ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Development 2018;145. pii:dev146829

Branching morphogenesis is a key process during organogenesis of ductal and exocrine organs, e.g. lung, kidney, pancreas, and liver¹. Regulatory components and local interactions for lung branching morphogenesis have been described in detail, mostly relying on receptor-ligand interactions between embryonic domains, respectively the lung endodermal epithelium and the surrounding mesenchyme.

Folliculogenesis is the major step of structural differentiation of the embryonic thyroid gland and a prerequisite for onset of thyroid hormone synthesis. During folliculogenesis, thyroid follicular cell precursors start to adhere laterally and polarize to develop functionally different cell compartments with distinct expression of the thyroid hormone biosynthesis machinery at the apical and the basolateral membrane.

Here, Liang et al. describe in extensive developmental experiments in the murine model a growth pattern of the embryonic murine thyroid reminiscent of the classic branching morphogenesis. This process was active during late thyroid development (E12-E14) before progenitor differentiation. In analogy with other organs, Sox9 expression identified a subset of proliferating progenitors at the tip of the branching thyroid follicular cell population. Branching growth of the thyroid was stimulated by mesenchymal Fgf10. Fgf10 inactivation caused normal migration of the thyroid but defective proliferation, folliculogenesis and formation of angiofollicular units. In summary, these results provide evidence for a branching morphogenetic process as major driver for proliferation and structural differentiation of the embryonic thyroid follicular cell population and provide possible molecular mechanisms for thyroid dysgenesis due to thyroid hypoplasia.

1. Affolter M, Zeller R, Caussinus E. Tissue remodeling through branching morphogenesis. Nat Rev Mol Cell Biol 2009;10:831-842.