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Characterization of the head organizer in hydra

Developmental Biology Center and Department of Developmental and Cell Biology, University of California, Irvine, California 92697, USA

View larger version (28K): [in a new window]   Fig. 1. Induction capacity of the three apical regions (hypostome, the tentacle zone and the 1-region) as measured by transplantation. (A) The procedure for the hypostome and 1-region, and (B) the results of the procedure. The number of epithelial cells per region is the average of three measurements. The value for the tentacle zone is 1300±190. Values for one-quarter regions are calculated from the measurements for the whole region. For the one-quarter tentacle zone, several axes derived from donor had a single apical tentacle instead of a complete head. All values are ±s.e.m.

View larger version (84K): [in a new window]   Fig. 2. Formation of second axes following transplantation. (A) Induction of a second axis by hypostomal tissue; (B) self-organization of a second axis by 1-region tissue. The host was labeled with India Ink.

View larger version (16K): [in a new window]   Fig. 3. Induction of a second axis using a hypostome-contact graft. (A) Graft procedure. (B) Increase in the fraction of second axes formed with increasing time of hypostome contact. The number of grafts/time point was 14-32.

View larger version (59K): [in a new window]   Fig. 4. Process of second axis formation in a hypostome-contact graft. (A) Seventy-two hour graft with an emerging second axis. (B) One hundred and twenty hour graft with tentacles forming at the apical end of the emerging second axis. In both A,B, the India Ink stained donor tissue (black dots) is on the left with the arrowheads indicating the border between donor and host. The arrows in A,B indicate emerging (A) or developing (B) tentacles. Samples in A,B were stained with the TS-19 antibody to identify the emerging and developing tentacles (Bode et al., 1988). (C) An induced second axis (head and body column facing left) after removal of the inducing donor tissue. The donor (on the left in A,B) was labeled with India Ink while the host was labeled in C. Arrowheads indicate the border between donor and host, and arrows indicate emerging or developing tentacles.

View larger version (22K): [in a new window]   Fig. 5. Induction capacity of three apical regions as measured with a contact graft. (A) Diagram and (B) results of the grafting procedure.

View larger version (19K): [in a new window]   Fig. 6. Effect of LiCl treatment on the ability of the hypostome and 1-region to form a second axis upon transplantation. (A) Diagram and (B) results of the procedure. The number of grafts/time point was 15-32.

View larger version (17K): [in a new window]   Fig. 7. Effect of LiCl treatment on the induction of a second axis in a hypostome-contact graft. (A) Diagram and (B) results of the two grafting procedures.

View larger version (19K): [in a new window]   Fig. 8. Effect of head inhibition on the activity of the inducing signal. (A) Diagram and (B) results of the grafting procedure. The number of grafts/time point was 11-32.

View larger version (19K): [in a new window]   Fig. 9. Effect of the presence of the donor hypostome on HyBra1 expression in the induced second axis. (A) Diagram and (B) results of the grafting procedure.

View larger version (55K): [in a new window]   Fig. 10. Development of HyBra1 expression with time in host tissue after end of contact with a donor hypostome.

View larger version (21K): [in a new window]   Fig. 11. Effect of the presence of the donor hypostome on the ability of the apical end of the induced second axis to form another axis upon transplantation. (A) Diagram and (B) results of the grafting procedure.

View larger version (16K): [in a new window]   Fig. 12. Axial distribution of inductive capacity and the self-organizing capacity.