TL;DR: RNA interference is used to knock down DMRT1 in early chicken embryos to support the Z dosage hypothesis for avian sex determination, and results indicate that D MRT1 is required for testis determination in the chicken.
Abstract: Sex in birds is chromosomally based, as in mammals, but the sex chromosomes are different and the mechanism of avian sex determination has been a long-standing mystery. In the chicken and all other birds, the homogametic sex is male (ZZ) and the heterogametic sex is female (ZW). Two hypotheses have been proposed for the mechanism of avian sex determination. The W (female) chromosome may carry a dominant-acting ovary determinant. Alternatively, the dosage of a Z-linked gene may mediate sex determination, two doses being required for male development (ZZ). A strong candidate avian sex-determinant under the dosage hypothesis is the conserved Z-linked gene, DMRT1 (doublesex and mab-3-related transcription factor 1). Here we used RNA interference (RNAi) to knock down DMRT1 in early chicken embryos. Reduction of DMRT1 protein expression in ovo leads to feminization of the embryonic gonads in genetically male (ZZ) embryos. Affected males show partial sex reversal, characterized by feminization of the gonads. The feminized left gonad shows female-like histology, disorganized testis cords and a decline in the testicular marker, SOX9. The ovarian marker, aromatase, is ectopically activated. The feminized right gonad shows a more variable loss of DMRT1 and ectopic aromatase activation, suggesting differential sensitivity to DMRT1 between left and right gonads. Germ cells also show a female pattern of distribution in the feminized male gonads. These results indicate that DMRT1 is required for testis determination in the chicken. Our data support the Z dosage hypothesis for avian sex determination.
TL;DR: It is found that CRISPR–Cas9-targeted disruption of the intron 4–exon 5 boundary aimed at blocking the formation of functional AgdsxF did not affect male development or fertility, whereas females homozygous for the disrupted allele showed an intersex phenotype and complete sterility.
Abstract: In the human malaria vector Anopheles gambiae, the gene doublesex (Agdsx) encodes two alternatively spliced transcripts, dsx-female (AgdsxF) and dsx-male (AgdsxM), that control differentiation of the two sexes. The female transcript, unlike the male, contains an exon (exon 5) whose sequence is highly conserved in all Anopheles mosquitoes so far analyzed. We found that CRISPR-Cas9-targeted disruption of the intron 4-exon 5 boundary aimed at blocking the formation of functional AgdsxF did not affect male development or fertility, whereas females homozygous for the disrupted allele showed an intersex phenotype and complete sterility. A CRISPR-Cas9 gene drive construct targeting this same sequence spread rapidly in caged mosquitoes, reaching 100% prevalence within 7-11 generations while progressively reducing egg production to the point of total population collapse. Owing to functional constraint of the target sequence, no selection of alleles resistant to the gene drive occurred in these laboratory experiments. Cas9-resistant variants arose in each generation at the target site but did not block the spread of the drive.
TL;DR: The male sexual regulatory gene mab-3 from the nematode Caenorhabditis elegans is isolated and found that it is related to the Drosophila melanogasterSexual regulatory gene doublesex (dsx), which encodes proteins with a DNA-binding motif that is named the ‘DM domain’.
Abstract: Most metazoans occur as two sexes. Surprisingly, molecular analyses have hitherto indicated that sex-determining mechanisms differ completely between phyla. Here we present evidence to the contrary. We have isolated the male sexual regulatory gene mab-3 from the nematode Caenorhabditis elegans and found that it is related to the Drosophila melanogaster sexual regulatory gene doublesex (dsx)2. Both genes encode proteins with a DNA-binding motif that we have named the 'DM domain'. Both genes control sex-specific neuroblast differentiation and yolk protein gene transcription; dsx controls other sexually dimorphic features as well. The form of DSX that is found in males can direct male-specific neuroblast differentiation in C. elegans. This structural and functional similarity between phyla suggests a common evolutionary origin of at least some aspects of sexual regulation. We have identified a human gene, DMT1, that encodes a protein with a DM domain and find that DMT1 is expressed only in testis. DMT1 maps to the distal short arm of chromosome 9, a location implicated in human XY sex reversal. Proteins with DM domains may therefore also regulate sexual development in mammals.
TL;DR: Genetic and molecular data suggest that sequences including and adjacent to the female-specific splice acceptor site play an important role in the regulation of dsx expression by the transformer and transformer-2 loci.
TL;DR: It is shown that murine Dmrt1 is essential for postnatal testis differentiation, with mutant phenotypes similar to those caused by human chromosome 9p deletions that remove the gene.
Abstract: The only molecular similarity in sex determination found so far among phyla is between the Drosophila doublesex (dsx) and Caenorhabditis elegans mab-3 genes. dsx and mab-3 contain a zinc finger-like DNA-binding motif called the DM domain, perform several related regulatory functions, and are at least partially interchangeable in vivo. A DM domain gene called Dmrt1 has been implicated in male gonad development in a variety of vertebrates, on the basis of embryonic expression and chromosomal location. Such evidence is highly suggestive of a conserved role(s) for Dmrt1 in vertebrate sexual development, but there has been no functional analysis of this gene in any species. Here we show that murine Dmrt1 is essential for postnatal testis differentiation, with mutant phenotypes similar to those caused by human chromosome 9p deletions that remove the gene. As in the case of 9p deletions, Dmrt1 is dispensable for ovary development in the mouse. Thus, as in invertebrates, a DM domain gene regulates vertebrate male development.