Dichlorodiphenyltrichloroethane metabolites inhibit DNMT1 activity which confers methylation-specific modulation of the sex determination pathway

Dichlorodiphenyltrichloroethane (DDT) poses a significant health risk to humans which is associated with genomic DNA hypomethylation. However, the mechanism and biological consequences remain poorly understood. In vitro assays confirmed that the DDT metabolites 2,2-bis(p-chlorophenyl)-acetic acid (DDA) and 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (DDMU), but not other DDT metabolites, significantly inhibited DNA methyltransferase 1 (DNMT1) activity, leading to genomic hypomethylation in cell culture assays. DNMT1 as a target for DNA hypomethylation induced by DDT metabolites was also confirmed using cell cultures in which DNMT1 was silenced or highly expressed. DDA and DDMU can modify methylation markers in the promoter regions of sexual development-related genes, and change the expression of Sox9 and Oct4 in embryonic stem cells. Molecular docking indicated that DDA and DDMU bound to DNMT1 with high binding affinity. Molecular dynamic simulation revealed that DDA and DDMU acted as allosteric modulators that reshaped the conformation of the catalytic domain of DNMT1. These findings provide a new insight into DDT-induced abnormalities in sexual development and demonstrate that selective binding to DNMT1 by DDA and DDMU can interfere with human DNMT1 activity and regulate the expression of the Sox9 and Oct4 genes.

Sexual Differentiation and Sex Differences in Neural Development

Sex determination occurs at the moment of conception, as a result of XX or XY chromosome pairing. From that point, the body undergoes the process of sexual differentiation, inducing the development of physical characteristics that are easily distinguishable between the sexes and are often reflected in one's physical appearance and gender identity. Although less apparent, the brain also undergoes sexual differentiation. Sex differences in the brain are organized during a critical period of neural development and have an instrumental role in determining the physiology and behavior of an individual throughout the lifespan. Understanding the extent of sex differences in neurodevelopment also influences our understanding of the potential risk for a number of neurodevelopmental, neurological, and mental health disorders that exhibit strong sex biases. Advances made in our understanding of sexually dimorphic brain nuclei, sex differences in neural cell communication, and sex differences in the communication between the brain and peripheral organs are all research fields that have provided valuable information related to the physiological and behavioral outcomes of sex differences in brain development. More recently, investigations into the impact of epigenetic mechanisms on sexual differentiation of the brain have indicated that changes in gene expression, via epigenetic modifications, also contribute to sexual differentiation of the developing brain. Still, there are a number of important questions and ideas that have arisen from our current understanding of sex differences in neurodevelopmental processes that necessitate more time and attention in this field.

Expression pattern and functional analysis of R-spondin1 in tongue sole Cynoglossus semilaevis

R-spondin 1 (Rspo1) is a potential female-determining gene in mammals that could regulate the Wnt/β-catenin signaling pathway. The deletion of Rspo1 causes sex reversal in females. To investigate sexual determination and differentiation, we cloned and analyzed the Rspo1 gene in Cynoglossus semilaevis. Phylogenetic and gene structure analyses revealed that Rspo1 gene exhibited high sequence conservation and contained an N-terminal signal peptide, two furin-like cysteine-rich domains (FU1 and FU2), a thrombospondin type 1 repeat, and a C-terminal region enriched with basic charged amino acids. qRT-PCR revealed that Rspo1 expressed sexual dimorphism in gonad, with higher expression levels in the ovary than in the testis, thus, suggesting the involvement of Rspo1 in gonad differentiation. In situ hybridization results demonstrated that Rspo1 was expressed in premature germ cells, including spermatogonia and spermatocytes in the testis and stage II and stage III oocytes in the ovary. The methylation levels in two CpG sites of Rspo1 promoter significantly differed among females, males, and pseudomales. After 30days of exposure to high temperature, the expression of Rspo1 significantly decreased in female individuals, some of which were prone to males. However, no difference of Rspo1 gene expression was observed between the control group and high-temperature group in males. These preliminary findings suggested that Rspo1 played a crucial role in sex determination and development. This study laid the groundwork for further sex control breeding techniques in C. semilaevis.

Testicular XX (SRY-Negative) Disorder of Sex Development in Cat

In most mammals, the sex of an individual is genetically determined by the Y chromosome-specific SRY gene. The presence of at least one functional copy of this gene determines the development of the primordial gonads into testes. However, testicular tissue does develop in the absence of SRY, albeit rarely, which is the case in testicular XX (SRY-negative) disorder of sex development (DSD). This condition is very important for studying the process of sexual determination because it allows the identification of genetic factors that are able to promote the male developmental pathway in the absence of SRY and thereby enables a better understanding of this process. Until now, this condition has been identified in various animal species but has never been reported in cat. In this study, we describe the first case of an XX (SRY-negative) DSD cat. The cat possesses a tortoiseshell coat associated with male-like external genitalia, including normal scrotum with 2 palpably normal testicles. Histological analysis confirmed the presence of the testes, and cytogenetic and genetic analyses showed a female karyotype associated with the absence of the SRY gene. Finally, sequencing of the RSPO1 gene revealed no mutation, and FISH analysis of the SOX9 locus did not reveal any large abnormalities.

Identification and characterization of a Masculinizer (Masc) gene involved in sex differentiation in Artemia

The sex of relatively primitive animals such as invertebrates is mostly determined by environmental factors and chromosome ploidy. Heteromorphic chromosomes may also play an important role, as in the ZW system in lepidopterans. However, the mechanisms of these various sex determination systems are still largely undefined. In the present study, a Masculinizer gene (Ar-Masc) was identified in the crustacean Artemia franciscana Kellogg 1906. Sequence analysis revealed that the 1140-bp full-length open reading frame of Ar-Masc encodes a 380-aa protein containing two CCCH-type zinc finger domains having a high degree of shared identities with the MASC protein characterized in the silkworm Bombyx mori, which has been determined to participate in the production of male-specific splice variants. Furthermore, although Ar-Masc could be detected in almost all stages in both sexual and parthenogenetic Artemia, there were significant variations in expression between these two reproductive modes. Firstly, qRT-PCR and Western blot analysis showed that levels of both Ar-Masc mRNA and protein in sexual nauplii were much higher than in parthenogenetic nauplii throughout the hatching process. Secondly, both sexual and parthenogenetic Artemia had decreased levels of Ar-Masc along with the embryonic developmental stages, while the sexual ones had a relatively higher and more stable expression than those of parthenogenetic ones. Thirdly, immunofluorescence analysis determined that sexual individuals had higher levels of Ar-MASC protein than parthenogenetic individuals during embryonic development. Lastly, RNA interference with dsRNA showed that gene silencing of Ar-Masc in sexual A. franciscana caused the female-male ratio of progeny to be 2.19:1. These data suggest that Ar-Masc participates in the process of sex determination in A. franciscana, and provide insight into the evolution of sex determination in sexual organisms.