Polo-like kinase 4 (Plk4) is a key regulator of centriole duplication, an event critical for the maintenance of genomic integrity. Here we showed that Plk4 relocalizes from the inner Cep192 ring to the outer Cep152 ring as newly recruited Cep152 assembles around the Cep192-encircled daughter centriole. Crystal structure analyses revealed that Cep192 - and Cep152-derived peptides bind the cryptic polo box (CPB) of Plk4 in opposite orientations and in a mutually exclusive manner. The Cep152-peptide bound to the CPB markedly better than the Cep192-peptide and effectively snatched the CPB away from a preformed CPB–Cep192-peptide complex. A cancer-associated Cep152 mutation impairing the Plk4 interaction induced defects in procentriole assembly and chromosome segregation. Thus, Plk4 is intricately regulated in time and space through ordered interactions with two distinct scaffolds, Cep192 and Cep152, and a failure in this process may lead to human cancer.

The Wiskott-Aldrich syndrome is an inherited X-linked immunodeficiency characterized by thrombocytopenia, eczema, and a tendency toward lymphoid malignancy. Lymphocytes from affected individuals have cytoskeletal abnormalities, and monocytes show impaired motility. The Wiskott-Aldrich syndrome protein (WASP) is a multi-domain protein involved in cytoskeletal organization. In a two-hybrid screen, we identified the protein Cdc42-interacting protein 4 (CIP4) as a WASP interactor. CIP4, like WASP, is a Cdc42 effector protein involved in cytoskeletal organization. We found that the WASP-CIP4 interaction is mediated by the binding of the Src homology 3 domain of CIP4 to the prolinerich segment of WASP. Cdc42 was not required for this interaction. Co-expression of CIP4 and green fluorescent protein-WASP in COS-7 cells led to the association of WASP with microtubules. In vitro experiments showed that CIP4 binds to microtubules via its NH 2 terminus. The region of CIP4 responsible for binding to active Cdc42 was localized to amino acids 383-417, and the mutation I398S abrogated binding. Deletion of the Cdc42-binding domain of CIP4 did not affect the colocalization of WASP with microtubules in vivo. We conclude that CIP4 can mediate the association of WASP with microtubules. This may facilitate transport of WASP to sites of substrate adhesion in hematopoietic cells.The Wiskott-Aldrich syndrome is an inherited X-linked immunodeficiency with associated thrombocytopenia, eczema, and a tendency toward development of malignancy of the lymphoreticular system (1, 2). Affected individuals have lymphocytes that respond poorly to certain stimulants in vitro (3, 4) and show abnormalities of cytoskeletal structure (5-8). Impaired monocyte motility is also observed (9 -11). The gene mutated in Wiskott-Aldrich syndrome was cloned in 1994, and was shown to encode a proline-rich protein of 502 amino acids (12)(13)(14) (18,29). WASP has been shown to interact directly with actin through the verprolin homology domain (30). A WASP homolog expressed in neural and other tissues, N-WASP, has the ability to depolymerize actin filaments in vitro (28,29). WASP, N-WASP, and the related proteins Scar1 in human and Bee1/Las17 in yeast interact with the Arp2/3 complex, a key regulator of actin polymerization (31, 32). WASP-coated microspheres exhibit cytoplasmic actin-based motility, dependent on the presence of the Arp2/3 complex (33). Taken together, these studies suggest that WASP is a mediator of Cdc42/Rac signaling, and has direct effects on the actin cytoskeleton via actin-binding domains and activation of the Arp2/3 complex. SH3 protein interactions may play a role in localization of WASP and/or transmission of extracellular signals to and through WASP. We performed a yeast two-hybrid screen to look for novel WASP-interacting proteins. One WASP-interacting clone encoded a portion of the protein CIP4. This protein was identified previously as interacting with the active form of Cdc42 (34). CIP4 is a 545-amino acid protein, widely expressed, tha...

This paper reviewed the deep learning‐based studies for medical imaging synthesis and its clinical application. Specifically, we summarized the recent developments of deep learning‐based methods in inter‐ and intra‐modality image synthesis by listing and highlighting the proposed methods, study designs, and reported performances with related clinical applications on representative studies. The challenges among the reviewed studies were then summarized with discussion.

Structures of type-1 human immunodeficiency virus (HIV-1) reverse transcriptase (RT) have been determined in several forms, but only one contains an RNA/DNA hybrid. Here we report three structures of HIV-1 RT complexed with a non-nucleotide RT inhibitor (NNRTI) and an RNA/DNA hybrid. In the presence of an NNRTI, the RNA/DNA structure differs from all prior nucleic acid bound to RT including the RNA/DNA hybrid. The enzyme structure also differs from all previous RT–DNA complexes. As a result, the hybrid has ready access to the RNase H active site. These observations indicate that an RT–nucleic acid complex may adopt two structural states, one competent for DNA polymerization and the other for RNA degradation. RT mutations that confer drug resistance but are distant from the inhibitor-binding sites often map to the unique RT–hybrid interface that undergoes conformational changes between two catalytic states.