Genomic Novelty at the Vertebrate Ancestor

Abstract

The group of vertebrates includes diverse evolutionary lineages, and typical laboratory‐model vertebrates are confined to only limited groups (tetrapods and teleost fishes) of its entire diversity. Accumulating information of the molecular sequence for the still‐missing lineages including jawless fishes can now provide deeper insights into the definition of the taxon Vertebrata at the genomic level. Above all, the so‐called two‐round whole genome duplications are described to have occurred in the early vertebrate evolution. Recent molecular phylogenetic analyses for some gene families resulted in a scenario in which the genome expansion might have been completed before the split of the lineage of cyclostomes (extant jawless fishes including hagfishes and lampreys) from the future jawed vertebrate lineage. In addition to this genome expansion, key features of genomic contents of the vertebrate ancestor are inferable, provided secondary changes introduced later in individual lineages are taken into deep consideration in ancestral phylogenetic reconstruction. Key Concepts: Large‐scale sequencing of genomes and transcriptomes of non‐model vertebrates in crucial phylogenetic positions provided valuable information about the vertebrates' entire diversity. The two‐round genome duplications likely define the vertebrates genomically. De novo genes should also have contributed to the vertebrate gene repertoire. Lineage‐specific molecular changes should be taken into deep consideration in reconstructing the ancestral state as in morphological comparison. Large‐scale sequence resources for early branching vertebrates are expected to provide clearer insights into the genomics' novelty which established the vertebrates.

Two Lamprey Hedgehog Genes Share Non-Coding Regulatory Sequences and Expression Patterns with Gnathostome Hedgehogs

“…Uchida and colleagues [22] had proposed that duplication of Bmp2/4 , hypothalamic expression of Fgf8 and involvement of Shh in the hypophyseal placode were developmental novelties acquired in gnathostomes for the control of pituitary organogenesis. However, recent phylogenetic analyses suggest that the lamprey Bmp2/4/16 family has well undergone duplications and secondary losses [43]; Fgf8 expression in the lamprey hypothalamus is now demonstrated [25]; and here we found LfHh expression in the nhp. Thus, it appears that most of the key players involved in pituitary development were already recruited in the common ancestor of all vertebrates, in line with the idea that the lamprey hypothalamo-hypophyseal system displays strong similarities with its gnathostome homolog (e.g., [44]).…”