Left-right function of dmrt2 genes is not conserved between zebrafish and mouse

Genome-wide identification, phylogeny and expressional profile of the Dmrt gene family in Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon Dmrt gene family was identified and characterized for the first time. A total of 5 putative Dmrt genes were identified. The gene structure, conserved protein domain and the phylogenetic relationship of Dmrt gene family were systematically analyzed. The expressed profile of Chinese sturgeon Dmrt genes in gonad, pituitary and hypothalamus in the male and female were investigated. The results indicated that the accumulation of Dmrt genes was involved in different tissues, and the expression profile also differed among each Dmrt genes. ASDmrt1A, ASDmrt2, ASDmrt3, and ASDmrtA1 were highly expressed in the testis in comparison with other tissue. This result showed that ASDmrt1A, ASDmrt2, ASDmrt3, and ASDmrtA1 played an important role in the development of testicle, and may be useful tool in distinguishing between male and female of Chinese sturgeon. Our study will provide a basis for additional analyses of Chinese sturgeon Dmrt genes. This systematic analysis provided a foundation for further functional characterization of Dmrt genes with an aim of study of Chinese sturgeon Dmrt gene family.

Genome-wide identification and expression analysis of Dmrt gene family and their role in gonad development of Pacific oyster (Crassostrea gigas)

Doublesex and Mab-3-related transcription factor (Dmrt) is a type of transcription factor with a zinc-finger DM structural domain, which plays a significant role in sex determination and differentiation in animals. Although Dmrt has been reported in many vertebrates and invertebrates, it has rarely been studied in bivalves. In this study, a total of three members of the Dmrt gene family were identified and characterized in Crassostrea gigas, and all these CgDmrt genes contained a conserved DM domain. Analysis of the phylogenetic tree and gene structure revealed that Dmrt genes clustered on one branch may have similar functions in bivalves. Expression profiling of CgDmrt mRNA in different tissues and stages of gonad development indicated that CgDmrt3 exhibited sexually dimorphic expression and played an important role in the development of the male gonad in C. gigas. Furthermore, analysis of CgDmrt mRNA expression between fertile triploids and sterile triploids showed that CgDmrt3 may be involved in sperm production. Collectively, the systematic analysis of the CgDmrt genes will provide potential insights into the function of these genes in gonadal development.

A chromosome-level assembly supports genome-wide investigation of the DMRT gene family in the golden mussel (Limnoperna fortunei)

BACKGROUND

The golden mussel (Limnoperna fortunei) is a highly invasive species that causes environmental and socioeconomic losses in invaded areas. Reference genomes have proven to be a valuable resource for studying the biology of invasive species. While the current golden mussel genome has been useful for identifying new genes, its high fragmentation hinders some applications.

FINDINGS

In this study, we provide the first chromosome-level reference genome for the golden mussel. The genome was built using PacBio HiFi, 10X, and Hi-C sequencing data. The final assembly contains 99.4% of its total length assembled to the 15 chromosomes of the species and a scaffold N50 of 97.05 Mb. A total of 34,862 protein-coding genes were predicted, of which 84.7% were functionally annotated. A significant (6.48%) proportion of the genome was found to be in a hemizygous state. Using the new genome, we have performed a genome-wide characterization of the Doublesex and Mab-3 related transcription factor gene family, which has been proposed as a target for population control strategies in other species.

CONCLUSIONS

From the applied research perspective, a higher-quality genome will support genome editing with the aim of developing biotechnology-based solutions to control invasion. From the basic research perspective, the new genome is a high-quality reference for molecular evolutionary studies of Mytilida and other Lophotrochozoa, and it may be used as a reference for future resequencing studies to assess genomic variation among different golden mussel populations, unveiling potential routes of dispersion and helping to establish better control policies.

dmrt2 and myf5 Link Early Somitogenesis to Left-Right Axis Determination in Xenopus laevis

The vertebrate left-right axis is specified during neurulation by events occurring in a transient ciliated epithelium termed left-right organizer (LRO), which is made up of two distinct cell types. In the axial midline, central LRO (cLRO) cells project motile monocilia and generate a leftward fluid flow, which represents the mechanism of symmetry breakage. This directional fluid flow is perceived by laterally positioned sensory LRO (sLRO) cells, which harbor non-motile cilia. In sLRO cells on the left side, flow-induced signaling triggers post-transcriptional repression of the multi-pathway antagonist dand5. Subsequently, the co-expressed Tgf-β growth factor Nodal1 is released from Dand5-mediated repression to induce left-sided gene expression. Interestingly, Xenopus sLRO cells have somitic fate, suggesting a connection between LR determination and somitogenesis. Here, we show that doublesex and mab3-related transcription factor 2 (Dmrt2), known to be involved in vertebrate somitogenesis, is required for LRO ciliogenesis and sLRO specification. In dmrt2 morphants, misexpression of the myogenic transcription factors tbx6 and myf5 at early gastrula stages preceded the misspecification of sLRO cells at neurula stages. myf5 morphant tadpoles also showed LR defects due to a failure of sLRO development. The gain of myf5 function reintroduced sLRO cells in dmrt2 morphants, demonstrating that paraxial patterning and somitogenesis are functionally linked to LR axis formation in Xenopus.

High Polymorphism in the Dmrt2a Gene Is Incompletely Sex-Linked in Spotted Scat, Scatophagus argus

Unlike mammals and birds, many fishes have young sex chromosomes, providing excellent models to study sex chromosome differentiation at early stages. Previous studies showed that spotted scat possesses an XX-XY sex determination system. The X has a complete Dmrt3 copy (termed normal) and a truncated copy of Dmrt1 (called Dmrt1b), while the Y has the opposite (normal Dmrt1, which is male-specific, and a truncated Dmrt3 called Dmrt3△-Y). Dmrt1 is the candidate sex determination gene, while the differentiation of other sex-linked genes remains unknown. The spotted scat has proven to be a good model to study the evolution of sex chromosomes in vertebrates. Herein, we sequenced a neighbor gene of this family, Dmrt2, positioned farther from Dmrt1 and closer to Dmrt3 in the spotted scat, and analyzed its sequence variation and expression profiles. The physical locations of the three genes span across an estimated size of >40 kb. The open reading frames of Dmrt2a and its paralog Dmrt2b are 1578 bp and 1311 bp, encoding peptides of 525 and 436 amino acid residues, respectively. Dmrt2a is positioned close to Dmrt3 but farther from Dmrt1 on the same chromosome, while Dmrt2b is not. Sequence analysis revealed several mutations; insertions, and deletions (indels) on Dmrt2a non-coding regions and single-nucleotide polymorphisms (SNPs) on the Dmrt2a transcript. These indels and SNPs are sex-linked and showed high male heterogeneity but do not affect gene translation. The markers designed to span the mutation sites tested on four different populations showed varied concordance with the genetic sexes. Dmrt2a is transcribed solely in the gonads and gills, while Dmrt2b exists in the gonads, hypothalamus, gills, heart, and spleen. The Dmrt2a and Dmrt2b transcripts are profoundly expressed in the male gonads. Analyses of the transcriptome data from five other fish species (Hainan medaka (Oryzias curvinotus), silver sillago (Sillago sihama), Nile tilapia (Oreochromis niloticus), Hong Kong catfish (Clarias fuscus), and spot-fin porcupine fish (Diodon hystrix)) revealed testes-biased expression of Dmrt1 in all, similar to spotted scat. Additionally, the expression of Dmrt2a is higher in the testes than the ovaries in spotted scat and Hainan medaka. The Dmrt2a transcript was not altered in the coding regions as found in Dmrt1 and Dmrt3 in spotted scat. This could be due to the functional importance of Dmrt2a in development. Another possibility is that because Dmrt2a is positioned farther from Dmrt1 and the chromosome is still young, meaning it is only a matter of time before it differentiates. This study undeniably will aid in understanding the functional divergence of the sex-linked genes in fish.

Multiple Functions of the Dmrt Genes in the Development of the Central Nervous System

The Dmrt genes encode the transcription factor containing the DM (doublesex and mab-3) domain, an intertwined zinc finger-like DNA binding module. While Dmrt genes are mainly involved in the sexual development of various species, recent studies have revealed that Dmrt genes, which belong to the DmrtA subfamily, are differentially expressed in the embryonic brain and spinal cord and are essential for the development of the central nervous system. Herein, we summarize recent studies that reveal the multiple functions of the Dmrt genes in various aspects of vertebrate neural development, including brain patterning, neurogenesis, and the specification of neurons.

dmrt11E ortholog is a crucial factor for oogenesis of the domesticated silkworm, Bombyx mori

DMRT (Doublesex and Mab-3-related transcription factor) is a highly conserved transcription factor family involved in sex determination in numerous animal species. One DMRT, dmrt2/dmrt11E, has entirely different functions in invertebrate and vertebrate species, indicating unpredicted functions. Here, we performed functional analysis of the dmrt11E gene in the domesticated silkworm, Bombyx mori. This gene was preferentially expressed in ovarioles at the last larval instar stage. Its mRNA accumulated in ovarian eggs during the adult stage. CRISPR/Cas9-mediated knockout of Bombyx dmrt11E (Bmdmrt11E) caused defects in oogenesis, resulting in the production of abnormal eggs with transparent liquids. These eggs had significantly reduced fertility and lipid levels. Transcriptomic comparisons between ovaries of control and mutant insects at two developmental stages identified six genes that may be under the control of Bmdmrt11E. Finally, we provide a possible model for lipid uptake and storage in eggs of Bombyx mori.

Altered Cogs of the Clock: Insights into the Embryonic Etiology of Spondylocostal Dysostosis

Spondylocostal dysostosis (SCDO) is a rare heritable congenital condition, characterized by multiple severe malformations of the vertebrae and ribs. Great advances were made in the last decades at the clinical level, by identifying the genetic mutations underlying the different forms of the disease. These were matched by extraordinary findings in the Developmental Biology field, which elucidated the cellular and molecular mechanisms involved in embryo body segmentation into the precursors of the axial skeleton. Of particular relevance was the discovery of the somitogenesis molecular clock that controls the progression of somite boundary formation over time. An overview of these concepts is presented, including the evidence obtained from animal models on the embryonic origins of the mutant-dependent disease. Evidence of an environmental contribution to the severity of the disease is discussed. Finally, a brief reference is made to emerging in vitro models of human somitogenesis which are being employed to model the molecular and cellular events occurring in SCDO. These represent great promise for understanding this and other human diseases and for the development of more efficient therapeutic approaches.

Physiological Effects of Water Flow Induced Swimming Exercise in Seabream Sparus aurata

A longer on-land rearing period of Gilthead seabream Sparus aurata before transfer to sea-cages would allow the farmer to benefit from exercise-enhanced growth, resilience, and robustness as induced by increasing water flow in the tanks. In this study, the physiological effects of flow-conditioning were investigated by subjecting large groups of experimental fish to minimal flow or to flow regimes inducing swimming exercise at 1 or 2 body length (BL) s⁻¹ for a period of 8 months (February–October) in 1,500 L tanks. Fish representing the three treatment groups were then used for: (1) a stress challenge netting test and plasma cortisol measurement (baseline, peaking, and recovery levels), (2) blood plasma measurements of glucose, triglycerides, lactate, cholesterol, growth hormone (GH), and insulin-like growth factor 1 (IGF1), and (3) heart and muscle gene expression of the GH and IGF1 receptors and the muscle transcriptome by deep RNA sequencing (RNAseq). Fish size after 8 months of flow conditioning was 92 ± 27 g body weight (BW) for fish under minimal flow, 106 ± 24 g BW (+15%) at 1 BL s⁻¹, and 125 ± 27 g BW (+36%) at 2 BL s⁻¹. Flow conditioning at 1 BL s⁻¹ provided optimal conditions for growth and uniformity, but also stress (lowest baseline plasma cortisol), robustness (higher condition factor and larger hearts), and energy mobilization (increased plasma glucose). Although flow enhanced growth linearly with swimming speed, also the percentage of lordotic fish increased with exercise, particularly high for swimming at 2 BL s⁻¹. The absence of important differences in plasma GH and IGF1, and expression levels of their receptors in heart and white skeletal muscle, indicated that other factors may be involved in growth enhancement. RNAseq of the white skeletal muscle showed upregulated expression of genes involved in muscle contraction, muscle development and its molecular regulation, and immune genes that may play a role in the muscle repair mechanism. An exercise regime of swimming at 1 BL s⁻¹ can be considered as optimal for farming robust seabream although the increase of skeletal deformities should be avoided.

lncRNA DMRT2-AS acts as a transcriptional regulator of dmrt2 involving in sex differentiation in the Chinese tongue sole (Cynoglossus semilaevis)

Long non-coding RNAs (lncRNAs) contribute to various biological processes, including sexual development. As a member of the DMRT family, dmrt2 plays a very important role in sex determination and differentiation. In this study, we cloned and characterized the lncRNA DMRT2-AS (referred to as dmrt2 antisense) associated with dmrt2 from the gonads of the Chinese tongue sole (Cynoglossus semilaevis). The full-length cDNA of DMRT2-AS was 537 bp. Based on a sequence alignment, DMRT2-AS overlapped with dmrt2 in reverse on exon 4 and intron 3, with a region of overlap of 221 bp on exon 4. RT-qPCR showed that DMRT2-AS was highly expressed in the testis of Chinese tongue sole. In addition, the expression of DMRT2-AS increased continuously during male gonadal development. In vitro experiments and bioinformatics predictions showed that DMRT2-AS promoted the expression of dmrt2 at the transcriptional level. These results suggest that DMRT2-AS acts as a transcriptional regulator of dmrt2 and plays an important role in the gonadal differentiation of male.

Comparative Genomics Studies on the dmrt Gene Family in Fish

Doublesex and mab-3-related transcription factor (dmrt) genes are widely distributed across various biological groups and play critical roles in sex determination and neural development. Here, we applied bioinformatics methods to exam cross-species changes in the dmrt family members and evolutionary relationships of the dmrt genes based on genomes of 17 fish species. All the examined fish species have dmrt1-5 while only five species contained dmrt6. Most fish harbored two dmrt2 paralogs (dmrt2a and dmrt2b), with dmrt2b being unique to fish. In the phylogenetic tree, 147 DMRT are categorized into eight groups (DMRT1-DMRT8) and then clustered in three main groups. Selective evolutionary pressure analysis indicated purifying selections on dmrt1-3 genes and the dmrt1-3-2(2a) gene cluster. Similar genomic conservation patterns of the dmrt1-dmrt3-dmrt2(2a) gene cluster with 20-kb upstream/downstream regions in fish with various sex-determination systems were observed except for three regions with remarkable diversity. Synteny analysis revealed that dmrt1, dmrt2a, dmrt2b, and dmrt3-5 were relatively conserved in fish during the evolutionary process. While dmrt6 was lost in most species during evolution. The high conservation of the dmrt1-dmrt3-dmrt2(2a) gene cluster in various fish genomes suggests their crucial biological functions while various dmrt family members and sequences across fish species suggest different biological roles during evolution. This study provides a molecular basis for fish dmrt functional analysis and may serve as a reference for in-depth phylogenomics.

Making and breaking symmetry in development, growth and disease

Consistent asymmetries between the left and right sides of animal bodies are common. For example, the internal organs of vertebrates are left-right (L-R) asymmetric in a stereotyped fashion. Other structures, such as the skeleton and muscles, are largely symmetric. This Review considers how symmetries and asymmetries form alongside each other within the embryo, and how they are then maintained during growth. I describe how asymmetric signals are generated in the embryo. Using the limbs and somites as major examples, I then address mechanisms for protecting symmetrically forming tissues from asymmetrically acting signals. These examples reveal that symmetry should not be considered as an inherent background state, but instead must be actively maintained throughout multiple phases of embryonic patterning and organismal growth.

Expression analysis and characterization of dmrt2 in Chinese tongue sole (Cynoglossus semilaevis)

Dmrt2 is a member of the dmrt gene family with a conserved zinc finger-like DNA-binding motif (DM domain). In the present study, CS-dmrt2 was cloned from the gonads of Chinese tongue sole (Cynoglossus semilaevis). The full-length cDNA of CS-dmrt2 is 2834 bp in length, with a 251 bp 5'-untranslated region (UTR), a 1086 bp 3'-UTR and a 1503 bp open reading frame (ORF) that encodes a 501-amino-acid peptide. qPCR revealed that CS-dmrt2 was mainly expressed in C. semilaevis testes. In situ hybridization (ISH) showed CS-dmrt2 expression throughout early gonadal development (36 days after hatching (dah) and 86 dah), but the expression was higher in male gonads than in female gonads. CS-dmrt2 mRNA was highly expressed in male germ cells. Comparison of methylation levels between females and males demonstrated hypo-methylated levels of the CS-dmrt2 promoter in the male gonads, which is consistent with the high mRNA expression. These results suggest that the CS-dmrt2 gene may play a functional role in gonadal differentiation/development and germ cell maturation in the testis.

Identification and Characterization of the DMRT11E Gene in the Oriental River Prawn Macrobrachium nipponense

The doublesex and mab-3 related transcription factor (DMRT) gene family involvement in sex development is widely conserved from invertebrates to humans. In this study, we identified a DM (Doublesex/Mab-3)-domain gene in Macrobrachium nipponense, which we named MniDMRT11E because it has many similarities to and phylogenetically close relationships with the arthropod DMRT11E. Amino acid alignments and structural prediction uncovered conservation and putative active sites of the DM domain. Real-time PCR analysis showed that the MniDMRT11E was highly expressed in the ovary and testis in both males and females. Cellular localization analysis showed that DMRT11E was mainly located in the oocytes of the ovary and the spermatocyte of the testis. During embryogenesis, the expression level of MniDMRT11E was higher at the cleavage stage than at other stages. During the different stages of ovarian development, MniDMRT11E expression gradually increased from OI to OIII and decreased to the lowest level at the end of OIV. The results indicated that MniDMRT11E probably played important roles in embryonic development and sex maturity in M. nipponense. MniDMRT11E dsRNA injection also significantly reduced vitellogenin (VG) expression and significantly increased insulin-like androgenic gland factor (IAG) expression, indicating a close relationship in gonad development.

Immunolocalization of DMRTB1 in human testis with normal and impaired spermatogenesis

BACKGROUND

The transcription factor DMRTB1 plays a pivotal role in coordinating the transition between mitosis and meiosis in murine germ cells. No reliable data are available for human testis.

OBJECTIVES

The present study aims to examine the testicular expression pattern of DMRTB1 in men showing normal and impaired spermatogenesis.

MATERIALS AND METHODS

Immunohistochemistry was performed using 54 human testicular biopsy specimens and a commercial rabbit polyclonal anti-DMRTB1 primary antibody. RT-PCR complemented immunohistochemistry. To further characterize immunopositive cells and possible co-localization, the proliferation marker Ki-67, the tumor marker PLAP, and an anti-DMRT1 antibody were used.

RESULTS

In men with normal spermatogenesis, a strong immunoreactivity was detectable in a subset of spermatogonia (38.34 ± 2.14%). Some spermatocytes showed a weak immunostaining. Adjacent Sertoli cells were immunonegative. Compared with a hematoxylin and eosin overview staining, these immunopositive cells were almost exclusively identified as A_pale and B spermatogonia and primary spermatocytes in (pre-)leptotene, zygotene, and pachytene stages. In patients with spermatogenic arrest at spermatogonial level, an altered staining pattern was found. No immunoreactivity was detected in Sertoli cells in Sertoli cell-only syndrome. In germ cell neoplasia in situ (GCNIS) tubules, except for a few (0.4 ± 0.03%), pre-invasive tumor cells were immunonegative. Seminoma cells showed no immunostaining.

DISCUSSION

According to previous findings in mice, it seems reasonable that DMRTB1 is expressed in these normal germ cell populations. Moreover, altered staining pattern in spermatogenic arrest at spermatogonial stage suggests a correlation with mitosis and transformation into B spermatogonia. The absence of DMRTB1 in GCNIS cells and tumor cells might be associated with uncontrolled neoplastic cell proliferation and progression into invasive germ cell tumors. Further research is required to elucidate, for example, the role of DMRTB1 in the malignant transformation of human germ cells.

CONCLUSION

Our data indicate a relevant role for DMRTB1 regarding the entry of spermatogonia into meiosis in men.

Endodermal pouch-expressed dmrt2b is important for pharyngeal cartilage formation

Pharyngeal pouches, a series of outpocketings derived from the foregut endoderm, are essential for craniofacial skeleton formation. However, the molecular mechanisms underlying endodermal pouch-regulated head cartilage development are not fully understood. In this study, we find that zebrafish dmrt2b, a gene encoding Doublesex- and Mab-3-related transcription factor, is specifically expressed in endodermal pouches and required for normal pharyngeal cartilage development. Loss of dmrt2b doesn't affect cranial neural crest (CNC) specification and migration, but leads to prechondrogenic condensation defects by reducing cxcl12b expression after CNC cell movement into the pharyngeal arches. Moreover, dmrt2b inactivation results in reduced proliferation and impaired differentiation of CNC cells. We also show that dmrt2b suppresses crossveinless 2 expression in endodermal pouches to maintain BMP/Smad signaling in the arches, thereby facilitating CNC cell proliferation and chondrogenic differentiation. This work provides insight into how transcription factors expressed in endodermal pouches regulate pharyngeal skeleton development through tissue-tissue interactions.

Identification of Dmrt2a downstream genes during zebrafish early development using a timely controlled approach

BACKGROUND

Dmrt2a is a zinc finger like transcription factor with several roles during zebrafish early development: left-right asymmetry, synchronisation of the somite clock genes and fast muscle differentiation. Despite the described functions, Dmrt2a mechanism of action is unknown. Therefore, with this work, we propose to identify Dmrt2a downstream genes during zebrafish early development.

RESULTS

We generated and validated a heat-shock inducible transgenic line, to timely control dmrt2a overexpression, and dmrt2a mutant lines. We characterised dmrt2a overexpression phenotype and verified that it was very similar to the one described after knockdown of this gene, with left-right asymmetry defects and desynchronisation of somite clock genes. Additionally, we identified a new phenotype of somite border malformation. We generated several dmrt2a mutant lines, but we only detected a weak to negligible phenotype. As dmrt2a has a paralog gene, dmrt2b, with similar functions and expression pattern, we evaluated the possibility of redundancy. We found that dmrt2b does not seem to compensate the lack of dmrt2a. Furthermore, we took advantage of one of our mutant lines to confirm dmrt2a morpholino specificity, which was previously shown to be a robust knockdown tool in two independent studies. Using the described genetic tools to perform and validate a microarray, we were able to identify six genes downstream of Dmrt2a: foxj1b, pxdc1b, cxcl12b, etv2, foxc1b and cyp1a.

CONCLUSIONS

In this work, we generated and validated several genetic tools for dmrt2a and identified six genes downstream of this transcription factor. The identified genes will be crucial to the future understanding of Dmrt2a mechanism of action in zebrafish.

The transcriptomic signature of different sexes in two protogynous hermaphrodites: Insights into the molecular network underlying sex phenotype in fish

Sex differentiation is a puzzling problem in fish due to the variety of reproductive systems and the flexibility of their sex determination mechanisms. The Sparidae, a teleost family, reflects this remarkable diversity of sexual mechanisms found in fish. Our aim was to capture the transcriptomic signature of different sexes in two protogynous hermaphrodite sparids, the common pandora Pagellus erythrinus and the red porgy Pagrus pagrus in order to shed light on the molecular network contributing to either the female or the male phenotype in these organisms. Through RNA sequencing, we investigated sex-specific differences in gene expression in both species' brains and gonads. The analysis revealed common male and female specific genes/pathways between these protogynous fish. Whereas limited sex differences found in the brain indicate a sexually plastic tissue, in contrast, the great amount of sex-biased genes observed in gonads reflects the functional divergence of the transformed tissue to either its male or female character. Α common "crew" of well-known molecular players is acting to preserve either sex identity of the gonad in these fish. Lastly, this study lays the ground for a deeper understanding of the complex process of sex differentiation in two species with an evolutionary significant reproductive system.

New Insights Into the Role of RNA-Binding Proteins in the Regulation of Heart Development

The regulation of gene expression during development takes place both at the transcriptional and posttranscriptional levels. RNA-binding proteins (RBPs) regulate pre-mRNA processing, mRNA localization, stability, and translation. Many RBPs are expressed in the heart and have been implicated in heart development, function, or disease. This chapter will review the current knowledge about RBPs in the developing heart, focusing on those that regulate posttranscriptional gene expression. The involvement of RBPs at each stage of heart development will be considered in turn, including the establishment of specific cardiac cell types and formation of the primitive heart tube, cardiac morphogenesis, and postnatal maturation and aging. The contributions of RBPs to cardiac birth defects and heart disease will also be considered in these contexts. Finally, the interplay between RBPs and other regulatory factors in the developing heart, such as transcription factors and miRNAs, will be discussed.

A Novel Female-Specific and Sexual Reproduction-Associated Dmrt Gene Discovered in the Stony Coral, Euphyllia ancora

Transcription factors encoded by the Dmrt gene family regulate multiple aspects of animal reproduction. Most studies investigating the Dmrt gene family were conducted in model organisms from bilateral species, with a particular emphasis on gene function in male sex determination. It is still unclear whether the E. ancora Dmrt (EaDmrt) genes found in basal metazoans such as cnidarians share similar characteristics with orthologs in other metazoans. In this study, seven full Dmrt gene transcript sequences for a gonochoric coral, Euphyllia ancora (phylum: Cnidaria; class: Anthozoa), were obtained through transcriptome data mining, RT-PCR analysis, rapid amplification of cDNA ends, and sequencing. These EaDmrts were subjected to quantitative assays measuring temporal and tissue-specific expression. Results demonstrated a unique gene expression pattern for EaDmrtE, which is enriched in female germ cells during the spawning season. Based on the phylogenetic analyses performed across the homologous Dmrt genes in metazoans, we found that the female-specific EaDmrtE gene is not related to the DM1 gene of Acropora spp. coral nor to Dmrt1 of vertebrates, which are involved in sexual reproduction, especially in sex determination (vertebrate Dmrt1). Additionally, high levels of EaDmrtE transcripts detected in unfertilized mature eggs are retained in newly formed zygotes but decrease during embryonic development. We suggest that the newly discovered gene may play a role in oogenesis and early embryogenesis as a maternal factor in corals. Therefore, the sexual reproduction-associated Dmrt gene(s) should have arisen in cnidarians and might have evolved multiple times in metazoans.

Identification of Dmrt genes and their up-regulation during gonad transformation in the swamp eel (Monopterus albus)

The swamp eel is a teleost fish with a characteristic of natural sex reversal and an ideal model for vertebrate sexual development. However, underlying molecular mechanisms are poorly understood. We report the identification of five DM (doublesex and mab-3) domain genes in the swamp eel that include Dmrt2, Dmrt2b, Dmrt3, Dmrt4 and Dmrt5, which encode putative proteins of 527, 373, 471, 420 and 448 amino acids, respectively. Phylogenetic tree showed that these genes are clustered into corresponding branches of the DM genes in vertebrates. Southern blot analysis indicated that the Dmrt1-Dmrt3-Dmrt2 genes are tightly linked in a conserved gene cluster. Notably, these Dmrt genes are up-regulated during gonad transformation. Furthermore, mRNA in situ hybridisation showed that Dmrt2, Dmrt3, Dmrt4 and Dmrt5 are expressed in developing germ cells. These results are evidence that the DM genes are involved in sexual differentiation in the swamp eel.

Expanding roles for the evolutionarily conserved Dmrt sex transcriptional regulators during embryogenesis

Dmrt genes encode a large family of transcription factors characterized by the presence of a DM domain, an unusual zinc finger DNA binding domain. While Dmrt genes are well known for their important role in sexual development in arthropodes, nematodes and vertebrates, several new findings indicate emerging functions of this gene family in other developmental processes. Here, we provide an overview of the evolution, structure and mechanisms of action of Dmrt genes. We summarize recent findings on their function in sexual regulation and discuss more extensively the role played by these proteins in somitogenesis and neural development.

The myotomal basement membrane: insight into laminin-111 function and its control by Sonic hedgehog signaling

The importance of laminin-containing basement membranes (BM) for adult muscle function is well established, in particular due to the severe phenotype of congenital muscular dystrophies in patients with mutations disrupting the BM-muscle cell interaction. Developing muscles in the embryo are also dependent on an intact BM. However, the processes controlled by BM-muscle cell interactions in the embryo are only beginning to be elucidated. In this review, we focus on the myotomal BM to illustrate the critical role of laminin-111 in BM assembly and function at the surface of embryonic muscle cells. The myotomal BM provides also an interesting paradigm to study the complex interplay between laminins-containing BM and growth factor-mediated signaling and activity.

Sex and the singular DM domain: insights into sexual regulation, evolution and plasticity

Most animals reproduce sexually, but the genetic and molecular mechanisms that determine the eventual sex of each embryo vary remarkably. DM domain genes, which are related to the insect gene doublesex, are integral to sexual development and its evolution in many metazoans. Recent studies of DM domain genes reveal mechanisms by which new sexual dimorphisms have evolved in invertebrates and show that one gene, Dmrt1, was central to multiple evolutionary transitions between sex-determining mechanisms in vertebrates. In addition, Dmrt1 coordinates a surprising array of distinct cell fate decisions in the mammalian gonad and even guards against transdifferentiation of male cells into female cells in the adult testis.