Alternative RNA splicing plays an important role in cancer. To determine which factors involved in RNA processing are essential in prostate cancer, we performed a genome-wide CRISPR/Cas9 knockout screen to identify the genes that are required for prostate cancer growth. Functional annotation defined a set of essential spliceosome and RNA binding protein (RBP) genes, including most notably heterogeneous nuclear ribonucleoprotein L (HNRNPL). We defined the HNRNPL-bound RNA landscape by RNA immunoprecipitation coupled with next-generation sequencing and linked these RBP-RNA interactions to changes in RNA processing. HNRNPL directly regulates the alternative splicing of a set of RNAs, including those encoding the androgen receptor, the key lineage-specific prostate cancer oncogene. HNRNPL also regulates circular RNA formation via back splicing. Importantly, both HNRNPL and its RNA targets are aberrantly expressed in human prostate tumors, supporting their clinical relevance. Collectively, our data reveal HNRNPL and its RNA clients as players in prostate cancer growth and potential therapeutic targets.CRISPR screen | HNRNPL | prostate cancer | RNA binding protein | alternative splicing P rostate cancer is among the most prevalent adult malignancies in developed countries. The principal treatment for prostate cancer once it is no longer amenable to surgery or radiation treatment is androgen deprivation therapy, which targets androgen or androgen receptor (AR) signaling. However, resistance to androgen deprivation therapy often develops and leads to a state termed "castration-resistant prostate cancer," which still lacks an effective cure (1-3). Therefore, significant efforts have been devoted to better understand the mechanism of oncogenesis and to develop additional effective therapeutics targeting pivotal oncogenes, cancer-related signal transduction pathways, and epigenetic regulators (4, 5).Alternative RNA splicing is a fundamental cellular process by which a single gene can give rise to multiple different transcripts and proteins. This process is tightly regulated by core spliceosomes and other splicing factors, such as the serine/ arginine-rich family of proteins and heterogeneous nuclear ribonucleoproteins (hnRNPs) (6, 7). Multiple studies indicate that deregulation of alternative splicing is implicated in cancer progression and that the splicing machinery may be targeted therapeutically (8-10). In addition to RNA splicing, the physical interactions between RNAs and RNA binding proteins (RBPs) underlie multiple RNA processing steps, such as capping, polyadenylation, transport, localization, modification, and translation, thereby regulating many aspects of RNA fate (11).Which RBPs and their related RNA processing steps are functionally important, especially in prostate cancer, remains elusive.The recent implementation of the clustered regularly interspaced short palindromic repeats (CRISPR)-associated nuclease Cas9 genome editing system has proved effective in high-throughput lossof-function screens (12)(13)(14)...

X-linked neutropenia (XLN, OMIM #300299) is a rare form of severe congenital neutropenia. It was originally described in a three-generation family with 5 affected members and with an L270P mutation in the GTP-ase binding domain (GBD) of the Wiskott-Aldrich-syndrome protein (WASP) (Devriendt, et al 2001). Here, we report and describe a large three-generation family with XLN, with 10 affected males and 8 female carriers. A c.882T>C WAS gene mutation was identified, resulting in an I294T mutation. The infectious course is variable and mild in view of the deep neutropenia. In addition to the original description, low-normal IgA levels, low to low-normal platelet counts and reduced NK-cell counts also appear as consistent XLN features. However, inverted CD4/CD8 ratios were not found in this family, nor were cases identified with myelodysplastic syndrome or acute myeloid leukaemia. Female carriers exhibited a variable attenuated phenotype. Like L270P WASP, I294T WASP is constitutively active towards actin polymerisation In conclusion, this largest XLN kindred identified to date provides new independent genetic evidence that mutations disrupting the auto-inhibitory GBD of WASP are the cause of XLN. Reduced NK cells, low to low normal platelet counts and low to low-normal IgA levels are also features of XLN.