Abstract
During embryonic development, symmetric ectodermal thickenings [olfactory placodes (OP)] give rise to several cell types that comprise the olfactory system, such as those that form the terminal nerve ganglion (TN), gonadotropin releasing hormone-1 neurons (GnRH-1ns), and other migratory neurons in rodents. Even though the genetic heterogeneity among these cell types is documented, unidentified cell populations arising from the OP remain. One candidate to identify placodal derived neurons in the developing nasal area is the transcription factor Isl1, which was recently identified in GnRH-3 neurons of the terminal nerve in fish, as well as expression in neurons of the nasal migratory mass (MM). Here, we analyzed the Isl1 genetic lineage in chemosensory neuronal populations in the nasal area and migratory GnRH-1ns in mice using in situ hybridization, immunolabeling a Tamoxifen inducible Isl1CreERT and a constitutive Isl1Cre knock-in mouse lines. In addition, we also performed conditional Isl1 ablation in developing GnRH neurons. We found Isl1 lineage across non-sensory cells of the respiratory epithelium and sustentacular cells of OE and VNO. We identified a population of transient embryonic Isl1 + neurons in the olfactory epithelium and sparse Isl1 + neurons in postnatal VNO. Isl1 is expressed in almost all GnRH neurons and in approximately half of the other neuron populations in the MM. However, Isl1 conditional ablation alone does not significantly compromise GnRH-1 neuronal migration or GnRH-1 expression, suggesting compensatory mechanisms. Further studies will elucidate the functional and mechanistic role of Isl1 in development of migratory endocrine neurons.
Highlights
Cranial placodes are specialized regions of ectoderm, that give rise to the pituitary gland, sensory organs, and ganglia of the vertebrate head (Brugmann and Moody, 2005; Schlosser, 2006)
Strong Isl1/2 immunoreactivity appeared localized in sparse nuclei ventral to the developing VNO and the putative respiratory epithelium (Figures 3C,D)
Our data indicate very selective expression of Isl1 in neurons forming in the olfactory placodes (OPs) including the GnRH-1ns, various migratory neuronal populations and some cells in the VNO, terminal nerve and sustentacular cells on the more medial and lateral portions of the OE
Summary
Cranial placodes are specialized regions of ectoderm, that give rise to the pituitary gland, sensory organs, and ganglia of the vertebrate head (Brugmann and Moody, 2005; Schlosser, 2006). They form as a result of specific expression patterns of transcription factors in pre-placodal ectoderm surrounding the anterior neural plate (Brugmann and Moody, 2005; Bailey and Streit, 2006). The mechanisms and molecules that drive progenitors of the developing olfactory pit into early migratory cells types remain largely unknown
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