Breaking the Y

Interaction mapping between nucleoporins in the fission yeast Schizosaccharomyces pombe using mass-spectrometry

Nuclear pore complexes (NPCs) act as gateways across the nuclear envelope for molecular transport between the nucleus and the cytoplasm in eukaryotes. NPCs consist of several subcomplexes formed by multiple copies of approximately 30 different proteins known as nucleoporins (Nups). In the fission yeast Schizosaccharomyces pombe, the NPC structure is unique, particularly in its outer ring subcomplexes, where the cytoplasmic and nucleoplasmic outer rings are composed of distinct sets of proteins. However, it remains unclear how this unique outer ring structure in S. pombe is supported by interactions between subcomplexes or individual Nups. In this study, we investigated protein-protein interactions between S. pombe Nups using mass spectrometry and identified Nups that interact with each subcomplex or a specific Nup. The cytoplasmic outer ring Nups bind to both the cytoplasmic filament Nups and the inner ring Nups, while the nucleoplasmic outer ring Nups bind to the nuclear basket Nups in addition to the inner ring Nups. Among the inner ring Nups, Nup155 interacts with most of the cytoplasmic and nucleoplasmic outer ring Nups, suggesting that Nup155 may serve as a hub supporting the uniquely asymmetric outer ring structure of the S. pombe NPC.

Dissecting the Genetic and Etiological Causes of Primary Microcephaly

Autosomal recessive primary microcephaly (MCPH; “small head syndrome”) is a rare, heterogeneous disease arising from the decreased production of neurons during brain development. As of August 2020, the Online Mendelian Inheritance in Man (OMIM) database lists 25 genes (involved in molecular processes such as centriole biogenesis, microtubule dynamics, spindle positioning, DNA repair, transcriptional regulation, Wnt signaling, and cell cycle checkpoints) that are implicated in causing MCPH. Many of these 25 genes were only discovered in the last 10 years following advances in exome and genome sequencing that have improved our ability to identify disease-causing variants. Despite these advances, many patients still lack a genetic diagnosis. This demonstrates a need to understand in greater detail the molecular mechanisms and genetics underlying MCPH. Here, we briefly review the molecular functions of each MCPH gene and how their loss disrupts the neurogenesis program, ultimately demonstrating that microcephaly arises from cell cycle dysregulation. We also explore the current issues in the genetic basis and clinical presentation of MCPH as additional avenues of improving gene/variant prioritization. Ultimately, we illustrate that the detailed exploration of the etiology and inheritance of MCPH improves the predictive power in identifying previously unknown MCPH candidates and diagnosing microcephalic patients.