Recent key findings have stimulated the debate about the division mode of adult stem cells and raise the question as to whether there is an ancestral (asymmetric) and/or derived (symmetric) mode of stem cell progression in mammals in particular and vertebrates in general. An answer to this question could shed light on the interplay between the presence of stem cells and the formation of tumours: adult stem cells with self-renewing properties are crucial for tissue homeostasis and have properties which closely resemble those of tumour cells.
Recently, a stochastic model of symmetrical stem cell division followed by neutral drift has been proposed for intestinal stem cells (ISCs), which has been suggested to represent the predominant mode of stem cell progression in mammals. In contrast, stem cells in the retina of teleost fish show an asymmetric division mode. This suggests that independent of the phylogenetic position of the organism, stem cells could divide by symmetric or asymmetric division in a niche-specific manner.
To ascertain the mode of stem cell division in the fish intestine, scientists working in the framework of the X-Regio project have analyzed the medaka intestine by high-resolution X-ray microcomputed tomography (microCT) and combined the histological and gene expression analysis with the lineage tracing tools. This study shows a preferential symmetric division mode of medaka ISCs, which is in clear contrast to the fish retina, indicating the mode of stem cell division is not a species-specific feature, but rather characteristic for the type of stem cell niche and the function of the niche in tissue growth and/or homeostasis.
Narges Aghaallaei, Franziska Gruhl, Colin Q. Schaefer, Tobias Wernet, Venera Weinhardt, Lázaro Centanin, Felix Loosli, Tilo Baumbach and Joachim Wittbrodt: Identification, visualization and clonal analysis of intestinal stem cells in fish , Development (Cambridge), 143 (19) 3470 - 3480