Differential expression pattern of Annexin A6 in chick neural crest and placode cells during cranial gangliogenesis

Abstract

The cranial trigeminal and epibranchial ganglia are components of the peripheral nervous system that possess an important somatosensory role. These ganglia arise from the intermixing and coalescence of two different migratory cell types, neural crest cells and neurogenic placodes cells, and thus typify the phenomena of cell migration and intercellular interactions for their creation. The underlying molecular mechanisms of ganglia formation, however, are still poorly understood. To address this, we have analyzed the spatio-temporal expression profile of Annexin A6 during chick gangliogenesis, as Annexin proteins play important, conserved roles in ganglia development and physiology. We observe Annexin A6 protein in cranial neural crest cells prior to, during and after their emergence from the neural tube. Fully migratory cranial neural crest cells, however, are devoid of Annexin A6. Interestingly, we note Annexin A6 protein in trigeminal and epibranchial placode cells as these cells ingress from the ectoderm to initiate ganglia formation. This expression is also maintained in the sensory placodes later on when they coalesce with neural crest cells to assemble the cranial ganglia. These results suggest that the dynamic expression of Annexin A6 in various embryonic cell types may allow Annexin A6 to serve distinct functions throughout embryonic development.

Annexin A6 controls neuronal membrane dynamics throughout chick cranial sensory gangliogenesis

“…2B, D′, arrowheads, n = 9 ganglia), further validating the specificities of the Annexin A6 MO and antibody. We also observe comparable results for epibranchial neurons depleted for Annexin A6 since they possess a similar pattern of Annexin A6 expression and subsequent neurogenesis (see (Shah and Taneyhill, 2015) (Smith et al, 2015); data not shown). Collectively, our results indicate that depletion of Annexin A6 from trigeminal or epibranchial neuronal precursors does not adversely affect trigeminal or epibranchial neuron ingression, differentiation, or position.…”

“…Our previous studies demonstrated that Annexin A6 is expressed predominantly on the membrane of placodal sensory precursors in the ectoderm and their neuronal derivatives that have ingressed into the mesenchyme (Shah and Taneyhill, 2015). To determine the function of Annexin A6 within cranial sensory neurons, we used an ectodermal electroporation method described previously (Shiau et al, 2008) to introduce the control or Annexin A6 MO into the precursor sensory ectoderm at Hamburger-Hamilton (HH) 10.…”

“…How these changes in gene expression relate to essential morphological alterations in these neurons, however, is still not known. Our previous studies revealed that Annexin A6 is expressed in placode cell-derived neuroblasts and neurons during chick gangliogenesis (Shah and Taneyhill, 2015). Herein, we demonstrate that the chick embryo head contains two Annexin A6 transcripts with a common translational start site, allowing both variants to be targeted by the same translation-blocking MO to address Annexin A6 function.…”

“…Annexin A6 (Abnova; 1:100) immunostaining was carried out on transverse sections as described in previous studies (Shah and Taneyhill, 2015). After de-gelatinizing the sections on the slides, the sections were blocked for 1–2 hours in 1X phosphate-buffered saline + 0.1% TritonX-100 (PBSTX) + 10% sheep serum.…”

“…In the chick, our prior work revealed that Annexin A6 modulates early cranial neural crest cell migration (Wu and Taneyhill, 2012). Intriguingly, later in chick development, Annexin A6 is expressed in trigeminal and epibranchial placode cell-derived neuroblasts and is maintained in these neurons throughout ganglia assembly (Shah and Taneyhill, 2015). The function of Annexin A6 during cranial gangliogenesis, however, has not been elucidated.…”