Huixian Zhang1,2*, Vydianathan Ravi1*, Boon-Hui Tay1, Sumanty Tohari1, Nisha E. Pillai1, Aravind Prasad1, Qiang Lin2, Sydney Brenner1 and Byrappa Venkatesh1,3
1 Institute of Molecular and Cell Biology, A*STAR, Biopolis, Singapore 138673.
2 CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China.
3 Department of Paediatrics, Yong Loo Lin School of Medicine, NUS, Singapore 119228
Published in PNAS online on 7th Aug 2017.
ParaHox genes (Gsx, Pdx, and Cdx) are an ancient family of developmental genes closely related to the Hox genes. They play critical roles in the patterning of brain and gut. The basal chordate, amphioxus, contains a single ParaHox cluster comprising one member of each family, whereas nonteleost jawed vertebrates contain four ParaHox genomic loci with six or seven ParaHox genes. Teleosts, which have experienced an additional whole-genome duplication, contain six ParaHox genomic loci with six ParaHox genes. Jawless vertebrates, represented by lampreys and hagfish, are the most ancient group of vertebrates and are crucial for understanding the origin and evolution of vertebrate gene families. We have previously shown that lampreys contain six Hox gene loci. Here we report that lampreys contain only two ParaHox gene clusters (designated as α- and β-clusters) bearing five ParaHox genes (Gsxα, Pdxα, Cdxα, Gsxβ, and Cdxβ). The order and orientation of the three genes in the α-cluster are identical to that of the single cluster in amphioxus. However, the orientation of Gsxβ in the β-cluster is inverted. Interestingly, Gsxβ is expressed in the eye, unlike its homologs in jawed vertebrates, which are expressed mainly in the brain. The lamprey Pdxα is expressed in the pancreas similar to jawed vertebrate Pdx genes, indicating that the pancreatic expression of Pdx was acquired before the divergence of jawless and jawed vertebrate lineages. It is likely that the lamprey Pdxα plays a crucial role in pancreas specification and insulin production similar to the Pdx of jawed vertebrates
Figure legend: (A) ParaHox gene clusters in representative chordates. TGD, teleost-specific genome duplication. (B) VISTA plot showing conserved noncoding elements (CNEs, potential cis-regulatory elements) in the ParaHox gene loci of Japanese lamprey and other representative vertebrates. Blue peaks represent conserved exons whereas pink peaks represent CNEs.
For more information on BV's laboratory, please click here.