Identification of nerve growth factor receptors in primary cultures of chick neural crest cells

Effects of nerve growth factor on sympathetic neuron development in normal and limbless chick embryos

Wing bud removal in chick embryos has been shown to affect the generation of sympathetic neurons prior to the normal period of limb innervation [Saltis and Rush (1995) J. auton. nerv. Sys., 51, 117-127.]. Pyknotic activity occurred earlier within the peripherally deprived ganglion, suggesting that a precocious cell death of dividing sympathoblasts led to the reduced neuronal population. We have now sought to test whether the effect of limb bud extirpation can be overcome by the administration of nerve growth factor (NGF). Specifically, the peripherally deprived ganglion has been examined for mitotic activity and total neuronal numbers. In brachial ganglia from the operated side, neuron numbers decreased by 67% by embryonic day (E) 13, but by only 28% when NGF was administered from E9. Ganglia on the unoperated side were unaffected by the NGF treatment. In contrast, in embryos receiving NGF from E5 to E9, neuron numbers in the ganglia increased by more than 100%, on both the intact and operated side. This increase was accompanied by a greater proportion of 3H-thymidine-labelled neurons. We therefore conclude that NGF, in addition to its previously described role of preventing naturally occurring neuron death, can also affect the generation of sympathetic neurons. This ability of NGF to affect gangliogenesis is most likely achieved by increasing the survival of dividing neuroblasts, although a direct effect on mitosis has not been excluded.

Nerve growth factor and neuronal cell death

The regulation of neuronal cell death by the neuronotrophic factor, nerve growth factor (NGF), has been described during neural development and following injury to the nervous system. Also, reduced NGF activity has been reported for the aged NGF-responsive neurons of the sympathetic nervous system and cholinergic regions of the central nervous system (CNS) in aged rodents and man. Although there is some knowledge of the molecular structure of the NGF and its receptor, less is known as to the mechanism of action of NGF. Here, a possible role for NGF in the regulation of oxidant--antioxidant balance is discussed as part of a molecular explanation for the known effects of NGF on neuronal survival during development, after injury, and in the aged CNS.

Catecholaminergic cells and support cell precursors in neural crest cultures differentially express nerve growth factor receptors

Long-term neural crest cultures grown in the continuous absence of exogenous nerve growth factor (NGF) contain a subpopulation of cells with NGF receptors exclusively of the low affinity subtype (Kd of approximately 3.2 nM). The current studies combined immunocytochemistry, using GIN1 (a support cell marker) or tyrosine hydroxylase antibodies, with radioautography following exposure to iodinated nerve growth factor (125I-NGF). The majority of cells specifically binding 125I-NGF were found to be immunoreactive for GIN1, indicating that the primary cell phenotype expressing receptors for NGF appear to be support cell precursors, at least under these conditions. These cells are likely to be responsive to and/or dependent upon NGF; the nature of this response or dependency remains to be determined. Some cells exhibiting silver grains were not immunoreactive for GIN1, suggesting that other cell phenotypes in neural crest cultures also have NGF receptors. In addition, some neural crest cells were found that stained with GIN1 and lacked 125I-NGF binding. Tyrosine hydroxylase-like immunoreactive cells apparently did not bind 125I-NGF under these culture conditions. Catecholaminergic sympathetic and sensory neurons from embryonic ganglia, derived from the neural crest, express both the high and low affinity forms of the NGF receptor. In order to determine whether the microenvironment played a role in the type of catecholaminergic cells appearing in culture, neural crest cells were grown in the continuous presence of exogenous NGF. Under these conditions, many tyrosine hydroxylase-like immunoreactive cells were found that specifically bound 125I-NGF. In addition, silver grains were still detected on these cells following a chase with nonradioactive NGF, designed to eliminate 125I-NGF bound to low affinity sites. Therefore, the catecholaminergic cells possess both the low and high affinity forms of the receptor. NGF's ability to modulate tyrosine hydroxylase activity, as it does in mature catecholaminergic neurons, was tested in this system. Surprisingly, there was no statistically significant difference in tyrosine hydroxylase activity in cultures grown in the absence or presence of exogenous NGF. This raises the possibility that embryonic catecholaminergic cells are unable to respond to NGF in this specific way, even though the receptors for the factor are present.

Neuron-like cells in long-term neural crest cultures are not targets of nerve growth factor

It has been shown previously that a subpopulation of long-term (7-14 days) cultured neural crest cells undergoing differentiation possesses receptors for nerve growth factor (NGF). These cells are likely to be targets of NGF during the early stages of embryonic development. This study was conducted to determine whether cells exhibiting neuron-like characteristics (i.e. process formation, presence of putative neurotransmitters) in neural crest cultures have NGF receptors. This was accomplished by combining 125I-NGF radioautography and immunocytochemistry using antibodies against tyrosine hydroxylase, serotonin, and vasoactive intestinal polypeptide. Examination of light microscopic radioautographs revealed that none of the neuron-like cells with tyrosine hydroxylase-like, serotonin-like, or vasoactive intestinal polypeptide-like immunoreactivity bound 125I-NGF, and, therefore, do not possess NGF receptors. It is not known whether the lack of NGF receptors on neuron-like cells is due to the early developmental stage of these cells, or is caused by a difference in the microenvironment in vitro as compared to in vivo. The identity of the cultured neural crest cells which do possess NGF receptors remains to be determined.

Characterization of nerve growth factor binding to cultured neural crest cells: evidence of an early developmental form of the NGF receptor

Cultured neural crest cells undergoing differentiation have been shown to contain a subpopulation of cells with specific receptors for nerve growth factor (NGF). These cells are the potential targets of NGF during differentiation and development. This study was done to pharmacologically characterize the binding of NGF to long-term (1- to 3-week) cultures of quail neural crest cells. The data indicate that 125I-NGF binding was specific and saturable, with less than 20% nonspecific binding. Scatchard analysis revealed the presence of one type (class) of receptors with a binding constant (Kd) similar to that of the low-affinity binding site described for embryonic dorsal root and sympathetic ganglia (approximately 3.2 nM). This was corroborated by displacement experiments (Kd of 1.3 nM), in which 125I-NGF binding was measured in the presence of increasing concentrations of nonradioactive NGF. In addition, affinity labeling revealed that the 125I-NGF-receptor complex had a molecular weight of about 93K, characteristic of the low-affinity NGF receptor of PC12 cells. The NGF receptor of cultured neural crest cells was trypsin-sensitive, as is typical of the low-affinity NGF binding sites. These findings indicate that differentiating neural crest cells lack high-affinity 125I-NGF binding sites. In contrast, embryonic dorsal root and sympathetic ganglia cells, known NGF targets, have both high- and low-affinity receptors. Measurements of the differential release of surface-bound 125I-NGF indicated that a relatively small amount (about 14%) of NGF is internalized over a 1-hr period. Cultured neural crest cells which bear NGF receptors were also shown by light microscopic radioautographic techniques to incorporate [3H]thymidine. I suggest, therefore, that cultured neural crest cells which have not terminally differentiated, as judged by morphological criteria and continued proliferation, may express an early developmental form of the NGF receptor.

Ontogeny of the nerve growth factor receptor in primary cultures of neural crest cells

Neural crest cells maintained as primary cultures for 4-7 days demonstrated specific binding of radioiodinated nerve growth factor ([125I]NGF); occasionally, significant binding of ([125I]NGF could be detected in 3-day cultures. Parallel cultures processed for indirect immunofluorescence revealed that the NGF receptor-positive neural crest cells represented a subpopulation of the total cells in culture. Cultures aged 4-7 days demonstrated fluorescent cells which were often grouped as aggregates. Some 3-day cultures contained faintly fluorescent cells. One- and two-day cultures were non-fluorescent. Melanocytes did not appear to bind NGF. Preliminary flow cytofluorometric analysis indicated that ca. 28% of neural crest cells in 5-day cultures possessed specific receptors for NGF.

Appearance of nerve growth factor receptors on cultured neural crest cells

Light microscopic radioautography of differentiating quail neural crest cultures (1 to 2 weeks after explanation) incubated with Iodine-125-labeled nerve growth factor (125I-NGF) revealed that approximately 35% of the cells bound NGF. The binding was specific and saturable; it was blocked by an excess of nonradioactive NGF, and was not detected following incubation with biologically inactive 125I-NGF. In addition, the binding did not appear to be blocked or diminished by insulin. Cell cultures prepared from somites or notochord showed no specific binding of 125I-NGF. Melanocytes comprised approximately 10% of the cell population in these cultures and appeared to be unlabeled. The subpopulation of cells with NGF receptors that were morphologically similar to other non-melanocyte unlabeled cells present in the neural crest cultures are probably the targets of the factor during differentiation and development. In contrast, there was no evidence of 125I-NGF binding by premigratory neural crest (adherent to the isolated neural tube) or by early migratory neural crest cells (24 hr after explantation). Both of these types of neural crest cells are relatively undifferentiated. The cells of the neural tube were also unlabeled. The binding of 125I-NGF to differentiating neural crest cells was not noticeably diminished by a brief pretreatment with trypsin or Dispase, enzymes used in the isolation of neural tubes. Hence, the absence of NGF receptors on premigratory neural crest and early migratory neural crest cultures was not due to enzymatic alterations of the receptor. It seems, therefore, that receptors for NGF appear on neural crest cells during the time when these cells are acquiring their phenotypic characteristics.

Placodal sensory neurons in culture: nodose ganglion neurons are unresponsive to NGF, lack NGF receptors but are supported by a liver-derived neurotrophic factor

Explant and dissociated neuron-enriched cultures of nodose ganglia (inferior or distal sensory ganglion of the Xth cranial nerve) were established from chick embryos taken between embryonic Day 4 (E4) and Day 16 (E16). The response of each type of culture to nerve growth factor (NGF) was examined over this developmental range. At the earliest ages taken (E4-E6), NGF elicited modest neurite outgrowth from ganglion explants cultured in collagen gel for 24 hr, although the effect of NGF on ganglia taken from E4 chicks was only marginally greater than spontaneous neurite extension from control ganglia of the same developmental age. The response of nodose explants to NGF was maximal at E6-E7, but declined to a negligible level in ganglia taken from E9-E10 or older chick embryos. In dissociated neuron-enriched cultures, nodose ganglion neurons were unresponsive to NGF throughtout the entire developmental age range between E5 and E12. In contrast to the lack of effect of NGF, up to 50% of nodose ganglion neurons survived and produced extensive neurites in dissociated cultures, on either collagen- or polylysine-coated substrates, in the presence of extracts of late embryonic or early posthatched chick liver (E18-P7). Antiserum to mouse NGF did not block the neurotrophic activity of chick (or rat or bovine) liver extracts. Whether cultured with chick liver extract alone or with chick liver extract plus NGF, nodose ganglion neurons taken from E6-E12 chick embryos and maintained in culture for 2 days were devoid of NGF receptors, as assessed by autoradiography of cultures incubated with 125I-NGF. Under similar conditions 70-95% of spinal sensory neurons (dorsal root ganglion--DRG) were heavily labeled. 2+

Increased adhesion response of anaplastic glioma cells to nerve growth factor and the presence of specific receptors

A trypsin-degradable nerve growth factor (NGF) receptor associated with the phospholipid component of the surface membrane has been detected on F98 anaplastic glioma cells. NGF also bound to the nucleus of F98 cells. Bound NGF was not displaceable by insulin, cytochrome C, growth hormone, or bovine serum albumin. Specific binding of NGF occurred with a Kd of 8.79 X 10(-12) M as determined by Scatchard analysis with approximately 34,000 receptors per cell. Specific NGF binding was also evident to C6 rat glioma cells and IMR-32 human neuroblastoma cells, but not to 3T3 mouse fibroblasts. These observations coupled with previous findings suggest that the NGF receptor may be a marker found on cells of neural derivation. As little as 1 ng/ml NGF caused an increase in the adhesiveness of F98 cells to culture flasks. Increased adhesiveness could be observed in as little as 5 min and was apparent for at least 45 min. At 25 min in NGF-containing medium, 24 +/- 3% of the cells adhered to the flasks compared to 13 +/- 1% of control cells. The NGF-induced increase in adhesiveness was not duplicated by epidermal growth factor, insulin, cytochrome c, bovine serum albumin, dibutyryl cyclic AMP, or sodium butyrate. Oxidized NGF blocked the effect of native NGF, but had little or no adhesion-promoting activity itself. Pretreatment of the cells with NGF was also effective in promoting adhesion, even though nerve growth factor was not added to the binding medium. The effect of this pretreatment was reversible; when NGF-pretreated cells were grown in medium without supplemental NGF, the adhesiveness of the cells returned to control levels or lower.