Abstract
The hypothalamus is a brain region with vital functions, and alterations in its development can cause human disease. However, we still do not have a complete description of how this complex structure is put together during embryonic and early postnatal stages. Radially oriented, outside-in migration of cells is prevalent in the developing hypothalamus. In spite of this, cell contingents from outside the hypothalamus as well as tangential hypothalamic migrations also have an important role. Here we study migrations in the hypothalamic primordium by genetically labeling the Foxb1 diencephalic lineage. Foxb1 is a transcription factor gene expressed in the neuroepithelium of the developing neural tube with a rostral expression boundary between caudal and rostral diencephalon, and therefore appropriate for marking migrations from caudal levels into the hypothalamus. We have found a large, longitudinally oriented migration stream apparently originating in the thalamic region and following an axonal bundle to end in the anterior portion of the lateral hypothalamic area. Additionally, we have mapped a specific expansion of the neuroepithelium into the rostral diencephalon. The expanded neuroepithelium generates abundant neurons for the medial hypothalamus at the tuberal level. Finally, we have uncovered novel diencephalon-to-telencephalon migrations into septum, piriform cortex and amygdala.
Highlights
The hypothalamus is a brain region subserving vital functions, and alterations in its development can cause disease
In the mouse progeny that we obtained upon crossing the Foxb1-Cre mouse line with a reporter mouse line, every cell expressing Foxb1 carried a reporter gene made permanently active by the Cre recombinase
One caveat is that inside the rostral diencephalon there is a source of Foxb1-lineage cells, the mammillary area, which contributes cells to more rostral regions
Summary
The hypothalamus is a brain region subserving vital functions, and alterations in its development can cause disease. The hypothalamus originates in the rostral diencephalon which, because of its situation between telencephalon and caudal diencephalon (including the thalamic region; Fig. 1), undergoes complex patterning (Puelles & Rubenstein, 2003). The longitudinal axis of the neural tube divides the primordium into dorsal and ventral portions (Shimamura et al, 1995). The hypothalamus is subdivided into four areas (preoptic, anterior, tuberal and mammillary; Swanson, 1987; Simerly, 2004), of which the first two are dorsal and the last two are ventral (according to embryonic topology; Fig. 1), they appear arranged rostrocaudally in the adult brain.
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