A transient decrease in N-myc expression and its biological role during differentiation of human embryonal carcinoma cells

Induction of Sp1 in differentiating human embryonal carcinoma cells triggers transcription of the fibronectin gene

Cells of the human embryonal carcinoma line NEC14 proliferate as densely packed clusters consisting of small, polygonal stem cells and do not express a detectable level of fibronectin (FN). Upon induction of differentiation by treatment with N,N'-hexamethylene bisacetamide (HMBA), the level of FN mRNA increased steeply within 24 h and FN began to be accumulated, along with the organization of actin filaments in the cells. The FN promoter elements required for the activation were analyzed in reference to a cluster of GC boxes by using the chloramphenicol acetyltransferase (CAT) gene fused to 5' sequential-deletion derivatives of the promoter and promoters carrying base substitutions in the GC boxes. Among four GC boxes, GC boxes 2 and 3 had the greatest effect on promoter activation, and base substitutions in these GC boxes resulted in 80% reduction in promoter activity. The pattern of DNA-protein complex formation with these GC boxes changed drastically after induction of differentiation. The extract prepared from undifferentiated NEC14 cells formed fast-migrating complexes (UnD complexes), while the extract prepared from NEC14 cells treated with HMBA for 24 h formed slow-migrating complexes containing Sp1. Both complexes were formed predominantly with GC box 2. Base substitutions within the GC boxes completely abolished the formation of both UnD and Sp1 complexes. Consistent with these changes, the Sp1 level increased steeply within 24 h. Induction of Sp1 expression in NEC14 cells effectively stimulated the promoter activity of the transfected FN promoter-CAT constructs. These results indicate that activation of the FN promoter in differentiating NEC14 cells occurs by the steep induction of Sp1, which prevents an undifferentiated cell factor from binding to the Sp1 sites.

Immunoreactive neuron-specific enolase (NSE) is expressed in testicular carcinoma-in-situ

Neuron-specific enolase (NSE) is a well-known marker of tumours that have neuroendocrine origin. High levels of NSE have also been described in various types of testicular germ cell neoplasms, particularly in seminomas. To evaluate the presence of NSE in testicular carcinoma-in situ (CIS), a preinvasive stage of testicular germ cell tumours, a panel of CIS tissue specimens was examined. Fifteen of 18 (83 per cent) CIS samples showed immunohistochemical staining with anti-NSE monoclonal antibody. Immunoreactivity has also been found in overt testicular germ cell tumours, including seminomas, non-seminomas, and a mixed germ cell tumour. As the co-existence of high NSE production and gene amplification of N-myc has been reported in some tumours, including germ cell tumours, the expression of the protein product of N-myc was also examined in this study, but only sporadic cases showed N-myc staining. These results are evidence against a relationship between NSE and N-myc in testicular germ cell tumours. The high expression of NSE in CIS and overt germ cell tumours may be due to the increased gene dosage effect associated with the overrepresentation of isochromosome 12p.

TGF beta 1 inhibits branching morphogenesis and N-myc expression in lung bud organ cultures

Lung buds isolated from 11.5 days post coitum mouse embryos survive and undergo branching morphogenesis in culture. This organ culture system was used to examine the role of TGF beta 1 and N-myc expression in lung branching morphogenesis. By 24 hours, TGF beta 1 reversibly inhibited branching morphogenesis in a concentration-dependent manner. N-myc is known to be expressed during embryonic development in epithelial cells involved in branching morphogenesis and homozygous null N-myc mice have defects in lung development. In the present study, TGF beta 1 was shown to inhibit the steady-state level of N-myc RNA 3- to 4-fold at 14 and 48 hours of treatment as measured by northern blot and RNase protection analysis. Suppression of N-myc expression in epithelium was confirmed by in situ hybridization. Since inhibition of N-myc occurred prior to the observed changes in morphology and previous genetic studies have demonstrated and important role for N-myc in lung development, a model is proposed in which TGF beta 1 inhibits tracheobronchial development by inhibiting expression of N-myc.

Culturing the epiblast cells of the pig blastocyst

Pig epiblast cells that had been separated from other early embryonic cells were cultured in vitro. A three-step dissection protocol was used to isolate the epiblast from trophectoderm and primitive endoderm before culturing. Blastocysts collected at 7 to 8 days postestrus were immunodissected to obtain the inner cell mass (ICM) and destroy trophectodermal cells. The ICM was cultured for 2 to 3 days on STO feeder cells. The epiblast was then physically dissected free of associated primitive endoderm. Epiblast-derived cells, grown on STO feeders, produced colonies of small cells resembling mouse embryonic stem cells. This primary cell morphology changed as the colonies grew and evolved into three distinct colony types (endodermlike, neural rosette, or complex). Cell cultures derived from these three colony types spontaneously differentiated into numerous specialized cell types in STO co-culture. These included fibroblasts, endodermlike cells, neuronlike cells, pigmented cells, adipogenic cells, contracting muscle cells, dome-forming epithelium, ciliated epithelium, tubule-forming epithelium, and a round amoeboid cell type resembling a plasmacyte after Wright staining. The neuronlike cells, contracting muscle cells, and tubule-forming epithelium had normal karyotypes and displayed finite or undefined life spans upon long-term STO co-culture. The dome-forming epithelium had an indefinite life span in STO co-culture and also retained a normal karyotype. These results demonstrate the in vitro pluripotency of pig epiblast cells and indicate the epiblast can be a source for deriving various specialized cell cultures or cell lines.

Subtractive cDNA cloning using oligo(dT)30-latex and PCR: isolation of cDNA clones specific to undifferentiated human embryonal carcinoma cells

The human embryonal carcinoma cell line NEC14 can be induced to differentiate by the addition of 10(-2)M N,N'-hexamethylene-bis-acetamide (HMBA). A subtractive cDNA library specific to undifferentiated NEC14 cells was constructed using oligo(dT)30-Latex and polymerase chain reaction (PCR). The method was designed to improve the efficiency of subtraction and the enrichment of cDNA clones corresponding to low abundance mRNAs. The single strand of cDNA was made from mRNA prepared from the HMBA-treated NEC14 cells using an oligo(dT)30 primer covalently linked to Latex particles. After removal of the mRNA template by heat-denaturation and centrifugation, the subtractive hybridization was carried out between the cDNA-oligo(dT)30-Latex and mRNA from untreated NEC14 cells. Unhybridized mRNA collected by centrifugation was hybridized repeatedly to the cDNA-oligo(dT)30-Latex and subtractive mRNA was converted to cDNA. The subtractive cDNA was then amplified by PCR and cloned into pBluescript II KS-. The cDNA library thus constructed consisted of approximately 10,000 independent clones with cDNA inserts of 1.7 Kb on average. Differential hybridization of these transformants indicated that approximately 3% of them contained cDNA inserts specific to the undifferentiated EC cells, some of which were derived from low abundance mRNAs.

Interaction of nuclear factors with the regulatory region of the N-myc gene during differentiation of human embryonal carcinoma cells

The human embryonal carcinoma cell line, NEC14, can be induced to differentiate by the addition of 10(-2) M N,N'-hexamethylene-bis-acetamide (HMBA). During the early stage of HMBA-induced differentiation, the level of N-myc expression decreased steeply and transiently, and then quickly returned to its original level after reaching a minimal level at 18 h after addition of HMBA. Nuclear run-on experiments indicated that this transient decrease is regulated at the transcription start point. To investigate the mechanism of this down-regulation, the 5'-flanking region of the human N-myc gene was cloned and sequenced. Computer analysis of the sequence revealed high homology with the 5'-flanking region of the mouse N-myc gene, especially (greater than 80%) in the region of nt positions -1777 to -1732, nt positions -763 to -501 and nt positions -260 to + 1. The patterns of protein binding to the upstream region during the early stage of NEC14 cell differentiation were analyzed by gel retardation assay. The DNA fragments VIII and X, containing the sequences of nt positions -1437 to -1237 and nt positions -1863 to -1710, respectively, formed the DNA-protein complexes which were greatly reduced in quantity in the cell extract prepared 18 h after the addition of HMBA. This reduction, however, was not observed with an extract similarly prepared from the NEC14 derivative cell line, H10, expressing the N-myc gene constitutively. These results suggest a causal connection between the complex formation and the high-level transcription of the N-myc gene.