Expression of the gene encoding tyrosine hydroxylase in a subpopulation of quail dorsal root ganglion cells cultured in the presence of insulin or chick embryo extract

Immortalized human dorsal root ganglion cells differentiate into neurons with nociceptive properties

A renewable source of human sensory neurons would greatly facilitate basic research and drug development. We had established previously conditionally immortalized human CNS cell lines that can differentiate into functional neurons (). We report here the development of an immortalized human dorsal root ganglion (DRG) clonal cell line, HD10.6, with a tetracycline-regulatable v-myc oncogene. In the proliferative condition, HD10.6 cells have a doubling time of 1.2 d and exhibit a neuronal precursor morphology. After differentiation of clone HD10.6 for 7 d in the presence of tetracycline, v-myc expression was suppressed, and >50% of the cells exhibited typical neuronal morphology, stained positively for neuronal cytoskeletal markers, and fired action potentials in response to current injection. Furthermore, this cell line was fate-restricted to a neuronal phenotype; even in culture conditions that promote Schwann cell or smooth muscle differentiation of neural crest stem cells, HD10.6 differentiated exclusively into neurons. Moreover, differentiated HD10.6 cells expressed sensory neuron-associated transcription factors and exhibited capsaicin sensitivity. Taken together, these data indicate that we have established an immortalized human DRG cell line that can differentiate into sensory neurons with nociceptive properties. The cell line HD10.6 represents the first example of a human sensory neuronal line and will be valuable for basic research, as well as for the discovery of novel drug targets and clinical candidates.

The developing CNS: a scenario for the action of proinsulin, insulin and insulin-like growth factors

The multifunctional cytokines of the family of insulin and insulin-like growth factors (IGFs) have not yet gained general recognition as essential cell signals for the development of the vertebrate nervous system. This is, in part, a consequence of previous constraints in our thinking, focused for many years on the endocrine roles of these factors in late mammalian development and postnatal stages. The cellular distribution of the components of the insulin and IGFs signalling system in the developing mammalian and avian CNS is remarkably conserved. While receptors are widespread, the much less abundant factors and modulatory proteins are highly regulated in time and space. Progression of neural development through the steps of cell proliferation, differentiation, maturation and survival is stimulated, at least in culture, by proinsulin and insulin and the IGFs. Thus, these factors might be important autocrine and paracrine signals during development of the CNS.

The tyrosine hydroxylase gene is expressed in endoderm and pancreas of early quail embryos

The initial expression of the gene encoding tyrosine hydroxylase (TH) was studied in the trunk of quail embryos by in situ hybridization. We detected the presence of quail TH mRNA on embryonic day 3.5 (E3.5) in the sympathetic ganglia and aortic plexus, both neural crest derived structures. In contrast, the TH gene was expressed much earlier in the endodermal layer of E2 embryos, i.e. from the 8-somite stage onwards. TH mRNA was found also in the pancreatic bud, an endoderm-derived structure. The TH protein and catecholamines were subsequently looked for in these structures. TH immunoreactivity was found in cells of E2 explanted endoderm, but no catecholamine histofluorescence was observed before or after a few days in culture. TH-positive cells were also detected in cultures of pancreatic rudiments, explanted from E3 to E6 quail embryos. We suggest that the TH-positive cells of the endoderm are the progenitors of the catecholaminergic cells of the pancreas and of the enterochromaffin cells of the gut. The hypothesis that the TH-positive cells of the endoderm are involved in the expression of the catecholaminergic phenotype by neural crest cells is discussed.

Plasticity in neural crest cell differentiation

The neural crest is a pluripotent population of cells that are endowed with migratory capacities. It has long been known that the differentiation pathway taken by cells derived from the neural crest is largely controlled by the microenvironment to which they home after their migration phase, indicating a high degree of plasticity in their developmental fate. Recent progress has been made concerning the factors which influence survival, growth and differentiation of selected sets of precursors in each embryonic site colonised by derivatives of the neural crest.

Quox-1, an Antp-like homeobox gene of the avian embryo: a developmental study using a Quox-1-specific antiserum

Quox-1 is an homeogene isolated in the quail by using the Drosophila Antp cDNA as a probe. Quox-1 homeodomain sequence homology is 98% and 100% with Antp and mouse Hox1.1 homeodomains respectively. The region of the molecule 3' to the homeodomain has no homology with any known protein sequence (Xue et al., 1991). We have raised an antiserum, designated anti-Quox-1, to the C-terminal portion of the quail Quox-1 protein. By Western blot analysis the polyclonal antibody detects proteins of the same apparent molecular weight in quail and chick embryo extracts. The developmental expression of the Quox-1 protein was examined by immunocytochemistry in whole-mount preparations or on sections of quail and chick embryos and in cell cultures. The same binding patterns were observed in the two species examined. The initial expression of Quox-1 protein was detected in the neural primordium at presomitic stages. The immunoreactivity is concentrated in the head fold and progressively extends over the fore- and midbrain when the neural tube closes. Later in development, the Quox-1 protein becomes widespread over the whole central nervous system, including forebrain and eyes. The Quox-1 gene is also active in a subpopulation of neural crest cells at the early phase of their migration in vivo and in vitro. Later on, the sensory neurons of the DRG showed anti-Quox-1 immunoreactivity, whereas sympathetic ganglia did not express this gene. Expression of Quox-1 in somitic mesenchyme is at first detected in virtually all cell nuclei of the early segmented somites, but after sclerotome-dermomyotome dichotomy, Quox-1 expression becomes restricted to the myotome. These results show that in contrast to the other vertebrate class I Hox genes, whose homeobox is of Antp type, Quox-1 has a domain of expression that includes fore- and midbrain, as well as the rest of the neural anlage.