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PubMed2006

Gene expression divergence and the origin of hybrid dysfunctions.

Hybrids between closely related species are often sterile or inviable as a consequence of failed interactions between alleles from the different species. Most genetic studies have focused on localizing the alleles associated with these failed interactions, but the mechanistic/biochemical nature of the failed interactions is poorly understood. This review discusses recent studies that may contribute to our understanding of these failed interactions. We focus on the possible contribution of failures in gene expression as an important contributor to hybrid dysfunctions. Although regulatory pathways that share elements in highly divergent taxa may contribute to hybrid dysfunction, various studies suggest that misexpression may be disproportionately great in regulatory pathways containing rapidly evolving, particularly male-biased, genes. We describe three systems that have been analyzed recently with respect to global patterns of gene expression in hybrids versus pure species, each in Drosophila. These studies reveal that quantitative misexpression of genes is associated with hybrid dysfunction. Misexpression of genes has been documented in sterile hybrids relative to pure species, and variation in upstream factors may sometimes cause the over- or under-expression of genes resulting in hybrid sterility or inviability. Studying patterns of evolution between species in regulatory pathways, such as spermatogenesis, should help in identifying which genes are more likely to be contributors to hybrid dysfunction. Ultimately, we hope more functional genetic studies will complement our understanding of the genetic disruptions leading to hybrid dysfunctions and their role in the origin of species.

Alleles↗
PubMed2026

Genome-Wide Characterization and Salt-Responsive Expression Divergence of Chromosome Group 2 and Group 6 TaBADH Genes in Wheat.

Betaine aldehyde dehydrogenase (BADH) catalyzes the final step in glycine betaine biosynthesis, but the evolutionary divergence and differential salt responsiveness of BADH homeologs in bread wheat remain unclear. We identified six TaBADH genes and analyzed their phylogenetic relationships, conserved motifs, gene structures, promoter cis-acting elements and synteny. RNA-seq and qRT-PCR were used to compare expression in salt-tolerant Jimai 60 and salt-sensitive Chinese Spring under 200 mM NaCl, and BADH activity, glycine betaine, H2O2 and malondialdehyde (MDA) were measured during treatment. The genes separated into chromosome group 2 and group 6 clades with distinct structural and transcriptional patterns. TaBADH-2B encoded a shorter protein and lacked several conserved motifs. Group 6 genes showed stronger salt-responsive expression in Jimai 60, with TaBADH-6D displaying the strongest and most sustained induction. Jimai 60 also showed higher BADH activity and glycine betaine accumulation and lower H2O2 and MDA contents at later time points. Expression of TaBADH-6D improved E. coli growth under 200 mM NaCl. These findings identify homeolog-specific divergence within the BADH wheat family and support TaBADH-6D as a candidate for plant-level functional validation.

TaBADH-6D↗
PubMed1996

Acetylcholinesterase and nicotinic acetylcholine receptor expression diverge in muscular dysgenic mice lacking the L-type calcium channel.

L-type Ca2+ channels play critical roles in achieving stabilization of acetylcholinesterase (AChe) mRNA during myogenesis in C2-C12 skeletal muscle cells. To ascertain the importance of this signaling pathway in AChE expression during skeletal muscle development in the animal, we examined AChE mRNA levels in skeletal muscle and heart from control (+/+) and muscular dysgenic (mdg/mdg) mice that lack the skeletal, but not the cardiac, muscle L-type Ca2+ channels. RNase protection analysis showed 40-60% reductions in content of AChE mRNA in leg muscle, but not heart, from newborn and day 18 embryonic dysgenic mice. AChE activity was also reduced uniquely in skeletal muscle. In contrast to AChE transcripts, mRNA levels of the alpha-subunit of the nicotinic acetylcholine receptors (nAChRs) were increased in dysgenic skeletal muscle. Similar alterations in activity and mRNA levels of AChE were also observed form skeletal muscle cell lines derived from mdg mice. Because run-on transcription revealed no corresponding decrease in transcription rate, the decrease in mRNA content is likely a consequence of the inability of the dysgenic muscle cells to stabilize AChE mRNA during differentiation. These findings indicate that L-type Ca2+ channels play an important role in regulation of AChE expression during skeletal muscle development in vivo. The differential influence of muscle dysgenesis on mRNA levels of AChE and nAChRs provides additional evidence for distinct mechanisms of regulation of these two proteins.

Acetylcholinesterase↗
PubMed2004

Cathepsin D protein levels in colorectal tumors: divergent expression patterns suggest complex regulation and function.

Cathepsin D protein patterns were analyzed in 59 colorectal tumors by Western blotting, glycosylation and immunohistochemical assays. Measurement of protein content by laser densitometry of tumor/normal pairs on Western blots revealed loss of cathepsin D protein in more than 50% of colorectal tumors. Independent loading controls and statistical estimates of reproducibility on duplicate assays confirmed frequent decreases in cathepsin D. For cases having a tumor/normal ratio (T/N) <1, the average T/N was 0.50+/-0.19, equivalent to the loss of one cathepsin D allele. However, 2-fold increases in cathepsin D protein levels were also observed in approximately 1/3 of tumors, supporting the concept that colorectal cancers develop via divergent molecular pathways and that cathepsin D may function differently in different cancers. Although normal cathepsin D expression was detected in some earlier stage tumors, protein levels became increasingly bimodal with progression such that cathepsin D levels were increased in 1/3 but decreased in 2/3 of stage III and IV cancers. Other laboratories have reported both significant loss and gain of chromosome 11 (site of the cathepsin D gene) in different colorectal tumors, providing a possible mechanism for our observations on cathepsin D. However, differential regulation of cathepsin D expression by mutant versus wild-type p53 may also contribute to variable cathepsin D levels in colorectal cancers. Immunohistochemical studies demonstrated a shift from a predominantly punctate distribution of cathepsin D protein in normal mucosa to a more diffuse cytoplasmic distribution in tumor tissues. Mutant forms of cathepsin D were not detected in tumors either as changes in electrophoretic mobility or altered glycosylation but minor changes in protein sequence could not be ruled out. Loss of cathepsin D protein may provide an advantage to colorectal tumors related to a loss of cathepsin D function in proapototic or antiangiogenic pathways while increased cathepsin D may promote cancer cell proliferation or invasion.

Apoptosis↗
PubMed1989

Karyotypic analysis of two related cervical carcinoma cell lines that contain human papillomavirus type 18 DNA and express divergent differentiation.

The cell lines C-4I and C-4II were established in culture from a nonkeratinizing squamous carcinoma of the uterine cervix. Both lines contain human papillomavirus (HPV) type 18 DNA (Brandt et al., Cold Spring Harbor Laboratories, 5:179, 1987) and both are hypodiploid with similar, but not identical, karyotypes. Each line expresses multiple characteristics of ectocervical epithelial differentiation, but the characteristics differ between the lines. In the present study, G banding of the lines showed that cells of both lines have two normal chromosomes 1-5, 8-10, 13, 16, and 17, one normal chromosome 12 and 14, and no normal chromosomes 15 and 18. The lines share three abnormal chromosomes, der(8)t(8q;12q), der(18)t(18q;?), and i(5p). There are specific differences between the lines. C-4I has two normal chromosomes 6, while C-4II has one; C-4II has two chromosomes 11 and der(18)t(18q;?), while C-4I lacks both chromosomes 11 and has one der(18)t(18q;?). Each line has unique markers that include del(11)(p11), del(22)(q12), and del(21)(q21) in C-4I and i(15q), der(X)t(Xq;9p), der(6)t(6p;14q), and del(4)(q21) in C-4II. The results show that these phenotypically distinct lines are derived from the same clone and that the 8q arm (the site of HPV 18 integration) is present in three copies in both lines. They also define several chromosome rearrangements that are compatible with the expression of specific differentiation markers.

Carcinoma↗
PubMed2026

Evolution and Expression Divergence of Legume PAL Genes Suggest Associations with Drought Response and Root Nodule Development.

Comparative genomic analyses provide insight into the mechanisms underlying gene-family evolution and crop adaptation. Here, we used the legume phenylalanine ammonia-lyase (PAL) gene family as a model and integrated pan-genomic, phylogenetic, molecular evolutionary, duplication-mode, and transcriptomic analyses, while developing GFtool for gene family identification. Across 45 genomes, we identified 302 PAL genes and classified them into five Groups. Groups 1-3 represented ancient lineages shared with outgroups, whereas Groups 4 and 5 were legume-specific. Molecular-clock analyses placed the divergence of Group 2 near the Paleocene-Eocene transition, while Groups 4 and 5 diversified from the middle Eocene to the early Oligocene. WGD/segmental duplication broadly contributed to PAL copy-number expansion, whereas tandem duplication was enriched in Group 5 of Papilionoideae. Group 2 genes showed drought-induced expression, whereas Group 5 genes were associated with early root nodule development. GFtool provides a scalable framework for gene-family studies.

Fabaceae↗
PubMed2006

Dioecious Schistosoma mansoni express divergent gene repertoires regulated by pairing.

Pairing of adult Schistosoma mansoni parasites initiates a cascade of events including mating and egg production that ultimately leads to immuno-pathological lesions during schistosomiasis. To identify genes associated with this important biological process, we studied parasites isolated from single- versus mixed-sex cercariae-infected mice using DNA microarray analysis to uncover pair-regulated transcriptional profiles. We report that: (i) transcriptomes of parasites isolated from single-sex infections are significantly more complex than their mixed-sex counterparts; (ii) transcriptomes of single-sex males are distinct from mixed-sex males; and (iii) not all transcripts, previously hypothesized to be critical in female egg production, are regulated by pairing.

Animals↗
PubMed1999

Conserved and divergent expression patterns of the proteolipid protein gene family in the amphibian central nervous system.

The recent discovery of a proteolipid protein gene family has revealed that its members are in fact widely distributed and are not exclusively associated with myelination. To date, three different gene products, DMalpha/DM-20/PLP, DMbeta/M6a, and DMgamma/M6b, have been isolated from certain primitive fish species, mouse, and human central nervous system (CNS). We cloned Xenopus laevis orthologues of DMbeta/M6a and DMgamma/M6b and investigated the expression patterns of these gene transcripts as well as that of PLP in developing Xenopus CNS. As is the case in shark and mouse, the mRNA encoding the major myelin integral protein, PLP, is first detected at stage 42/43 in tadpoles and is exclusively found in morphologically recognizable oligodendrocytes throughout the brain, while DMbeta mRNA is solely expressed in young presumptive neurons in the gray matter. There exist two distinct DMgamma mRNAs and, in contrast to these evolutionarily conserved expression patterns, DMgamma mRNAs distribute uniquely within the ventricular zone in young tadpoles (stage 25) through maturity. Furthermore, both DMbeta and DMgamma are expressed in the developing retina, and their distributions are different from one other. In Xenopus CNS, therefore, the expression patterns of three proteolipid proteins, PLP, DMbeta, and DMgamma, are distinct from each other, implying very different roles for their protein products within the cell populations in which they are expressed.

Amino Acid Sequence↗
PubMed2002

Oligodendrocyte precursor cells from different brain regions express divergent properties consistent with the differing time courses of myelination in these regions.

Different CNS regions exhibit different temporal patterns of oligodendrocyte generation and myelinogenesis. Characterization of oligodendrocyte-type-2 astrocyte progenitor cells (here abbreviated as O-2A/OPCs) isolated from different regions indicates these developmental patterns are consistent with properties of the specific O-2A/OPCs resident in each region. Marked differences were seen in self-renewal and differentiation characteristics of O-2A/OPCs isolated from cortex, optic nerve and optic chiasm. In conditions where optic nerve-derived O-2A/OPCs generated oligodendrocytes within 2 days, oligodendrocytes arose from chiasm-derived cells after 5 days and from cortical O-2A/OPCs only after 7-10 days. These differences, which appear to be cell-intrinsic (and may be related to intracellular redox state), were manifested both in reduced percentages of clones producing oligodendrocytes and in a lesser representation of oligodendrocytes in individual clones. In addition, responsiveness of optic nerve-, chiasm- and cortex-derived O-2A/OPCs to thyroid hormone (TH) and ciliary neurotrophic factor (CNTF), well-characterized inducers of oligodendrocyte generation, was inversely related to the extent of self-renewal observed in basal division conditions. Our results demonstrate hitherto unrecognized complexities among the precursor cells thought to be the immediate ancestors of oligodendrocytes, and suggest that the properties of these different populations may contribute to the diverse time courses of myelination in different CNS regions.

Animals↗
PubMed2002

Divergent expression and localization of aquaporin 5, an exocrine-type water channel, in the submandibular gland of Sprague-Dawley rats.

By Western blot analysis, the expression level of aquaporin (AQP) 5 in the submandibular gland (SMG) was found to be different among individual rats of the Sprague-Dawley (SD) strain. Such differences were observed for AQP5 but not for AQP1 and consequently the SD strain was divided into two groups, one expressing a high level of AQP5 and the other a low one. The difference in average intensity of expression between the two groups was more than twofold. Immunohistochemical analysis of the SMG demonstrated that the AQP5 protein was localized in the basal and apical/lateral plasma membrane of acinar cells in rats expressing the high level of AQP5. In the rat expressing the low level, however, this channel protein was localized strongly in the apical/lateral plasma membrane, but only very weakly in the basal membrane of the acinar cells. Such a diverse localization of AQP5 was confirmed by Western blotting as well. Breeding between brother and sister was repeated for two times within high expressers and low expressers to obtain the third generation progenies (F2); the AQP5 level of the SMG in the third generation (F2 rats) from high expressers was significantly higher than the F2 from low expressers. Our present study suggests the existence of genetic variation in the expression of a water channel protein, AQP5, in rats.

Animals↗
PubMed2001

Divergent expression of delayed rectifier K(+) channel subunits during mouse heart development.

The repolarization phase of the cardiac action potential is dependent on transmembrane K(+) currents. The slow (I(Ks)) and fast (I(Kr)) components of the delayed-rectifier cardiac K(+) current are generated by pore-forming alpha subunits KCNQ1 and KCNH2, respectively, in association with regulatory beta-subunit KCNE1, KCNE2 and perphaps KCNE3. In the present study we have investigated the distribution of transcripts encoding these five potassium channel-forming subunits during mouse heart development as well as the protein distribution of KCNQ1 and KCNH2. KCNQ1 and KCNH2 mRNAs (and protein) are first expressed at embryonic day (E) 9.5, showing comparable levels of expression within the atrial and ventricular myocardium during the embryonic and fetal stages. In contrast, the beta-subunits display a more dynamic pattern of expression during development. KCNE1 expression is first observed at E9.5 throughout the entire myocardium and progressively is confined to the ventricular myocardium. With further development (E16.5), KCNE1 expression is mainly confined to the compact ventricular myocardium. KCNE2 is first expressed at E9.5 and it is restricted already to the atrial myocardium. KCNE3 is first expressed at E8.5 throughout the myocardium and with further development, it becomes restricted to the atrial myocardium. The fact that alpha subunits are homogeneously distributed within the myocardium, whereas the beta subunits display a regionalized expression profile during cardiac development, suggest that differences in the slow and fast component of the delayed-rectifier cardiac K(+) currents between the atrial and the ventricular cardiomyocytes are mainly determined by differential beta-subunit distribution.

Animals↗
PubMed1985

Divergent expression of HLA-DC/MB, -DR, and -SB region products on normal and pathological tissues as detected by monoclonal antibodies.

A group of eight monoclonal antibodies directed against different monomorphic determinants of HLA-class II molecules was used to investigate the distribution of HLA-DC/DS/MB, -DR and -SB-like antigens on normal and pathological lymphoid and nonlymphoid tissues of human adult and fetal donors. HLA-MB/DC/DS-like molecules, as defined by the antibody TU 22, showed the most limited distribution as they were detected on B-lymphocytes, monocyte/macrophage subpopulations and distinct interstitial cells of various organs. HLA-DR and -SB-like antigens characterized by the other anti-HLA-class II reagents (TU34, TU35, TU37, TU39, TU43, TU58) were also present on these cell types. However, selective expression of HLA-DR and/or -SB like molecules was demonstrated with these antibodies on certain vascular endothelia, as well as different B-cell lymphomas and distinct epithelial cells in adults. Exclusive reactivity of the antibody TU39 shown on endothelial cells of fetal liver and kidney suggested specific functions of HLA-SB antigens during ontogeny. Furthermore, HLA-DR and/or -SB like molecules but not TU22+ HLA-DC/MB antigens were found to be inducible on normally Ia-like antigen negative epithelial cells of various diseased organs. Implications of this differential tissue distribution of HLA-DC/MB/DS, -DR and -SB like products in relation to organ transplantation, regulation of immune responses and cell differentiation are discussed.

Adult↗
PubMed2000

Conserved and divergent expression of T-box genes Tbx2-Tbx5 in Xenopus.

We report here the identification of four members of T-box family genes, Xltbx2-Xltbx5, in Xenopus. Two of them are probable pseudovariant genes of XTbx5 and ET, a putative Xenopus ortholog of Tbx3. We compared their expression patterns in both embryos and limbs. In embryos, expression of Xltbx2 and Xltbx3 showed novel diversities, such as Xltbx2 in the neural crest cells and Xltbx3 in the ventral spinal cord, together with mutual similarities in the following regions: dorsal retina, proctoderm, lateral line organ, cement gland and cranial ganglia. The patterns in limbs were highly conserved with mouse and chick orthologs, including the limb-type specific expression of Xltbx4 and Xltbx5. In addition, RT-PCR analysis showed that they are expressed weakly even in adult limbs as previously reported in the newt.

Amino Acid Sequence↗
PubMed1985

Divergent expression of cytotoxic and microbicidal functions of rabbit alveolar and peritoneal macrophages: effects of non-specific activation and a natural microbicidal peptide, MCP-1.

Alveolar macrophages from NZW rabbits were intrinsically toxic to 6 xenogeneic cell lines and to Candida albicans in vitro. Macrophage-mediated candidacidal activity, but not cytostasis (inhibition of [3H] thymidine incorporation by target cells) or cytotoxicity (reduction in target cell number), was enhanced by prior injection of rabbits with Freund's complete adjuvant (FCA). Compared with alveolar macrophages, peritoneal macrophages were less candidacidal (median C. albicans killed, 24% versus 16%, p less than 0.01). In contrast to alveolar macrophages, peritoneal macrophages were not consistently cytostatic or cytotoxic. Only candidacidal activity was enhanced in FCA-elicited peritoneal macrophages (median C. albicans killed 28% versus 16% for resident peritoneal macrophages, p less than 0.01). Microbicidal concentrations of a cationic peptide produced by rabbit alveolar macrophages (MCP-1, 25-100 micrograms/ml) did not inhibit growth of 4 murine cell lines in vitro. Macrophage-mediated cytostasis and cytotoxicity were not enhanced by culture with exogenous MCP-1. Macrophage-mediated cytostasis was also unchanged in cultures containing 10(-5) 2' deoxycytidine. We conclude that rabbit macrophage populations are restricted in their expression of cytostatic and cytotoxic functions, that microbicidal activation can occur independently of cytotoxic activation and that in this system mechanisms of macrophage-mediated cytotoxicity to xenogeneic target cells are independent of MCP-1 and thymidine.

Animals↗
PubMed2002

Up-regulation of the dendritic cell marker CD83 on polymorphonuclear neutrophils (PMN): divergent expression in acute bacterial infections and chronic inflammatory disease.

Upon cultivation with interferon-gamma (IFN-gamma ) and granulocyte/macrophage-colony stimulating factor (GM-CSF) polymorphonuclear neutrophils (PMN) acquire characteristics of dendritic cells, including expression of major histocompatibility complex (MHC) class II antigens, of the co-stimulatory antigens CD80, CD86 and of CD83, the latter considered to be specific for dendritic cells. Dendritic-like PMN were also able to present to T cells antigens in a MHC class II-restricted manner. To assess whether dendritic-like PMN are also generated in vivo, cells of patients with acute bacterial infections and of patients with chronic inflammatory diseases (primary vasculitis) were tested. During acute infection up to 80% of PMN acquired CD83, but remained negative for MHC class II, CD80 or CD86. PMN of patients with primary vasculitis expressed MHC class II antigens, CD80 and CD86, but not CD83, indicating that up-regulation of MHC class II and of CD83 are not necessarily linked to each other. Indeed, parallel studies with PMN of healthy donors showed that while IFN-gamma and granulocyte/macrophage colony stimulating factor (GM-CSF) induced both, MHC class II and CD83, tumour necrosis factor (TNF)-alpha selectively induced de novo synthesis of CD83. The function of CD83 on PMN is still elusive. A participation in the MHC class II-restricted antigen presentation could be ruled out, consistent with the segregation of MHC class II and CD83 expression. Regardless, however, of its function, CD83 expression could serve as a marker to differentiate between acute and chronic inflammation.

Acute Disease↗
PubMed2002

Divergent expression of inflammatory dermal chemokines in cutaneous leishmaniasis.

Human leishmaniasis is caused by protozoan Leishmania (L.) parasites and comprises a heterogeneous group of clinical appearances ranging from visceral to cutaneous leishmaniasis. In the New World, L. mexicana mediates American cutaneous leishmaniasis, one of the most common forms of this disease. Two different disease progressions can be observed: (i) self-healing localized cutaneous leishmaniasis (LCL) and (ii) progressive diffuse cutaneous leishmaniasis (DCL). These different forms are associated with a T helper 1 (Th1) or Th2 response, respectively, and are additionally characterized by opposing dermal chemokine profiles. Lesions of LCL show high expression of CCL2/MCP-1, CXCL9/MIG, CXCL10/IP-10 and only low amounts of CCL3/MIP-1alpha. In contrast, lesions of chronic DCL are dominated by the expression of CCL3/MIP-1alpha. This finding implies that CCL2/MCP-1 contributes to the healing process. Indeed, CCL2/MCP-1 induces leishmanicidal activities in human monocytes in contrast to CCL3/MIP-1alpha. This effect is enhanced by interferon-gamma and abrogated by interleukin-4. In the murine model of leishmaniasis, the impact of CCL2/MCP-1 is well documented. Normally resistant mice become susceptible for Leishmania infections if CCR2, the receptor for CCL2/MCP-1, is knocked out. Based on this evidence, we propose that tissue specific expression of these small molecules actively regulates cell traffic and tissue localization of effector cells and, additionally, has direct immunological effects.

Animals↗
PubMedDate not supplied

Additional hox clusters in the zebrafish: divergent expression patterns belie equivalent activities of duplicate hoxB5 genes.

The evolution of metazoan body plans has involved changes to the Hox genes, which are involved in patterning the body axis and display striking evolutionary conservation of structure and expression. Invertebrates contain a single Hox cluster whereas tetrapods possess four clusters. The zebrafish has seven unlinked hox clusters, a finding that is difficult to reconcile with the notion that genomic complexity, reflected by Hox cluster number, and morphological complexity are causally linked, as the body plan of the zebrafish is not obviously more complex than that of the mouse or human. Why have the additional hox genes in zebrafish been conserved? To address the role of these additional zebrafish hox genes, we have examined the duplicate hoxB5 genes, hoxB5a, and hoxB5b. Conservation of gene duplicates can occur when one gene acquires a new function (neofunctionalization), or when the ancestral function is divided between the two duplicates (subfunctionalization). hoxB5a and hoxB5b are expressed in distinct domains, and their combined expression domain is strikingly similar to that of single Hoxb5 genes in other species. The biochemical functions encoded by the two genes were studied by overexpression, which resulted in identical developmental defects in the anterior hindbrain and cranial neural crest, suggesting strongly that hoxB5a and hoxB5b have equivalent biochemical properties with respect to early development. From these studies, we conclude that conservation of hoxB5a and hoxB5b is likely the result of division of the ancestral Hoxb5 function between the two genes, without significant changes in biochemical activity. These results suggest a resolution to the conundrum of the extra hox genes and clusters in the zebrafish, since if any of the additional hox genes in the zebrafish are similarly subfunctionalized, they are unlikely to supply novel genetic functions. Thus, the morphological complexity potentially conferred by the majority of additional zebrafish hox clusters may not be substantially greater than that conferred by the four tetrapod clusters.

3' Untranslated Regions↗
PubMed2004

Divergent expression changes of telomerase and E6/E7 mRNA, following integration of human papillomavirus type 33 in cultured epithelial cells.

Expression of the viral oncogenes E6 and E7, and telomerase, was investigated, using a cell line from a mild dysplastic vaginal lesion containing human papillomavirus (HPV) type 33. During passaging of the cells, there was a change towards a cancer phenotype, and a shift from episomal to integrated HPV. Levels of hTERT (catalytic subunit of telomerase) mRNA, and telomerase activity in cells carrying episomal virus seemed constant during passaging. During passaging of cells containing integrated HPV, however, the levels of oncogene mRNA decreased, while hTERT mRNA and telomerase activity increased sharply. Thus, in those cells there is no direct correlation between changes of oncogene and telomerase expression. Conceivably, viral oncogene expression might trigger telomerase up-regulation in an early subpopulation of cells, which during subsequent passaging could be selected for.

Cell Line, Tumor↗