Regeneration of Tetrathyridia of Mesocestoides (Cestoda: Cyclophyllidea) In vivo and In vitro

Abstract

Fragments of tetrathyridia of the cestode Mesocestoides, bearing one or more suckers, can regenerate in vivo and axenically in vitro a normal tetrathyridium which is capable of both asexual proliferation and strobilization. Naturally occurring fragments lacking a scolex apparently cannot regenerate a scolex; with experimental fragments lacking a scolex similar results are usually obtained. Wound repair, restoration, and behavior of cut fragments are described. Among the invertebrates, regeneration is a relatively common phenomenon and is usually associated with the ability to reproduce asexually. Regeneration may be divided into two phases (Needham, 1952). Through the stimulus of wounding, a regressive phase is initiated which consists of wound closure, demolition of damaged cells, defense against infection and chemicals, and the determination of the cells utilized in the progressive phase of regrowth. The latter repair phase may be subdivided into blastema formation, its regrowth, and ultimate differentiation. Excellent reviews of the regeneration of invertebrates are found in the work of Needham (1952), Barth (1955), Brondsted (1955), Wolff (1961), Kiortsis and Trampusch (1965), and Hay (1966). While the classic example of regeneration is probably that of planaria, the extent of the ability of related, parasitic platyhelminths to regenerate is unknown. Attempts to demonstrate trematode regeneration in vivo (Manter, 1930; Sinitsin, 1932; Beaver, 1937; Fried and Penner, 1964) suggest that it is limited to wound repair only. An exception to this is the unsubstantiated observation of Senft and Weller (1956) who noted that four Schistosoma mansoni, lacking the posterior one-third to one-half part of the body, regenerated the missing structures in vitro. Studies on the sparganum of Spirometra mansonoides have demonstrated that scolexReceived for publication 15 December 1967. * Supported in part by U. S. Public Health Service Training Grant No. 2-T01-AI-00132-07. t Part of dissertation submitted to University of California, Los Angeles, California in partial fulfillment of the requirements for Ph.D. + Present address: Biology Department, Merrimack College, North Andover, Massachusetts 01845. bearing fragments occasionally retain their ability to strobilate when injected into mice (Mueller, 1938b) but fragments lacking the scolex cannot regenerate this region (Mueller, 1938a; Mueller and Coulston, 1941). Similarly, Joyeux and Baer (1939) noted that only the scolex-bearing fragments of pseudophyllid plerocercoids, which had fragmented, were able to regenerate. Goodchild (1958) investigated the ability of mutilated adult Hymenolepis diminuta to regenerate in vivo. As summarized in Figure 1, the asexual development of the tetrathyridia of Mesocestoides sp. is characterized by the proliferation of suckers and of excretory bladders along one side of the body and, subsequently, by the development of a longitudinal plane of separation (Specht and Voge, 1965; Hart, 1967). Fragments lacking suckers, the brain region, and associated cells of the scolex region are frequently encountered among tetrathyridia from liver digests and from the peritoneal cavity of the host. Whether these natural tail fragments are capable of regenerating a scolex is unknown. Since this organism can be easily propagated in vitro (Voge and Coulombe, 1966) and possesses a high capacity for asexual reproduction, it was a logical choice for experimental studies on regeneration. Media supporting only growth and maintenance, but not propagation, were employed. MATERIALS AND METHODS Employing sterile procedures, tetrathyridia were removed from the peritoneal cavity of Swiss Albino mice and placed in sterile 0.85% saline containing 600 units of penicillin and 600 ,ug of dihydrostreptomycin per ml. From this stock, approximately 50 organisms were transferred to a sterile disposable plastic petri dish containing the salineantibiotic mixture. Under a dissecting microscope, tetrathyridia with four suckers were transected