Early development of the mesencephalic trigeminal nucleus

Abstract

The cells of the mesencephalic trigeminal nucleus (MTN) are the proprioceptive sensory neurons that innervate the jaw muscles. Interestingly, their evolution is generally thought to have been concomitant with that of the jaws. They are also the first born neurons of the mesencephalon, and their axons pioneer some of the major tracts within the brain. The cells of the MTN are also paradoxical in being the only group of intramedullary primary sensory neurons in amniotes. However, we know little about the early development of these important neurons, and we have analysed this here. To study the earliest stages of MTN development, we have used a battery of neural crest markers to try and pinpoint the progenitors of the MTN. We find that, contrary to current perceptions, the progenitors of the MTN are not highlighted by these markers, suggesting that they are not neural crest derived. However, the cells of the MTN are marked by means of their expression of Brn-3a. This gene labels cells that arise either side of the dorsal midline, extending rostrally from the isthmus across the roof of the mesencephalon. We have further demonstrated that the MTN develops under the influence of the Fgf-8 secreted by the isthmus. Ectopic Fgf-8 application promotes MTN development, whereas inhibiting Fgf-8 function in vivo drastically affects MTN development.

A role forfoxd3andsox10in the differentiation of gonadotropin-releasing hormone (GnRH) cells in the zebrafishDanio rerio

“…Thus, they do not appear to be 'unique primitive population along the dorsal midline', as has been described for Mes5 neurons (Sanchez et al, 2002). Furthermore, loss of fgf8 in the isthmus did not affect the number of gnrh2 cells, as it does for the Mes5 neurons (Hunter et al, 2001). Our data support the idea that gnrh2 cells arise from neural crest-derived cells that migrate into the neural tube during development.…”

Migratory routes and fates of cells transcribing the Wnt‐1 gene in the murine hindbrain

“…Cells of this migration appear to originate from the ring itself, although a contribution from the dorsal midline of the midbrain cannot be ruled out. This migration appears to follow the lateral longitudinal fasciculus, which includes fibers of the mesencephalic trigeminal nucleus (Hunter et al, 2001).…”

The derivatives of the Wnt3a lineage in the central nervous system

“…Me5 cells represent the only primary sensory neurons within the neural tube, receiving proprioceptive information from the muscles of the jaw; their embryonic origin has been uncertain (Narayanan and Narayanan, 1978;Straznicky and Rush, 1985;Stainier and Gilbert, 1990;Hunter et al, 2001). The present study clarifies the origins of Me5 neurons.…”

“…A neural crest origin is consistent with their kinship with sensory neurons of the dorsal root ganglia. However, Me5 neurons neither respond to NGF (as other neural crest derivatives) (Straznicky and Rush, 1985) nor express markers of the neural crest (Hunter et al, 2001).…”