Tunic Cells Research Articles

Surgical fusion between incompatible colonies of the compound ascidian, Botrylloides fuscus

In the compound ascidian Botrylloides fuscus, allorecognition responses were observed at the colonial margin (natural growing edge) as necrotic reactions in the subcuticular region of the facing tunic. However, artificial cut surface contacts between incompatible colonies resulted in the formation of chimeras with common vascular systems, termed “surgical fusion.” The occurrence of surgical fusion in B. fuscus contrasts with rejection occurring under the same conditions in other botryllids. Together the two observations suggest that self-nonself recognition may be a specialized function of tunic cells and their precursors in the blood, and the fusion (vascular interconnection) is a different process than rejection with different effectors and recognition systems. In all pairwise combinations among 12 and 14 colonies, more than 60% of combinations resulted in fusion when colonies were assayed by growing edge contact. This rate of fusible combinations is much higher than those of the other botryllid ascidians previously studied.

Acquiring embryo-derived cell cultures and aseptic metamorphosis of larvae from the colonial protochordateBotryllus schlosseri

Summary The initiation of the first embryo-derived cell cultures and the establishment of in vitro metamorphosis from aseptic tadpole larvae are described in the cosmopolitan, shallow water colonial tunicate, Botryllus schlosseri. A total of more than 1,600 embryos, collected from different colonies at various stages of blastogenic cycles, were used in ten experiments (up to 350 embryos/experiment). Embryos were fully dissociated by mechanical or chemical treatments. In three experiments we succeeded in initiating continuous cell lines from embryonic tissue (designated NIO-BSE-1 to −3). Using different substrates and supplements, we found that embryonic cells cultured in botryllid cell culture medium (Rinkevich and Rabinowitz, 1993) supplemented with either chick embryo extract or heat inactivated Botrylloides hemolymph and on plastic or gelatin coated substrates may acquire cell-line characteristics. Tunic cells of maternal origin were found in all wells of primary cultures but subsequently disappeared. ...

Invertebrate cytokines: tunicate cell proliferation stimulated by an interleukin 1-like molecule.

Tunicate pharyngeal cells include lymphocyte-like cells and granular amoebocytes. They are involved in the specific allogeneic and phagocytic reactions of tunicates. Little is known about their regulation or control. A tunicate interleukin 1 (IL-1)-like fraction is shown to stimulate the proliferation of these cells in vitro. This fraction, designated tunicate IL-1 beta, was isolated from tunicate hemolymph by gel filtration and chromatofocusing chromatography. Mitogenic responses to tunicate IL-1 beta were dose dependent and could be eliminated rapidly by removing tunicate IL-1 beta from culture medium. A second tunicate hemolymph fraction had no effect on tunicate cell proliferation even though it exhibited IL-1-like activity in a mouse thymocyte proliferation assay. Phytohemagglutin did not act synergistically with either fraction. These data are discussed in terms of the function and evolution of IL-1-like molecules in invertebrates.

The Intrinsic Origin of Bioluminescence in the Ascidian,Clavelina miniata

Bioluminescence was observed in the ascidian, Clavelina miniata (Tunicata: Ascidiacea). This is the first report of luminescence in ascidians. A green light was evoked by mechanical stimulation, by increasing the concentration of K+ ions, or by hypotonic conditions. The source of the light was a type of tunic cell (cell type II). This luminescence is attributed to an intrinsic system, not to bacterial symbionts.

Intracellular acidity in the ascidian

1. 1. Morula cells of three Ascidiidae and two Perophoridae from the suborder Phlebobranchia, and one Holozoidae and one Clavelinidae from the suborder Aplousobranchia were acidic to neutral red; where methyl red was used, the stain corresponded to pH values between 4.6 and 6.0 depending on species. Five Didemnids (Aplousobranchia), and two Pyuridae, two Styelidae, and one Molgulidae (Stolidobranchia) had neutral morula cells. All compartment cells were neutral. 2. 2. Phosphorus-31 NMR spectrum of blood cells of Pyura stolonifera (Stolidobranchia) had P i signals corresponding to pH 6.4 and 6.1, probably from phosphate within the globules and cytoplasm of the morula cells. The 31P NMR spectra of whole colonies of Diplosoma similis and Diplosoma virens had signals corresponding to P i at pH values of 5.58 and 5.65. 3. 3. In Phlebobranchia, acid released by vanadocytes upon lysis could not be accounted for solely by the hydrolysis of V(III) and Fe(III), but within the vanadocytes the pH is too high for the metals to be in hydrated forms. 4. 4. Tunic acid was examined. The tunic cells of many species of Aplousobranchia and Phlebobranchia released acid on lysis but the intact cells were neutral.

AGGREGATION AND FUSION BETWEEN CONSPECIFICS OF A SOLITARY ASCIDIAN

Fusion between conspecifics in a solitary ascidian is reported for the first time. Molgula complanata Alder and Hancock showed aggregated settlement on Perspex panels in the field, allowing contact between conspecifics after some increase in size. Histological sections of adult animals which were in contact with one or more conspecifics showed that some individuals were fused to others. The frequency of fusion between contacting specimens was 20%. The outer membranes of the tunics were absent between fused animals but present in unfused ones. Fusion was thus characterized by contiguous matrices, which contained cellular elements. No barrier to interchange of tunic cells between fused animals was observed. It is suggested that fusion may oppose inbreeding in hermaphroditic, viviparous ascidians with minimal dispersal.