# Comparative transcriptomics reveal the common anteroposterior molecular blueprint of adult bilaterian guts

## TL;DR

This study compares gut transcriptomes across five species to reveal conserved and modified molecular patterns in adult bilaterian guts.

## Contribution

The study identifies conserved transcription factor modules defining gut compartments across bilaterians, including lineage-specific modifications.

## Key findings

- Bipartite transcriptional programs define anteroposterior gut subdivisions in adult bilaterians.
- Hox, ParaHox, and other TFs involved in larval gut formation are maintained in adult gut tissues.
- Five conserved TF modules correspond to gut compartments, showing lineage-specific elaboration or shifts.

## Abstract

A through-gut is one of the major features of bilaterians. Comparative work among bilaterians has identified common molecular mechanisms during early gut patterning, but the primordial gut later often undergoes different degrees of reorganization in each lineage to form a fully differentiated adult gut with specializations along its anteroposterior (AP) axis. Yet, how the conserved embryonic gut AP pattern relates to the adult guts in diverse bilaterians after metamorphosis is still poorly understood. To unravel the molecular subdivisions of adult guts, we investigated the gut through transcriptomic analyses of five phylogenetically informative species: an annelid, a sea urchin, a hemichordate, a cephalochordate, and a vertebrate. We identified bipartite transcriptional programs defining the AP functional subdivisions. Patterning systems composed of Hox, ParaHox, and, surprisingly, other transcription factors (TFs) known to be involved in gut formation in sea urchin larvae are maintained in these adult tissues. Using unbiased analyses, we identified five conserved TF modules corresponding to the AP compartments of the guts that are elaborated or shifted in different species. Our study inferred conserved and modified adult AP patterning modules along bilaterian guts enabling the reconstruction of ancestral bilaterian features with profound implications for the evolution of the bilaterian body plan.

Bilaterian guts share conserved embryonic patterning, but how does this relates to adult gut organization? This study uses transcriptomic analyses across five species to reveal conserved transcription factor modules that define anteroposterior gut compartments, alongside lineage-specific modifications, offering insights into ancestral bilaterian gut evolution and body plan diversification.