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Meiotic drivers are selfish genetic elements that skew transmission in their favor. In the filamentous fungus N. crassa, one such meiotic driver is Spore killer-3 (Sk-3). In a cross between Sk-3 and a spore killer-sensitive mating partner (Sk-S), only half of the ascospores (sexual spores) survive. Nearly all of the survivors inherit the genes for spore killing. Previous studies have established that a gene called rfk-2 (required for spore killing) is essential for the spore killing activity of Sk-3. The rfk-2 gene has been mapped to Chromosome III, but its exact location is unknown. The goal of this study is to help identify the exact location of rfk-2. Towards this goal, I investigated a DNA interval called v378. Preliminary findings suggested that this interval may be important for spore killing. To determine if v378 is required for spore killing, I constructed and used a transformation vector to replace v378 with a hygromycin resistance gene (hph+) in an N. crassa Sk-3 strain. Strains deleted of v378 were then crossed with two spore killing-sensitive tester strains. The spore sacs containing ascospores from these crosses were imaged to analyze the effects of replacement of v378 on Sk-3-based spore killing. My findings demonstrate that v378 is required for spore killing. The potential implications of my findings with respect to our understanding of meiotic drive elements, and their potential applications, is discussed.
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Refining the rfk-2 Locus of Sk-3 using the DNA Interval v373 In Neurospora crassa
Meiotic drive is a non-Mendelian inheritance phenomenon where selfish genetic elements change gene transmission in their own favor. This phenomenon occurs in the fungus Neurospora crassa during spore killing. When a strain carrying a spore killer genetic element is crossed with a non-spore killing wild type strain, the cross will produce half viable and half inviable offspring. The N. crassa Sk-3 spore killer is found on Chromosome III. Sk-3 is one of the most studied meiotic drive elements in Neurospora fungi and it is thought to require a killer gene and a resistance gene for spore killing. While the killer gene has not been identified, recent work has isolated a mutation (rfk-2UV) that disrupts spore killing. Although this mutation has been mapped to Chromosome III, its exact location is not known. In this work, I investigate the role of one DNA interval in Sk-3-based spore killing. This DNA interval, referred to as v373, is thought to reside within or near rfk-2UV. My results will contribute to future efforts to identify the Sk-3 killer gene.
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- Award ID(s):
- 2005295
- PAR ID:
- 10649511
- Publisher / Repository:
- ISU ReD: Research and eData
- Date Published:
- Subject(s) / Keyword(s):
- Senior Thesis
- Format(s):
- Medium: X
- Institution:
- Illinois State University
- Sponsoring Org:
- National Science Foundation
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Meiotic drive describes a process in which selfish alleles are recovered in more than half of a progeny generation. It is a type of gene drive and it has been discovered in strains of Neurospora, a filamentous fungus, through its spore killing mechanism. One of the most studied meiotic drive elements within N. crassa is Spore killer-3 (Sk-3). Previous studies have indicated that there is a genomic region within Sk-3 that encodes resistance to spore killing and another that encodes an element that is required for spore killing. Sk-3’s resistance gene, rsk, has been identified. However, the exact region that mediates Sk-3’s spore killing mechanism is currently unknown. In a previous study, it was found that a mutation called rfk-2UV disrupts spore killing by Sk-3. To better understand the region of Chromosome III in which rfk-2UV is located (its exact location is unknown), I constructed a deletion vector to replace a DNA interval (v374) with a hygromycin resistance gene marker (hph). Transformants were crossed to produce offspring, and offspring were tested to determine if they possess the ability to kill ascospores. These findings will contribute to future efforts to determine the molecular nature of rfk-2UV and why this mutation disrupts the ability of Sk-3 to kill spores.more » « less
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Some isolates of the fungus Neurospora crassa possess a chromosomal factor that causes spore killing, leading to death of ascospores. It has been shown that these chromosomal factors are genetic elements called spore killers. For example, if a cross is performed between a parent with an Sk-S (sensitive) allele and a parent with an Sk-K (killer) allele, the cross will produce half viable offspring and half inviable offspring, where the inviable half has been killed by spore killing. This phenomenon can be explained by meiotic drive, wherein a selfish gene disrupts the randomness of sexual transmission, favoring its own success. In this study, I focus on a Neurospora Spore killer known as Sk-3. Sk-3 is thought to possess both a killer element and a resistance element. The resistance element is rsk, a gene that keeps ascospores alive and viable when in the presence of the killer element. However, the mechanism by which the killer element kills ascospores is unknown. A major obstacle to studying the killing mechanism is that the identity of the Sk-3 killer element itself has remained elusive. My goal is to help identify the Sk-3 killer element. Preliminary results by others have narrowed the search to the left arm of Chromosome III. These results have also shown that deletion of a 1.3 kb DNA interval, called v350, causes loss of spore killing. This suggests that a regulatory element, or a hidden gene, may overlap with the v350 interval. To help determine why v350 deletion correlates with loss of spore killing, I investigated a related DNA interval, called v384. My results suggest that v384, like v350, is required for spore killing.more » « less
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Neurospora crassa is a fungus that serves as a model organism for genetic research. N. crassa Spore killer-3 (Sk-3) is a genetic element transmitted to offspring through spore killing. Sk-3 is located on Chromosome III and it is thought to require two genes for spore killing. These two genes are the poison gene, for killing, and the antidote gene, for resistance to killing. While the Sk-3 resistance gene has been identified (rsk), the Sk-3 killer gene has not. The primary goal of this study is to help identify the killer gene by investigating the role of a DNA interval called v377 in spore killing. To determine if this interval is required for spore killing, a DNA deletion vector (Vector v377) was constructed and used to replace the v377 interval with a hygromycin resistance gene in strain RDGR170.3. My results demonstrate that v377 is required for spore killing. The possibility that v377 is within a gene required for spore killing, or a regulatory element that controls spore killing, is discussed.more » « less
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Meiotic drive elements, sometimes called selfish genes, are genetic elements that are passed on to their offspring more favorably than other genes. Meiotic drive elements have been observed in many organisms, including fungi of the Neurospora genus. Three different meiotic drive elements, called Spore killers, have been identified in Neurospora fungi. One of these Spore killers is called Spore killer 3 (Sk-3), and the molecular mechanism by which Sk-3 acts as a meiotic drive element is poorly understood. Previous work has identified a genetic locus within Sk-3 that may control spore killing. In this thesis, I investigate an interval of DNA within this locus called v375. Through gene deletion and spore killing assays, I show that deletion of v375 disrupts Sk-3-based spore killing in N. crassa. Possible explanations for why interval v375 is required for spore killing by Sk-3 are discussed.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Dissertation:
- https://doi.org/10.30707/1734473261.414558
