SOX2 como posible biomarcador pronóstico y diana molecular en el cáncer de pulmón: metaanálisis.

OBJECTIVE: To determine the association of SOX2 with the prognosis in lung cancer, studies providing survival information were selected based on multivariate Cox regression analysis. MATERIAL AND METHODS: PubMed, Embase, and Web of Science databases were searched to identify eligible studies before June 19, 2021. The hazard ratios (HR) with 95% confidence intervals (CI) were calculated to assess the prognostic impact of SOX2 based on multivariate Cox regression analysis. Publication bias was used to assess the risk of bias. Functional analysis of SOX2 was also conducted. RESULTS: 13 studies with a total of 2008 patients with lung cancer were included. SOX2 expression was not correlated with overall survival in lung cancer (10 studies with 1591 cases). Between-study heterogeneity was noted (I2=85.6%, p<0.0001). Subgroup analysis suggested that no correlation was found between SOX2 expression and overall survival in non-small cell lung cancer (NSCLC: eight studies with 1319 cases) and small-cell lung cancer (SCLC: two studies with 272 cases). SOX2 expression was significantly associated with worse time-to-progression (two studies with 104 cases: HR=3.50, 95% CI=1.34-9.15) and recurrence-free survival (two studies with 335 cases: HR=1.45, 95% CI=1.12-1.87) in NSCLC. Function analysis demonstrated that SOX2 was involved in DNA repair, cell cycle, regulation of stem cell population maintenance, and Hippo signaling pathway. CONCLUSION: SOX2 may be an independent prognostic factor in time-to-progression and recurrence-free survival and may become a promising therapeutic target. More studies are essential to further our findings.

Identification of estrone-degrading Betaproteobacteria in activated sludge by microautoradiography fluorescent in situ hybridization.

UNLABELLED: Natural oestrogens, which are degraded but not completely removed in wastewater treatment plants, are suspected of causing the endocrine disruption of aquatic organisms in the receiving water body. While several bacterial isolates were reported to be oestrogen-degrading bacteria, our previous study implied that only the unidentified rod-shaped Betaproteobacteria in chains were responsible for estrone (E1) degradation by activated sludge especially at the sub-milligram per litre level. The Betaproteobacteria were suspected to be related to genera Sphaerotilus and Leptothrix according to morphological observations. Probe Spha823 was newly developed to target 16S rRNA gene clones obtained from activated sludge and closely related to the above genera. [(3) H]E1-incubated sludge samples showed that most of the (3) H-labelled cells hybridized with probe Spha823 by microautoradiography (MAR) fluorescent in situ hybridization. Spha823-defined cells were present in all three activated sludge samples tested, where they accounted for up to 3% of the total microbial biomass. Spha823-defined cells comprised 59·5-80·1% of the total MAR-positive cells, which suggested that the Sphaerotilus-Leptothrix-related bacteria were the most abundant micro-organisms involved in E1 degradation (at 200 µg l(-1) ) in the activated sludge samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Estrone (E1) is one of the natural estrogens, which can be degraded but is not always completely removed in wastewater treatment plants. E1 is suspected of causing the endocrine disruption of aquatic organisms in the receiving water body. We identified dominant E1-incorporating bacteria, which should include E1-degrading bacteria, in activated sludge treating domestic wastewater. Sphaerotilus-Leptothrix-related bacteria, which had never been reported in the previous attempts based on culture-dependent approach, occupied 60-80% of the E1-incorporating bacteria. This study demonstrates the identification of functionally active bacteria to degrade micro-pollutants at sub-milligram per litre level.

Breast milk leptin and adiponectin in relation to infant body composition up to 2 years.

BACKGROUND: Adipokines in breast milk have been associated with infant growth trajectories. OBJECTIVE: We aimed to explore the relationship of leptin and adiponectin in breast milk with infant weight gain and body composition up to the age of 2 years. METHODS: Breast milk samples were collected from exclusively or partially breastfeeding mothers at 6 weeks (n = 152) and 4 months (n = 120) post-partum. Leptin and adiponectin were determined in skim breast milk and related to infant growth and fat mass assessed by skin-fold thickness measurements. A total of 118 infants were examined at 2 years. RESULTS: The levels of both milk adipokines were slightly lower at 4 months compared with 6 weeks post-partum. Breast milk leptin was largely unrelated to infant anthropometric measures up to 2 years. Milk adiponectin tended to be inversely related to early infant anthropometry up to 4 months, but beyond was positively associated with weight gain and the sum of skin-folds up to 2 years. CONCLUSIONS: Our results suggest that higher adiponectin levels in breast milk might be associated with greater weight gain and higher fat mass in the offspring up to 2 years.

DNA methylation studies on imprinted loci in a male monozygotic twin pair discordant for Beckwith-Wiedemann syndrome.

Beckwith­Wiedemann syndrome (BWS) is one of the most prevalent congenital disorders predominantly caused by epigenetic alterations. Here we present an extensive case study of a monozygotic monochorionic male twin pair discordant for BWS. Our analysis allows to correlate BWS symptoms, like a protruding tongue, indented ears and transient neonatal hypoglycaemia, to an abnormal methylation at the KvDMR1. DNAs extracted from peripheral blood, skin fibroblasts, saliva and buccal swab of both twins, their sister and parents were analysed at 11 differentially methylated regions (DMRs) including all four relevant DMRs of the BWS region. The KvDMR1 was exclusively found to be hypomethylated in all cell types of the affected BWS twin, while the unaffected twin and the relatives showed normal methylation in fibroblasts, buccal swab and saliva DNA. Interestingly, the twins share a common blood-specific hypomethylation phenotype most probably caused by a feto-fetal transfusion between both twins. Because microsatellite analysis furthermore revealed a normal biparental karyotype for chromosome 11, our results point to an exclusive correlation of the observed BWS symptoms to locally restricted epimutations at the KvDMR1 of the maternal chromosome.

High rate of constitutional chromosomal rearrangements in apparently sporadic ALS.

Of 85 patients with ALS, the authors identified 3 patients with balanced translocations and 2 patients with pericentric inversions, all affecting distinct chromosomal loci. The high rate of constitutional aberrations (5.9%) suggests that ALS is, in part, associated with recombination-based rearrangements of genomic sequences.

Frequent mitotic errors in tumor cells of genetically micro-heterogeneous glioblastomas.

Glioblastoma multiforme (GBM) is characterized by intratumoral heterogeneity as to both histomorphology and genetic changes, displaying a wide variety of numerical chromosome aberrations the most common of which are monosomy 10 and trisomy 7. Moreover, GBM in vitro are known to have variable karyotypes within a given tumor cell culture leading to rapid karyotype evolution through a high incidence of secondary numerical chromosome aberrations. The aim of our study was to investigate to what extent this mitotic instability of glioblastoma cells is also present in vivo. We assessed the spatial distribution patterns of numerical chromosome aberrations in vivo in a series of 24 GBM using two-color in situ hybridization for chromosomes 7/10, 8/17, and 12/18 on consecutive 6-microm paraffin-embedded tissue slides. The chromosome aberration patterns were compared with the histomorphology of the investigated tumor assessed from a consecutive HE-stained section, and with the in vitro karyotype of cell cultures established from the tumors. All investigated chromosomes showed mitotic instability, i.e., numerical aberrations within significant amounts of tumor cells in a scattered distribution through the tumor tissue. As to chromosomes 10 and 17, only monosomy occurred, as to chromosome 7 only trisomy/polysomy, apparently as a result of selection in favor of the respective aberration. Conversely, chromosomes 8, 12, and 18 displayed scattered patterns of monosomy as well as trisomy within a given tumor reflecting a high mitotic error rate without selective effects. The karyotypes of the tumor cell cultures showed less variability of numerical aberrations apparently due to clonal adaptation to in vitro conditions. We conclude that glioblastoma cells in vivo are characterized by an extensive tendency to mitotic errors. The resulting clonal diversity of chromosomally aberrant cells may be an important biological constituent of the well-known ability of glioblastomas to preserve viable tumor cell clones under adaptive stress in vivo, in clinical terms to rapidly recur after antitumoral therapy including radio- or chemotherapy.

Predictive value of progression-associated chromosomal aberrations for the prognosis of meningiomas: a retrospective study of 198 cases.

OBJECT: The goal of this study was to determine whether in meningiomas cytogenetic findings are suitable as a predictive parameter relevant to prognosis. METHODS: Between 1992 and 1998 at the Department of Neurosurgery, Saarland University, 198 patients underwent surgery to resect meningiomas. The meningiomas were investigated cytogenetically and the patients were followed up for a mean period of 33 months. On the basis of the cytogenetic findings, the meningiomas were subdivided into four groups: Group 0 meningiomas displayed a normal diploid chromosome set; Group 1 tumors were found to have monosomy 22 as the sole cytogenetic aberration; Group 2 tumors were markedly hypodiploid meningiomas with loss of additional autosomes in addition to monosomy 22; and Group 3 meningiomas had deletions of the short arm of a chromosome 1, as well as additional chromosomal aberrations including loss of one chromosome 22. One hundred ninety-eight patients in whom tumor resections were determined to be Simpson Grade I or II could be followed up after complete tumor extirpation. In 20 patients, one or several recurrences were documented during the period of observation. The tumors were classified according to their different, but mostly uniform chromosomal aberrations. Recurrences were found in six (4.3%) of 139 tumors in Groups 0 and 1 and in two (10.5%) of 19 tumors in Group 2; the highest rate of recurrence was found in 12 (30%) of 40 tumors in Group 3. This supports the notion that the deletion of the short arm of one chromosome 1 is an important prognostic factor in meningiomas. The results of this study document a significant correlation between histological grade (p < 0.0001), location (p < 0.0001), and recurrences of meningiomas (p < 0.0001) (significance determined using chi-square tests). CONCLUSIONS: The cytogenetic classification of meningiomas provides a significant contribution to the predictability of tumor recurrence and is, therefore, a valuable criterion for the neurosurgeon's postoperative management protocol.

Meningioma: a cytogenetic model of a complex benign human tumor, including data on 394 karyotyped cases.

Meningioma is the most frequent tumor of neuroectodermal origin in humans. It is usually benign. Only a minority of cases shows progression to an anaplastic tumor (WHO grade II and III). Meningioma is generally a sporadic tumor. Multiple and familial cases are rare and mostly associated with (hereditary) neurofibromatosis 2 (NF2). Meningiomas show an unexpectedly high recurrence rate. Also, completely removed low-grade tumors can recur. Recurrence and multiplicity are correlated with the formation of a peritumoral edema. On the cytogenetic level, meningioma is the best-studied tumor in humans. Grade I tumors show either uniform monosomy 22 or a diploid karyotype. The majority of high-grade, but only a minority of low-grade, meningiomas show loss of merlin, a cytoskeleton-cytoplasm-linker protein. Merlin is the product of the NF2 gene located on chromosome 22. A second tumor suppressor gene on chromosome 22 has not yet been detected. In contrast to other solid tumors, progression of meningiomas is correlated with increasing hypodiploidy, showing characteristic clonal evolutions that mostly include chromosomes 14, 18, and 19 and, more rarely, 6 and 10. Structural aberrations are infrequent, except for the loss of the short arm of chromosome 1, which appears to be the decisive step for anaplastic growth. Comparative histochemical and molecular cytogenetic studies point to the alkaline phosphatase gene (ALPL, liver-bone-kidney type) located on 1p36.1-->p34 as a candidate tumor suppressor gene. A model is proposed that tries to explain - with a minimum number of essential steps - the origin, progression, infiltration, and recurrence of meningiomas.

Distribution of epidermal growth factor receptor protein correlates with gain in chromosome 7 revealed by comparative genomic hybridization after microdissection in glioblastoma multiforme.

In a recent study, 23 microdissected areas of 10 glioblastoma multiforme (GBM) were investigated for quantitative genomic aberrations using comparative genomic hybridization (CGH). To validate the chromosomal aberrations, as revealed by CGH after microdissection, parallel tissue sections were stained immunohistochemically with an antibody that detects both wild-type epidermal growth factor receptor (EGFR) and the deletion mutant form of the receptor (EGFRvIII). Immunostaining was correlated with CGH data of chromosome 7, because chromosome 7 is the most frequently aberrant chromosome in GBM (here four of 10 tumors), and this aberration often indicates an abnormality of EGFR. Nine of nine areas that showed gain in or amplification (2 areas) of chromosome 7 with CGH contained EGFR-immunoreactive cells. Only three of 14 areas without abnormality of chromosome 7 in CGH contained EGFR-immunoreactive cells; eleven of 14 areas were immunonegative. Our findings demonstrate a strong correlation between immunohistochemistry of EGFR and the copy numbers of chromosome 7, as revealed by CGH after microdissection in glioblastoma multiforme.

Comparative genomic hybridization reveals recurrent enhancements on chromosome 20 and in one case combined amplification sites on 15q24q26 and 20p11p12 in glioblastomas.

We examined homogenized tissue samples of biopsies from 19 astrocytomas of different grades for genetic imbalances using comparative genomic hybridization (CGH): three astrocytomas grade II, and 16 astrocytomas grade IV (glioblastoma multiforme), one of the glioblastomas representing the recurrence of a benign oligoastrocytoma. In two of three cases of astrocytoma grade II, a gain of chromosome 7 was found. The alterations in the glioblastomas were complex, and most frequently showed the characteristic gain of chromosome 7 and loss of chromosome 10. The single analyzed case of recurrence of an oligoastrocytoma was characterized by a unique CGH pattern. This tumor showed two distinct alterations: apart from an amplification on 15q24q26, we found a distinct amplification of a small region on 20p11.2p12, which has not been previously described in brain tumors. Partial or complete gains of chromosome 20 arose in six other tumors; we conclude that chromosome 20 in particular 20p11. 2p12, may harbor relevant genes for glioma progression.

p53 and c-Jun functionally synergize in the regulation of the DNA repair gene hMSH2 in response to UV.

The tumor suppresser protein p53 is critical for guarding the genome from incorporation of damaged DNA (Lane, D. P. (1992) Nature 358, 15-16). A relevant stress that activates p53 function is UV light (Noda, A., Toma-Aiba, Y., and Fujiwara, Y. (2000) Oncogene 19, 21-31). Another well known component of the mammalian UV response is the transcription factor c-Jun (Angel, P., and Karin, M. (1991) Biochim. Biophys. Acta 1072, 129-157). We show here that upon UV irradiation p53 activates transcription of the human mismatch repair gene MSH2. Interestingly, this up-regulation critically depends on functional interaction with c-Jun. Hence, the synergistic interaction of a proto-oncogene with a tumor suppresser gene is required for the regulation of the mammalian stress response through activation of expression of MSH2.

The role of brain-derived neurotrophic factor receptors in the mature hippocampus: modulation of long-term potentiation through a presynaptic mechanism involving TrkB.

The neurotrophin BDNF has been shown to modulate long-term potentiation (LTP) at Schaffer collateral-CA1 hippocampal synapses. Mutants in the BDNF receptor gene trkB and antibodies to its second receptor p75NTR have been used to determine the receptors and cells involved in this response. Inhibition of p75NTR does not detectably reduce LTP or affect presynaptic function, but analyses of newly generated trkB mutants implicate TrkB. One mutant has reduced expression in a normal pattern of TrkB throughout the brain. The second mutant was created by cre-loxP-mediated removal of TrkB in CA1 pyramidal neurons of this mouse. Neither mutant detectably impacts survival or morphology of hippocampal neurons. TrkB reduction, however, affects presynaptic function and reduces the ability of tetanic stimulation to induce LTP. Postsynaptic glutamate receptors are not affected by TrkB reduction, indicating that BDNF does not modulate plasticity through postsynaptic TrkB. Consistent with this, elimination of TrkB in postsynaptic neurons does not affect LTP. Moreover, normal LTP is generated in the mutant with reduced TrkB by a depolarization-low-frequency stimulation pairing protocol that puts minimal demands on presynaptic terminal function. Thus, BDNF appears to act through TrkB presynaptically, but not postsynaptically, to modulate LTP.

Cortical degeneration in the absence of neurotrophin signaling: dendritic retraction and neuronal loss after removal of the receptor TrkB.

To examine functions of TrkB in the adult CNS, TrkB has been removed from neurons expressing CaMKII, primarily pyramidal neurons, using Cre-mediated recombination. A floxed trkB allele was designed so that neurons lacking TrkB express tau-beta-galactosidase. Following trkB deletion in pyramidal cells, their dendritic arbors are altered, and cortical layers II/III and V are compressed, after which there is an apparent loss of mutant neurons expressing the transcription factor SCIP but not of those expressing Otx-1. Loss of neurons expressing SCIP requires deletion of trkB within affected neurons; reduction of neuronal ER81 expression does not, suggesting both direct and indirect effects of TrkB loss. Thus, TrkB is required for the maintenance of specific populations of cells in the adult neocortex.

Deletion of chromosome 1p and loss of expression of alkaline phosphatase indicate progression of meningiomas.

Meningiomas are cytogenetically characterized by loss of one chromosome 22 as a typical primary aberration and progression-associated secondary chromosome changes, of which monosomy 1p is the most common. The aim of this study was to evaluate the significance of monosomy 1p and enzyme activity loss of tissue nonspecific alkaline phosphatase (ALPL), whose gene maps to chromosome 1p36.1-p34, as parameters for the diagnosis of progression-prone meningiomas. We analyzed smear preparations of 56 meningiomas and additional paraffin sections of 17 of the cases by two-color fluorescence in situ hybridization (FISH) using the D1Z1 and D1Z2 probes and by a metaphase cytogenetic analysis of 30 of these tumors. The results were compared to clinical and morphological parameters and the expression of ALPL. Smear preparations showed deletion of 1p36 in 27% of common-type, 70% of atypical (intermediate-type), and 100% of anaplastic meningiomas. Monosomy 1p, as detected by FISH or the karyotype, was strongly associated with complete loss of ALPL activity. Intermediate-type and anaplastic meningiomas of younger patients displayed an increasing rate of cells with trisomy 1q and relative loss of 1p. The highly significant correlation of FISH results and ALPL histochemistry with clinical parameters gives evidence of their strong prognostic relevance. The complete activity loss of ALPL and the immunologically detected loss of ALPL protein in areas of meningiomas with monosomy 1p indicate a cytogenetically undetectable inactivation of the homologous Alpl allele. The apparently homozygous loss of expression of ALPL supports the notion that Alpl is a candidate tumor suppressor gene in meningiomas.

Genetic heterogeneity in human astrocytomas: spatial distribution of P16 and TP53 deletions in biopsies.

Smear preparations of 23 fresh astrocytoma biopsies were analyzed by two-color fluorescence in situ hybridization with cosmids specific for the P16 and the TP53 genes. Additionally, tissue sections of the same tumors were immunostained with the use of a monoclonal antibody that recognizes both wild-type and mutant TP53 protein. In 21 astrocytomas, loss of P16 was observed in a significant proportion of cells. Cells with homozygous P16 loss were present in 13 astrocytomas; 14 astrocytomas showed cells with heterozygous loss of P16. Remarkably, 5 astrocytomas showed a scattered mosaic pattern of cells with homozygous and, respectively, heterozygous p16 loss. Homozygous deletion of TP53 was not observed. Cells with heterozygous TP53 loss were detected in 12 tumors, in 7 of them in association with P16 loss. One tumor showed aberrant cells for neither TP53 nor P16 but strong immunostaining for TP53. Positive TP53 immunostaining was found in 16 astrocytomas. Heterozygous loss of TP53 was significantly correlated with TP53 protein expression. We conclude that, unlike typical tumor suppressor genes, P16 might enhance cellular proliferation after heterozygous loss through a dosage effect and that the distribution of cells with homozygous loss of P16 speaks in favor of a polyclonal loss of the second copy of this gene.

Evidence of focal genetic microheterogeneity in glioblastoma multiforme by area-specific CGH on microdissected tumor cells.

The term "multiforme" in glioblastoma multiforme (GBM) indicates the highly variable histomorphology that cannot be addressed by studies on homogenized tissue probes. In order to relate genetic findings with histomorphologically distinct areas we used microdissection to procure defined cell populations from microscopic tissue sections under direct visualization. Formalin-fixed and paraffin-embedded tissue sections of 10 GBM were evaluated for intratumoral genetic heterogeneity by microdissection of multiple areas of 20-50 tumor cells and DOP-PCR of DNA isolated from the dissected cell groups, followed by comparative genomic hybridization (CGH). Microdissected cells from histomorphologically normal extratumoral blood vessels from the same slides served as controls. The individual tumors showed variable combinations of primary chromosomal gains and losses common to all studied areas of a given case along with secondary, area-specific additional aberrations. CGH displayed a wider variety of chromosomal aberrations than metaphase cytogenetics of cell cultures from the same tumors. The most frequent aberrations observed were previously unperceived gains on chromosomes 4q (8/10) and 5q (5/10). Other nonrandom aberrations were gains on 12q (6/10), 13q (6/10), and 7 (5/10), and losses of 22 (5/10). Amplifications on 7p were intratumorally heterogeneous and only found in single areas of 2 tumors. In contrast to normal extratumoral vessels, vascular proliferates in most cases demonstrated chromosomal aberrations (CGH) which were partially different from the aberrations observed in the tumor itself. The described method gives evidence of considerable intratumoral genetic heterogeneity in GBM and provides a sensitive tool for the detection of quantitative chromosomal changes that are present only regionally within a given tumor.

Unbalanced translocation t(1;3)(p12-13;q11) in meningiomas as the unique feature of chordoid differentiation.

Chordoid meningioma is a rare histological subtype of meningiomas. Cytogenetic analysis of three cases revealed the unique feature of an unbalanced translocation der(1)t(1;3)(p12-13;q11) that was ascertained by chromosome microdissection and reverse fluorescence in situ hybridization. As the t(1;3) has not been observed in other subtypes of meningioma, it may represent a specific cytogenetic marker of chordoid meningiomas. It is not yet clear whether a fusion gene or the combined loss of genes from chromosome arms 1p and 3p is the pathogenetically important outcome of the translocation.

POU domain factor Brn-3a controls the differentiation and survival of trigeminal neurons by regulating Trk receptor expression.

Mice lacking the POU domain-containing transcription factor Brn-3a have several neuronal deficits. In the present paper, we show that Brn-3a plays two distinct roles during development of the trigeminal ganglion. In this ganglion, neurons expressing the neurotrophin receptors, TrkB and TrkC, are born between E9.5 and E11.5. In the absence of Brn-3a, very few neurons ever express TrkC, but TrkB-expressing neurons are present at E12.5 in elevated numbers, suggesting that Brn-3a may be a constituent of a regulatory circuit determining which Trk receptor is expressed by these early-born neurons. Most neurons expressing the neurotrophin receptor TrkA are generated between E11.5 and E13.5 in this ganglion and their initial generation is not prevented by absence of Brn-3a. However, after E12. 5, absence of Brn-3a results in a progressive loss in neuronal TrkA and TrkB expression, which leads to a massive wave of apoptosis that peaks at E15.5. Despite complete absence of the Trk receptors at E17. 5 and P0, approximately 30% of the normal complement of neurons survive to birth in Brn-3a mutants. Approximately 70% of these express the GDNF receptor subunit, c-ret; many can be sustained by GDNF, but not by NGF in culture. Thus, the vast majority of surviving neurons are probably sustained in vivo by trophic factor(s) whose receptors are not regulated by Brn-3a. In conclusion, our data indicate the specific functions of Brn-3a in controlling the survival and differentiation of trigeminal neurons by regulating expression of each of the three Trk receptors.

The yeast two-hybrid system reveals no interaction between p73 alpha and SV40 large T-antigen.

SV40 and/or DNA sequences indistinguishable from SV40 have been detected in several types of human tumours. The oncoprotein of Simian virus 40, SV40 large T-antigen (Tag), is known to bind and inactivate tumour suppressor proteins, such as members of the retinoblastoma family and p53, thereby promoting cell transformation. In this study, we used the yeast two-hybrid system to investigate whether the Simian virus 40 (SV40) large T-antigen is able to interact with p73, a noval discovered putative tumour suppressor, that is homologous both structurally and functionally to p53. The yeast two-hybrid system is a genetic method to detect protein-protein-interactions in vivo. Our results suggest that the SV40 large T-antigen is not able to bind p73 in yeast although both proteins are expressed in the transformed yeast strain as was shown by western blot analysis.

Expression of Trk receptors in the developing mouse trigeminal ganglion: in vivo evidence for NT-3 activation of TrkA and TrkB in addition to TrkC.

Animals lacking neurotrophin-3 (NT-3) are born with deficits in almost all sensory ganglia. Among these, the trigeminal ganglion is missing 70% of the normal number of neurons, a deficit which develops during the major period of neurogenesis between embryonic stages (E) 10.5 and E13.5. In order to identify the mechanisms for this deficit, we used antisera specific for TrkA, TrkB, and TrkC to characterize and compare the expression patterns of each Trk receptor in trigeminal ganglia of wild type and NT-3 mutants between E10.5 and E15.5. Strikingly, TrkA, TrkB, and TrkC proteins appear to be exclusively associated with neurons, not precursors. While some neurons show limited co-expression of Trk receptors at E11.5, by E13. 5 each neuron expresses only one Trk receptor. Neuronal birth dating and cell counts show that in wild-type animals all TrkB- and TrkC-expressing neurons are generated before E11.5, while the majority of TrkA-expressing neurons are generated between E11.5 and E13.5. In mice lacking NT-3, the initial formation of the ganglion, as assessed at E10.5, is similar to that in wild-type animals. At E11.5, however, the number of TrkC-expressing neurons is dramatically reduced and the number of TrkC-immunopositive apoptotic profiles is markedly elevated. By E13.5, TrkC-expressing neurons are virtually eliminated. At E11.5, compared to wild type, the number of TrkB-expressing neurons is also reduced and the number of TrkB immunoreactive apoptotic profiles is increased. TrkA neurons are also reduced in the NT-3 mutants, but the major deficit develops between E12.5 and E13.5 when elevated numbers of TrkA-immunoreactive apoptotic profiles are detected. Normal numbers of TrkA- and TrkB-expressing neurons are seen in a TrkC-deficient mutant. Therefore, our data provide evidence that NT-3 supports the survival of TrkA-, TrkB- and TrkC-expressing neurons in the trigeminal ganglion by activating directly each of these receptors in vivo.