Forkhead containing transcription factor Albino controls tetrapyrrole-based body pigmentation in planarian

Abstract

Pigmentation processes occur from invertebrates to mammals. Owing to the complexity of the pigmentary system, in vivo animal models for pigmentation study are limited. Planarians are capable of regenerating any missing part including the dark-brown pigments, providing a promising model for pigmentation study. However, the molecular mechanism of planarian body pigmentation is poorly understood. We found in an RNA interference screen that a forkhead containing transcription factor, Albino, was required for pigmentation without affecting survival or other regeneration processes. In addition, the body color recovered after termination of Albino double stranded RNA feeding owing to the robust stem cell system. Further expression analysis revealed a spatial and temporal correlation between Albino and pigmentation process. Gene expression arrays revealed that the expression of three tetrapyrrole biosynthesis enzymes, ALAD, ALAS and PBGD, was impaired upon Albino RNA interference. RNA interference of PBGD led to a similar albinism phenotype caused by Albino RNA interference. Moreover, PBGD was specifically expressed in pigment cells and can serve as a pigment cell molecular marker. Our results revealed that Albino controls planarian body color pigmentation dominantly via regulating tetrapyrrole biogenesis. These results identified Albino as the key regulator of the tetrapyrrole-based planarian body pigmentation, suggesting a role of Albino during stem cell-pigment cell fate decision and provided new insights into porphyria pathogenesis.

FOX and ETS family transcription factors regulate the pigment cell lineage in planarians

“…In total, 436 transcripts were found to decrease by ≥2-fold with depigmentation (Table S1), 75 of which were cloned and screened by whole-mount in situ hybridization (WISH) ( Fig. S1) for patterns consistent with pigment cell-specific or enriched expression (Stubenhaus et al, 2016;Wang et al, 2016). From this screen, two classes of pigment cell markers were identified.…”

“…Biochemical and genetic evidence indicate that the body pigment in Schmidtea mediterranea is composed of ommochromes and cyclic tetrapyrroles called porphyrins (Hase et al, 2006;Stubenhaus et al, 2016). Enzymes in the ommochrome and porphyrin biosynthesis pathways are expressed in a candidate pigment cell population that is highly dendritic in morphology, and RNAi knockdown of some of these genes led to white animals (Stubenhaus et al, 2016;Wang et al, 2016). Porphyrins react with oxygen to form free radicals when exposed to light.…”

Dark pigmentation limits thermal niche position in birds

“…The universal, most common mechanism is the production of melanin pigments, whose broadband absorption properties keep the cells from being directly exposed to UV (Brenner & Hearing, 2008). This means that the external body surface of organisms from all taxonomic groups is coated with melanins (Wang et al, 2016).…”

Raman spectroscopy quantification of eumelanin subunits in natural unaltered pigments

“…Melanins are pigments found in virtually all organisms, from bacteria to humans (Wang et al., ). This biological ubiquity is mainly due to the essential role fulfilled by the nonsulphurated form of melanin, termed eumelanin, in protection from the mutagenic effects of solar ultraviolet (UV) radiation (Brenner & Hearing, ).…”