B1 SOX Coordinate Cell Specification with Patterning and Morphogenesis in the Early Zebrafish Embryo

Yuichi Okuda,Yusuke Kamachi,Eri Ogura,Hisato Kondoh,Veronica Van Heyningen

doi:10.1371/journal.pgen.1000936

Abstract

The B1 SOX transcription factors SOX1/2/3/19 have been implicated in various processes of early embryogenesis. However, their regulatory functions in stages from the blastula to early neurula remain largely unknown, primarily because loss-of-function studies have not been informative to date. In our present study, we systematically knocked down the B1 sox genes in zebrafish. Only the quadruple knockdown of the four B1 sox genes sox2/3/19a/19b resulted in very severe developmental abnormalities, confirming that the B1 sox genes are functionally redundant. We characterized the sox2/3/19a/19b quadruple knockdown embryos in detail by examining the changes in gene expression through in situ hybridization, RT–PCR, and microarray analyses. Importantly, these phenotypic analyses revealed that the B1 SOX proteins regulate the following distinct processes: (1) early dorsoventral patterning by controlling bmp2b/7; (2) gastrulation movements via the regulation of pcdh18a/18b and wnt11, a non-canonical Wnt ligand gene; (3) neural differentiation by regulating the Hes-class bHLH gene her3 and the proneural-class bHLH genes neurog1 (positively) and ascl1a (negatively), and regional transcription factor genes, e.g., hesx1, zic1, and rx3; and (4) neural patterning by regulating signaling pathway genes, cyp26a1 in RA signaling, oep in Nodal signaling, shh, and mdkb. Chromatin immunoprecipitation analysis of the her3, hesx1, neurog1, pcdh18a, and cyp26a1 genes further suggests a direct regulation of these genes by B1 SOX. We also found an interesting overlap between the early phenotypes of the B1 sox quadruple knockdown embryos and the maternal-zygotic spg embryos that are devoid of pou5f1 activity. These findings indicate that the B1 SOX proteins control a wide range of developmental regulators in the early embryo through partnering in part with Pou5f1 and possibly with other factors, and suggest that the B1 sox functions are central to coordinating cell fate specification with patterning and morphogenetic processes occurring in the early embryo.

Highlights

The developing embryo must control gene expression to coordinate various embryonic processes such as cell fate specification, embryo patterning and morphogenesis
We found that the activity of the B1 sox genes is required for the expression of a wide range of developmental regulators including transcription factors, signaling pathway components, and cell adhesion molecules
These findings suggest that the B1 sox functions are central to coordinating diverse embryonic processes, those that occur during the development of the primordium of the central nervous system

Summary

Introduction

The developing embryo must control gene expression to coordinate various embryonic processes such as cell fate specification, embryo patterning and morphogenesis. The group B1 SOX transcription factors are good candidates as coordinators of these embryonic processes They have been implicated in cell fate specification in the early embryo [1,2,3,4,5,6,7] and patterning and morphogenetic processes [8,9,10]. Sox3/19a/19b are expressed in the blastula [11], whereas the corresponding early expression in mice is covered by Sox2 [1]. Following this stage, the B1 sox genes are thought to be important for specification of the embryonic ectoderm into the neuroectoderm lineage. As development proceeds to the neurula stage, expression of the B1 sox genes continues in neural precursors, where they function to maintain the neural progenitor states [13,14,15]

Methods

Results

Discussion

Conclusion