Morphogenetic gradients in multiple‐graft Hydra viridis. I. The effects of colcemid and colchicine

Abstract

The morphogenesis of so-called secondary (2 degree) heads, budding regions and feet, and separations at graft borders, is studied in multiple-graft animals containing three gastric regions (3g animals) treated with Colcemid or colchicine. Control animals consist of three non-treated pieces. Animals consisting of two non-treated and one treated piece are also employed. The main effects of Colcemid are the promotion of graft healing at the distal graft border, and of 2 degree head formation on the proximal gastric region (g-1). Colchicine also promotes graft healing at the distal graft border, but in contrast to the effect of Colcemid, promotes the formation of ectopic feet (tertiary feet) and inhibits head regeneration at the distal end of the middle gastric region (g-2). Colchicine also accelerates an inversion of polarity in 2 degree budding regions on the g-2 pieces of animals with 2 degree heads on their g-1 pieces. Treatment of a distal graft piece with Colcemid promotes 2 degree head formation on the nearest proximal piece which is not treated, but the inhibition of 2 degree head formation by colchicine occurs only on colchicine treated pieces. The morphogenetic effects of the drugs are interpreted as consequences of their actions on nerve differentiation and cell division. The paper argues that homeostatic control of a hydra's cell population depends on dividing cells influencing cell loss, and that similar mechanisms are involved in the rejection of a graft and the separation of a bud.

Is Hydra an Alarm Clock?

“…The greater number of buds present on parents at cooler temperatures (first row) is consistent with buds taking longer to develop at cooler temperatures (third row down) [37]. Conceivably, fewer buds are initiated per day at colder temperatures (second row down) because these parents are growing slower or accumulating larger bud primordia.…”

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“…Epithelial cells involved in the bud's foot formation and bud detachment, however, would seem disconnected from the greater part of the bud module. Buds just beginning to develop on animals treated briefly with colchicine or Colcimid form double headed animals with one original head and one retained bud [47,48]. If the colchicine or Colcimid inhibited cell division in the bud rudiment, it would seem that epithelial cell division is required for foot development and detachment.…”

PATTERN REGULATION IN AUTOGRAFTS OFHYDRA OLIGACTIS: POSITIONAL VALUES AND DIFFUSABLE MORPHOGENS

“…The occurrence of the diffusable inhibitor of head formation, which exists as a gradient decreasing in the direction of the foot, was demonstrated in multiply-grafted Hydra viridis (Shostak, 1972(Shostak, , 1973Shostak and Adams, 1975). Significantly greater frequencies for secondary (2°) head regeneration were observed at graft borders located progressively farther from the terminal head in multiply-grafted animals with three tandemly arranged gastric regions (3g hydras).…”