Turbellarian taxonomic database

Abstract / Notes

 "We investigated how planarians organize their left-right axis by using ectopic
grafting. Planarians have three body axes: anteroposterior (A-P), dorsoventral
(D-V), and left-right (L-R). When a small piece is implanted into an ectopic
region along the A-P and D-V axes, intercalary structures are always formed to
compensate for positional gaps. There are two hypotheses regarding L-R axis
formation in this organism: first, that the left and right sides of the animal
may be recognized as different parts, and L-R intercalation can induce midline
structures (asymmetry hypothesis); second, that both sides may have symmetrical
positional values, and mediolateral (M-L) intercalation creates positional
values along the L-R axis (symmetry hypothesis). We performed ectopic grafting
experiments in the head region of the planarian, Dugesia japonica, to examine
these hypotheses, A left lateral fragment containing a left auricle was
implanted into the medial region of the host. Ectopic structures were always
formed only on the left side of the graft, where lateral tissues abutted onto
the medial tissues. However, no morphologic change was induced on the right
side of the graft, where left-sided tissues faced onto right-sided tissues.
Molecular marker analyses indicated that ectopic structures formed on the left
side of the graft were induced by M-L intercalation, supporting the "symmetry
hypothesis." When the midline tissues were implanted into a lateral region,
they induced a complete ectopic head, demonstrating that M-L intercalation may
be sufficient to establish the L-R axis in planarians."

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