The first embryo, the origin of cancer and animal phylogeny. I. A presentation of the neoplastic process and its connection with cell fusion and germline formation

Abstract

The decisive role of Embryology in understanding the evolution of animal forms is founded and deeply rooted in the history of science. It is recognized that the emergence of multicellularity would not have been possible without the formation of the first embryo. We speculate that biophysical phenomena and the surrounding environment of the Ediacaran ocean were instrumental in co-opting a neoplastic functional module (NFM) within the nucleus of the first zygote. Thus, the neoplastic process, understood here as a biological phenomenon with profound embryologic implications, served as the evolutionary engine that favored the formation of the first embryo and cancerous diseases and allowed to coherently create and recreate body shapes in different animal groups during evolution. In this article, we provide a deep reflection on the Physics of the first embryogenesis and its contribution to the exaptation of additional NFM components, such as the extracellular matrix. Knowledge of NFM components, structure, dynamics, and origin advances our understanding of the numerous possibilities and different innovations that embryos have undergone to create animal forms via Neoplasia during evolutionary radiation. The developmental pathways of Neoplasia have their origins in ctenophores and were consolidated in mammals and other apical groups.

Keywords: cancer; co-option; embryology; evolution; evolutionary radiation; metazoa; neoplasia; unicellular holozoa.

FIGURE 1

General scheme of the neoplastic functional module. Chromosomal domains were associated topologically by the physical impact of embryo construction. The projected points and lines of the geometric figures represent the impact of embryonic morphogenesis on the cell nucleus. The cells depicted in the figure are multipotent cells that receive most of the biophysical impact promoting embryo patterning. Neoplasia is the driving force of embryo formation. The disease cancer is imbued in embryo construction and masked by its organization. The last cell of the scheme is one of the 2 cells of the hermaphroditic germ line of the first embryo, which harbors the neoplastic functional module and mechanical memory, elements that contribute to the reconstruction of the process in the following generation. Emergence of animal phylogeny, cancer, and the first embryo is implicit in the events represented in this diagram.

FIGURE 2

Zygotic meiosis and its modifications in sexual reproduction. (A) The zygote divides by meiosis to produce a vegetative cell. (B) Gamonts are produced by mitosis of vegetative cells. (C) A coenocytic-like division can produce two haploid nuclei that, by autogamy, produce a zygote. In this case, the modification lies in the omission of cell division (also known as endomitosis). Autogamy and fertilization can produce a zygote. (D) A further simplification (which can scarcely still be considered “normal”) consists in the total omission of nuclear division. What remains is the reduplication of chromosomes without spindle formation, characterizing a case of endomitosis. Endomitosis allows the formation of a diploid cell. (E) Through (reverse) endomitosis, it is also possible to reduce polyploidy. Figure adapted from Grell (1973).