Maleness gene in malaria mosquitoes discovered

Scientists have isolated a gene which determines maleness in the mosquito species responsible for transmitting malaria, an advance that may help control the deadly disease.
The gene, dubbed Yob, is the master regulator of the sex determination process in the African malaria mosquito, Anopheles gambiae, and determines the male sex, according to scientists from The Pirbright Institute and Liverpool School of Tropical Medicine in the UK.
In insects, sex is commonly determined by a primary genetic signal that during the first hours of life activates a short cascade of genes, whose sex-specific products ultimately control whether an individual will develop as male or female.

The molecular mechanisms underlying these developmental processes are extremely variable, and in particular the primary sex-determining genes drastically differ in their nature between different groups of insects, researchers said.
Similar to humans, many insects possess a pair of sex chromosomes, with females carrying identical XX chromosomes and males XY chromosomes, the Y chromosome harbouring a dominant male-determining gene, they said.
The molecular identity of such maleness genes has remained enigmatic. Yob represents only the second known case in insects, researchers said.

To identify Yob, scientists used high-throughput sequencing to sample all transcripts (genetic messages) produced in the Anopheles gambiae male and female embryos.

After comparison of the sequencing data, they found, exclusively in males, fragments of transcripts corresponding to Yob.
Further research showed that Yob is encoded on the Y chromosome, and that activity of Yob was limited to males and was necessary to generate male-specific products of the sex determination pathway genes, scientists said.
Unexpectedly, Yob transcripts are highly detrimental to females. When injected into mixed-sex early embryos of Anopheles gambiae, or another African mosquito species, Anopheles arabiensis, Yob kills females before they hatch from eggs, but leaves male development unaffected, they said.
Conversely, silencing normal embryonic Yob activity is lethal to males.

The results indicate that, apart from determining maleness, Yob is vital for the control of another fundamental developmental process, called dosage compensation, which balances levels of transcripts from genes located on the single X chromosome in males and on two X chromosomes in females, researchers said.
"Our research may have far-reaching implications for the control of malaria," said Jaroslaw Krzywinski from Pirbright.
"Currently, application of insecticides to control mosquitoes remains the most efficient way of combating the disease, but with a rampant spread of resistance to chemicals in mosquito populations, the insecticides may soon become ineffective," said Krzywinski.
The findings were published in the journal Science.