Biology subjects

Kostlbacher, S.

Publications and source records attributed to Kostlbacher, S..

4 recordsLinked to original sources

bioRxiv2023

RNA-guided RNA silencing by an Asgard archaeal Argonaute

Eukaryotic Argonaute proteins achieve gene repression and defense against viruses and transposons by RNA-guided RNA silencing. By contrast, known prokaryotic Argonautes adopt single-stranded DNA as guides and/or targets, leaving the evolutionary origin of RNA-guided RNA silencing elusive. Here, we show an evolutionary expansion of Asgard archaeal Argonautes (asAgos), including the discovery of HrAgo1 from the Lokiarchaeon Candidatus Harpocratesius repetitus that shares a common origin with eukaryotic PIWI proteins. HrAgo1 exhibits RNA-guided RNA cleavage in vitro and RNA silencing in human cells. The cryo-EM structure of HrAgo1 combined with quantitative single-molecule experiments reveals that HrAgo1 possesses hybrid structural features and target binding modes bridging those of the eukaryotic AGO and PIWI clades. Finally, genomic evidence suggests that eukaryotic Dicer-like processing of double-stranded RNA likely emerged as a mechanism of generating guide RNA for asAgos prior to eukaryogenesis. Our study provides new insights into the evolutionary origin and plasticity of Argonaute-based RNA silencing.

microbiology↗

bioRxiv2023

Type III-B CRISPR-Cas signaling-based cascade of proteolytic cleavages

Type III CRISPR-Cas systems provide a sequence-specific adaptive immune response that protects prokaryotic hosts against viruses and other foreign genetic invaders. These crRNA-guided Cas effector complexes bind and cleave complementary RNA targets. Specific target binding stimulates the Cas10 subunit to generate cyclic oligoadenylate (cOA) signaling molecules, that in turn allosterically activate proteins carrying cognate sensory domains: CARF or SAVED. Here, we characterize an elaborate set of genes associated with the type III-B CRISPR-Cas system from Haliangium ochraceum, which includes a signal transduction module of a CBASS defense system with two caspase-like proteases, SAVED-CHAT and PCaspase (Prokaryotic Caspase). We show that binding of a 3-nucleotide cOA (cA3) to the SAVED domain of SAVED-CHAT induces its oligomerization into long filaments that activate the proteolytic activity of the CHAT domain. Surprisingly, we find that activated SAVED-CHAT specifically cleaves and activates the second protease, PCaspase. In turn, activated PCaspase cleaves a multitude of other proteins, including a putative sigma factor and a PCaspase-inhibitor. We expressed the type III-B system and its associated genes in E. coli and observed a strong abortive phenotype when offering a complementary target RNA, but only in the presence of both SAVED-CHAT and PCaspase. Together, our findings show an intriguing cascade of proteolytic activities (conceptually similar to eukaryotic caspases) in this bacterial immune system that reveals yet another strategy to effectively defend against mobile genetic elements.

biochemistry↗

bioRxiv2021

The evolutionary origin of host association in an ancient bacterial clade

The evolution of obligate host-association of bacterial symbionts and pathogens remains poorly understood. The Rickettsiales represent an order of obligate alphaproteobacterial endosymbionts and parasites that infect a wide variety of eukaryotic hosts, including humans, livestock, insects and protists. Induced by their host-associated lifestyle, Rickettsiales genomes have undergone reductive evolution, leading to small, AT-rich genomes with limited metabolic capacities. We describe several genomes of deep-branching, environmental alphaproteobacteria that branch basal to previously sampled Rickettsiales, and whose genome content are reminiscent of free-living and biofilm-associated lifestyles. Ancestral genome content reconstruction across the Rickettsiales tree revealed that the free-living to host-association transition of this group occurred more recently than previously anticipated, and likely involved the repurposing of a type IV secretion system. One-Sentence SummaryDeep-branching Rickettsiales provide insights into the evolution of obligate host-associated lifestyle

microbiology↗

bioRxiv2021

A masculinizing supergene underlies an exaggerated male reproductive morph in a spider.

In many species, individuals can develop into strikingly different morphs, which are determined by a simple Mendelian locus. How selection shapes loci that control complex phenotypic differences remains poorly understood. In the spider Oedothorax gibbosus, males either develop into a hunched morph with conspicuous head structures or as a fast developing flat morph with a female-like appearance. We show that the hunched-differs from the flat-determining allele by a hunch-specific genomic fragment of approximately 3 megabases. This fragment comprises dozens of genes that duplicated from genes found at different chromosomes. All functional duplicates, including doublesex - a key sexual differentiation regulatory gene, show male-specific expression, which illustrates their combined role as a masculinizing supergene. Our findings demonstrate how extensive indel polymorphisms and duplications of regulatory genes may contribute to the evolution of co-adapted gene clusters, sex-limited reproductive morphs, and the enigmatic evolution of exaggerated sexual traits in general.

evolutionary biology↗