Segregation Of Lines Research Articles

Rapid and Synchronous Breeding of Cytoplasmic Male Sterile and Maintainer Line Through Mitochondrial DNA Rearrangement Using Doubled Haploid Inducer in Brassica napus.

When homozygously fertile plants were induced using doubled haploid (DH) induction lines Y3380 and Y3560, the morphology of the induced F1 generation was basically consistent with the female parent, but the fertility was separated, showing characteristics similar to cytoplasmic male sterile (CMS) and maintainer lines. In this study, the morphology, fertility, ploidy, and cytoplasm genotype of the induced progeny were identified, and the results showed that the sterile progeny was polima cytoplasm sterile (pol CMS) and the fertile progeny was nap cytoplasm. The molecular marker and test-cross experimental results showed that the fertile progeny did not carry the restorer gene of pol CMS and the genetic distance between the female parent and the offspring was 0.002. This suggested that those inductions which produced sterile and fertile progeny were coordinated to CMS and maintainer lines. Through the co-linearity analysis of the mitochondrial DNA (mtDNA), it was found that the rearrangement of mtDNA by DH induction was the key factor that caused the transformation of fertility (nap) into sterility (pol). Also, when heterozygous females were induced with DH induction lines, the induction F2 generation also showed the segregation of fertile and sterile lines, and the genetic distance between sterile and fertile lines was approximately 0.075. Therefore, the induction line can induce different types of female parents, and the breeding of the sterile line and the maintainer line can be achieved through the rapid synchronization of sister crosses and self-crosses. The induction of DH inducer in B. napus can provide a new model for the innovation of germplasm resources and open up a new way for its application.

Abstract A26: Genomic and epigenomic analysis reveal a distinct and targetable transcriptional signature of HNSCC subtypes

Abstract Head and neck squamous cell carcinoma (HNSCC) is a complex disease of significant morbidity and mortality with poor survival rates that have persisted despite advances in therapy. The lack of improved outcome can be attributed, in part, to a gap in the understanding of the drivers of the disease and the paucity of novel targeted treatments. Although recent studies into the genomic landscapes of HNSCC have highlighted a striking mutational heterogeneity, the identification of pervasive and broadly actionable driver mutations and/or other genetic alterations remains elusive. In parallel with this genetic diversity, the heterogeneity of HNSCC is also manifested in distinct gene expression-defined subtypes. This raises the possibility that these heterogeneous gene expression programs are shaped by regulatory networks that are closely interwoven with an intrinsic and heritable epigenetic state. We thus hypothesize that there exist key oncogenic transcriptional regulators that confer subtype specificity and dependency and that these factors are linked with and potentially configure the epigenetic states of HNSCC. We have examined the distributions of histone modification marks by ChIP-Seq and steady-state transcriptomes by RNA-Seq across several cell lines that represent the subtypes of HNSCC. Interestingly, our molecular profiling demonstrated differential enrichment patterns of enhancer-associated H3K27Ac signals that recapitulate the segregation of cell lines based on subtype-specific differential gene expression profiles. We have further probed the enhancer landscape to identify cis-regulatory networks (CRM) specific to HPV-ve subtypes (basal and mesenchymal) and the HPV+ve (atypical) subtype. Embedded within the regulatory domains of the CRMs, we find the DNA-binding motifs of transcription factor (TF) families, including AP-1, ETS and p53/p63, to be consistently enriched and highly correlated with the expression of specific genes that define a given subtype. To dissect the functional role of enhancers and their regulators in directing expression, we have defined global cistromes of two key HNSCC-enriched TFs, ETS1 and dNp63, by ChIP-seq and RNA-seq experiments in representative cell lines. These studies, boosted by integrated meta-analysis of HNSCC patient datasets, reveal that the master TF-dependent core gene signatures are associated with key cellular processes that are specifically enriched in HNSCC subtypes. This includes EMT and invasion for the mesenchymal, inflammation for the basal, and drug metabolism processes in the HPV+ve atypical subtype. Finally, we have leveraged network analysis and drug discovery algorithms to identify novel subtype-specific small molecules that can potentially disrupt the CRMs in targeted fashion. Our systematic approach to epigenomically define and characterize the hardwired underpinnings of tumor heterogeneity has unveiled TF-dependent pathways and downstream effectors that are primed for future drug discovery and clinical trials. Citation Format: Christian Gluck, Akinsola Oyelakin, Alexandra Glathar, Michael Buck, Rose-Anne Romano, Satrajit Sinha. Genomic and epigenomic analysis reveal a distinct and targetable transcriptional signature of HNSCC subtypes [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr A26.

Comparative proteome analysis across non-small cell lung cancer cell lines

Non-small cell lung cancer (NSCLC) cell lines are widely used model systems to study molecular aspects of lung cancer. Comparative and in-depth proteome expression data across many NSCLC cell lines has not been generated yet, but would be of utility for the investigation of candidate targets and markers in oncogenesis. We employed a SILAC reference approach to perform replicate proteome quantifications across 23 distinct NSCLC cell lines. On average, close to 4000 distinct proteins were identified and quantified per cell line. These included many known targets and diagnostic markers, indicating that our proteome expression data represents a useful resource for NSCLC pre-clinical research. To assess proteome diversity within the NSCLC cell line panel, we performed hierarchical clustering and principal component analysis of proteome expression data. Our results indicate that general proteome diversity among NSCLC cell lines supersedes potential effects common to K-Ras or epidermal growth factor receptor (EGFR) oncoprotein expression. However, we observed partial segregation of EGFR or KRAS mutant cell lines for certain principal components, which reflected biological differences according to gene ontology enrichment analyses. Moreover, statistical analysis revealed several proteins that were significantly overexpressed in KRAS or EGFR mutant cell lines.

Transcriptionally repressed genes become aberrantly methylated and distinguish tumors of different lineages in breast cancer

Aberrant promoter hypermethylation is frequently observed in cancer. The potential for this mechanism to contribute to tumor development depends on whether the genes affected are repressed because of their methylation. Many aberrantly methylated genes play important roles in development and are bivalently marked in ES cells, suggesting that their aberrant methylation may reflect developmental processes. We investigated this possibility by analyzing promoter methylation in 19 breast cancer cell lines and 47 primary breast tumors. In cell lines, we defined 120 genes that were significantly repressed in association with methylation (SRAM). These genes allowed the unsupervised segregation of cell lines into epithelial (EPCAM+ve) and mesenchymal (EPCAM-ve) lineages. However, the methylated genes were already repressed in normal cells of the same lineage, and >90% could not be derepressed by treatment with 5-aza-2'-deoxycytidine. The tumor suppressor genes APC and CDH1 were among those methylated in a lineage-specific fashion. As predicted by the epithelial nature of most breast tumors, SRAM genes that were methylated in epithelial cell lines were frequently aberrantly methylated in primary tumors, as were genes specifically repressed in normal epithelial cells. An SRAM gene expression signature also correctly identified the rare claudin-low and metaplastic tumors as having mesenchymal characteristics. Our findings implicate aberrant DNA methylation as a marker of cell lineage rather than tumor progression and suggest that, in most cases, it does not cause the repression with which it is associated.

Identification of wheat-Thinopyrum intermedium alien disomic addition lines conferring resistance to stripe rust

Thinopyrum intermedium carries many useful traits for wheat genetic improvement. To identify genes conferring resistance to stripe rust caused by Puccinia striiformis f. sp. tritici in Zhong4, one of the Zhong series of partial amphiploids from the hybrids of common wheat × Th. intermedium, a cross was made between Zhong4 and a Chinese Spring ph1b mutant (CS-ph1b). The parents, F1, F2 plants and F5 lines of the cross were tested with Chinese predominant race CYR31 of P. striiformis f. sp. tritici in the seedling stage under controlled greenhouse conditions. Of 201 F2 seedlings tested with race CYR31, 149 were resistant and 52 were susceptible. The segregation fit a 3 resistant:1 susceptible ratio, indicating that a single dominant gene conferred resistance to the race CYR31. This result was further confirmed by the segregation of F5 lines into 1:1 ratio (P = 0.77). Using the Schiff dyeing method, the chromosome number in the root-tip cells of 10 F5 resistant lines (total 42 plants) was determined. Two alien addition lines (5-1-2-1-1-5, 5-1-2-1-1-6) with the smallest chromosome number (2n = 42 + II) were identified. A total of 105 pollen mother cells were examined at metaphase 1 (PMCs MI) for meiotic chromosome pairing. The lines 5-1-2-1-1-5 and 5-1-2-1-1-6 showed regular meiosis, exhibiting 22 ring or rod bivalents (2n = 22 II). The GISH results indicated that lines 5-1-2-1-1-5 and 5-1-2-1-1-6 were wheat-Th. intermedium alien disomic addition lines with 21 pairs of wheat chromosomes and one pair of Th. intermedium chromosomes. These two lines were all resistant to stripe rust, suggesting that they can be used as donors of stripe rust resistance genes and have great potential to play important roles in wheat stripe rust resistance breeding programs in China and the world.Key words: Wheat-Thinopyrum intermedium, stripe rust, GISH, cytological identification

Genetics of resistance to Ustilago tritici in ‘Glenlea’ wheat (Triticum aestivum)

‘Glenlea’ wheat (Triticum aestivum) is resistant to prevalent races of loose smut (Ustilago tritici) found on the Canadian prairies. Little is known about the genetics of this resistance. This study was undertaken to determine if ‘Glenlea’ possesses a single gene with broad resistance to multiple loose smut races representing virulence found on the Canadian prairies. ‘Glenlea’ was crossed with the susceptible cultivar ‘AC Taber’, and doubled haploid lines were produced from the resulting F, plants. Each of the 62 lines was inoculated with U. tritici races T2, T9, TIO, T15, T19, and T39. The differential segregation of lines to these races could be explained by no fewer than three major and possibly two minor genes within ‘Glenlea’. No one major gene provided complete or moderate resistance to all races representing the prominent virulence of U. tritici on the prairies (T2, T9, T10, and T39). The implications for marker development are that at least two markers would be required, one to each of the genes that complement each other to provide broad resistance.

Barley Chromosome Identification Using Genomic in Situ Hybridization in the Genome of Backcrossed Progeny of Barley–Wheat Amphiploids [Hordeum geniculatum All. (2n = 28) × Triticum aestivum L. (2n = 42)] (2n = 70)

Genomic in situ hybridization (GISH) has been used to study characteristics of the formation of alloplasmic lines detected among self-pollinated backcrossed progeny (BC1F5-BC1F8) of barley--wheat amphiploids [Hordeum geniculatum All. (2n = 28) x Triticum aestivum L. (2n = 42)] (2n = 70). The chromosome material of the wild barley H. geniculatum has been shown to contribute to these lines. For example, fifth-generation plants (BC1F5) had genotypes (2n = 42w + 2g), (2n = 42w + 1g + 1tg), and (2n = 41w + 1g), where w is common wheat chromosomes, g is barley (H. geniculatum) chromosomes, and tg is the telocentric chromosome of wild barley. Beginning from the BC1F6 generation, alloplasmic telocentric addition lines (2n = 42 + 2tg) and (2n = 42 + 1tg) appear. This lines has been found cytogenetically unstable. The progeny of each of these cytological types include not only the (2n = 42 + 2tg) and (2n = 42 + 2tg) addition plants, but also plants with the monosomic (2n = 41 + 1tg) and the disomic (2n = 40 + 2tg) substitutions, as well as the (2n = 41 + 2tg) plants, which lack one wheat chromosome and have two telocentric barley chromosomes. It has been demonstrated that the selection for well-filled grains favors the segregation of telocentric addition lines (2n = 42 = 2tg) and (2n = = 42 + 1tg).

Cell-selfish modes of evolution and mutations directed after transcriptional bypass

During transcription, prokaryotic and eukaryotic RNA polymerases bypass and misread (transcriptional mutagenesis) several classes of DNA lesions. For example, misreading of 8-OH-dG generates mRNAs containing G to T transversions. After translation, if the mutant protein briefly allowed the cell a growth-DNA replication advantage, then precocious DNA replication would bypass that unrepaired 8-OH-dG and misinsert dA opposite the directing DNA lesion with a higher probability than would be experienced for 8-OH-G lesions at other positions in otherwise identical neighboring cells. Such retromutations would have been tested for their imparted growth advantage as mRNA before they became heritable DNA mutations. The logical properties of a mode of evolution that utilizes directed-retromutagenesis were compared one by one with those of the standard neo-Darwinian mode. The retromutagenesis mode, while minimizing mutational load, is cell-selfish; fitness is for an immediate growth advantage rather than future reproductive potential. In prokaryotes, an evolutionary mode that involves standard Darwinian fitness testing of novel alleles in the genetic background of origin followed by clonal expansion also favors cell-selfish allele combinations when linkage disequilibrium is practiced. For metazoa and plants to have evolved organized tissues, cell-selfish modes of evolution represent systems-poisons that must be totally suppressed. The feedback loops that allow evolution to be cell-serving in prokaryotes are actively blocked in eukaryotes by traits that restrict fitness to future reproductive potential. These traits include (i) delay of fitness testing until after the mutation is made permanently heritable, (ii) diploidy to further delay fitness testing, (iii) segregation of somatic lines from germ lines, (iv) testing of novel alleles against randomized allele combinations constructed by obligate sex, and (v) obligate genetic death to insure that that the most basic systems unit of selfish allele combinatorial uniqueness is the species instead of the cell. The analyses indicate that modes of evolution in addition to our neo-Darwinian one could have existed utilizing known molecular mechanisms. The evolution of multicellularity was as much the discarding of old cell-selfish habits as the acquisition of new altruistic ones.

Present and future of quantitative trait locus analysis in plant breeding

AbstractThe joint analysis of genotype marker segregation and phenotypic values of individuals or lines enables the detection and location of loci affecting quantitative traits (QTL). The availability of DNA markers and powerful biometric methods has led to considerable progress in QTL mapping in plants.The most obvious applications of QTL analysis seem to be marker‐assisted selection (MAS) in breeding and pre‐breeding and QTL cloning. However, other areas are envisaged where QTL analysis can contribute decisively. These are: the understanding of complex traits such as plant‐pathogen interaction; plant genomics, connecting proteins and regulatory elements of known functions to QTL by candidate gene analysis; and germplasm enhancement through a characterization that allows its efficient utilization. The success in all these applications depends primarily on the reliability and accuracy of the QTL analysis itself. Therefore, the discussion of its limitations will constitute an important part of this review.

Effects of Elevated CO2 Concentration on the Respiratory Behavior of the Branches of Field-Grown Hinoki Cypress (Chamaecyparis obtusa)

The effects of elevated atmospheric CO2 concentrations on the nighttime respiration were examined for two sample branches of a hinoki cypress tree (Chamaecyparis obtusa) growing in the field with an open gas exchange system for a one-year period from July 1994 to June 1995. The branches were of a similar size and located at a similar position within the crown. One branch was subjected to an elevated CO2 concentration of 800 μmol mol−1 and the other was subjected to ambient air which had a CO2 concentration of about 370 μmol mol−1. Nighttime respiration rate was higher in elevated CO2 level than in ambient CO2 level. The relationship between nighttime respiration and the corresponding nighttime air temperature was fitted by the exponential function in every month of the year. The segregation of regression lines between the two CO2 treatments increased gradually as the seasons progressed during the treatment period. TheQ10 values for nighttime respiration were lower in elevated CO2 (1.9 ≤Q10 ≤ 3.7) than in ambient CO2 (2.4 ≤Q10 ≤ 4.5) in every month of the year. TheQ10 was inversely related to the monthly mean nighttime air temperature in both elevated and ambient CO2. The estimated daily nighttime respiration rate under both CO2 treatments had a similar seasonal pattern, which almost synchronized with the temperature change. The respiration ratio of elevated CO2 to ambient CO2 increased gradually from 1.1 to 1.6 until the end of the experiment. Our results indicate that the CO2 level and the temperature have a strong interactive effect on respiration and suggest that a potential increase in respiration of branches will occur when ambient CO2 increases.

Genetics of Stem Rust Resistance in Wheat Cvs. Pasqua and AC Taber

ABSTRACT Canadian wheat cvs. Pasqua and AC Taber were examined genetically to determine the number and identity of stem rust resistance genes in both. The two cultivars were crossed with stem rust susceptible line RL6071, and sets of random F(6) lines were developed from each cross. The F(6) lines, parents, and tester lines with single stem rust resistance genes were grown in a field rust nursery, inoculated with a mixture of stem and leaf rust races, and evaluated for rust resistance. The same wheat lines were tested by inoculation with specific stem rust races in seedling tests to postulate which Sr genes were segregating in the F6 lines. Segregation of F(6) lines indicated that Pasqua had three genes that conditioned field resistance to stem rust and had seedling genes Sr5, Sr6, Sr7a, Sr9b, and Sr12. Leaf rust resistance gene Lr34, which is in Pasqua, was associated with adult-plant stem rust resistance in the segregating F(6) lines. Adult-plant gene Sr2 was postulated to condition field resistance in AC Taber, and seedling genes Sr9b, Sr11, and Sr12 also were postulated to be in AC Taber.

Growth responses of mutants of spring barley to fumigation with SO2 and NO2in combination

SUMMARYThis study was undertaken to evaluate the range of variation in growth responses of sodium azide‐induced M2mutants (stocks SI and S2) of spring barley, Hordeum vulgare. L. cv. Maris Mink, in relation to air pollution tolerance or sensitivity. The preliminary screening experiment with 150 nl l−1concentrations of SO2 and NO2 in combination for 10 d, yielded well‐defined sensitive and tolerant lines in both the stocks. However, the percentage frequency distribution of plants in different injury classes varied and stock S2 showed a better segregation of different lines. In a subsequent experiment, treatment with a mixture of each gas at 100 nl l−lconcentration for 22 d caused a variable degree of growth reduction. As a result of air pollution treatment, most of the growth parameters were significantly (P < 0.001) reduced in the sensitive lines of both the stocks, whereas the tolerant lines showed a marked resistance to the growth inhibitory effect of the pollutants. The magnitude of the difference between the sensitivities of different lines was usually double or more, and the effects were, more pronounced in stock S2 than in stock SI. Root dry weight was more adversely affected than shoot dry weight in sensitive lines of both the stocks. The results indicated that inter‐line differences in growth responses of these mutants were wide ranging, distinct and consistent. In conclusion, this study clearly demonstrates that artificial mutations may cause a markedly broad base of variation in air pollution sensitivity of crop plants which may be used in future plant breeding programmes of pollution tolerant cultivars.

Auditory stream segregation by musical timbre.

A series of experiments examined the acoustic attributes of timbre that most contribute to auditory stream segregation. In the first experiment, listeners heard short sequences of repeated pairs of tones from orchestral instruments, and were asked to rate how strongly the tones formed different streams. These ratings were used as difference measures, and were fit to a two-dimensional space using multidimensional scaling. One dimension corresponded to average spectral frequency, and the other to multiple dynamic factors. These ratings were highly correlated with similarity judgments from a previous study. A second experiment assessed if the dynamic factors indirectly contributed to streaming by influencing perceptual attack time. The perceptual attack time of each tone was measured, and new sequences were recorded with the perceptual attacks isochronous. The results were highly correlated with the first experiment, and the effect of the dynamic factors was not diminished. These experiments indicate that streaming and similarity judgments are based on the same acoustic attributes. Implications for the segregation of melodic lines in music will be discussed.

Developmental capacities of avian embryonic dorsal root ganglion cells: neuropeptides and tyrosine hydroxylase in dissociated cell cultures

Dorsal root ganglia (DRG) from quail embryos of 10–15 days of incubation (E10–15) contain a subpopulation of cells, distinct from postmitotic neurons, that can, under suitable conditions of culture in vitro, differentiate into neuron-like cells that display a variety of adrenergic properties, including tyrosine hydroxylase (TH) immunoreactivity (Xue et al., Proc. Natl. Acad. Sci. U.S.A., 82 (1985) 8800–8804). The present study was undertaken to determine whether other markers typical of autonomic sympathetic nerve cells are also expressed in the same system. Cells immunoreactive for vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY) were found to differentiate continually from non-dividing precursors in all cultures of dissociated E10 quail DRG grown in the presence of chick embryo extract. Whereas VIP was already present (in a minute number of cells) in DRG in situ, NPY could not be detected before 3 days of culture, when it appeared simultaneously with TH. Double immunostaining experiments showed that most VIP-positive cells and about half the NPY-positive cells also displayed TH-immunoreactivity. On the other hand, there was no overlap between the substance P-containing neuronal population and any of the cells containing TH, NPY or VIP. These observations are pertinent to the problem of the segregation of autonomic and sensory cell lines during peripheral nervous system ontogeny.

Genetic considerations in the effects of ethanol in mice. II. A trans-acting inducibility regulator(s) affecting alcohol dehydrogenase (ADH) activity.

The inducibility of alcohol dehydrogenase (ADH) has been recognized in different systems including maize, Drosophila, and mice. Our earlier results showed strain-specific ADH responses to chronic ethanol administration relative to matched littermate controls in mice. For this study we used two strains which showed "induction" (BALB/c and S.W.) and two strains which showed "repression" (C57BL/6J and 129/ReJ) to produce three sets of F1 hybrids and their reciprocals and one set (BALB/c X C57BL/6J) of recombinant inbred (RI) lines. The ADH properties of the resulting genotypes were again evaluated following 15% ethanol treatment in drinking water (2 weeks) in relation to their littermate matched controls in replicated trials. Our F1 results suggest complete dominance for induction over repression at the phenotypic level, and the two repressed strains showed complementation. No significant differences were observed in the reciprocal F1's and all pairs of a given genotype-treatment combination yielded consistent results. The 1:1 segregation of RI lines suggests a single gene difference for ADH inducibility between BALB/c and C57BL/6J. These findings suggest the presence of a trans-acting inducibility regulator(s) for ADH which may or may not represent a single locus. Variability for such regulatory elements may provide an explanation for the commonly observed individual differences in natural populations for response to alcohol including alcohol metabolism.

Early segregation of a neuronal precursor cell line in the neural crest as revealed by culture in a chemically defined medium

This article addresses the problem of the segregation of cell lines during the development of peripheral nervous system components from the neural crest. We show here that committed precursors of peripheral neurons are present in the crest before the migration of its cells has started. If cultured in a serum-deprived medium, a subpopulation of the crest cells readily differentiates into neurons without dividing. Neuronal markers such as neurofilament proteins and receptor sites for tetanus toxin are not expressed in the committed neuronal precursors, but appear after a few hours in culture. They are coexpressed in neurons with the mesenchymal intermediate filament protein, vimentin, which is common to all neural crest cells regardless of their prospective fate. A strong inhibitory effect of serum factor(s) on neurite outgrowth is demonstrated. We show also that conditions stimulating proliferation of crest cells are incompatible with promotion of neuronal differentiation and viceversa.

Genetic Relationships of Brown Planthopper Resistance to Dwarf Disease and Stripe Disease Resistance in Rice

In order to clarify the linkage relationships among resistance genes to the brown planthopper, Nilaparvata lugens Stal., the dwarf disease and the stripe disease, intercrosses among Kanto PL 2, Kanto PL 3, Mineyutaka and Nipponbare were made. Kanto PL 2 is a parental line of japonica type rice resistant to the brown planthopper, and has Bph 1 gene derived from Mudgo. On the other hand, Kanto PL 3 is a japonica parental line resistant to the dwarf disease, and has one dominant gene derived from Pe-bi-hun. These two lines are also resistant to the stripe disease. Mineyutaka is the first resistant cultivar to the stripe disease in Japan, and has St2i gene derived from Modan. Firstly, based on the segregation of F3 lines of the reciprocal crosses between Kanto PL 2 and Kanto PL 3, it was estimated that Bph 1 is independent of the gene for resistance to the dwarf disease in Kanto PL 3.

Secondary homothallism in Bremia lactucae

Many isolates of Bremia lactucae are heterothallic; some, however, seemed to be self-fertile. Single conidial lines were derived from one self-fertile isolate. The majority of these lines were self-fertile, but some were self-sterile. The self-fertile lines were stable over many asexual generations when subcultured using large numbers of conidia. Attempts to restore self-fertility by culturing self-sterile lines together were not successful. Both normal and abnormal patterns of gametangial development were observed by scanning electron microscopy of a self-fertile line. The pattern of segregation of self-fertile and self-sterile lines from a self-fertile isolate of B. lactucae is similar to that described for the homothallic isolates of Phytophthora drechsleri. It is suggested that self-fertility in B. lactucae, as in P. drechsleri, may be due to the chromosomal determinants of compatibility-type being trisomic following numerical nondisjunction at meiosis. The segregation of self-sterile lines from the self-fertile isolate may have involved at least transitory heterokaryosis.

Chapter 2 Migration and Differentiation of Neural Crest Cells

Publisher Summary This chapter reviews the present state of knowledge concerning the cell types derived from the neural crest and discusses recent advances concerning the migratory process. It focuses on the migration and differentiation of the peripheral nervous system. Among the fundamental problems raised by the ontogeny of the neural crest, the molecular basis of crest cell migration and localization still remains a poorly understood question. Because active investigation of this problem has been recently initiated in several laboratories, one can expect some progress to emerge in this field in the near future. In regard to the other basic question concerning segregation of the various cell lines arising from the neural crest, interesting advances have been made. The experimental analysis of autonomic nerve cell differentiation has shown that the choice of transmitter synthesis remains labile for a while during differentiation of the autonomic neuroblasts into fully functional adrenergic or cholinergic neurons. One of the most attractive hypotheses that could account for the experimental data is that the autonomic neuroblast normally goes through a state during which it is able to synthesize both transmitters (catecholamine and ACh). Thereafter, environmental cues stimulate selectively one or the other of these metabolic pathways until the stable state of chemical differentiation is finally reached.

In vitro segregation of different cell lines with neuronal and glial properties from a stem cell line of rat neurotumor RT4.

A clonal stem cell line, RT4-AC, of the rat peripheral neurotumor RT4 differentiates in culture into morphologically distinct cell types RT4-B, RT4-D, and RT4-E (cell type conversion). The multipotential stem cell type RT4-AC and cell type RT4-D produce a glial marker, S100 protein, but RT4-B and RT4-E do not. The stem cells also show a small but significant response to veratridine on voltage-dependent Na+ influx. Cell types RT4-B and RT4-E show a clear response of voltage-dependent Na+ influx to veratridine, typical of neuronal cells, whereas cell type RT4-D is completely negative. These results indicate that (i) the stem cell type RT4-AC shows both neuronal and glial properties, (ii) cell types RT4-B and RT4-E have a neuronal property, and (iii) cell type RT4-D has a glial property. Therefore, cell type conversion of stem cell RT4-AC to RT4-B and RT4-E cells seems to result in differentiation towards neuronal cell types, and cell type conversion of RT4-AC to RT4-D results in differentiation towards a glial type in culture.