Pax3 isoforms in sensory neurogenesis: Expression and function in the ophthalmic trigeminal placode

Abstract

Background In the trigeminal placode, Pax3 is classified as necessary but not sufficient for sensory neuron differentiation. One hypothesis is that different Pax3 isoforms regulate cellular differentiation uniquely. Pax3 is known to sometimes activate and sometimes repress gene transcription, and its activity can be dependent on the isoforms present. Pax3 isoforms had not previously been characterized in chick sensory neurogenesis. Results RT-PCR analysis revealed three well-expressed Pax3 splice variants: Full-length (flPax3), Pax3V1 and Pax3V2. Each was characterized for its effect on neurogenesis by misexpression in placodal ectoderm. The differences observed were more apparent under conditions of enhanced neurogenesis (via Notch inhibition), where flPax3 and Pax3V1 caused failed differentiation, while Pax3V2 misexpression resembled the neuronal differentiation seen in controls. qPCR analysis revealed a progressive increase in Pax3 expression, but no significant change in relative isoform expression. Interestingly, Notch inhibition led to a significant increase in Pax3 expression. Conclusions We can conclude that: 1) flPax3 and Pax3V1 inhibit neuronal differentiation; 2) Pax3V2 is permissive for neuronal differentiation; 3) while absolute levels change over time, relative splice form expression levels are largely maintained in the trigeminal placode domain; and 4) Pax3 expression generally increases in response to Notch inhibition.

Prdm12 Directs Nociceptive Sensory Neuron Development by Regulating the Expression of the NGF Receptor TrkA

“…It is not detected at that stage at the trunk level in primary intramedullar Rohon-Beard sensory neurons but is expressed in extramedullar sensory neurons at later tadpole stages (Figure 6A). We first examined the role of the Ngn1/2 proneural factors and of two other transcription factors that are known to regulate sensory differentiation: Zic1 expressed in the developing anterior neural plate and Pax3, an early marker of the trigeminal placode, in the control of Prdm12 expression (Adams et al, 2014;Dude et al, 2009;Jaurena et al, 2015;Perron et al, 1999). In gain-of-function experiments in both animal cap (AC) explants and embryos at neurula stage, we found that only Zic1 efficiently induces Prdm12 (Figures 6B and 6C).…”