Spontaneous self-assembly of DNA fragments into nucleus-like structures from yolk granules of fertilized chicken eggs: Antoine Béchamp meets Bong Han Kim via Olga Lepeshinskaya

Open questions on the functional biology of the yolk granules during embryo development

Biogenesis and consumption of the yolk are well-conserved aspects of the reproductive biology in oviparous species. Most egg-laying animals accumulate yolk proteins within the oocytes thus creating the source of nutrients and energy that will feed embryo development. Yolk accumulation drives the generation of a highly specialized oocyte cytoplasm with maternal mRNAs, ribosomes, mitochondria, and, mainly, a set of organelles collectively referred to as yolk granules (Ygs). Following fertilization, the Ygs are involved in regulated mechanisms of yolk degradation to fuel the anabolic metabolism of the growing embryo. Thus, yolk accumulation and degradation are essential processes that allow successful development in many species. Nevertheless, the molecular machinery and mechanisms dedicated to the programmed yolk mobilization throughout development are still enigmatic and remain mostly unexplored. Moreover, while the Ygs functional biology as a nutritional source for the embryo has been acknowledged, several reports have suggested that Ygs cargoes and functions go far beyond yolk storage. Evidence of the role of Ygs in gene expression, microbiota harboring, and paracrine signaling has been proposed. In this study, we summarize the current knowledge of the Ygs functional biology pointing to open questions and where further investigation is needed.

Darwin's Pangenesis: A Theory of Everything?

This chapter briefly discusses Darwin's The Origin of Species and its companion volume The Variation of Animals and Plants under Domestication. It is in the second great book that Darwin took a broad survey of the whole range of variation and heredity, and developed his Pangenesis, an expanded cell theory and a unified genetical theory that would strengthen his theory of evolution and explains the numerous phenomena of life. The essential assumption of Pangenesis is the existence of inherited particles or molecules called gemmules, and their production by cells at each stage of development. He assumed that besides the ordinary cellular division, cells could also "throw off" numerous and minute gemmules, which were capable of self-replication and dormancy, diffusion from cell to cell or circulation through the body, modification by the effects of use and disuse or environmental changes, union with nascent cells, aggregation into buds and germ cells, and transmission from parent to offspring. By his Pangenesis, Darwin not only explained the general phenomena pertaining to inheritance, variation, development and reproduction, but also the inheritance of acquired characters, prepotency, graft hybridization, reversion, regeneration, xenia, telegony, transposition, sex-linked inheritance, the inheritance and non-inheritance of mutilation, and many other facts. Darwin called Pangenesis his "beloved child", and firmly believed that it "will turn out true some day!"

Evidence for novel age-dependent network structures as a putative primo vascular network in the dura mater of the rat brain

With chromium-hematoxylin staining, we found evidence for the existence of novel age-dependent network structures in the dura mater of rat brains. Under stereomicroscopy, we noticed that chromium-hematoxylin-stained threadlike structures, which were barely observable in 1-week-old rats, were networked in specific areas of the brain, for example, the lateral lobes and the cerebella, in 4-week-old rats. In 7-week-old rats, those structures were found to have become larger and better networked. With phase contrast microscopy, we found that in 1-week-old rats, chromium-hematoxylin-stained granules were scattered in the same areas of the brain in which the network structures would later be observed in the 4- and 7-week-old rats. Such age-dependent network structures were examined by using optical and transmission electron microscopy, and the following results were obtained. The scattered granules fused into networks with increasing age. Cross-sections of the age-dependent network structures demonstrated heavily-stained basophilic substructures. Transmission electron microscopy revealed the basophilic substructures to be clusters with high electron densities consisting of nanosized particles. We report these data as evidence for the existence of age-dependent network structures in the dura mater, we discuss their putative functions of age-dependent network structures beyond the general concept of the dura mater as a supporting matrix.