Periodic Reporting for period 1 - P-MaleReg (Establishment of P-element silencing in Drosophila simulans dysgenic males)
Période du rapport: 2019-01-16 au 2021-04-15
Genomes are thought of blueprints-- collections of the genetic instructions for development and function and organisms. But genomes also contain other material, often including substantial amounts of parasitic DNA, in the form of transposable elements (TEs). TEs act as parasites by using their host genomes replication and metabolic machinery to reproduce themselves. They are successful parasites when they replicate within genomes faster than their hosts' own genes; in fact, they can be so successful that they make up major fractions of the genomes of a wide variety of organisms.
Like many parasites, TEs can also be harmful: as they replicate within genomes, they necessarily break the backbone of the DNA molecule, which can disrupt host genes and threaten the integrity of the genome. Hence, organisms have evolved to repress TE replication, especially in reproductive cells (e.g. eggs and sperm), where new mutations can be transmitted to offspring. As a result, active TEs tend to be those that have only recently invaded host genomes from another species.
In this project, we are investigating the evolution of host repression of TEs, taking advantage of an active TE that has recently invaded a fruit fly (Drosophila) species. Most similar work focuses on females, where transposable elements can have a major effect on fertility. Here, we focused on males. First, we asked if the TE also has a negative effect on male fertility, showing that it does. Second, we asked if the flies have evolved suppression of the TE in the testes as a result; results from this part of the project are forthcoming.
As a result of their important impact on the genomes of so many organisms, understanding the basic biology of TEs is a societal good, which may have long-term benefits in understanding the biology of genetic disease.
Like many parasites, TEs can also be harmful: as they replicate within genomes, they necessarily break the backbone of the DNA molecule, which can disrupt host genes and threaten the integrity of the genome. Hence, organisms have evolved to repress TE replication, especially in reproductive cells (e.g. eggs and sperm), where new mutations can be transmitted to offspring. As a result, active TEs tend to be those that have only recently invaded host genomes from another species.
In this project, we are investigating the evolution of host repression of TEs, taking advantage of an active TE that has recently invaded a fruit fly (Drosophila) species. Most similar work focuses on females, where transposable elements can have a major effect on fertility. Here, we focused on males. First, we asked if the TE also has a negative effect on male fertility, showing that it does. Second, we asked if the flies have evolved suppression of the TE in the testes as a result; results from this part of the project are forthcoming.
As a result of their important impact on the genomes of so many organisms, understanding the basic biology of TEs is a societal good, which may have long-term benefits in understanding the biology of genetic disease.
During the course of the project, we performed the following prepatory work:
-We developed and used a set of genetic crosses to obtain otherwise genetically identical males that a) were and b) were not expected to be affected by replication of the TE.
Once we obtained these males, we used them the following experiments, always using males expected to be unaffected by TE activity as a control:
-We tested fertility and testes morphology in males, showing that TE activity resulted in lower peak fertility.
-We prepared material to look for DNA damage, resuting in DNA breakage, occurring in testes.
-We prepared material to look for signatures of repression of the TE, and disruption of this repression in the face of unregulated TE activity.
-We prepared material to look for changes in TE regulation with age in males.
-Finally, we looked for evidence TE activity in males results in successful replication of TEs and inheritance in their offspring.
-We developed and used a set of genetic crosses to obtain otherwise genetically identical males that a) were and b) were not expected to be affected by replication of the TE.
Once we obtained these males, we used them the following experiments, always using males expected to be unaffected by TE activity as a control:
-We tested fertility and testes morphology in males, showing that TE activity resulted in lower peak fertility.
-We prepared material to look for DNA damage, resuting in DNA breakage, occurring in testes.
-We prepared material to look for signatures of repression of the TE, and disruption of this repression in the face of unregulated TE activity.
-We prepared material to look for changes in TE regulation with age in males.
-Finally, we looked for evidence TE activity in males results in successful replication of TEs and inheritance in their offspring.
Here, we have shown that TE activity does impact males in this system, though to a lesser extent than it impacts females. We expect to be able to show whether there are further impacts on the genome, including those potentially inherited by offspring. We also hope to show whether or not there are signs that testes have evolved to repress this TE activity. Unfortunately, due to serious disruption by COVID, results from many of our objectives are delayed or could not be achieved as planned. In some, but not all, cases, we were able to adjust our approaches to achieve similar objectives. Understanding how the invasion of a new TE impacts the host organism at different levels - establishment of repression mechanisms as response, alterations of genome structure and changes in life history traits - is crucial to disentangle the dynamics between TE and host organisms, which can ultimately help understanding the role of TEs in health and disease.