Figure 7.

Albino mediates neoblast-pigment cell differentiation. (a) Double FISH for smedwi-1 with Albino at different times of regeneration showing that smedwi-1 and Albino colocalize at the blastema during regeneration. Scale bar: 20 μm. Yellow circles indicate double-positive cells, whereas red and green circles indicate Albino and smedwi-1 single-positive cells, respectively. Images are single confocal sections. (b) Quantification of smedwi-1 and Albino double-positive cells. Cells in 0.1 mm² were counted in three independent experiments. Error bar=s.d.; *P<0.0001; significance determined with Student’s t-test. (c) Cartoon illustrates that Albino controls the expression of PBGD, and smedwi-1-positive neoblasts initially specialize into smedwi-1 and Albino double-positive cells and then fully differentiate into pigment cells expressing Albino and PBGD. During regeneration, Albino-expressing neoblasts accumulate in the blastema at 3 dpa and initiate the expression of tetrapyrrole biogenesis enzymes. The Albino and PBGD double-positive cells accumulate within blastema since 7 dpa, and finally these cells generate tetrapyrroles that get the planarians pigmented.