Reference: Biol. Bull.. 158: 91-102. (February, 1980) ECDYSONE METABOLISM AND THE INTERRUPTION OF PROECDYSIS IN THE LAND CRAB, GECARC1NUS LATERALIS 1 JOHN F. MCCARTHY University of Tennessee. Oak Ridge Graduate School of Bioniedical Sciences, Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 In the brachyuran crabs, there is a complex interaction between limb regener-ation and the intermolt cycle. The majority of limb regeneration occurs during the premolt period of the intermolt cycle (proecdysis; stage D) during which the animal undergoes preparation for ecdysis. However, regeneration can, in turn, influence the progress of proecdysis : autotomy of limbs or partially regenerated limbs before a critical stage in proecdysis (stage Dj) results in a temporary suspen-sion of proecdysis while a new round of regeneration occurs at the sites of the missing limbs. During this suspension in stage D , not only is there a cessation of the growth of partial regenerates remaining on the crab (Holland and Skinner, 1976), but gastrolith deposition and the cytological activation of the epidermis are also delayed. This suspension of proecdysis is associated with a rapid decline of serum ecdysteroid titers from ~ 70 to ~ 15 ng/ml within a day of the autotomy; ecdysteroid titers remain low for two weeks while the recently autotomized limbs undergo basal regeneration. Titers then re-initiate their normal pattern of pro-ecdysial increases ; events which had been temporarily suspended resume develop-ment in association with the increased hormone titer so that the animal undergoes a normal, but delayed, ecdysis and releases a full compliment of regenerated limbs (McCarthy and Skinner, 1977b). This interaction between regeneration and the molt cycle suggests that changes in the titer of 20-hydroxyecdysone, the biologically active ecdysteroid, regulate the progress of proecdysial events ; and that the accepted paradigm of molt regula-tion (Passano, 1960), is incomplete, since these same interactions occur even in animals deprived of eyestalks, the source of the molt-inhibitory hormone (McCarthy and Skinner, 1977b). In this paper, the metabolic fate of ecdysone [a-ecdysone, the secretory product of the Y-organ (Chang and O'Connor, 1977)] is examined in animals in late stage DO either with or without the simultaneous autotomy of four partially regenerated limbs. The purposes of this study are: to support and extend our earlier studies on ecdysteroid metabolism in crabs in the intermolt (stage C 4 ; McCarthy and Skinner, 1979) and mid-to-late premolt (stages Dj to D 2 and stage D 3 ; McCarthy, in preparation) stages of the intermolt cycle; to examine the biochemical mechanisms by which the rapid decline in ecdysteroid titers is achieved following limb autotomy in stage D ; and to provide additional informa-tion on the nature of the regulatory mechanisms responsible for the interruption and re-initiation of proecdysis. 1 Research sponsored by the Division of Biomedical and Environmental Research, U. S. Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corporation. 91
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