Romaniuk, Y. | bioRxiv Science

bioRxiv2026

MULTIPLE DEFECTS IN MOUSE STEM CELL BASED EMBRYO MODELS LACKING ALL HOX FUNCTION

Mammals have four genomic copies of an ancestral Hox cluster, with a total of 39 genes. While gene inactivation approaches and full cluster deletions have revealed their critical functions during early development, the effect of removing all Hox function has remained elusive due to both biological and technological challenges. We have used mouse gastruloids, an ES cells-derived embryo model where Hox genes are properly activated in time and space, to assess the effect of their complete absence. We report that gastruloids lacking Hox function can still elongate and reach a general shape resembling their control counterparts, with a well-established AP polarity. However, unlike controls, they fail to produce any endoderm and are unable to properly segment their presomitic mesoderm into persistent somite-like structures. Instead, they produce a type of mesoderm with a more anterior identity. We thus propose that, in this system at least, HOX proteins are necessary to posteriorize an existing anterior ground-state structure, in part by promoting and/or maintaining the epithelialization of cellular condensations. Multiomes analysis revealed range of modifications in chromatin accessibility in the absence of any HOX proteins, involving in particular variations in the binding of the co-factor PBX1. In contrast, neuro-mesodermal progenitor (NMP) cells are not overtly affected in mutant gastruloids, even though they normally initiate strong Hox gene transcription, suggesting that these cells are used as vehicles to translate a temporal sequence of activation into an AP colinear transcript distribution, which becomes functional at a later stage only.

Developmental Biology↗

bioRxiv2023

Cadherins modulate the self-organizing potential of gastruloids

Gastruloids have recently emerged as an efficient four-dimensional model for studying some aspects of post-implantation embryonic patterning. They undergo gastrulation-like processes leading to the self-organization into highly reproducible biological objects. Here, we sought to uncover the molecular and cellular mechanism underlying this remarkable property. We report that self-organization competence is associated with a cell-specific coordination of a Cadherin switch. We find that N-Cadherin hinders gastruloids morphogenetic competence, for its inactivation leads to the formation of trunk-like structures in absence of extra-cellular matrix analogues. In contrast, E-Cadherin repression by Snai1 is critical for self-organization: Snai1 establishes a cell-specific repressive pace by triggering the repression of a pluripotency-associated transcription program and its chromatin landscape, thus allowing a proper transition from E-to N-Cadherin to occur. Altogether, this work establishes a molecular mechanism that integrates the exit from pluripotency and the pace of cell differentiation, leading to the observed self-organizing potential of gastruloids.

developmental biology↗