Function of FMRP Domains in Regulating Distinct Roles of Neuronal Protein Synthesis

The Fragile-X Mental Retardation Protein (FMRP) is an RNA binding protein that regulates translation of mRNAs essential for synaptic development and plasticity. FMRP interacts with a specific set of mRNAs, aids in their microtubule-dependent transport and regulates their translation through its association with ribosomes. However, the biochemical role of FMRP's domains in forming neuronal granules and associating with microtubules and ribosomes is currently undefined. We report that the C-terminus domain of FMRP is sufficient to bind to ribosomes akin to the full-length protein. Furthermore, the C-terminus domain alone is essential and responsible for FMRP-mediated neuronal translation repression. However, dendritic distribution of FMRP and its microtubule association is favored by the synergistic combination of FMRP domains rather than individual domains. Interestingly, we show that the phosphorylation of hFMRP at Serine-500 is important in modulating the dynamics of translation by controlling ribosome association. This is a fundamental mechanism governing the size and number of FMRP puncta that contain actively translating ribosomes. Finally through the use of pathogenic mutations, we emphasize the hierarchical contribution of FMRP's domains in translation regulation.

NMDAR mediated dynamic changes in m6A inversely correlates with neuronal translation

Epitranscriptome modifications are crucial in translation regulation and essential for maintaining cellular homeostasis. N6 methyladenosine (m⁶A) is one of the most abundant and well-conserved epitranscriptome modifications, which is known to play a pivotal role in diverse aspects of neuronal functions. However, the role of m⁶A modifications with respect to activity-mediated translation regulation and synaptic plasticity has not been studied. Here, we investigated the role of m⁶A modification in response to NMDAR stimulation. We have consistently observed that 5 min NMDAR stimulation causes an increase in eEF2 phosphorylation. Correspondingly, NMDAR stimulation caused a significant increase in the m⁶A signal at 5 min time point, correlating with the global translation inhibition. The NMDAR induced increase in the m⁶A signal is accompanied by the redistribution of the m⁶A marked RNAs from translating to the non-translating pool of ribosomes. The increased m⁶A levels are well correlated with the reduced FTO levels observed on NMDAR stimulation. Additionally, we show that inhibition of FTO prevents NMDAR mediated changes in m⁶A levels. Overall, our results establish RNA-based molecular readout which corelates with the NMDAR-dependent translation regulation which helps in understanding changes in protein synthesis.

Effect of neoadjuvant chemotherapy on resectability of stage III and IV hepatoblastoma

Background

The potential for surgical resection of primary hepatoblastoma tumours was assessed at diagnosis, and after two and four cycles of neoadjuvant chemotherapy.

Methods

Available radiographic images for patients with stage III and IV hepatoblastoma diagnosed between 1991 and 2008 were reviewed. The extent of disease was determined at diagnosis using the PRETEXT staging system, and after two and four cycles of therapy by POST-TEXT staging. Tumour resectability based on radiographic studies was assessed independently by two surgeons with expertise in hepatic surgery who were blinded to treatment and clinical outcome.

Results

Radiographic images from 20 patients with hepatoblastoma were reviewed. Six of 20 tumours were downstaged after two cycles, and three additional tumours were downstaged following four cycles. All PRETEXT stage III and IV tumours were determined to be surgically unresectable at diagnosis. The number of tumours considered unresectable decreased from 16 of 20 at diagnosis to seven of 20 after two cycles, and to four of 20 after four cycles. Five of the seven tumours that were unresectable after two cycles, and all four tumours that were unresectable after four cycles would have qualified for liver transplant based on radiographic studies.

Conclusion

The majority of stage III and IV hepatoblastomas achieved radiographic resectability after two cycles of chemotherapy. There may be an opportunity for earlier surgical intervention and potential for a reduction in chemotherapy in a considerable number of patients.