Tolloid cleavage activates latent GDF8 by priming the pro‐complex for dissociation

Growth differentiation factor 8 (GDF8)/myostatin is a latent TGF‐β family member that potently inhibits skeletal muscle growth. Here, we compared the conformation and dynamics of precursor, latent, and Tolloid‐cleaved GDF8 pro‐complexes to understand structural mechanisms underlying latency and activation of GDF8. Negative stain electron microscopy (EM) of precursor and latent pro‐complexes reveals a V‐shaped conformation that is unaltered by furin cleavage and sharply contrasts with the ring‐like, cross‐armed conformation of latent TGF‐β1. Surprisingly, Tolloid‐cleaved GDF8 does not immediately dissociate, but in EM exhibits structural heterogeneity consistent with partial dissociation. Hydrogen–deuterium exchange was not affected by furin cleavage. In contrast, Tolloid cleavage, in the absence of prodomain–growth factor dissociation, increased exchange in regions that correspond in pro‐TGF‐β1 to the α1‐helix, latency lasso, and β1‐strand in the prodomain and to the β6′‐ and β7′‐strands in the growth factor. Thus, these regions are important in maintaining GDF8 latency. Our results show that Tolloid cleavage activates latent GDF8 by destabilizing specific prodomain–growth factor interfaces and primes the growth factor for release from the prodomain.     

Literature-Informed Analysis of a Genome-Wide Association Study of Gestational Age in Norwegian Women and Children Suggests Involvement of Inflammatory Pathways

BackgroundFive-to-eighteen percent of pregnancies worldwide end in preterm birth, which is the major cause of neonatal death and morbidity. Approximately 30% of the variation in gestational age at birth can be attributed to genetic factors. Genome-wide association studies (GWAS) have not shown robust evidence of association with genomic loci yet.MethodsWe separately investigated 1921 Norwegian mothers and 1199 children from pregnancies with spontaneous onset of delivery. Individuals were further divided based on the onset of delivery: initiated by labor or prelabor rupture of membranes. Genetic association with ultrasound-dated gestational age was evaluated using three genetic models and adaptive permutations. The top-ranked loci were tested for enrichment in 12 candidate gene-sets generated by text-mining PubMed abstracts containing pregnancy-related keywords.ResultsThe six GWAS did not reveal significant associations, with the most extreme empirical p = 5.1 × 10⁻⁷. The top loci from maternal GWAS with deliveries initiated by labor showed significant enrichment in 10 PubMed gene-sets, e.g., p = 0.001 and 0.005 for keywords "uterus" and "preterm" respectively. Enrichment signals were mainly caused by infection/inflammation-related genes TLR4, NFKB1, ABCA1, MMP9. Literature-informed analysis of top loci revealed further immunity genes: IL1A, IL1B, CAMP, TREM1, TFRC, NFKBIA, MEFV, IRF8, WNT5A.ConclusionOur analyses support the role of inflammatory pathways in determining pregnancy duration and provide a list of 32 candidate genes for a follow-up work. We observed that the top regions from GWAS in mothers with labor-initiated deliveries significantly more often overlap with pregnancy-related genes than would be expected by chance, suggesting that increased sample size would benefit similar studies.     

The Catalytic Activity of the Ubp3 Deubiquitinating Protease Is Required for Efficient Stress Granule Assembly in Saccharomyces cerevisiae

The interior of the eukaryotic cell is a highly compartmentalized space containing both membrane-bound organelles and the recently identified nonmembranous ribonucleoprotein (RNP) granules. This study examines in Saccharomyces cerevisiae the assembly of one conserved type of the latter compartment, known as the stress granule. Stress granules form in response to particular environmental cues and have been linked to a variety of human diseases, including amyotrophic lateral sclerosis. To further our understanding of these structures, a candidate genetic screen was employed to identify regulators of stress granule assembly in quiescent cells. These studies identified a ubiquitin-specific protease, Ubp3, as having an essential role in the assembly of these RNP granules. This function was not shared by other members of the Ubp protease family and required Ubp3 catalytic activity as well as its interaction with the cofactor Bre5. Interestingly, the loss of stress granules was correlated with a decrease in the long-term survival of stationary-phase cells. This phenotype is similar to that observed in mutants defective for the formation of a related RNP complex, the Processing body. Altogether, these observations raise the interesting possibility of a general role for these types of cytoplasmic RNP granules in the survival of G₀-like resting cells.     

Ribonucleoprotein formation by the ORF1 protein of the non-LTR retrotransposon Tx1L in Xenopus oocytes.

The Tx1L elements constitute a family of site-specific non-LTR retrotransposons found in the genome of the frog Xenopus laevis . The elements have two open reading frames (ORFs) with homology to proteins of retroviruses and other retroelements. This study demonstrates an expected activity of one of the element-encoded proteins. The RNA binding properties of ORF1p, the product of the first ORF of Tx1L, were examined after expression from RNA injected into Xenopus oocytes. Using sucrose gradient sedimentation and non-denaturing gel electrophoresis, we show that ORF1p associates with RNA in cytoplasmic ribonucleoprotein (RNP) particles. Discrete RNPs are formed with well-defined mobilities. The ORF1p RNPs are distinct from endogenous RNPs that contain stored oocyte mRNAs and two specific endogenous mRNAs do not become associated with ORF1p. ORF1p appears to be capable of associating with its own mRNA and with other injected RNAs, independent of specific recognition sequences. Although nuclear localization of ORF1p was anticipated, based both on the supposed mechanism of transposition and on the presence of a potential nuclear localization signal, no significant fraction of the protein was found in the oocyte nucleus. Nonetheless, the RNA binding capability of ORF1p is consistent with the proposed model for transposition of non-LTR retrotransposons.