The Pax6b homeodomain is dispensable for pancreatic endocrine cell differentiation in zebrafish.
Pax6 is a well conserved transcription factor that contains two DNA-binding domains, a paired domain and a homeodomain, and plays a key role in the development of eye, brain, and pancreas in vertebrates. The recent identification of the zebrafish sunrise mutant, harboring a mutation in the pax6b homeobox and presenting eye abnormalities but no obvious pancreatic defects, raised a question about the role of pax6b in zebrafish pancreas. We show here that pax6b does play an essential role in pancreatic endocrine cell differentiation, as revealed by the phenotype of a novel zebrafish pax6b null mutant and of embryos injected with pax6b morpholinos. Pax6b-depleted embryos have almost no beta cells, a strongly reduced number of delta cells, and a significant increase of epsilon cells. Through the use of various morpholinos targeting intron-exon junctions, pax6b RNA splicing was perturbed at several sites, leading either to retention of intronic sequences or to deletion of exonic sequences in the pax6b transcript. By this strategy, we show that deletion of the Pax6b homeodomain in zebrafish embryos does not disturb pancreas development, whereas lens formation is strongly affected. These data thus provide the explanation for the lack of pancreatic defects in the sunrise pax6b mutants. In addition, partial reduction of Pax6b function in zebrafish embryos performed by injection of small amounts of pax6b morpholinos caused a clear rise in alpha cell number and in glucagon expression, emphasizing the importance of the fine tuning of the Pax6b level to its biological activity.
Verbruggen
Vincianne
V
Unit of Molecular Biology and Genetic Engineering, University of Liège, GIGA-R, B34, Avenue de l'Hôpital 1, B-4000 Liège, Belgium.
Ek
Olivier
O
Georlette
Daphné
D
Delporte
François
F
Von Berg
Virginie
V
Detry
Nathalie
N
Biemar
Frédéric
F
Coutinho
Pedro
P
Martial
Joseph A
JA
Voz
Marianne L
ML
Manfroid
Isabelle
I
Peers
Bernard
B
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D055098:Endocrine Cells / Q000166:cytology / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D005934:Glucagon / Q000096:biosynthesis / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010179:Pancreas / Q000166:cytology / Q000196:embryology*; D012326:RNA Splicing / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D029961:Zebrafish Proteins; D005934:Glucagon