Altered ISGylation drives aberrant macrophage-dependent immune responses during SARS-CoV-2 infection.

Ubiquitin-like protein ISG15 (interferon-stimulated gene 15) (ISG15) is a ubiquitin-like modifier induced during infections and involved in host defense mechanisms. Not surprisingly, many viruses encode deISGylating activities to antagonize its effect. Here we show that infection by Zika, SARS-CoV-2 and influenza viruses induce ISG15-modifying enzymes. While influenza and Zika viruses induce ISGylation, SARS-CoV-2 triggers deISGylation instead to generate free ISG15. The ratio of free versus conjugated ISG15 driven by the papain-like protease (PLpro) enzyme of SARS-CoV-2 correlates with macrophage polarization toward a pro-inflammatory phenotype and attenuated antigen presentation. In vitro characterization of purified wild-type and mutant PLpro revealed its strong deISGylating over deubiquitylating activity. Quantitative proteomic analyses of PLpro substrates and secretome from SARS-CoV-2-infected macrophages revealed several glycolytic enzymes previously implicated in the expression of inflammatory genes and pro-inflammatory cytokines, respectively. Collectively, our results indicate that altered free versus conjugated ISG15 dysregulates macrophage responses and probably contributes to the cytokine storms triggered by SARS-CoV-2.

Dmrt5 controls corticotrope and gonadotrope differentiation in the zebrafish pituitary.

Dmrt transcription factors control sex determination or sex-specific differentiation across all invertebrate and vertebrate species, in which they have been studied so far. In addition to important functions in the reproductive system, also nongonadal roles have been assigned to several dmrt family members. One example is dmrt5, which was shown to guide neurogenesis in the forebrain of some vertebrates including fish. Here we show that in zebrafish, dmrt5 is also expressed adjacent to the pituitary anlage and later in the anterior pars distalis in which it organizes differentiation of endocrine cells. We find that pituitary induction, cell survival, proliferation, and early lineage specification in the pituitary is independent of dmrt5. Instead, dmrt5 is required for terminal differentiation of corticotropes and gonadotropes. Gene knockdown and mutant analysis revealed that dmrt5 promotes corticotrope differentiation via tbx19 expression, whereas it prevents gonadotrope differentiation in the anterior pars distalis. In dmrt5 morphants and mutants, reduced corticotrope numbers may result in irregular positioning and reduced maintenance of lactotropes. In conclusion, our study establishes a novel function for dmrt5 for cell differentiation in the anterior pituitary. Intriguingly, its effect on gonadotrope numbers defines a first nongonadal role for a dmrt family member that appears crucial for the activity of the reproductive system.