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Meuwissen and collaborators define a novel genetic cause of pseudo-TORCH syndrome, which resembles the sequelae of congenital infection and represents a novel type I interferonopathy., Pseudo-TORCH syndrome (PTS) is characterized by microcephaly, enlarged ventricles, cerebral calcification, and, occasionally, by systemic features at birth resembling the sequelae of congenital infection but in the absence of an infectious agent. Genetic defects resulting in activation of type 1 interferon (IFN) responses have been documented to cause Aicardi-Goutières syndrome, which is a cause of PTS. Ubiquitin-specific peptidase 18 (USP18) is a key negative regulator of type I IFN signaling. In this study, we identified loss-of-function recessive mutations of USP18 in five PTS patients from two unrelated families. Ex vivo brain autopsy material demonstrated innate immune inflammation with calcification and polymicrogyria. In vitro, patient fibroblasts displayed severely enhanced IFN-induced inflammation, which was completely rescued by lentiviral transduction of USP18. These findings add USP18 deficiency to the list of genetic disorders collectively termed type I interferonopathies. Moreover, USP18 deficiency represents the first genetic disorder of PTS caused by dysregulation of the response to type I IFNs. Therapeutically, this places USP18 as a promising target not only for genetic but also acquired IFN-mediated CNS disorders.

The Saccharomyces cerevisiae Rad52 protein has a crucial role in the repair of DNA double-strand breaks by homologous recombination. In vitro, Rad52 displays DNA binding and strand annealing activities and promotes Rad51-mediated strand exchange. Schizosaccharomyces pombe has two Rad52 homologues, Rad22A and Rad22B. Whereas rad22A deficient strains exhibit severe defects in repair and recombination, rad22B mutants have a much less severe phenotype. To better understand the role of Rad22A and Rad22B in double-strand break repair, both proteins were purified to near homogeneity. Using gel retardation and filter binding assays, binding of Rad22A and Rad22B to short single-stranded DNAs was demonstrated. Binding of Rad22A to double-stranded oligonucleotides or linearized plasmid molecules containing blunt ends or short single-stranded overhangs could not be detected. Rad22B also does not bind efficiently to short duplex oligonucleotides but binds readily to DNA fragments containing 3'-overhangs. Rad22A as well as Rad22B efficiently promote annealing of complementary single-stranded DNAs. In the presence of Rad22A annealing of complementary DNAs is almost 90%. Whereas in reactions containing Rad22B the maximum level of annealing is 60%, most likely due to inhibition of the reaction by duplex DNA. Gel-filtration experiments and electron microscopic analyses indicate self-association of Rad22A and Rad22B and the formation of multimeric structures as has been observed for Rad52 in yeast and man.

In meiotic prophase, synaptonemal complexes (SCs) closely appose homologous chromosomes (homologs) along their length. SCs are assembled from two axial elements (AEs), one along each homolog, which are connected by numerous transverse filaments (TFs). We disrupted the mouse gene encoding TF protein Sycp1 to analyze the role of TFs in meiotic chromosome behavior and recombination. Sycp1-/- mice are infertile, but otherwise healthy. Sycp1-/- spermatocytes form normal AEs, which align homologously, but do not synapse. Most Sycp1-/- spermatocytes arrest in pachynema, whereas a small proportion reaches diplonema, or, exceptionally, metaphase I. In leptotene Sycp1-/- spermatocytes, γH2AX (indicative of DNA damage, including double-strand breaks) appears normal. In pachynema, Sycp1-/- spermatocytes display a number of discrete γH2AX domains along each chromosome, whereas γH2AX disappears from autosomes in wild-type spermatocytes. RAD51/DMC1, RPA, and MSH4 foci (which mark early and intermediate steps in pairing/recombination) appear in similar numbers as in wild type, but do not all disappear, and MLH1 and MLH3 foci (which mark late steps in crossing over) are not formed. Crossovers were rare in metaphase I of Sycp1-/- mice. We propose that SYCP1 has a coordinating role, and ensures formation of crossovers. Unexpectedly, Sycp1-/- spermatocytes did not form XY bodies.

In fission yeast two RAD52 homologs have been identified, rad22A(+) and rad22B(+). Two-hybrid experiments and GST pull-down assays revealed physical interaction between Rad22A and Rad22B, which is dependent on the N-terminal regions. Interaction with Rhp51 is dependent on the C-terminal parts of either protein. Both Rad22A and Rad22B also interact with RPA. The expression of rad22B(+) in mitotically dividing cells is very low in comparison with rad22A(+) but is strongly enhanced after induction of meiosis, in contrast to rad22A(+). Rad22B mutant cells are not hypersensitive to DNA-damaging agents (X-rays, UV and cisplatin) and display normal levels of recombination. In these respects the Schizosaccharomyces pombe rad22B mutant resembles the weak phenotype of vertebrate cells deficient for RAD52. Mutation of rad22A(+) leads to severe sensitivity to DNA-damaging agents and to defects in recombination. In a rad22Arad22B double mutant a further increase in sensitivity to DNA-damaging agents and additional mitotic recombination defects were observed. The data presented here indicate that Rad22A and Rad22B have overlapping roles in repair and recombination, although specialized functions for each protein cannot be excluded.