Phosphoproteomic differences in major depressive disorder postmortem brains indicate effects on synaptic function

There is still a lack in the molecular comprehension of major depressive disorder (MDD) although this condition affects approximately 10% of the world population. Protein phosphorylation is a posttranslational modification that regulates approximately one-third of the human proteins involved in a range of cellular and biological processes such as cellular signaling. Whereas phosphoproteome studies have been carried out extensively in cancer research, few such investigations have been carried out in studies of psychiatric disorders. Here, we present a comparative phosphoproteome analysis of postmortem dorsolateral prefrontal cortex tissues from 24 MDD patients and 12 control donors. Tissue extracts were analyzed using liquid chromatography mass spectrometry in a data-independent manner (LC-MSE). Our analyses resulted in the identification of 5,195 phosphopeptides, corresponding to 802 non-redundant proteins. Ninety of these proteins showed differential levels of phosphorylation in tissues from MDD subjects compared to controls, being 20 differentially phosphorylated in at least 2 peptides. The majority of these phosphorylated proteins were associated with synaptic transmission and cellular architecture not only pointing out potential biomarker candidates but mainly shedding light to the comprehension of MDD pathobiology

The nano-architecture of the axonal cytoskeleton

International audienceThe cytoskeleton is a cellular shapeshifter. Like these creatures of mythology and speculative fiction, the cytoskeleton can alter its physical form and shape to accommodate the immediate needs of the cell. Indeed, many a rapt student has watched the cytoskeleton of a dividing cell seemingly miraculously transform into an organized mitotic spindle and then dissolve into an indiscrete mass, right before their eyes. The extreme polarization of neurons (that is, their fundamental asymmetry, arising due to the presence of elongated processes), along with their lifelong plasticity, creates unique demands on the cytoskeleton. A remarkable example is the axon, which can grow to enormous lengths and must generate and maintain its form and function throughout life — a burden that rests largely on the cytoskeleton. The axonal cytoskeleton has three major constituents: microtubules, neurofilaments and actin (BOX 1). Each is unique, associating with its own set of binding proteins and performing specialized roles within the axon. Most of these cytoskeletal proteins are synthesized in the neu­ ronal soma and are transported along the axon. Such transport is a constitutive phenomenon that occurs throughout the life of the neuron. Thus, the axonal cytoskeleton is best understood by considering both its anatomical organization and its dynamics (including axonal transport). Given the complex morphology and physiology of neurons, the field of neurobiology has traditionally been at the forefront of adopting new optical techno­ logies as they arise. Advances in microscopy now allow us to observe cells with unprecedented spatial resolu­ tion and to follow dynamic processes with exquisite temporal detail 1. For example, super­resolution strat­ egies that circumvent the diffraction limit of optical microscopy appeared more than ten years ago (BOX 2) and have been used to reveal aspects of neuronal organ­ ization down to the scale of macromolecular com­ plexes 2. These techniques have provided key insights into the organization and function of the axonal cytoskeleton — and in particular the organization of actin and microtubules — revealing how it builds the axon and maintains its intricate architecture. Focusing on the cytoskeleton within the axon initial segment (AIS) and the more distal axon shaft, in this Review, we highlight these recent discoveries and place them in the context of earlier findings, giving the reader a tentative vision of the future. Overview of the axonal cytoskeleton The history of cytoskeletal research is essentially the pursuit of tools and techniques that allowed an ever­ closer view of this elaborate structure, a quest that continues to this day. Early studies by 17th­century microscopy pioneers highlighted a network of 'neu­ rofibrils' , which we now know were most likely neuro­ filaments 3. With the advent of electron microscopy, two types of fibrils were seen in axons: filaments measuring approximately 10 nm in diameter, corresponding to neurofilaments, and others measuring approximately 20–30 nm in diameter, corresponding to structures that eventually came to be known as microtubules 4,5. Abstract | The corporeal beauty of the neuronal cytoskeleton has captured the imagination of generations of scientists. One of the easiest cellular structures to visualize by light microscopy, its existence has been known for well over 100 years, yet we have only recently begun to fully appreciate its intricacy and diversity. Recent studies combining new probes with super-resolution microscopy and live imaging have revealed surprising details about the axonal cytoskeleton and, in particular, have discovered previously unknown actin-based structures. Along with traditional electron microscopy, these newer techniques offer a nanoscale view of the axonal cytoskeleton, which is important for our understanding of neuronal form and function, and lay the foundation for future studies. In this Review, we summarize existing concepts in the field and highlight contemporary discoveries that have fundamentally altered our perception of the axonal cytoskeleton

Membrane-targeted WAVE mediates photoreceptor axon targeting in the absence of the WAVE complex in Drosophila

The Abelson interactor (Abi) has a conserved role in Arp2/3-dependent actin polymerization, regulating WASP and WAVE. In this study, the function of Abi was analyzed in the context of the developing fly visual system, and the steps in the molecular regulation of WAVE activity by its regulatory complex in vivo were identified