Die entstehung der sexualzellen bei den hydromedusen : zugleich ein Betrag zur Kenntniss des Baues und der Lebenserscheinungen dieser Gruppe / von August Weismann

Stem cell differentiation trajectories inHydraresolved at single-cell resolution

“…Since the neurons remained attached to the epithelia, differentially expressed genes between the ectodermal and endodermal samples included neuron-specific genes, and the presence of these genes allowed us to score our neuronal clusters as ectodermal or endodermal. We clearly identified three endodermal neuronal clusters (2,3,8) and nine ectodermal neuronal clusters (1,4-7,9,10,12,14) ( Fig. 6A, Fig.…”

“…Hydrozoans have fascinated biologists for hundreds of years and have been at the center of fundamental discoveries in developmental biology, including animal regeneration (1) and stem cells. In fact, hydrozoan stem cells were the first to be described (2,3). Among hydrozoans, stem cells and their differentiation pathways are best understood in the freshwater polyp Hydra, which have a relatively simple tissue structure and a small number of cell types.…”

Pluripotent Gametogenic Stem Cells of Asexually Reproducing Invertebrates

“…It was Weismann who determined that the germ cells of hydroids originate from the embryonic reserve of undifferentiated cells, and he did not associate the concept of germ cell line with the early isolation of this line (Weismann, 1892). Weismann has shown that the germ cells of hydroids differentiate not during embryonic development, but much later, in generations formed by budding (Knospen-Generationen: Weismann, 1883). The idea of early germ cell segregation and of the continuity of these cells in the sequence of generations was first of all formulated by Nussbaum (1880), who believed that interstitial cells of Hydra maintain the germline way.…”

“…It was later shown that the interstitial cells of hydroids, stem cells continuously undergoing the mitotic cycle, produce both germ cells and some types of somatic cells (see Bode, 1996;Bosch, 2008;Frank et al, 2009). Thus, hydroids, with their late specification of germline cells, differentiating from the interstitial cells during the entire lifespan of the colony and producing also somatic derivates, paradoxically became the main object of the studies that resulted in the emergence of the idea of early segregation of the totipotent germ cell line from somatic cells (Nussbaum, 1880), and to Weismann's "germ plasm" theory (Weismann, 1883(Weismann, , 1892(Weismann, , 1893. Weismann supposed that germ cells preserve all the factors of inheritance, whereas each somatic cell loses, in the course of differentiation, part of the germ plasm and of the initial potential of the egg (Weissman, 1892(Weissman, , 1893); Weismann's concept has been criticized in the light of modern biological data (see, e.g., Frank et al, 2009).…”

“…The problem of cell line having unlimited morphogenetic potential stems from A. Weismann' "germ plasm" theory. August Weismann (1834Weismann ( -1914 was the first to discover and describe metazoan stem cells (Stammzellen) and primary germ cells (UrKeimzellen) in the course of his detailed study of colonial hydroids (Weismann, 1883; see also Frank et al, 2009). According to Weismann (1892Weismann ( , 1893, stem cells, retaining the "germ plasm" (Keimplasma, the nuclear hereditary substance containing the determinants of germ cells), are capable of differentiating into gametes, providing for the continuity of the immortal germ line, the germline way (Keimbahn) and the continuation of life in the sequence of generations.…”