Scientists genetically modify ‘sexual’ fruit fly to reproduce asexually

Subject: Science and tech

Section: Biotechnology

Context:

In a recent development, researchers from Cambridge University and the California Institute of Technology achieved a significant milestone by engineering a sexually reproducing species of fruit fly (Drosophila melanogaster) to reproduce asexually.
This transformation, demonstrating the extensive biological implications of minor genetic modifications, was first reported in a study published in July 2023, with a follow-up study appearing in the February 2024 issue of Heredity.

The Drosophila family:

The Drosophila family encompasses over 1,600 identified species, showcasing a broad spectrum of natural diversity. Among these, researchers have discovered a unique case of parthenogenesis, a type of reproduction where females produce offspring without male fertilization.
- Parthenogenesis is a form of reproduction in which an egg can develop into an embryo without being fertilized by a sperm.
Specifically, the species Drosophila mangebeiraiconsists solely of females that can lay eggs developing directly into new female progeny without sperm.
Furthermore, approximately 76% of Drosophila species, typically reproducing sexually, have shown the capability to hatch a minor fraction of eggs laid by isolated virgin females into larvae, and an even smaller fraction of these can develop into adults.
This occasional capability for parthenogenesis is termed facultative parthenogenesis, with Drosophila mercatorum being an example. However, Drosophila melanogaster, the canonical species extensively used in genetics research, engages strictly in sexual reproduction, highlighting the diverse reproductive strategies within the Drosophila family.

The genes for parthenogenesis:

The research aimed to unveil the genetic mechanisms enabling parthenogenesis in Drosophila mercatorum and to replicate these conditions in Drosophila melanogaster to induce parthenogenesis.
Through RNA sequencing,44 genes were identified in D. mercatorum eggs that exhibited differential expression during parthenogenetic development compared to their sexually reproducing counterparts.

Engineering asexual reproduction:

Researchers succeeded in engineering asexual reproduction in Drosophila melanogaster by manipulating the expression levels of specific genes identified in Drosophila mercatorum, a species that can reproduce through parthenogenesis.
By adjusting the expression of 44 genes to match those found in the parthenogenetic eggs of D. mercatorum, they achieved parthenogenesis in D. melanogaster.
Specifically, introducing two additional copies of the pologene, an extra copy of the Myc gene, and reducing the expression of the Desat2 gene resulted in 1.4% of D. melanogaster eggs developing parthenogenetically into adults.
These parthenogenetically born flies were also capable of mating with males and producing offspring, thus converting a species that reproduces strictly sexually into one that can reproduce facultatively through parthenogenesis.

The polar bodies:

In the process of sexual reproduction in flies, each offspring inherits two sets of chromosomes, one from each parent, but only transmits one chromosome from each pair to its eggs or sperm.
Following fertilization, the egg contains five sets of genomes: one in the maternal pronucleus, one in the paternal pronucleus, and three additional sets in nuclei called polar bodies located at the egg’s periphery.
Polar bodies, normally a by-product of chromosome segregation, are typically discarded as the male and female pronuclei fuse to form the progeny nucleus.
However, in unfertilized eggs lacking the male pronucleus, the female pronucleusalone cannot initiate embryonic development.
Researchers discovered that modifying the protein levels of polo, Myc, and Desat2 made the sequestration and disposal of polar bodies inefficient, allowing them to potentially substitute for the absent male pronucleus and initiate embryonic development, thus enabling parthenogenesis.

Significance:

This finding has significant implications for pest control strategies that involve releasing sterilized males or males with genetically edited genomes to suppress progeny numbers. Such approaches may inadvertently select individuals capable of facultative parthenogenesis, thereby reducing their long-term effectiveness.

Source: TH