Human microcephaly protein RTTN interacts with STIL and is required to build full-length centrioles

Abstract

Mutations in many centriolar protein-encoding genes cause primary microcephaly. Using super-resolution and electron microscopy, we find that the human microcephaly protein, RTTN, is recruited to the proximal end of the procentriole at early S phase, and is located at the inner luminal walls of centrioles. Further studies demonstrate that RTTN directly interacts with STIL and acts downstream of STIL-mediated centriole assembly. CRISPR/Cas9-mediated RTTN gene knockout in p53-deficient cells induce amplification of primitive procentriole bodies that lack the distal-half centriolar proteins, POC5 and POC1B. Additional analyses show that RTTN serves as an upstream effector of CEP295, which mediates the loading of POC1B and POC5 to the distal-half centrioles. Interestingly, the naturally occurring microcephaly-associated mutant, RTTN (A578P), shows a low affinity for STIL binding and blocks centriole assembly. These findings reveal that RTTN contributes to building full-length centrioles and illuminate the molecular mechanism through which the RTTN (A578P) mutation causes primary microcephaly.

The Yin and Yang of Autosomal Recessive Primary Microcephaly Genes: Insights from Neurogenesis and Carcinogenesis

“…Centriole duplication [58,59] Cell proliferation, cell cycle G2/M phase and apoptosis (GC) [32] Centromere assembly [60] Cell proliferation and apoptosis (prostate cancer, PCa) [28] Cell cycle and chromosomal segregation [61] DNA repair (OC) [62] MCPH8 (CEP135)…”

“…This regulates the replication of centrioles in vivo [58]. Other studies have shown that the human microcephalic malformation protein rotatin (RTTN) directly interacts with STIL and acts downstream of STIL-mediated centrosome assembly [60], thereby affecting the development of the brain. MCPH8 (CEP135) is particularly important in the assembly, amplification, and microtubule binding of the centriole [99].…”

TetrahymenaPoc5 is a transient basal body component that is important for basal body maturation

“…Further, human POC5 (hPOC5) was found to be enriched in the distal portion of human centrioles, where it has an essential role in centriole elongation and maturation (Azimzadeh et al, 2009). This role for hPOC5 is notable because molecular mechanisms that contribute to building a full-length centriole/BB remain poorly understood, especially compared with the mechanistic and molecular understanding of early assembly (Chang et al, 2016; Chen et al, 2017; Comartin et al, 2013; Keller et al, 2009; Schmidt et al, 2009). Furthermore, a truncating mutation in hPOC5 was recently implicated in an inherited form of retinal degeneration, retinitis pigmentosa, characterized by progressive loss of photoreceptors, and Poc5 was found to colocalize with centrin in the connecting cilium of zebrafish photoreceptors, where it is important for normal retinal development and function (Weisz Hubshman et al, 2018; Wheway et al, 2014).…”

Primary microcephaly, primordial dwarfism, and brachydactyly in adult cases with biallelic skipping of RTTN exon 42

“…In humans, biallelic RTTN variants have been associated with rare cases of polymicrogyria, malformation of the developing cerebral cortex and seizures (Kheradmand Kia et al, ), microcephalic primordial dwarfism (Shamseldin et al, ), and simplified gyri (Chartier et al, ). The human RTTN gene (MIM# 610436) encodes Rotatin, a large centrosomal protein that interacts with the centriolar protein STIL for appropriate assembly of full‐length centrioles (Chen et al, ). To date, 15 cases belonging to eight families have been described with biallelic variants in the RTTN gene, neurodevelopmental delay, and variable associated features (Grandone et al, ; Stouffs et al, ; Wambach et al, ).…”

“…Rotatin is essential for building full‐length centrioles forming basal bodies of cilia as well as nucleation points for spindle formation during cell division (Chen et al, ). In humans, the importance of Rotatin for neural proliferation, cortical organization, and growth is shown by the identification of RTTN variants in patients with polymicrogyria (Kheradmand Kia et al, ) or with microcephaly and primordial dwarfism (Shamseldin et al, ).…”