SOX9 protein in the oocyte of three amphibian species, the urodelan Pleurodeles waltl, and two anurans, Xenopus laevis and Xenopus tropicalis. We demonstrate that SOX9 is associated with ribonucleoprotein (RNP) transcripts of lampbrush chromosomes in an RNA-dependent manner. This association can be visualized by Super-resolution Structured Illumination Microscopy (SIM). Our results suggest that SOX9, known to bind DNA, also carries an additional function in the posttranscriptional processes. We also discuss the significance of the acquisition or loss of Sox9 expression in the oocyte during evolution at the transition between anamniotes and amniotes.

Morphogenesis-related gene-expression profile in porcine oocytes before and after in vitro maturation

Mammalian oocyte maturation is achieved when oocytes reach metaphase II (MII) stage, and accumulate mRNA and proteins in the cytoplasm following fertilization. It has been shown that oocytes investigated before and after in vitro maturation (IVM) differ significantly in transcriptomic and proteomic profiles. Additionally, folliculogenesis and oogenesis is accompanied by morphogenetic changes, which significantly influence further zygote formation and embryo growth. This study aimed to determine new transcriptomic markers of porcine oocyte morphogenesis that are associated with cell maturation competence. An Affymetrix microarray assay was performed on an RNA template isolated from porcine oocytes before (n = 150) and after (n = 150) IVM. The brilliant cresyl blue (BCB) staining test was used for identification of cells with the highest developmental capacity. DAVID (Database for Annotation, Visualization, and Integrated Discovery) software was used for the extraction of the genes belonging to a cell morphogenesis Gene Ontology group. The control group consisted of freshly isolated oocytes. In total, 12,000 different transcripts were analysed, from which 379 genes were downregulated and 40 were upregulated in oocytes following IVM. We found five genes, SOX9, MAP1B, DAB2, FN1, and CXCL12, that were significantly upregulated in oocytes after IVM (in vitro group) compared with oocytes analysed before IVM (in vivo group). In conclusion, we found new transcriptomic markers of oocyte morphogenesis, which may be also recognized as significant mediators of cellular maturation capacity in pigs. Genes SOX9, MAP1B, DAB2, FN1, and CXCL12 may be involved in the regulation of the MII stage oocyte formation and several other processes that are crucial for porcine reproductive competence.

Methods for the Study of Gonadal Development

Current knowledge on gonadal development and sex determination is the product of many decades of research involving a variety of scientific methods from different biological disciplines such as histology, genetics, biochemistry, and molecular biology. The earliest embryological investigations, followed by the invention of microscopy and staining methods, were based on histological examinations. The most robust development of histological staining techniques occurred in the second half of the nineteenth century and resulted in structural descriptions of gonadogenesis. These first studies on gonadal development were conducted on domesticated animals; however, currently the mouse is the most extensively studied species. The next key point in the study of gonadogenesis was the advancement of methods allowing for the in vitro culture of fetal gonads. For instance, this led to the description of the origin of cell lines forming the gonads. Protein detection using antibodies and immunolabeling methods and the use of reporter genes were also invaluable for developmental studies, enabling the visualization of the formation of gonadal structure. Recently, genetic and molecular biology techniques, especially gene expression analysis, have revolutionized studies on gonadogenesis and have provided insight into the molecular mechanisms that govern this process. The successive invention of new methods is reflected in the progress of research on gonadal development.

An orphan gene is necessary for preaxial digit formation during salamander limb development

Limb development in salamanders differs from other tetrapods in that the first digits to form are the two most anterior (preaxial dominance). This has been proposed as a salamander novelty and its mechanistic basis is unknown. Salamanders are the only adult tetrapods able to regenerate the limb, and the contribution of preaxial dominance to limb regeneration is unclear. Here we show that during early outgrowth of the limb bud, a small cohort of cells express the orphan gene Prod1 together with Bmp2, a critical player in digit condensation in amniotes. Disruption of Prod1 with a gene-editing nuclease abrogates these cells, and blocks formation of the radius and ulna, and outgrowth of the anterior digits. Preaxial dominance is a notable feature of limb regeneration in the larval newt, but this changes abruptly after metamorphosis so that the formation of anterior and posterior digits occurs together within the autopodium resembling an amniote-like pattern.

Low concentrations of dihydrotestosterone induce female-to-male sex reversal in the frog Pelophylax nigromaculatus

Previous studies have demonstrated that some amphibian species can be sex-reversed by high concentrations of androgens. Little attention has focused on the effects of androgenic endocrine-disrupting chemicals (EDCs) on amphibians. The present study aimed to investigate the effects of lower concentrations of the androgenic EDC 5α-dihydrotestosterone (DHT) on gonadal differentiation and development in Pelophylax nigromaculatus, a true frog distributed widely in East Asia. Tadpoles at Gosner stage 24/25 were exposed to nominal concentrations of 40 ng/L, 400 ng/L, and 4000 ng/L DHT to complete metamorphosis. In all DHT treatment groups, males and ambiguous sexes were identified based on gonadal morphology, whereas no females were found; thus, all treatment groups exhibited male-skewed ratios compared with the control group. Gonadal histological examination revealed that ambiguous sexes displayed overall testicular structure with certain ovarian characteristics, demonstrating that DHT-induced sex-ambiguous gonads were incomplete ovary-to-testis reversals (IOTTRs). The expression levels of some ovary-biased genes in the IOTTRs were significantly higher than in the control testes but lower than in the control ovaries. These results show that low concentrations of DHT induced complete or incomplete female-to-male sex reversal in P. nigromaculatus, and incomplete sex reversal retained certain ovarian characteristics not only at gonadal morphological and histological levels but also at the molecular level. They present study highlights potential risks of DHT and other androgenic EDCs for P. nigromaculatus.

Müllerian inhibiting substance in the caudate amphibian Pleurodeles waltl

Müllerian inhibiting substance (MIS, also known as anti-Müllerian hormone), is a key factor of male sex differentiation in vertebrates. In amniotes, it is responsible for Müllerian duct regression in male embryos. In fish, despite the absence of Müllerian ducts, MIS is produced and controls germ cell proliferation during gonad differentiation. Here we show for the first time the presence of MIS in an amphibian species, Pleurodeles waltl. This is very astonishing because in caudate amphibians, Müllerian ducts do not regress in males. Phylogenetic analysis of MIS P. waltl ortholog revealed that the deduced protein segregates with MIS from other vertebrates and is clearly separated from other TGF-β family members. In larvae, MIS mRNA was expressed at higher levels in the developing testes than in the ovaries. In the testis, MIS mRNA expression was located within the lobules that contain Sertoli cells. Besides, expression of MIS was modified in the case of sex reversal: it increased after masculinizing heat treatment and decreased after estradiol feminizing exposure. In addition to the data obtained recently in the fish medaka, our results suggest that the role of MIS on Müllerian ducts occurred secondarily during the course of evolution.

Thyroid hormones in male reproductive development: evidence for direct crosstalk between the androgen and thyroid hormone axes

Thyroid hormones (THs) exert a broad range of effects on development in vertebrate species, demonstrating connections in nearly every biological endocrine system. In particular, studies have shown that THs play a role in sexual differentiation and gonadal development in mammalian and non-mammalian species. There is considerable evidence that the effects of THs on reproductive development are mediated through the female hormonal axis; however, recent findings suggest a more direct crosstalk between THs and the androgen axis. These findings demonstrate that THs have considerable influence in the sexual ontogeny of male vertebrates, through direct interactions with select sex-determining-genes and regulation of gonadotropin production in the hypothalamus-pituitary-gonad axis. THs also regulate androgen biosynthesis and signaling through direct and indirect regulation of steroidogenic enzyme expression and activity. Novel promoter analysis presented in this work demonstrates the potential for direct and vertebrate wide crosstalk at the transcriptional level in mice (Mus musculus), Western clawed frogs (Silurana tropicalis) and medaka (Oryzias latipes). Cumulative evidence from previous studies; coupled with novel promoter analysis suggests mechanisms for a more direct crosstalk between the TH and male reproductive axes across vertebrate species.

Molecular genetic system for regenerative studies using newts

Urodele newts have the remarkable capability of organ regeneration, and have been used as a unique experimental model for more than a century. However, the mechanisms underlying regulation of the regeneration are not well understood, and gene functions in particular remain largely unknown. To elucidate gene function in regeneration, molecular genetic analyses are very powerful. In particular, it is important to establish transgenic or knockout (mutant) lines, and systematically cross these lines to study the functions of the genes. In fact, such systems have been developed for other vertebrate models. However, there is currently no experimental model system using molecular genetics for newt regenerative research due to difficulties with respect to breeding newts in the laboratory. Here, we show that the Iberian ribbed newt (Pleurodeles waltl) has outstanding properties as a laboratory newt. We developed conditions under which we can obtain a sufficient number and quality of eggs throughout the year, and shortened the period required for sexual maturation from 18 months to 6 months. In addition, P. waltl newts are known for their ability, like other newts, to regenerate various tissues. We revealed that their ability to regenerate various organs is equivalent to that of Japanese common newts. We also developed a method for efficient transgenesis. These studies demonstrate that P. waltl newts are a suitable model animal for analysis of regeneration using molecular genetics. Establishment of this experimental model will enable us to perform comparable studies using these newts and other vertebrate models.