# Orthologs at the Base of the Olfactores Clade

## TL;DR

This paper explores how a small set of tunicate orthologs in the human genome contributed to the evolutionary diversification of the Olfactores clade, including vertebrates.

## Contribution

The paper identifies specific gene families and orthologs, particularly Type II cadherins, as key drivers in the evolutionary radiation of the Olfactores clade.

## Key findings

- The evolution of Type II cadherins allowed cells to detach from Type I neighbors, potentially leading to the formation of the neural crest.
- Expansions in muscle, nerve, and visual perception toolkits were crucial for the predatory capabilities of vertebrates.
- Tunicate orthologs, though few in number, played a pivotal role in the diversification of the Olfactores clade.

## Abstract

Tunicate orthologs in the human genome comprise just 84 genes of the 19,872 protein-coding genes and 23 of the 16,528 non-coding genes, yet they stand at the base of the Olfactores clade, which radiated to generate thousands of tunicate and vertebrate species. What were the powerful drivers among these genes that enabled this process? Many of these orthologs are present in gene families. We discuss the biological role of each family and the orthologs’ quantitative contribution to the family. Most important was the evolution of a second type of cadherin. This, a Type II cadherin, had the property of detaching the cell containing that cadherin from cells that expressed the Type I class. The set of such Type II cadherins could now detach and move away from their Type I neighbours, a process which would eventually evolve into the formation of the neural crest, “the fourth germ layer”, providing a wide range of possibilities for further evolutionary invention. A second important contribution were key additions to the broad development of the muscle and nerve protein and visual perception toolkits. These developments in mobility and vision provided the basis for the development of the efficient predatory capabilities of the Vertebrata.