Heterogeneous combinatorial expression of Hoxd genes in single cells during limb development

Area of Science:

• Developmental Biology
• Genomics
• Molecular Biology

Background:

• Gene expression patterns guide cell type and organ formation during development.
• Hox genes, specifically from the HoxD cluster, are crucial for mammalian limb development, with differential spatial and temporal control.
• Previous studies suggested a homogenous transcriptional program for Hox genes, but single-cell expression levels remained unclear.

Purpose of the Study:

• To investigate the heterogeneity of Hox gene expression at the single-cell level during mammalian limb development.
• To determine if Hox genes are expressed together at the same levels in the same cells within the developing limb.

Main Methods:

• Analysis of single-limb bud cell transcriptomes.
• Examination of Hox gene expression patterns, focusing on Hoxd9 to Hoxd13.
• Utilizing transcriptional diversity of limb progenitors to establish pseudo-time sequences.

Main Results:

• High heterogeneity observed in the expression of Hoxd11 and Hoxd13 genes.
• Hox genes are expressed in specific combinations that correlate with distinct cell types.
• Expression of the five key Hoxd genes (Hoxd9-Hoxd13) is unbalanced in cells forming digits.
• Combinatorial Hox gene expression follows a pseudo-time sequence linked to limb progenitor transcriptional diversity.

Conclusions:

• Distinct combinations of Hoxd genes exist at the single-cell level during limb development.
• Increasing combinatorial Hox gene expression correlates with specific transcriptional signatures.
• These signatures indicate a temporal progression in cell differentiation within the developing limb structure.