Ommochromes in invertebrates: biochemistry and cell biology

Ommochromes are widely occurring coloured molecules of invertebrates, arising from tryptophan catabolism through the so‐called Tryptophan → Ommochrome pathway. They are mainly known to mediate compound eye vision, as well as reversible and irreversible colour patterning. Ommochromes might also be involved in cell homeostasis by detoxifying free tryptophan and buffering oxidative stress. These biological functions are directly linked to their unique chromophore, the phenoxazine/phenothiazine system. The most recent reviews on ommochrome biochemistry were published more than 30 years ago, since when new results on the enzymes of the ommochrome pathway, on ommochrome photochemistry as well as on their antiradical capacities have been obtained. Ommochromasomes are the organelles where ommochromes are synthesised and stored. Hence, they play an important role in mediating ommochrome functions. Ommochromasomes are part of the lysosome‐related organelles (LROs) family, which includes other pigmented organelles such as vertebrate melanosomes. Ommochromasomes are unique because they are the only LRO for which a recycling process during reversible colour change has been described. Herein, we provide an update on ommochrome biochemistry, photoreactivity and antiradical capacities to explain their diversity and behaviour both in vivo and in vitro. We also highlight new biochemical techniques, such as quantum chemistry, metabolomics and crystallography, which could lead to major advances in their chemical and functional characterisation. We then focus on ommochromasome structure and formation by drawing parallels with the well‐characterised melanosomes of vertebrates. The biochemical, genetic, cellular and microscopic tools that have been applied to melanosomes should provide important information on the ommochromasome life cycle. We propose LRO‐based models for ommochromasome biogenesis and recycling that could be tested in the future. Using the context of insect compound eyes, we finally emphasise the importance of an integrated approach in understanding the biological functions of ommochromes.     

Neuronal and glial cell biology

Here, we review progress in our understanding of neuronal and glial cell biology during the past ten years, with an emphasis on glial cell fate specification, apoptosis, the cytoskeleton, neuronal polarity, synaptic vesicle recycling and targeting, regulation of the cytoskeleton by extracellular signals, and neuron-glia interactions.     

Web alert: Neuronal and glial cell biology

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Neurobiology.     

Evolutionarily conserved concepts in glial cell biology

The evolutionary conservation of glial cells has been appreciated since Ramon y Cajal and Del Rio Hortega first described the morphological features of cells in the nervous system. We now appreciate that glial cells have essential roles throughout life in most nervous systems. The field of glial cell biology has grown exponentially in the last ten years. This new wealth of knowledge has been aided by seminal findings in non-mammalian model systems. Ultimately, such concepts help us to understand glia in mammalian nervous systems. Rather than summarizing the field of glial biology, I will first briefly introduce glia in non-mammalian models systems. Then, highlight seminal findings across the glial field that utilized non-mammalian model systems to advance our understanding of the mammalian nervous system. Finally, I will call attention to some recent findings that introduce new questions about glial cell biology that will be investigated for years to come.     

Proteomics in reproductive biology: Beacon for unraveling the molecular complexities

Proteomics, an interface of rapidly evolving advances in physics and biology, is rapidly developing and expanding its potential applications to molecular and cellular biology. Application of proteomics tools has contributed towards identification of relevant protein biomarkers that can potentially change the strategies for early diagnosis and treatment of several diseases. The emergence of powerful mass spectrometry-based proteomics technique has added a new dimension to the field of medical research in liver, heart diseases and certain forms of cancer. Most proteomics tools are also being used to study physiological and pathological events related to reproductive biology. There have been attempts to generate the proteomes of testes, sperm, seminal fluid, epididymis, oocyte, and endometrium from reproductive disease patients. Here, we have reviewed proteomics based investigations in humans over the last decade, which focus on delineating the mechanism underlying various reproductive events such as spermatogenesis, oogenesis, endometriosis, polycystic ovary syndrome, embryo development. The challenge is to harness new technologies like 2-DE, DIGE, MALDI-MS, SELDI-MS, MUDPIT, LC–MS etc., to a greater extent to develop widely applicable clinical tools in understanding molecular aspects of reproduction both in health and disease.     

Non-Darwinian and Darwinian prokaryotic and eukaryotic evolution--an enigma in cell biology conservation

Our theory is embarrassingly simple. What made today's prokaryotes and modern cyanobacteria so robust is the fact that in their origin, back in the Archean (3 billion years ago), selection did not play a central role in evolution, it had only a transitory role. Asexual reproduction, mutation, drift and sampling variance in local demes were more important especially when they were accompanied by population catastrophes, where millions perished. Metazoans are generally macroscopic, sexually reproducing, ecologically specialized organisms whose history is full of extinctions and radiations leading to morphological change. On the other hand, prokaryotes, thanks to their origin, avoid extinction because as a group they have slowly evolved as generalists. Specialization appears to be less important than ecological versatility and metabolic unspecialization. Modern cyanobacteria keep on using that strategy.     

nm23: unraveling its biological function in cell differentiation

Tumor suppressor genes have a pivotal role in normal cells regulating cell cycle processes negatively. Furthermore, the inhibition of cell proliferation is a crucial step in the achievement of cell differentiation. Increasing evidence suggests that the nm23 genes, initially documented as suppressors of the invasive phenotype in some cancer types, are involved in the control of normal development and differentiation. In this review, we summarize some data concerning the involvement of the nm23 genes in development and differentiation, attempting to delineate an overall view of many facets of their biological role.