Pax4 is not essential for beta-cell differentiation in zebrafish embryos but modulates alpha-cell generation by repressing arx gene expression

BMC Developmental Biology

Bernard Peers²  Marianne L Voz²  Isabelle Manfroid²  Silke Rinkwitz¹  Elisabeth Manning¹  Minaka Ishibashi¹  Jean Giacomotto¹  Vincianne Verbruggen²  Joachim Djiotsa² 

[1] From Developmental Neurobiology and Genomics, Brain and Mind Research Institute, University of Sydney, Camperdown, NSW, 2050, Australia;From Unit of Molecular Biology and Genetic Engineering, Giga-Research, University of Liège, 1 avenue de l'Hôpital B34, Sart-Tilman B-4000, Belgium

关键词: Zebrafish;    Development;    mRNA export;    Arx;    pax4;    Pancreas;    Glucagon;    Insulin;   

Others  :  1086290
DOI  :  10.1186/1471-213X-12-37

 received in 2012-04-04, accepted in 2012-12-14,  发布年份 2012

【 摘 要 】

Background

Genetic studies in mouse have demonstrated the crucial function of PAX4 in pancreatic cell differentiation. This transcription factor specifies β- and δ-cell fate at the expense of α-cell identity by repressing Arx gene expression and ectopic expression of PAX4 in α-cells is sufficient to convert them into β-cells. Surprisingly, no Pax4 orthologous gene can be found in chicken and Xenopus tropicalis raising the question of the function of pax4 gene in lower vertebrates such as in fish. In the present study, we have analyzed the expression and the function of the orthologous pax4 gene in zebrafish.

Results

pax4 gene is transiently expressed in the pancreas of zebrafish embryos and is mostly restricted to endocrine precursors as well as to some differentiating δ- and ε-cells but was not detected in differentiating β-cells. pax4 knock-down in zebrafish embryos caused a significant increase in α-cells number while having no apparent effect on β- and δ-cell differentiation. This rise of α-cells is due to an up-regulation of the Arx transcription factor. Conversely, knock-down of arx caused to a complete loss of α-cells and a concomitant increase of pax4 expression but had no effect on the number of β- and δ-cells. In addition to the mutual repression between Arx and Pax4, these two transcription factors negatively regulate the transcription of their own gene. Interestingly, disruption of pax4 RNA splicing or of arx RNA splicing by morpholinos targeting exon-intron junction sites caused a blockage of the altered transcripts in cell nuclei allowing an easy characterization of the arx- and pax4-deficient cells. Such analyses demonstrated that arx knock-down in zebrafish does not lead to a switch of cell fate, as reported in mouse, but rather blocks the cells in their differentiation process towards α-cells.

Conclusions

In zebrafish, pax4 is not required for the generation of the first β- and δ-cells deriving from the dorsal pancreatic bud, unlike its crucial role in the differentiation of these cell types in mouse. On the other hand, the mutual repression between Arx and Pax4 is observed in both mouse and zebrafish. These data suggests that the main original function of Pax4 during vertebrate evolution was to modulate the number of pancreatic α-cells and its role in β-cells differentiation appeared later in vertebrate evolution.

【 授权许可】

   
2012 Djiotsa et al.; licensee BioMed Central Ltd.

【 图 表 】

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