Putative stem cells in the hemolymph and in the intestinal submucosa of the solitary ascidian Styela plicata

Juan Jiménez-Merino,Federico D. Brown,Isadora Santos de Abreu,Stefano Tiozzo,Silvana Allodi,Laurel S. Hiebert,Cintia M. De Barros

doi:10.1186/s13227-019-0144-3

Abstract

BackgroundIn various ascidian species, circulating stem cells have been documented to be involved in asexual reproduction and whole-body regeneration. Studies of these cell population(s) are mainly restricted to colonial species. Here, we investigate the occurrence of circulating stem cells in the solitary Styela plicata, a member of the Styelidae, a family with at least two independent origins of coloniality.ResultsUsing flow cytometry, we characterized a population of circulating putative stem cells (CPSCs) in S. plicata and determined two gates likely enriched with CPSCs based on morphology and aldehyde dehydrogenase (ALDH) activity. We found an ALDH + cell population with low granularity, suggesting a stem-like state. In an attempt to uncover putative CPSCs niches in S. plicata, we performed a histological survey for hemoblast-like cells, followed by immunohistochemistry with stem cell and proliferation markers. The intestinal submucosa (IS) showed high cellular proliferation levels and high frequency of undifferentiated cells and histological and ultrastructural analyses revealed the presence of hemoblast aggregations in the IS suggesting a possible niche. Finally, we document the first ontogenetic appearance of distinct metamorphic circulatory mesenchyme cells, which precedes the emergence of juvenile hemocytes.ConclusionsWe find CPSCs in the hemolymph of the solitary ascidian Styela plicata, presumably involved in the regenerative capacity of this species. The presence of proliferating and undifferentiated mesenchymal cells suggests IS as a possible niche.

Highlights

Most metazoans possess migratory cells within their bodies, referred to in coelomate animals as coelomocytes and/or hemocytes [1]
We found eight cell morphotypes that were previously described in S. plicata, as well as in other ascidians [5, 22, 25, 45, 46]: lymphocyte-like cells, hemoblasts, univacuolar refractile granulocytes, amoeboid granulocytes, compartment cells, univacuolar cells, morula cells, and pigment cells (Fig. 1a–x)
This size range and proportion of small cells in the hemolymph of Styela clava are very similar to the size range and proportion of small hemocytes we report here for S. plicata (3–6 μm in diameter and ~ 16.7%) and likely correspond to both small cell types combined, i.e., lymphocyte-like cells + hemoblasts

Summary

Introduction

Most metazoans possess migratory cells within their bodies, referred to in coelomate animals as coelomocytes and/or hemocytes [1]. The origin and function of circulating putative stem cells (CPSCs) have been described in ascidians of the subfamily Botryllinae (suborder: Stolidobranchia). In this group, multipotent cells in the hemolymph are progenitors of somatic tissues [9] and germline [10]. The differentiation potential of hemoblasts has been experimentally proven in colonies surgically reduced to the peripheral tunic with circulating vessels containing hemolymph [15,16,17] In these conditions, hemoblasts adhere to vessel walls and give rise to budlets, which mature into functional zooids [18, 19]. We investigate the occurrence of circulating stem cells in the solitary Styela plicata, a member of the Styelidae, a family with at least two independent origins of coloniality

Methods

Results

Conclusion