The eIF4E homolog 4EHP (eIF4E2) regulates hippocampal long-term depression and impacts social behavior

Eukaryotic translation initiation factor eIF4E-5 is required for spermiogenesis in Drosophila melanogaster

Drosophila sperm development is characterized by extensive post-transcriptional regulation whereby thousands of transcripts are preserved for translation during later stages. A key step in translation initiation is the binding of eukaryotic initiation factor 4E (eIF4E) to the 5' mRNA cap. In addition to canonical eIF4E-1, Drosophila has multiple eIF4E paralogs, including four (eIF4E-3, -4, -5, and -7) that are highly expressed in the testis. Among these, only eIF4E-3 has been characterized genetically. Here, using CRISPR/Cas9 mutagenesis, we determined that eIF4E-5 is essential for male fertility. eIF4E-5 protein localizes to the distal ends of elongated spermatid cysts, and eIF4E-5 mutants exhibit defects during post-meiotic stages, including a mild defect in spermatid cyst polarization. eIF4E-5 mutants also have a fully penetrant defect in individualization, resulting in failure to produce mature sperm. Indeed, our data indicate that eIF4E-5 regulates non-apoptotic caspase activity during individualization by promoting local accumulation of the E3 ubiquitin ligase inhibitor Soti. Our results further extend the diversity of non-canonical eIF4Es that carry out distinct spatiotemporal roles during spermatogenesis.

Cell-type-specific translational control of spatial working memory by the cap-binding protein 4EHP

The consolidation of learned information into long-lasting memories requires the strengthening of synaptic connections through de novo protein synthesis. Translation initiation factors play a cardinal role in gating the production of new proteins thereby regulating memory formation. Both positive and negative regulators of translation play a critical role in learning and memory consolidation. The eukaryotic initiation factor 4E (eIF4E) homologous protein (4EHP, encoded by the gene Eif4e2) is a pivotal negative regulator of translation but its role in learning and memory is unknown. To address this gap in knowledge, we generated excitatory (glutamatergic: CaMKIIα-positive) and inhibitory (GABAergic: GAD65-positive) conditional knockout mice for 4EHP, which were analyzed in various behavioral memory tasks. Knockout of 4EHP in Camk2a-expressing neurons (4EHP-cKO^exc) did not impact long-term memory in either contextual fear conditioning or Morris water maze tasks. Similarly, long-term contextual fear memory was not altered in Gad2-directed 4EHP knockout mice (4EHP-cKO^inh). However, when subjected to a short-term T-maze working memory task, both mouse models exhibited impaired cognition. We therefore tested the hypothesis that de novo protein synthesis plays a direct role in working memory. We discovered that phosphorylation of ribosomal protein S6, a measure of mTORC1 activity, is dramatically reduced in the CA1 hippocampus of 4EHP-cKO^exc mice. Consistently, genetic reduction of mTORC1 activity in either excitatory or inhibitory neurons was sufficient to impair working memory. Taken together, these findings indicate that translational control by 4EHP and mTORC1 in both excitatory and inhibitory neurons are necessary for working memory.

eIF4E-homologous protein (4EHP): a multifarious cap-binding protein

The cap-binding protein 4EHP/eIF4E2 has been a recent object of interest in the field of post-transcriptional gene regulation and translational control. From ribosome-associated quality control, to RNA decay and microRNA-mediated gene silencing, this member of the eIF4E protein family regulates gene expression through numerous pathways. Low in abundance but ubiquitously expressed, 4EHP interacts with different binding partners to form multiple protein complexes that regulate translation in a variety of biological contexts. Documented functions of 4EHP primarily relate to its role as a translational repressor, but recent findings indicate that it might also participate in the activation of translation in specific settings. In this review, we discuss the known functions, properties and mechanisms that involve 4EHP in the control of gene expression. We also discuss our current understanding of how 4EHP processes are regulated in eukaryotic cells, and the diseases implicated with dysregulation of 4EHP-mediated translational control.

Differences in gene expression patterns, revealed by RNA-seq analysis, between various Sanfilippo and Morquio disease subtypes

Mucopolysaccharidoses (MPS) are genetic disorders that affect up to 1 in 25,000 births. They are caused by dysfunctions of lysosomal hydrolases that degrade glycosaminoglycans (GAGs) which accumulate in cells, damaging their proper functioning. There are 7 types of MPS, distinguished by the kind of accumulated GAG and the defective enzyme, which differ significantly in the course of the disease. Despite the storage of the same GAGs, two of them (MPS III and IV) are divided into subtypes. While the course of MPS IV A and B is similar, the variability between MPS III A, B, C and D is high. This suggests that there are additional aspects that could influence the course of the disease. Therefore, the aim of this study was to determine differences of patterns of gene expression between all MPS III and IV subtypes. Transcriptomic studies, carried out with dermal fibroblasts from patients with all MPS III and IV subtypes, showed a significant variation in the gene expression pattern between individual MPS III subtypes, in contrast to MPS IV. Detailed analysis of transcripts with altered expression levels between MPS III subtypes indicated that these transcripts are mainly involved in maintaining the proper structure of connective tissue (COL4A1, COL4A2, COMP) and the structure of ribosomes (RPL10, RPL23, RPLP2). The results presented in this study indicate a significant role of genetic factors in the diversified course of MPS III subtypes.

Translational control in neurovascular brain development

The human brain carries out complex tasks and higher functions and is crucial for organismal survival, as it senses both intrinsic and extrinsic environments. Proper brain development relies on the orchestrated development of different precursor cells, which will give rise to the plethora of mature brain cell-types. Within this process, neuronal cells develop closely to and in coordination with vascular cells (endothelial cells (ECs), pericytes) in a bilateral communication process that relies on neuronal activity, attractive or repulsive guidance cues for both cell types and on tight-regulation of gene expression. Translational control is a master regulator of the gene-expression pathway and in particular for neuronal and ECs, it can be localized in developmentally relevant (axon growth cone, endothelial tip cell) and mature compartments (synapses, axons). Herein, we will review mechanisms of translational control relevant to brain development in neurons and ECs in health and disease.

Molecular Mechanisms of Aberrant Neuroplasticity in Autism Spectrum Disorders (Review)

This review presents the analysis and systematization of modern data on the molecular mechanisms of autism spectrum disorders (ASD) development. Polyetiology and the multifactorial nature of ASD have been proved. The attempt has been made to jointly review and systematize current hypotheses of ASD pathogenesis at the molecular level from the standpoint of aberrant brain plasticity. The mechanism of glutamate excitotoxicity formation, the effect of imbalance of neuroactive amino acids and their derivatives, neurotransmitters, and hormones on the ASD formation have been considered in detail. The strengths and weaknesses of the proposed hypotheses have been analyzed from the standpoint of evidence-based medicine. The conclusion has been drawn on the leading role of glutamate excitotoxicity as a biochemical mechanism of aberrant neuroplasticity accompanied by oxidative stress and mitochondrial dysfunction. The mechanism of aberrant neuroplasticity has also been traced at the critical moments of the nervous system development taking into account the influence of various factors of the internal and external environment. New approaches to searching for ASD molecular markers have been considered.