Giant ascospores and abnormal croziers in a mutant of Neurospora crassa

Raju, Namboori B.; Newmeyer, Dorothy

doi:10.1016/s0147-5975(77)80040-6

Cited by 65 publications

(27 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Perithecia were opened for detailed observations on developing asci and for photographing rosettes of asci. Four to 6-day-old perithecia containing asci at all stages of meiosis and ascospore delimitation were stained using iron-hematoxylin or acriflavin (Raju and Newmeyer 1977;Raju 1986). Rosettes of maturing asci from 7-to 10-day-old perithecia were lightly stained using 10-to 20-fold dilutions of ferric acetate and hematoxylin solutions.…”

Section: Strains and Crossesmentioning

confidence: 99%

Neurospora Spore KillersSk-2andSk-3Suppress Meiotic Silencing by Unpaired DNA

2007

View full text Add to dashboard Cite

In Neurospora crassa, pairing of homologous DNA segments is monitored during meiotic prophase I. Any genes not paired with a homolog, as well as any paired homologs of that gene, are silenced during the sexual phase by a mechanism known as meiotic silencing by unpaired DNA (MSUD). Two genes required for MSUD have been described previously: sad-1 (suppressor of ascus dominance), encoding an RNAdirected RNA polymerase, and sad-2, encoding a protein that controls the perinuclear localization of SAD-1. Inactivation of either sad-1 or sad-2 suppresses MSUD. We have now shown that MSUD is also suppressed by either of two Spore killer strains, Sk-2 and Sk-3. These were both known to contain a haplotype segment that behaves as a meiotic drive element in heterozygous crosses of killer 3 sensitive. Progeny ascospores not carrying the killer element fail to mature and are inviable. Crosses homozygous for either of the killer haplotypes suppress MSUD even though ascospores are not killed. The killer activity maps to the same 30-unit-long region within which recombination is suppressed in killer 3 sensitive crosses. We suggest that the region contains a suppressor of MSUD. S EXUAL reproduction in Neurospora crassa is mediated by the fusion of two haploid nuclei that carry compatible mating-type genes (mat A and mat a). The haploid nuclei proliferate in specialized premeiotic ascogenous tissue (precroziers and three-celled croziers) within the fertilized fruiting body (perithecium). Two nuclei of opposite mating type that are sequestered in the subapical cell of the crozier then migrate into a tubular sac (ascus) and fuse to create the zygote, which immediately undergoes two meiotic divisions and a postmeiotic mitosis. The resulting eight haploid nuclei reside in the same cytoplasm until they are sequestered into eight linearly ordered ascospores. The mating-type locus and other segregating markers show 1:1 segregation (Raju 1992;Davis 2000).Meiotic drive is a phenomenon in which certain chromosomal loci show a progeny ratio different from 1:1 and one allele is favored over the other. Examples of meiotic drive in animals include the segregation distorter (SD) system of Drosophila melanogaster and the t haplotype in the mouse (Lyttle 1991a,b;Schimenti 2000;Kusano et al. 2003). In heterozygous males, the meiotic products that do not carry the drive element (SD chromosome or t haplotype) fail to differentiate into functional sperm. Although meiotic drive is widespread in insects, mammals, plants, and fungi, very few cases have been dissected at the molecular level (Pennisi 2003;Burt and Trivers 2006).In Neurospora, Spore killers are chromosomal elements that cause the death of ascospores that do not contain the killer element (Turner and Perkins 1979, 1991). For example, in a cross of Spore killer 3 wild type (Sk sensitive), every mature ascus contains four normalsized, black, viable ascospores and four tiny, undeveloped ascospores that are inviable (see Figure 2A). All survivors carry the killer element. When both kill...

show abstract

Section: Strains and Crossesmentioning

confidence: 99%

Neurospora Spore KillersSk-2andSk-3Suppress Meiotic Silencing by Unpaired DNA

2007

View full text Add to dashboard Cite

show abstract

“…The fixation was in a freshly prepared solution containing 9:6:2 (vh) absolute ethanol, propionic acid, and 10% aqueous chromic acid. The fixed perithecia were hydrolyzed and stained using the iron-hematoxylin procedure described for Neurospora [Raju and Newmeyer, 1977;Raju, 19781.…”

Section: Cytologymentioning

confidence: 99%

Diverse programs of ascus development in pseudohomothallic species of Neurospora, Gelasinospora, and Podospora

Raju¹,

Perkins²

1994

Dev. Genet.

Self Cite

112

106

View full text Add to dashboard Cite

Meiosis and ascospore development in the four-spored pseudohomothallic ascomycetes Neurospora tetrasperma, Gelasinospora tetrasperma, Podospora anserina, and P. tetraspora have been reexamined, highlighting differences that reflect independent origins of the four-spored condition in the different genera. In these species, as in the heterothallic eight-spored N. crassa, fusion of haploid nuclei is followed directly by meiosis and a postmeiotic mitosis. These divisions take place within a single unpartitioned giant cell, the ascus, which attains a length of > 0.1 mm before nuclei are enclosed by ascospore walls. Two basically different modes underlie the delivery of opposite mating type nuclei into each of the four ascospores in the different genera. In N. tetrasperma on the one hand, the mating type locus is closely centromere-linked. Mating types therefore segregate at the first meiotic division. The second-division spindles of N. tetrasperma overlap and are usually parallel to one another, in contrast to the their tandem arrangement in N. crassa. As a result, nonsister nuclei of opposite mating type are placed close together in each half-ascus and a pair is enclosed in each ascospore. In the Podospora and Gelasinospora species on the other hand, the second-division spindles are in tandem, with sister nuclei of opposite mating type associated as a pair in each half-ascus. It is established for P. anserina and inferred for P. tetraspora and G. tetrasperma that a single reciprocal crossing over almost always occurs in the mating type-centromere interval, ensuring that mating types segregate at the second meiotic division and that nuclei of opposite mating type are enclosed in each ascospore. Other differences are also seen that are less fundamental. Neurospora tetrasperma differs from the other species in the orientation of chromosomes and spindle pole body plaques at interphase II. Third-division spindles are oriented parallel to the ascus wall in Gelasinospora but across the ascus in Podospora and Neurospora. The two Podospora species differ from one another in nuclear behavior following mitosis in the young ascospores. In P. tetraspora, two of the four nuclei migrate into the tail cell, which degenerates, leaving one functional nucleus of each mating type. In P. anserina, by contrast, only one of the four nuclei moves into the tail cell, leaving the germinating ascospore with two functional nuclei of one mating type and one of the other. The pseudohomothallic condition with its heterokaryotic vegetative phase has significant consequences for both the individual organism and the breeding system. Genetic controls of development and recombination are complex.(ABSTRACT TRUNCATED AT 400 WORDS)

show abstract

“…Homozygous killer × killer and sensitive × sensitive crosses are normal and yield 8B:0W asci (spore sacs). When sensitive nuclei are enclosed in the same spore with the killer ones, as seen in a giant-spored N. crassa mutant and in the four-spored (heterokaryotic) Neurospora tetrasperma, they can escape the elimination process (7,8). These observations suggest that the killer produces a resistance factor that shelters all nuclei residing in the same spore.…”

mentioning

confidence: 99%

Molecular dissection of Neurospora Spore killer meiotic drive elements

Hammond

Rehard

Xiao

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Meiotic drive is a non-Mendelian inheritance phenomenon in which certain selfish genetic elements skew sexual transmission in their own favor. In some cases, progeny or gametes carrying a meiotic drive element can survive preferentially because it causes the death or malfunctioning of those that do not carry it. In Neurospora, meiotic drive can be observed in fungal spore killing. In a cross of Spore killer (Sk) × WT (Sk-sensitive), the ascospores containing the Spore killer allele survive, whereas the ones with the sensitive allele degenerate. Sk-2 and Sk-3 are the most studied meiotic drive elements in Neurospora, and they each theoretically contain two essential components: a killer element and a resistance gene. Here we report the identification and characterization of the Sk resistance gene, rsk (resistant to Spore killer). rsk seems to be a fungal-specific gene, and its deletion in a killer strain leads to self-killing. Sk-2, Sk-3, and naturally resistant isolates all use rsk for resistance. In each killer system, rsk sequences from an Sk strain and a resistant isolate are highly similar, suggesting that they share the same origin. Sk-2, Sk-3, and sensitive rsk alleles differ from each other by their unique indel patterns. Contrary to long-held belief, the killer targets not only late but also early ascospore development. The WT RSK protein is dispensable for ascospore production and is not a target of the spore-killing mechanism. Rather, a resistant version of RSK likely neutralizes the killer element and prevents it from interfering with ascospore development.intragenomic conflict | segregation distortion | selfish elements I n fungi, plants, and animals, not all genes follow the Mendelian pattern of inheritance. Meiotic drive, sometimes referred to as segregation distortion, describes the phenomenon in which certain "cheating" alleles are recovered in more than half of the progeny (1). Two well-known examples are the segregation distorter (SD) in Drosophila and the t haplotype in Mus. In these cases, sperm not carrying the aggressive allele (the drive element) either degenerate (in flies) or become functionally impaired (in mice) (2, 3). In fungi, meiotic drive can be observed as spore killing, in which ascospores (sexual spores) that carry the "Spore killer" element survive preferentially (4). Examples of spore killing can be found in Neurospora sitophila, Neurospora intermedia, Podospora anserina, Gibberella fujikuroi, and Cochliobolus heterostrophus.Spore killer-2 (Sk-2) and Spore killer-3 (Sk-3), which behave similarly, are the most studied distortion elements in Neurospora (5). Originally discovered in N. intermedia, the two spore-killing factors have been introgressed into Neurospora crassa for extensive genetic studies. In a Spore killer (Sk) × WT (Sk-sensitive or Sk S ) cross, regardless of which acts as the female, the four Skcontaining spores are black (B) and viable, whereas the four Sksensitive spores are white (W) and inviable. Manifestation of killing does not occur until late ascospore de...

show abstract

Giant ascospores and abnormal croziers in a mutant of Neurospora crassa

Cited by 65 publications

References 18 publications

Neurospora Spore KillersSk-2andSk-3Suppress Meiotic Silencing by Unpaired DNA

Neurospora Spore KillersSk-2andSk-3Suppress Meiotic Silencing by Unpaired DNA

Diverse programs of ascus development in pseudohomothallic species of Neurospora, Gelasinospora, and Podospora

Molecular dissection of Neurospora Spore killer meiotic drive elements

Contact Info

Product

Resources

About