Neurospora Genetic Backgrounds Differ in Meiotic Silencing by Unpaired DNA (MSUD) Strength: Implications for Dp-Mediated Suppression of Repeat-Induced Point Mutation (RIP)

2019 ◽  
pp. 215-226
Author(s):  
Durgadas P. Kasbekar
Keyword(s):  
Point Mutation ◽  
Meiotic Silencing ◽  
Repeat Induced Point Mutation

scholarly journals The Neurospora crassa standard Oak Ridge background exhibits an atypically efficient meiotic silencing by unpaired DNA

2018 ◽  
Author(s):  
Dev Ashish Giri ◽  
Ajith V. Pankajam ◽  
Koodali T. Nishant ◽  
Durgadas P. Kasbekar
Keyword(s):  
Genetic Variation ◽  
Neurospora Crassa ◽  
Point Mutation ◽  
Genetic Background ◽  
Meiotic Silencing ◽  
Genetic Studies ◽  
Oak Ridge ◽  
General Abstract ◽  
Repeat Induced Point Mutation ◽  
Made In

AbstractMeiotic silencing by unpaired DNA (MSUD) was discovered in crosses made in the standard Oak Ridge (OR) genetic background of Neurospora crassa. However, MSUD often was decidedly less efficient when the OR-derived MSUD tester strains were crossed with wild-isolated strains (W), which suggested either that sequence heterozygosity in tester x W crosses suppresses MSUD, or that OR represents the MSUD-conducive extreme in the range of genetic variation in MSUD efficiency. Our results support the latter model. MSUD was much less efficient in near-isogenic crosses made in a novel N. crassa B/S1 and the N. tetrasperma 85 genetic backgrounds. Possibly, regulatory cues that in other genetic backgrounds calibrate the MSUD response are missing from OR. The OR versus B/S1 difference appears to be determined by loci on chromosomes 1, 2, and 5. OR crosses heterozygous for a duplicated chromosome segment (Dp) have for long been known to exhibit an MSUD-dependent barren phenotype. However, inefficient MSUD in N. tetrasperma 85 made Dp-heterozygous crosses non-barren. This is germane to our earlier demonstration that Dps can act as dominant suppressors of repeat-induced point mutation (RIP). Occasionally, during ascospore partitioning rare asci contained >8 nuclei, and round ascospores dispersed less efficiently than spindle-shaped ones.General abstractIn crosses made in the standard OR genetic background of Neurospora crassa, an RNAi-mediated process called MSUD efficiently silences any gene not properly paired with its homologue during meiosis. We found that MSUD was not as efficient in comparable crosses made in the N. crassa B/S1 and N. tetrasperma 85 backgrounds, suggesting that efficient MSUD is not necessarily the norm in Neurospora. Indeed, using OR strains for genetic studies probably fortuitously facilitated the discovery of MSUD and its suppressors. As few as three unlinked loci appear to underlie the OR versus B/S1 difference in MSUD.

scholarly journals Occurrence of Repeat Induced Point Mutation in Long Segmental Duplications of Neurospora

Genetics ◽  
1997 ◽  
Vol 147 (1) ◽  
pp. 125-136 ◽  
Author(s):  
David D Perkins ◽  
Brian S Margolin ◽  
Eric U Selker ◽  
S D Haedo
Keyword(s):  
Point Mutation ◽  
Sexual Cycle ◽  
Segmental Duplications ◽  
Wild Type ◽  
Single Chain ◽  
Base Pairs ◽  
Gene Size ◽  
Type Gene ◽  
Repeat Induced Point Mutation

Abstract Previous studies of repeat induced point mutation (RIP) have typically involved gene-size duplications resulting from insertion of transforming DNA at ectopic chromosomal positions. To ascertain whether genes in larger duplications are subject to RIP, progeny were examined from crosses heterozygous for long segmental duplications obtained using insertional or quasiterminal translocations. Of 17 distinct mutations from crossing 11 different duplications, 13 mapped within the segment that was duplicated in the parent, one was closely linked, and three were unlinked. Half of the mutations in duplicated segments were at previously unknown loci. The mutations were recessive and were expressed both in haploid and in duplication progeny from Duplication × Normal, suggesting that both copies of the wild-type gene had undergone RIP. Seven transition mutations characteristic of RIP were found in 395 base pairs (bp) examined in one ro-11 allele from these crosses and three were found in ~750 bp of another. A single chain-terminating C to T mutation was found in 800 bp of arg-6. RIP is thus responsible. These results are consistent with the idea that the impaired fertility that is characteristic of segmental duplications is due to inactivation by RIP of genes needed for progression through the sexual cycle.

scholarly journals High frequency repeat-induced point mutation (RIP) is not associated with efficient recombination in Neurospora.

Genetics ◽  
1994 ◽  
Vol 138 (4) ◽  
pp. 1093-1103 ◽  
Author(s):  
J T Irelan ◽  
A T Hagemann ◽  
E U Selker
Keyword(s):  
Point Mutation ◽  
Dna Sequences ◽  
High Frequency ◽  
Recombination Frequency ◽  
Single Copy ◽  
Sexual Cycle ◽  
Base Pairs ◽  
Copy Gene ◽  
The Relationship ◽  
Repeat Induced Point Mutation

Abstract Duplicated DNA sequences in Neurospora crassa are efficiently detected and mutated during the sexual cycle by a process named repeat-induced point mutation (RIP). Linked, direct duplications have previously been shown to undergo both RIP and deletion at high frequency during premeiosis, suggesting a relationship between RIP and homologous recombination. We have investigated the relationship between RIP and recombination for an unlinked duplication and for both inverted and direct, linked duplications. RIP occurred at high frequency (42-100%) with all three types of duplications used in this study, yet recombination was infrequent. For both inverted and direct, linked duplications, recombination was observed, but at frequencies one to two orders of magnitude lower than RIP. For the unlinked duplication, no recombinants were seen in 900 progeny, indicating, at most, a recombination frequency nearly three orders of magnitude lower than the frequency of RIP. In a direct duplication, RIP and recombination were correlated, suggesting that these two processes are mechanistically associated or that one process provokes the other. Mutations due to RIP have previously been shown to occur outside the boundary of a linked, direct duplication, indicating that RIP might be able to inactivate genes located in single-copy sequences adjacent to a duplicated sequence. In this study, a single-copy gene located between elements of linked duplications was inactivated at moderate frequencies (12-14%). Sequence analysis demonstrated that RIP mutations had spread into these single-copy sequences at least 930 base pairs from the boundary of the duplication, and Southern analysis indicated that mutations had occurred at least 4 kilobases from the duplication boundary.

scholarly journals Synthesis of Signals for De Novo DNA Methylation in Neurospora crassa

2003 ◽  
Vol 23 (7) ◽  
pp. 2379-2394 ◽  
Author(s):  
Hisashi Tamaru ◽  
Eric U. Selker
Keyword(s):  
Dna Methylation ◽  
Neurospora Crassa ◽  
Point Mutation ◽  
Dna Sequences ◽  
De Novo ◽  
Test Site ◽  
Minor Groove ◽  
Binding Motif ◽  
Repeat Induced Point Mutation

ABSTRACT Most 5-methylcytosine in Neurospora crassa occurs in A:T-rich sequences high in TpA dinucleotides, hallmarks of repeat-induced point mutation. To investigate how such sequences induce methylation, we developed a sensitive in vivo system. Tests of various 25- to 100-bp synthetic DNA sequences revealed that both T and A residues were required on a given strand to induce appreciable methylation. Segments composed of (TAAA) n or (TTAA) n were the most potent signals; 25-mers induced robust methylation at the special test site, and a 75-mer induced methylation elsewhere. G:C base pairs inhibited methylation, and cytosines 5′ of ApT dinucleotides were particularly inhibitory. Weak signals could be strengthened by extending their lengths. A:T tracts as short as two were found to cooperate to induce methylation. Distamycin, which, like the AT-hook DNA binding motif found in proteins such as mammalian HMG-I, binds to the minor groove of A:T-rich sequences, suppressed DNA methylation and gene silencing. We also found a correlation between the strength of methylation signals and their binding to an AT-hook protein (HMG-I) and to activities in a Neurospora extract. We propose that de novo DNA methylation in Neurospora cells is triggered by cooperative recognition of the minor groove of multiple short A:T tracts. Similarities between sequences subjected to repeat-induced point mutation in Neurospora crassa and A:T-rich repeated sequences in heterochromatin in other organisms suggest that related mechanisms control silent chromatin in fungi, plants, and animals.

Dense nonsymmetrical DNA methylation resulting from repeat-induced point mutation in Neurospora

Science ◽  
1993 ◽  
Vol 262 (5140) ◽  
pp. 1724-1728 ◽  
Author(s):  
E. Selker ◽  
D. Fritz ◽  
M. Singer
Keyword(s):  
Dna Methylation ◽  
Point Mutation ◽  
Repeat Induced Point Mutation
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