Inductive role of the nerve cord in regeneration of isolated postpharyngeal body sections of Dugesia dorotocephala

Abstract

Lateral cordless fragments isolated from the postpharyngeal section of Dugesia dorotocephala formed a large normal head at a 90" angle to the original antero-posterior polarity; postcerebrally, only a hump of undifferentiated tissue developed. This "head-hump'' pattern, and also other types observed in previous studies of lateral fragments, were attributed to the absence of the nerve cord. In order to confirm the inductive role of the nerve cord and to eliminate the possibility that the "head-hump syndrome" was due to the relative proportions of other tissues besides nerve, body fragments of two experimental groups were observed: (1) the five types of fragments which had no nerve cord but had varying proportions of other tissues present formed primarily "head-hump" types of regenerates.(2) Almost all fragments which had varying amounts of nerve cord present but the same proportions of other tissues formed regenerates of normal body proportions. Therefore, the absence of the nerve cord does determine the "head-hump syndrome."Isolated postpharyngeal half segments containing one nerve cord were allowed to regenerate for varying periods of time before the lateral cordless fragment was isolated. The number of "head-hump'' regenerates from lateral fragments isolated after a one-day or longer contact with the nerve cord gradually decreased, and the number of regenerates with incomplete head development or which were more elongated postcerebrally increased. These results indicate that the nerve cord acts gradually to determine the differentiation of specific tissues rather than rapidly to determine the overall body plan.

Regenerating the central nervous system: how easy for planarians!

“…Later, Lender and Gripon (1962) found that the retardation of eye formation because of the shorter nerve cord was only 24 h, but they nevertheless observed a delay. Sperry et al (1973) showed that lateral pieces with no VNC give rise to "head-hump" regenerates, which have an abnormally large head with no differentiation of post-cephalic structures. They suggested a head-inhibiting influence of the nerve cords during regeneration.…”

Regeneration and Growth as Modes of Adult Development: The Platyhelminthes as a Case Study

“…Some classical studies have reported that regeneration is inhibited by removal of the nervous system in planarians such as Leptoplana , Dendrocoelum , and Bdellocephala (Child 1904a , b ;Morgan 1905 ). In Dugesia dorotocephala , lateral pieces with no ventral nerve cord give rise to 'headbump' regenerates: an abnormally large head with no differentiation of post-cephalic structures (Sperry et al 1973 ). However, in other species, lateral pieces with no ventral nerve cord can regenerate a head (Morgan 1898(Morgan , 1900.…”

Effect of timing of cutting on patterning and proportion regulation during regeneration of the planarian Dugesia tigrina

“…This study centered on those abnormal animals with excess head structures, i.e., with two heads or a relatively large head but without a pharynx. Such abnormalities have been well documented (see Morgan, 1889Morgan, ,1902aMorgan, , 1902bSperry et al, 1973). Calculation of regression and statistical parameters was performed as Mead (1985) and Mead & Krump (1986) described.…”