Which mutant hydra has defects in budding due to excessive head inhibition signals?
L4 mutant was isolated in Hydra vulgaris screens searching for budding pattern defects. Phenotypically L4 shows scarce budding, increased bud spacing, and prolonged head inhibition field where existing head prevents nearby secondary heads or buds. Molecularly, enhanced production or range of head inhibition signal likely involving Wnt antagonist Sp5 spreading from hypostome organizer suppresses new axes. Wnt3 mutants lack heads, SHH absent in cnidarians, Notum overexpression differs. L4 demonstrates importance of long-range inhibition ensuring single dominant organizer and properly spaced asexual reproduction maintaining body plan polarity.
Ref: Development, Hydra L4 mutant - excessive head inhibition signals disrupt budding and patterning.