Loss of Elp1 disrupts trigeminal ganglion neurodevelopment in a model of Familial Dysautonomia

Familial Dysautonomia (FD) is a sensory and autonomic neuropathy caused by a mutation in Elongator complex protein 1 (ELP1). FD patients have small trigeminal nerves and impaired perception of facial pain and temperature. These signals are relayed by nociceptive neurons in the trigeminal ganglion, a structure comprised of both neural crest- and placode-derived cells. Mice lacking Elp1 in neural crest derivatives (“Elp1 CKO”) are born with smaller trigeminal ganglia, suggesting Elp1 is important for trigeminal ganglion development, yet the function of Elp1 in this context is unknown. We demonstrate Elp1 expression in both neural crest- and placode-derived trigeminal neurons, which our data suggest give rise to primarily TrkA- and TrkB/C-expressing neurons, respectively. While Elp1 is not required for initial trigeminal ganglion formation, Elp1 CKO trigeminal neurons exhibit abnormal axon outgrowth and decreased target innervation. Developing nociceptors that express the receptor TrkA are especially vulnerable to Elp1 loss. TrkA expression is decreased in Elp1 CKO trigeminal nerve endings, coinciding with increased cell death. Subsequently, fewer TrkA neurons are present in the Elp1 CKO trigeminal ganglion, indicating Elp1 supports the target innervation and survival of trigeminal nociceptors. These findings explain the loss of facial pain and temperature sensation in FD.