Prox1 is a marker of ectodermal placodes, endodermal compartments, lymphatic endothelium and lymphangioblasts

Area of Science:

• Developmental Biology
• Vascular Biology
• Genetics

Background:

• The origin of lymphatic endothelium was traditionally attributed to sprouting from specialized veins.
• Recent studies highlight the critical role of the homeobox transcription factor Prox1 in lymphatic development, as Prox1-deficient mice lack lymphatics.

Purpose of the Study:

• To investigate the expression patterns of Prox1 mRNA and protein in chick embryos and human fetuses.
• To elucidate the developmental origins and timing of lymphatic endothelium formation.

Main Methods:

• Expression analysis of Prox1 mRNA and protein in various tissues of chick embryos and human fetuses.
• Histological examination of early chick embryos to identify lymphatic anlagen and their relationship with vascular structures.

Main Results:

• Prox1 expression was identified in diverse embryonic tissues, including specific domains within the ectoderm, endoderm, and mesoderm.
• In the mesoderm, Prox1 is strongly expressed in lymphatic endothelium, with weaker expression in cardiomyocytes.
• Early lymphatic structures, including posterior lymph sacs and thoracic ducts, were observed in day-4 chick embryos, and Prox1-positive lymphangioblasts were found in the early mesoderm.

Conclusions:

• Lymphatic development commences earlier than previously understood.
• Lymphatics appear to arise independently from veins, originating from distinct Prox1-positive lymphangioblasts within the mesoderm.
• Prox1 is a crucial marker and regulator of lymphatic endothelial cell development across different germ layers.