Body Muscle-Cell Differentiation from Coelomic Stem Cells in Colonial Tunicates

Abstract

Body muscle-cell differentiation was ultrastructurally examined in palleal buds of the colonial tunicate Symplegma reptans. Undifferentiated coelomic cells accumulate near the primordial oral siphon and associate with the basal lamina beneath the epidermis. They initially display the characteristics of hemoblast cells that have a large nucleus with a prominent nucleolus and narrow cytoplasm filled with polysomes. However, they soon become unique due to the development of an indented contour of the nucleus. When the basal lamina of the epidermis develops into the fibrous extracellular matrix (ECM), the muscle precursor cell has the deeply-notched nucleus, and thick and thin filaments in the cytoplasm facing the ECM. Collagen fibril-like structures appear in the ECM. Myofilaments are arranged with the ratio of thick to thin filaments being 1:2.5. Dense bodies and plaques become evident before the oral siphon is perforated. These results show that in S. reptans, the sphincter muscle cells arise from undifferentiated hemoblasts, and that their differentiation begins with a morphological change in their nuclei. Epidermal cells and/or the ECM may have an inductive effect on muscle cell differentiation.

Evolution of the chordate regeneration blastema: Differential gene expression and conserved role of notch signaling during siphon regeneration in the ascidian Ciona

“…The same or closely related cells were previously identified as hematogenic stem cells in Ciona and other solitary ascidians (Ermak, 1975; 1976). A subset of these hemocytes is also the precursor of body muscle cells in colonial ascidians (Berrill, 1941; Sugino et al, 2007). The stem cells of the branchial sac initiate proliferation in response to distal injuries and invade the wounded areas to form the blastema (Jeffery, 2015b).…”

Cell proliferation dynamics of somatic and germline tissues during zooidal life span in the colonial tunicateBotryllus primigenus

“…When they become associated with the epidermis, the nucleus becomes indented and myofilaments appear in the cytoplasm facing the epidermis (Sugino et al, 2007). Similarly, in B. primigenus, coelomic free cells were associated with the siphon anlagen (Fig.…”

“…During asexual reproduction, coelomic undifferentiated cells, the hemoblasts, differentiate into various tissues such as muscle cells, pyloric gland, germ cells, and multipotent epithelium (Mukai and Watanabe, 1976;Nunzi et al, 1979;Kawamura and Nakauchi, 1986a;Sunanaga et al, 2006Sunanaga et al, , 2007Sugino et al, 2007). In Symplegma reptans, hemoblasts cluster around the siphon anlagen of de- Outer and inner pharyngeal epithelia and inner longitudinal vessels were stained.…”

Regeneration, Stem Cells, and Aging in the Tunicate Ciona

“…Stem cells in lymph nodes are involved in the renewal of coelomic hemoblast cells (Ermak, 1975b;1976b), which are dispersed throughout the animal and have many different functions (De Leo et al, 1987;Satoh, 1994). In colonial ascidians, coelomic hemoblasts differentiate into body wall muscle (Sugino et al, 2007). Fourth, small clusters of stem cells are present in the siphon walls, where they are localized within or near the OPO regeneration bands (Fig.…”