Two lamprey Hedgehog genes share non-coding regulatory sequences and expression patterns with gnathostome Hedgehogs.

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genomics

Background:

• Hedgehog (Hh) genes are crucial for animal development.
• Studies reveal significant evolutionary differences in Hh genes across chordates.
• Lampreys offer insights into vertebrate origins of Hh signaling.

Purpose of the Study:

• To characterize the evolution of Hh signaling at the vertebrate emergence.
• To identify and analyze Hh genes in lampreys (river and sea lamprey).
• To compare lamprey Hh gene evolution with gnathostomes.

Main Methods:

• Screening of river lamprey cosmid library and sea lamprey genome assembly.
• Phylogenetic analyses of Hh gene relationships.
• Expression pattern analysis in lamprey embryos.
• Genomic sequence alignment and identification of conserved non-coding elements (CNEs).
• Functional assays in zebrafish embryos.

Main Results:

• Lampreys have two Hh genes, Hha and Hhb, which are lamprey-specific paralogs of Sonic/Indian Hh genes.
• Hha and Hhb show Sonic Hh-like expression patterns in embryonic brain, including a novel nasohypophyseal placode domain.
• Lamprey Hh genes share conserved non-coding elements (CNEs) with gnathostome Hh genes, despite sequence divergence.
• Lamprey CNEs exhibit gnathostome-like midline enhancer activity in zebrafish embryos.
• Lamprey Hh genes display duplication and structural changes in regulatory regions.

Conclusions:

• Lamprey Hh genes are functionally similar to gnathostome Sonic Hedgehog (Shh) genes in expression and regulation.
• Lamprey Hh genes provide evidence for the early evolution of Shh-like signaling in vertebrates.
• Lamprey-specific features include gene duplication and altered intronic/regulatory sequences, highlighting unique evolutionary adaptations.