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A gene that makes the sexes look different

A "master gene" regulates physical differences between males and females.

This study is significant as it is the first to look at the effect of the dsx gene throughout the whole genome. It found that dsx isn't simply a "switch" that turns off certain male traits in females, as previously thought. Rather, it plays a highly complex role controlling the expression of physical differences at different points in the genome — based solely upon sex.

The paper's co-lead author is Eduardo Zattara, a postdoctoral researcher in the Department of Biology at Indiana University (IU). The senior author is Armin Moczek, a professor in the department. The work is published in the journal Feb. 27th issue of Nature Communications, and reveals new details about the behavior of the gene called "doublesex," or dsx.

"We want to know more about this gene because it helps us answer a major question about development and evolution: How do animals with similar genomes — such as males and females of the same species — produce different versions of the same trait? And why do some traits, like ornamental features that attract mates, vary so widely, while others, like legs, don't?"

Cris Ledón-Rettig PhD, Postdoctoral Researcher, Department of Biology, Indiana University, Bloomington College of Arts and Sciences, USA and study leader.

The exquisite control dsx exerts over male and female traits acts in a surprising variety of ways. By activating different genes in males and females, for example, it can promote male or female versions of the same physical trait, such as genitalia. Or, by activating the same genes in males while simultaneously inhibiting them in females, it can promote opposite traits.

"The power to prevent the expression of male traits in females, and vice versa, is a critical feature. It buffers traits that benefit only members of one sex from causing harm to the other."

Armin Moczek PhD, Professor, Department of Biology, Indiana University, Bloomington College of Arts and Sciences, USA, and senior author.

For example, in the beetle Onthophagus taurus, males possess elaborate horns to battle rivals for female attention. However, large horns offer no reproductive advantage to females, infact, they interfere with a female's ability to dig a nesting tunnel for her offspring. A similar dynamic exists in birds. Higher testosterone may attract more females to males, but decreases maternal nesting and feeding instincts.

Both examples underline the tension between sexual dimorphism. Exaggerated male traits may increase sexual attraction, but exaggerating the same trait in females harms maternal success. If a species lacks this ability to "buffer" between male and female traits, it risks extinction with self cancelling behaviors and traits.

In the study, IU scientists compared active genes expressed in normal beetles to other beetles with suppressed dsx genes. The comparison revealed that in the beetle there are over 1,000 points affected on the male genome by dsx, but only about 250 points affecting female gene function.

The majority of these points on the genome do not overlap. This indicates that dsx doesn't simply turn certain genes "on" or "off." For most traits studied, dsx affected gene expression solely based on sex.

"Essentially, dsx instructs the development of male and female versions of the same trait by influencing different [numbers of] genes in each sex."

Cris Ledón-Rettig PhD, Postdoctoral researcher, Indianna University, Bloomington College of Arts and Sciences, Department of Biology, and study leader.

Onthophagus taurus is one of the few insect species in which it's possible to conduct a whole genome analysis. Their  entire genome was sequenced during the i5k Project, or "The Manhattan Project of Entomology."  This was a large-scale effort supported by the U.S. Department of Agriculture that is continuing to transcribe the genomes of 5,000 insects and other arthropods.

"We're eager to extend our work on the role of dsx — and other genes — to sexual differences across other, closely related species of beetles," Ledón-Rettig adds. "These beetles are really a powerful platform for unraveling the fundamental mechanisms that underlie evolutionary diversification of sexual traits across species."

Sexual dimorphisms fuel significant intraspecific variation and evolutionary diversification. Yet the developmental-genetic mechanisms underlying sex-specific development remain poorly understood. Here, we focus on the conserved sex-determination gene doublesex (dsx) and the mechanisms by which it mediates sex-specific development in a horned beetle species by combining systemic dsx knockdown, high-throughput sequencing of diverse tissues and a genome-wide analysis of Dsx-binding sites. We find that Dsx regulates sex-biased expression predominantly in males, that Dsx's target repertoires are highly sex- and tissue-specific and that Dsx can exercise its regulatory role via two distinct mechanisms: as a sex-specific modulator by regulating strictly sex-specific targets, or as a switch by regulating the same genes in males and females in opposite directions. More generally, our results suggest Dsx can rapidly acquire new target gene repertoires to accommodate evolutionarily novel traits, evidenced by the large and unique repertoire identified in head horns, a recent morphological innovation.

This study was supported in part by the National Science Foundation.

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Mar 9, 2017   Fetal Timeline   Maternal Timeline   News   News Archive   

Using the beetle "Onthophagus taurus", researchers learned how the dsx gene
"matches" an increase in that physical traits in males to decreasing that trait in females.
Image Credit: Alex Wild


Phospholid by Wikipedia