ntr: diploid meiosis resulting in normal four-spored azygotic asci

[fypoadmin]

A meiosis in which a diploid cell undergoes meiosis without mating, to produce a four spored azygotic ascus (probably needs rewording)

(note that other terms imply this phenotype is abnormal, but I think its a low penetrance WT phenotype?)

PMID:24196444

The fission yeast S. pombe normally proliferates in a haploid state, but diploid strains can also be obtained. Karyogamy is required to produce a diploid nucleus, which then undergoes meiosis when two haploid cells mate (i.e., zygotic meiosis). However, karyogamy is dispensable for azygotic meiosis in which a diploid cell undergoes meiosis without mating. We reasoned that if the supernumerary spores in mal3Δ and mto1Δ mutant asci were due to defective karyogamy, azygotic meiosis should restore the normal number of spores in the asci. We therefore constructed mal3Δ/mal3Δ and wildtype mal3+/mal3+ diploid strains and plated them on sporulation medium. Both the wild-type and mal3Δ/mal3Δ strains produced azygotic asci containing four spores (Fig. 3A).

Original comment by: ValWood

[fypoadmin]

I used FYPO:0000279 but I think def and position need revising as this is a normal phenotype for a diploid

Original comment by: ValWood

[fypoadmin]

I've been wondering about the azygotic asci term all along, since it is indeed something that wild-type cells do depending on growth conditions, rather than something that's necessarily abnormal. In wild type it's not even necessarily low penetrance; it depends on growth conditions, especially timing of available nutrients. Upon further investigation, I am now inclined to make FYPO:0000279 obsolete (the child is ok as abnormal, so it can just be moved).

Of the genes with annotations to FYPO:0000279 in v41, all but one come from the screen in PMID:20404563. In that screen and an earlier one by the same group, for some deletion mutants they see azygotic asci which they attribute to having only the few stray diploids in an almost-all-haploid population survive. In other words, it turns out to be a rather indirect hint that the gene is essential. Quote from PMID:16169489:

"Another group of 29 deletion constructs formed very few colonies upon transformation. These mutants formed azygotic asci (ascus contains four meiotic products called spores) upon sporulation. An azygotic ascus is produced when meiosis takes place within a diploid cell and not within a zygote produced by conjugation. Azygotic asci are a sign, therefore, that transformation of cells with deletion constructs has taken place in rare diploid cells. Haploid homothallic S. pombe cultures normally contain a small fraction of diploid cells. We suspected that deletion of these 29 genes gives rise to azygotic asci because the genes are essential. Transformation gives rise to viable cells that are heterozygous for the deletion. Consistent with this hypothesis, only two spores of azygotic asci formed colonies upon tetrad dissection, and these colonies invariably carried a wild-type allele of the gene."

The one exception is cuf2; in PMID:22558440 they did some of the experiments under conditions that normally cause azygotic sporulation and ascus formation, i.e. it's just as experimental tool.

I've added a blurb to https://sourceforge.net/apps/trac/pombase/wiki/WildTypePhenotype

For the mal3 and mto1 mutants, they made homozygous diploids to see if it's a karyogamy problem that accounts for the extra spores in the zygotic asci. They got almost-normal azygotic sporulation -- 4 spores but lower spore viability. I think the curator meeting discussion may be sort of relevant to this too, because of the spore viability aspect.

Original comment by: mah11

[fypoadmin]

• labels: --> community curation
• summary: ntr: diploid meiosis resulting in normal for spored azygotic asci CC --> ntr: diploid meiosis resulting in normal for spored azygotic asci

Original comment by: mah11

[fypoadmin]

based on the feedback " Formation of azygotic ascus upon sporulation – Azygotic meiosis was our experimental strategy to show that the supernumerary spores in mal3deletion mutant asci were due to defective karyogamy.

"

from this session, but I guess changes are still required as you outlined

Val

Original comment by: ValWood

[fypoadmin]

OK, I have now made the azygotic sporulation term (FYPO:0000279) obsolete.

To annotate the mal3Δ homozygous diploid, you could use 'inviable spore' with low penetrance for the slight decrease in viability.

For the majority that do azygotic sporulation normally, you could annotate to normal sporulation, and note the conditions that give rise to azygotic sporulation, or I could pre-compose a "normal azygotic sporulation" term. Either way, it could have penetrance high-but-not-100%.

Original comment by: mah11

[fypoadmin]

• labels: community curation --> community curation, other ontology change, term obsoletion
• status: open --> closed-fixed
• assigned_to: Midori Harris

Original comment by: mah11

[fypoadmin]

will close this; can always open a new ticket if you want new terms

Original comment by: mah11

[fypoadmin]

• summary: ntr: diploid meiosis resulting in normal for spored azygotic asci --> ntr: diploid meiosis resulting in normal four-spored azygotic asci

Original comment by: mah11