In Search of Darwin's Imaginary Gemmules

Nucleus-independent transgenerational small RNA inheritance in Caenorhabditis elegans

In Caenorhabditis elegans worms, epigenetic information transmits transgenerationally. Still, it is unknown whether the effects transfer to the next generation inside or outside of the nucleus. Here, we use the tractability of gene-specific double-stranded RNA-induced silencing to demonstrate that RNA interference can be inherited independently of any nuclear factors via mothers that are genetically engineered to transmit only their ooplasm but not the oocytes' nuclei to the next generation. We characterize the mechanisms and, using RNA sequencing, chimeric worms, and sequence polymorphism between different isolates, identify endogenous small RNAs which, similarly to exogenous siRNAs, are inherited in a nucleus-independent manner. From a historical perspective, these results might be regarded as partial vindication of discredited cytoplasmic inheritance theories from the 19th century, such as Darwin's "pangenesis" theory.

Elevated brain-derived cell-free DNA among patients with first psychotic episode - a proof-of-concept study

Schizophrenia is a common, severe, and debilitating psychiatric disorder. Despite extensive research there is as yet no biological marker that can aid in its diagnosis and course prediction. This precludes early detection and intervention. Imaging studies suggest brain volume loss around the onset and over the first few years of schizophrenia, and apoptosis has been proposed as the underlying mechanism. Cell-free DNA (cfDNA) fragments are released into the bloodstream following cell death. Tissue-specific methylation patterns allow the identification of the tissue origins of cfDNA. We developed a cocktail of brain-specific DNA methylation markers, and used it to assess the presence of brain-derived cfDNA in the plasma of patients with a first psychotic episode. We detected significantly elevated neuron- (p=0.0013), astrocyte- (p=0.0016), oligodendrocyte- (p=0.0129), and whole brain-derived (p=0.0012) cfDNA in the plasma of patients during their first psychotic episode (n=29), compared with healthy controls (n=31). Increased cfDNA levels were not correlated with psychotropic medications use. Area under the curve (AUC) was 0.77, with 65% sensitivity at 90% specificity in patients with a psychotic episode. Potential interpretations of these findings include increased brain cell death, disruption of the blood-brain barrier, or a defect in clearance of material from dying brain cells. Brain-specific cfDNA methylation markers can potentially assist early detection and monitoring of schizophrenia and thus allow early intervention and adequate therapy.

The N-space Episenome unifies cellular information space-time within cognition-based evolution

Self-referential cellular homeostasis is maintained by the measured assessment of both internal status and external conditions based within an integrated cellular information field. This cellular field attachment to biologic information space-time coordinates environmental inputs by connecting the cellular senome, as the sum of the sensory experiences of the cell, with its genome and epigenome. In multicellular organisms, individual cellular information fields aggregate into a collective information architectural matrix, termed a N-space Episenome, that enables mutualized organism-wide information management. It is hypothesized that biological organization represents a dual heritable system constituted by both its biological materiality and a conjoining N-space Episenome. It is further proposed that morphogenesis derives from reciprocations between these inter-related facets to yield coordinated multicellular growth and development. The N-space Episenome is conceived as a whole cell informational projection that is heritable, transferable via cell division and essential for the synchronous integration of the diverse self-referential cells that constitute holobionts.

The Criticisms of Pangenesis: The Years of Controversy

When first published in 1868, Darwin's Pangenesis was almost uniformly rejected by his contemporaries. Until recently it has still been regarded as Darwin's biggest mistake or a brilliant blunder. There are three main reasons for this. First, Galton transfused the blood of one variety of rabbit into another, and then bred together the latter. The results of breeding showed no variations of characters in the offspring. Thus he concluded that Darwin's Pangenesis was incorrect. Second, there was no direct evidence for the existence of Darwin's imaginary gemmules. Third, Darwin's Pangenesis explained the Lamarckian inheritance of acquired characters, graft hybridization, xenia and telegony, which were largely thought to be doubtful phenomena. Now the discoveries of circulating cell-free DNA, mobile RNAs, prions and extracellular vesicles provide striking evidence for the chemical existence of Darwin's supposed gemmules. There is also convincing evidence for heritable changes induced by blood transfusion in which Galton failed to find such effects in his experiment. Moreover, there is increasing evidence for the inheritance of acquired characters, graft hybridization, xenia and other phenomena that Pangenesis was designed to explain. In light of the mounting evidence, it is not proper to continue to consider Pangenesis as Darwin's biggest mistake or a brilliant blunder.

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!"

The Influence of Darwin's Pangenesis on Later Theories

Although Darwin's Pangenesis received strong criticism and never gained any very wide acceptance, it was of great importance due to its stimulating effect on later work and thought. Nearly every major theory of heredity developed in the late 19th century began with a discussion of Darwin's Pangenesis. Darwin was shown to play a more important role in the history of genetics than hitherto attributed to him by historians through a detailed analysis of the influence of his Pangenesis on de Vries' "Intracellular Pangenesis" and "The Mutation Theory," Weismann's theory of "Continuity of the Germ-plasm," Galton's "A Theory of Heredity" and "Natural Inheritance," Brooks' "The Law of Heredity, Ross's "Graft Theory of Diseases", Haeckel's perigenesis and Kozo-Polyansky's hypothetical version of symbiogenesis. Without Darwin's Pangenesis they would not have the foundation on which they formulated. By comparing these theories, it may be concluded that Darwin's Pangenesis combines all advantages of its sister-theories, and is more valuable, comprehensive and convincing than any other genetical theories yet advanced.