HectD1 controls hematopoietic stem cell regeneration by coordinating ribosome assembly and protein synthesis.

Impaired ribosome function is the underlying etiology in a group of bone marrow failure syndromes called ribosomopathies. However, how ribosomes are regulated remains poorly understood, as are approaches to restore hematopoietic stem cell (HSC) function loss because of defective ribosome biogenesis. Here we reveal a role of the E3 ubiquitin ligase HectD1 in regulating HSC function via ribosome assembly and protein translation. Hectd1-deficient HSCs exhibit a striking defect in transplantation ability and ex vivo maintenance concomitant with reduced protein synthesis and growth rate under stress conditions. Mechanistically, HectD1 ubiquitinates and degrades ZNF622, an assembly factor for the ribosomal 60S subunit. Hectd1 loss leads to accumulation of ZNF622 and the anti-association factor eIF6 on 60S, resulting in 60S/40S joining defects. Importantly, Znf622 depletion in Hectd1-deficient HSCs restored ribosomal subunit joining, protein synthesis, and HSC reconstitution capacity. These findings highlight the importance of ubiquitin-coordinated ribosome assembly in HSC regeneration

A new ‘Linc’ between noncoding RNAs and blood development

A Perspective on the study by Hu et al. discussing long noncoding RNAs and the implications of identifying an erythroid-specific lncRNA with an anti-apoptotic role in red blood cell formation

FISH-Flow to quantify nascent and mature ribosomal RNA in mouse and human cells

Summary: FISH-Flow (fluorescence in situ hybridization-flow cytometry) involves hybridizing fluorescent oligos to RNA and quantifying fluorescence at a single-cell level using flow cytometry. Here, we present a FISH-Flow protocol to quantify nascent 47S and mature 18S and 28S rRNAs in mouse and human cells, including rRNA quantification across cell cycle stages using DNA staining. We describe steps for cell preparation, hybridization of fluorescent probes against rRNA, and DNA staining. We then detail procedures for flow cytometry and data analysis.For complete details on the use and execution of this protocol, please refer to Antony et al. (2022).1 : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics

PHF6 suppresses self-renewal of leukemic stem cells in AML

Acute myeloid leukemia is characterized by uncontrolled proliferation of self-renewing myeloid progenitors accompanied by a differentiation arrest. PHF6 is a chromatin-binding protein mutated in myeloid leukemias, and its isolated loss increases mouse HSC self-renewal without malignant transformation. We report here that Phf6 knockout increases the aggressiveness of Hoxa9-driven AML over serial transplantation, and increases the frequency of leukemia initiating cells. We define the in vivo hierarchy of Hoxa9-driven AML and identify a population that we term the “LIC-e” (leukemia initiating cells enriched) population. We find that Phf6 loss expands the LIC-e population and skews its transcriptome to a more stem-like state; concordant transcriptome shifts are also observed on PHF6 knockout in a human AML cell line and in PHF6 mutant patient samples from the BEAT AML dataset. We demonstrate that LIC-e accumulation in Phf6 knockout AML occurs not due to effects on cell cycle or apoptosis, but due to an increase in the fraction of its progeny that retain LIC-e identity. Our work indicates that Phf6 loss increases AML self-renewal through context-specific effects on leukemia stem cells