# The vertebrate small leucine-rich proteoglycans: amplification of a clustered gene family and evolution of their transcriptional profile in jawed vertebrates

## TL;DR

This paper explores how a family of proteins called SLRPs evolved in vertebrates, showing how gene duplication events shaped their diversity and function in skeletal tissues.

## Contribution

The study reveals the evolutionary history of SLRPs through phylogeny and synteny analysis, uncovering novel members and expression patterns in cartilaginous fish.

## Key findings

- SLRP genes expanded via tandem and whole-genome duplications before the last common ancestor of jawed vertebrates.
- Novel SLRP members and lineage-specific gene losses were identified in cartilaginous fish.
- SLRP expression patterns in the small-spotted catshark suggest conserved roles in skeletal and connective tissues.

## Abstract

Small Leucine-Rich Proteoglycans (SLRPs) are a major family of vertebrate proteoglycans. In bony vertebrates, SLRPs have a variety of functions from structural to signaling and are found in extracellular matrices, notably in skeletal tissues. However, there is little or no data on the diversity, function and expression patterns of SLRPs in cartilaginous fishes, which hinders our understanding of how these genes evolved with the diversification of vertebrates, in particular regarding the early events of whole-genome duplications that shaped gnathostome and cyclostome genomes. We used a selection of chromosome-level assemblies of cartilaginous fish and other vertebrate genomes for phylogeny and synteny reconstructions, allowing better resolution and understanding of the evolution of this gene family in vertebrates. Novel SLRP members were uncovered together with specific loss events in different lineages. Our reconstructions support that the canonical SLRPs have originated from different series of tandem duplications that preceded the extant vertebrate last common ancestor, one of them even preceding the extant chordate last common ancestor. They then further expanded with additional tandem and whole-genome duplications during the diversification of extant vertebrates. Finally, we characterized the expression of several SLRP members in the small-spotted catshark Scyliorhinus canicula and from this, inferred conserved and derived SLRP expression in several skeletal and connective tissues in jawed vertebrates.

Graphical Abstract

The evolution of vertebrates occurred more than 500 Mya with the development of a cartilaginous skeleton composed of a diversity of proteins that include proteoglycans such as the Small Leucine-Rich Proteoglycans (SLRPs). Gil et al. identified how the SLRP family expanded from one to more than twenty genes in the course of vertebrate evolution, over several events of gene tandem duplication and whole genome duplication events, generating canonical SLRP gene cluster. The authors’ gene expression data support their ancestral function in vertebrate skeletal development.