2015 — 2019 |
Phadnis, Nitin |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
The Molecular Basis of Speciation in Drosophila
? DESCRIPTION (provided by applicant): Understanding the molecular basis of hybrid sterility and hybrid inviability is a fundamental problem in speciation, the process by which one species splits into two. Studying hybrid dysfunction also provides a unique route to identifying genes that, despite functioning in essential cellular processes, evolve rapidly between species. Our goal is to understand the genetic and molecular bases of speciation in Drosophila using a highly multidisciplinary approach. In particular, my laboratory is interested in addressing the following questions: First, what are genes that underlie the sterility and inviability in hybrids between Drosophila species? Second, what are the molecular processes that are disrupted in hybrids? Third, what are the biological forces that drive the rapid evolution of genes that cause hybrid dysfunction? With recent technological advances in next-generation sequencing, genetic engineering, and cell biological approaches, it is now possible to address fundamental questions shrouding the molecular basis of speciation. First, my laboratory has designed a new genomics-based approach to efficiently identify hybrid sterility and hybrid inviability genes. We used this novel approach to successfully identify a new hybrid incompatibility gene, which is essential for mediating hybrid male inviability between D. melanogaster and D. simulans. We are studying the role of this gene in the cellular response to DNA damage, a process that is of critical importance in cancer biology. Second, we performing experiments to understand the function of Overdrive, a gene that we discovered for its essential role in both segregation distortion and male sterility in hybrids between the Bogota and USA subspecies of D. pseudoobscura. My laboratory is using genetic and cell biological approaches to understand the function of Overdrive in the meiotic chromosomal segregation. We are developing new tools to understand the developmental mechanisms in the germline that respond to errors in chromosomal segregation during meiosis, a process that has fundamental implications for the causes of birth defects. This line of work is also providing insights into the molecular mechanisms of segregation distortion. Lastly, we are using our new approach to identify the genes that interact with Overdrive to cause hybrid sterility and segregation distortion in hybrids between the Bogota and USA subspecies of Drosophila pseudoobscura. This represents a major step forward in gaining a complete picture of the genes and molecular processes that are important in the earliest stages of speciation, and provides an unprecedented opportunity to examine the role of segregation distorters as a driving force in the evolution of hybrid sterility. Together, these experiments will establish the Bogota-USA subspecies of D. pseudoobscura as one of the best-understood cases in speciation at the genetic, molecular and evolutionary levels.
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2021 |
Phadnis, Nitin |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
The Mechanisms of Segregation Distortion in Drosophila
Project Summary Segregation distorters are selfish genetic elements that operate by over-representing themselves in the mature gamete pool, thus fundamentally violating Mendel?s law. The evolutionary arms races triggered between distorter genes and their suppressors have long been recognized as a powerful force that shapes the evolution of genomes, cells, and species. Despite the ubiquity and importance of segregation distorters, we understand very little about the genetic basis and molecular mechanisms of this class of selfish genetic elements. A key barrier in understanding the mechanisms of segregation distorters is that they are present in non-model systems that lack genetic tools, and are almost always associated with chromosomal inversions that thwart traditional genetic approaches to gene discovery. Without characterizing the underlying genetic basis and molecular mechanisms it remains impossible to directly connect the arms race initiated by selfish elements to broader phenomena in the evolution of meiosis and sex chromosome systems. Here, we develop two independent methods to side-step traditional barriers presented by chromosomal inversions to gene discovery, and dissect the genetic basis underlying this selfish behavior in closely related Drosophila species. In our first aim, we develop a mutagenesis approach to identify the genes causing Sex- Ratio distortion in D. pseudoobscura. Through a combination of sequencing, in silico complementation, bulked- segregant mapping, and CRISPR/ Cas9 based editing, we are poised to resolve the complex genetic architecture that underlies distortion and to identify the complete set of genes, including modifiers and enhancers, that drive the selfish behavior of the D. pseudoobscura Sex-Ratio chromosome. In our second aim, we uncover cryptic variation within species for suppressors of distortion. Here, we aim to understand the molecular arms races between distorters and their suppressors through the identification of the genes and mechanisms of suppression of segregation distortion, and suppressors of suppressors-of-distortion. In our third aim, we engineer a synthetic chromosomal inversion to allow recombination mapping of Sex-Ratio distortion in D. persimilis. This approach adapts the Flp/FRT site-specific recombination tools to generate a perfectly collinear non-driving chromosome to allow free recombination in the region containing all necessary and sufficient genes for SR distortion. Once candidate genes are mapped, validated, and organized into a functional pathway for D. persimilis, a comparative analysis of these two systems will test whether SR mechanisms are unique or shared. Together, this work will provide the most complete genetic architecture of sex-linked segregation distorters to date, open the door to understanding the molecular mechanisms of distortion in two Sex-Ratio systems, and for the first time explicitly test independent or shared origins and mechanisms of Sex-Ratio distortion in these closely related species.
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