The programmed release of apoptogenic proteins from mitochondria is a core event of apoptosis, although ancestral roles of this phenomenon are not known. In mammals, one such apoptogenic protein is Endonuclease G (EndoG), a conserved mitochondrial nuclease that fragments the DNA of dying cells. In this work, we show that budding yeast executes meiotically programmed mitochondrial release of an EndoG homolog, Nuc1, during sporulation. In contrast to EndoG’s ostensible pro-death function during apoptosis, Nuc1 mitochondrial release is pro-survival, attenuating the cytosolic L-A and Killer double-stranded RNA mycoviruses and protecting meiotic progeny from the catastrophic consequences of their derepression. The protective viral attenuation role of this pathway illuminates a primordial role for mitochondrial release of EndoG, and perhaps of apoptosis itself.

The programmed release of apoptogenic proteins from mitochondria is a core event of apoptosis, though ancestral roles of this phenomenon are not known. In mammals, one such apoptogenic protein is Endonuclease G (EndoG), a conserved nuclease that fragments the DNA of dying cells.In this work, we show that budding yeast executes meiotically programmed mitochondrial release of an EndoG homologue, Nuc1, during sporulation. In contrast to EndoG's ostensible pro-death function during apoptosis, Nuc1 mitochondrial release attenuates the cytosolic dsRNA mycovirus, Killer, protecting spores from a lethal accumulation of its encoded toxin. Our identification of cell-protective viral attenuation as a target of this rudimentary apoptotic pathway illuminates a primordial role for mitochondrial release of EndoG. One Sentence SummaryYeast sporulation induces release of mitochondrial endonuclease G to accomplish viral attenuation. Main TextMathematical models suggest that host-virus conflicts drove the evolution of programmed cell death (PCD) in single celled eukaryotes(1, 2). Unicellular yeast species harbor numerous cytosolic viruses that have no extracellular phase and are only vertically transmitted through cytoplasmic inheritance(3). The most comprehensively studied of these is Killer, a paired system of the L-A and M double stranded RNA (dsRNA) viruses in Saccharomyces cerevisiae. L-A produces a viral particle that houses and propagates M, which itself encodes a secreted toxin that kills neighboring uninfected cells and confers immunity to the host(3). Genetic studies reveal that Killer exists in clear conflict with its host, though how and if this relates to PCD or other developmental occurrences in yeast is not known(4).Yeast sporulation employs internal meiotic divisions and culminates in the development of spore progeny within the remnant of the mother cell(5). PCD of this remnant cell occurs as an intrinsic aspect of sporulation and is executed through vacuolar rupture, leading to mother cell autolysis(6, 7).Spores survive this process, called meiotic PCD, through coordinated development of their protective spore coats(6). Under conditions of reduced carbon, undeveloped meiotic nuclei are frequently swept up in meiotic PCD and their DNA is fragmented into nucleosomal ladders in a manner requiring NUC1, the yeast homolog of the EndoG family of mitochondrial nucleases (7). This finding is reminiscent of EndoG promoting DNA fragmentation of apoptotic cells following its mitochondrial release, though Strains and media. Standard S. cerevisiae genetic and strain manipulation techniques were used for strain construction and tetrad analysis (1). Refer to Table S3 for strains used in this paper. For tetrad dissections, sporulated strains were incubated in 3 mg/mL 20T Zymolyase (Seikagaku Glycobiology) for 15-20 minutes at room temperature and spread on 1% yeast extract, 2% peptone, 0.004% adenine, 2% dextrose (YPD) plates for dissecting.Plasmids. The p5472 NUC1 CEN/ARS URA3 MOBY plasmid was obtained from Brenda Andrews (2). Th...

PURPOSE: Proline Rich 12 (PRR12) is a gene of unknown function with suspected DNA-binding activity, expressed in developing mice and human brains. Predicted loss-of-function variants in this gene are extremely rare, indicating high intolerance of haploinsufficiency. METHODS: Three individuals with intellectual disability and iris anomalies and truncating de novo PRR12 variants were described previously. We add 21 individuals with similar PRR12 variants identified via matchmaking platforms, bringing the total number to 24. RESULTS: We observed 12 frameshift, 6 nonsense, 1 splice-site, and 2 missense variants and one patient with a gross deletion involving PRR12. Three individuals had additional genetic findings, possibly confounding the phenotype. All patients had developmental impairment. Variable structural eye defects were observed in 12/24 individuals (50%) including anophthalmia, microphthalmia, colobomas, optic nerve and iris abnormalities. Additional common features included hypotonia (61%), heart defects (52%), growth failure (54%), and kidney anomalies (35%). PrediXcan analysis showed that phecodes most strongly associated with reduced predicted PRR12 expression were enriched for eye-(7/30) and kidney-(4/30) phenotypes, such as wet macular degeneration and chronic kidney disease. CONCLUSION: These findings support PRR12 haploinsufficiency as a cause for a novel disorder with a wide clinical spectrum marked chiefly by neurodevelopmental and eye abnormalities.

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