Central role of the habenulo-interpeduncular system in the neurodevelopmental basis of susceptibility and resilience to anxiety in mice

Having experienced stress during sensitive periods of brain development strongly influences how individuals cope with later stress. Some are prone to develop anxiety or depression, while others appear resilient. The as-yet-unknown mechanisms underlying these differences may lie in how genes and environmental stress interact to shape the circuits that control emotions. Here, we investigated the role of the habenulo-interpeduncular system (HIPS), a critical node in reward circuits, in early stress-induced anxiety in mice. We found that habenular and IPN components characterized by the expression of Otx2 are synaptically connected and particularly sensitive to chronic stress (CS) during the peripubertal period. Stress-induced peripubertal activation of this HIPS subcircuit elicits both HIPS hypersensitivity to later stress and susceptibility to develop anxiety. We also show that HIPS silencing through conditional Otx2 knockout counteracts these effects of stress. Together, these results demonstrate that a genetic factor, Otx2, and stress interact during the peripubertal period to shape the stress sensitivity of the HIPS, which is shown to be a key modulator of susceptibility or resilience to develop anxiety.

The caudo-ventral pallium is a novel pallial domain expressing Gdf10 and generating Ebf3-positive neurons of the medial amygdala

In rodents, the medial nucleus of the amygdala receives direct inputs from the accessory olfactory bulbs and is mainly implicated in pheromone-mediated reproductive and defensive behaviors. The principal neurons of the medial amygdala are GABAergic neurons generated principally in the caudo-ventral medial ganglionic eminence and preoptic area. Beside GABAergic neurons, the medial amygdala also contains glutamatergic Otp-expressing neurons cells generated in the lateral hypothalamic neuroepithelium and a non-well characterized Pax6-positive population. In the present work, we describe a novel glutamatergic Ebf3-expressing neuronal subpopulation distributed within the periphery of the postero-ventral medial amygdala. These neurons are generated in a pallial domain characterized by high expression of Gdf10. This territory is topologically the most caudal tier of the ventral pallium and accordingly, we named it Caudo-Ventral Pallium (CVP). In the absence of Pax6, the CVP is disrupted and Ebf3-expressing neurons fail to be generated. Overall, this work proposes a novel model of the neuronal composition of the medial amygdala and unravels for the first time a new novel pallial subpopulation originating from the CVP and expressing the transcription factor Ebf3.

A new genetically engineered mouse model of choroid plexus carcinoma

Choroid plexus carcinomas (CPCs) are highly malignant brain tumours predominantly found in children and associated to poor prognosis. Improved therapy for these cancers would benefit from the generation of animal models. Here we have created a novel mouse CPC model by expressing a stabilised form of c-Myc (MycT58A) and inactivating Trp53 in the choroid plexus of newborn mice. This induced aberrant proliferation of choroid plexus epithelial cells, leading to aggressive tumour development and death within 150 days. Choroid plexus tumours occurred with a complete penetrance in all brain ventricles, with prevalence in the lateral and fourth ventricles. Histological and cellular analysis indicated that these tumours were CPCs resembling their human counterparts. Comparison of gene expression profiles of CPCs and non-neoplastic tissues revealed profound alterations in cell cycle regulation and DNA damage responses, suggesting that dysregulation of cell division and DNA checkpoint pathways may represent key vulnerabilities. This novel animal model of CPC provides an invaluable tool to elucidate the mechanism of CPC formation and to develop successful therapies against this devastating paediatric cancer.

Comprehensive interactome of Otx2 in the adult mouse neural retina

The Otx2 homeodomain transcription factor exerts multiple functions in specific developmental contexts, probably through the regulation of different sets of genes. Protein partners of Otx2 have been shown to modulate its activity. Therefore, the Otx2 interactome may play a key role in selecting a precise target-gene repertoire, hence determining its function in a specific tissue. To address the nature of Otx2 interactome, we generated a new recombinant Otx2(CTAP-tag) mouse line, designed for protein complexes purification. We validated this mouse line by establishing the Otx2 interactome in the adult neural retina. In this tissue, Otx2 is thought to have overlapping function with its paralog Crx. Our analysis revealed that, in contrary to Crx, Otx2 did not develop interactions with proteins that are known to regulate phototransduction genes but showed specific partnership with factors associated with retinal development. The relationship between Otx2 and Crx in the neural retina should therefore be considered as complementarity rather than redundancy. Furthermore, study of the Otx2 interactome revealed strong associations with RNA processing and translation machineries, suggesting unexpected roles for Otx2 in the regulation of selected target genes all along the transcription/translation pathway. The Otx2(CTAP-tag) line, therefore, appears suitable for a systematic approach to Otx2 protein-protein interactions. genesis 53:685-694, 2015. © 2015 Wiley Periodicals, Inc.

Mitochondrial Protection by Exogenous Otx2 in Mouse Retinal Neurons

OTX2 (orthodenticle homeobox 2) haplodeficiency causes diverse defects in mammalian visual systems ranging from retinal dysfunction to anophthalmia. We find that the retinal dystrophy of Otx2(+/GFP) heterozygous knockin mice is mainly due to the loss of bipolar cells and consequent deficits in retinal activity. Among bipolar cell types, OFF-cone bipolar subsets, which lack autonomous Otx2 gene expression but receive Otx2 proteins from photoreceptors, degenerate most rapidly in Otx2(+/GFP) mouse retinas, suggesting a neuroprotective effect of the imported Otx2 protein. In support of this hypothesis, retinal dystrophy in Otx2(+/GFP) mice is prevented by intraocular injection of Otx2 protein, which localizes to the mitochondria of bipolar cells and facilitates ATP synthesis as a part of mitochondrial ATP synthase complex. Taken together, our findings demonstrate a mitochondrial function for Otx2 and suggest a potential therapeutic application of OTX2 protein delivery in human retinal dystrophy.

Otx2 is a target of N-myc and acts as a suppressor of sensory development in the mammalian cochlea

Transcriptional regulatory networks are essential during the formation and differentiation of organs. The transcription factor N-myc is required for proper morphogenesis of the cochlea and to control correct patterning of the organ of Corti. We show here that the Otx2 gene, a mammalian ortholog of the Drosophila orthodenticle homeobox gene, is a crucial target of N-myc during inner ear development. Otx2 expression is lost in N-myc mouse mutants, and N-myc misexpression in the chick inner ear leads to ectopic expression of Otx2. Furthermore, Otx2 enhancer activity is increased by N-myc misexpression, indicating that N-myc may directly regulate Otx2. Inactivation of Otx2 in the mouse inner ear leads to ectopic expression of prosensory markers in non-sensory regions of the cochlear duct. Upon further differentiation, these domains give rise to an ectopic organ of Corti, together with the re-specification of non-sensory areas into sensory epithelia, and the loss of Reissner's membrane. Therefore, the Otx2-positive domain of the cochlear duct shows a striking competence to develop into a mirror-image copy of the organ of Corti. Taken together, these data show that Otx2 acts downstream of N-myc and is essential for patterning and spatial restriction of the sensory domain of the mammalian cochlea.

Head formation: OTX2 regulates Dkk1 and Lhx1 activity in the anterior mesendoderm

The Otx2 gene encodes a paired-type homeobox transcription factor that is essential for the induction and the patterning of the anterior structures in the mouse embryo. Otx2 knockout embryos fail to form a head. Whereas previous studies have shown that Otx2 is required in the anterior visceral endoderm and the anterior neuroectoderm for head formation, its role in the anterior mesendoderm (AME) has not been assessed specifically. Here, we show that tissue-specific ablation of Otx2 in the AME phenocopies the truncation of the embryonic head of the Otx2 null mutant. Expression of Dkk1 and Lhx1, two genes that are also essential for head formation, is disrupted in the AME of the conditional Otx2-deficient embryos. Consistent with the fact that Dkk1 is a direct target of OTX2, we showed that OTX2 can interact with the H1 regulatory region of Dkk1 to activate its expression. Cross-species comparative analysis, RT-qPCR, ChIP-qPCR and luciferase assays have revealed two conserved regions in the Lhx1 locus to which OTX2 can bind to activate Lhx1 expression. Abnormal development of the embryonic head in Otx2;Lhx1 and Otx2;Dkk1 compound mutant embryos highlights the functional intersection of Otx2, Dkk1 and Lhx1 in the AME for head formation.

Deletion of OTX2 in neural ectoderm delays anterior pituitary development

OTX2 is a homeodomain transcription factor that is necessary for normal head development in mouse and man. Heterozygosity for loss-of-function alleles causes an incompletely penetrant, haploinsufficiency disorder. Affected individuals exhibit a spectrum of features that range from developmental defects in eye and/or pituitary development to acephaly. To investigate the mechanism underlying the pituitary defects, we used different cre lines to inactivate Otx2 in early head development and in the prospective anterior and posterior lobes. Mice homozygous for Otx2 deficiency in early head development and pituitary oral ectoderm exhibit craniofacial defects and pituitary gland dysmorphology, but normal pituitary cell specification. The morphological defects mimic those observed in humans and mice with OTX2 heterozygous mutations. Mice homozygous for Otx2 deficiency in the pituitary neural ectoderm exhibited altered patterning of gene expression and ablation of FGF signaling. The posterior pituitary lobe and stalk, which normally arise from neural ectoderm, were extremely hypoplastic. Otx2 expression was intact in Rathke's pouch, the precursor to the anterior lobe, but the anterior lobe was hypoplastic. The lack of FGF signaling from the neural ectoderm was sufficient to impair anterior lobe growth, but not the differentiation of hormone-producing cells. This study demonstrates that Otx2 expression in the neural ectoderm is important intrinsically for the development of the posterior lobe and pituitary stalk, and it has significant extrinsic effects on anterior pituitary growth. Otx2 expression early in head development is important for establishing normal craniofacial features including development of the brain, eyes and pituitary gland.

Purkinje cells and Bergmann glia are primary targets of the TRα1 thyroid hormone receptor during mouse cerebellum postnatal development

Thyroid hormone is necessary for normal development of the central nervous system, as shown by the severe mental retardation syndrome affecting hypothyroid patients with low levels of active thyroid hormone. The postnatal defects observed in hypothyroid mouse cerebellum are recapitulated in mice heterozygous for a dominant-negative mutation of Thra, the gene encoding the ubiquitous TRα1 receptor. Using CRE/loxP-mediated conditional expression approach, we found that this mutation primarily alters the differentiation of Purkinje cells and Bergmann glia, two cerebellum-specific cell types. These primary defects indirectly affect cerebellum development in a global manner. Notably, the inward migration and terminal differentiation of granule cell precursors is impaired. Therefore, despite the broad distribution of its receptors, thyroid hormone targets few cell types that exert a predominant role in the network of cellular interactions that govern normal cerebellum maturation.

Otx2 ChIP-seq reveals unique and redundant functions in the mature mouse retina

During mouse retinal development and into adulthood, the transcription factor Otx2 is expressed in pigment epithelium, photoreceptors and bipolar cells. In the mature retina, Otx2 ablation causes photoreceptor degeneration through a non-cell-autonomous mechanism involving Otx2 function in the supporting RPE. Surprisingly, photoreceptor survival does not require Otx2 expression in the neural retina, where the related Crx homeobox gene, a major regulator of photoreceptor development, is also expressed. To get a deeper view of mouse Otx2 activities in the neural retina, we performed chromatin-immunoprecipitation followed by massively parallel sequencing (ChIP-seq) on Otx2. Using two independent ChIP-seq assays, we identified consistent sets of Otx2-bound cis-regulatory elements. Comparison with our previous RPE-specific Otx2 ChIP-seq data shows that Otx2 occupies different functional domains of the genome in RPE cells and in neural retina cells and regulates mostly different sets of genes. To assess the potential redundancy of Otx2 and Crx, we compared our data with Crx ChIP-seq data. While Crx genome occupancy markedly differs from Otx2 genome occupancy in the RPE, it largely overlaps that of Otx2 in the neural retina. Thus, in accordance with its essential role in the RPE and its non-essential role in the neural retina, Otx2 regulates different gene sets in the RPE and the neural retina, and shares an important part of its repertoire with Crx in the neural retina. Overall, this study provides a better understanding of gene-regulatory networks controlling photoreceptor homeostasis and disease.

Otx2 gene deletion in adult mouse retina induces rapid RPE dystrophy and slow photoreceptor degeneration

Background

Many developmental genes are still active in specific tissues after development is completed. This is the case for the homeobox gene Otx2, an essential actor of forebrain and head development. In adult mouse, Otx2 is strongly expressed in the retina. Mutations of this gene in humans have been linked to severe ocular malformation and retinal diseases. It is, therefore, important to explore its post-developmental functions. In the mature retina, Otx2 is expressed in three cell types: bipolar and photoreceptor cells that belong to the neural retina and retinal pigment epithelium (RPE), a neighbour structure that forms a tightly interdependent functional unit together with photoreceptor cells.

Methodology/Principal Findings

Conditional self-knockout was used to address the late functions of Otx2 gene in adult mice. This strategy is based on the combination of a knock-in CreERT2 allele and a floxed allele at the Otx2 locus. Time-controlled injection of tamoxifen activates the recombinase only in Otx2 expressing cells, resulting in selective ablation of the gene in its entire domain of expression. In the adult retina, loss of Otx2 protein causes slow degeneration of photoreceptor cells. By contrast, dramatic changes of RPE activity rapidly occur, which may represent a primary cause of photoreceptor disease.

Conclusions

Our novel mouse model uncovers new Otx2 functions in adult retina. We show that this transcription factor is necessary for long-term maintenance of photoreceptors, likely through the control of specific activities of the RPE.

OTX5 regulates pineal expression of the zebrafish REV-ERB alpha through a new DNA binding site

The pineal gland plays a central role in the photoneuroendocrine system and acts as a photosensory organ in lower vertebrates. The orphan nuclear receptor Rev-erbalpha (NR1D1) has previously been shown to be expressed in the pineal and to be regulated with a robust circadian rhythm during zebrafish embryogenesis. This early pineal expression is under the control of the transcription factor Orthodenticle homeobox 5 (Otx5). In this paper, we show that Otx5 regulates the second zfRev-erbalpha promoter, ZfP2. Despite the absence of a classical Otx-binding site within ZfP2, this regulation depends on the integrity of the Otx5 homeodomain. Mapping experiments as well as EMSAs show that this interaction between Otx5 and ZfP2 depends on a noncanonical bipartite Otx-binding site (GANNCTTA and TAAA) that we called pineal expression related element (PERE). We showed that PERE is necessary for pineal expression in vivo by injecting zebrafish embryos with wild type and mutated versions of zfRev-erbalpha promoter fused to green fluorescent protein. Interestingly, PERE is found upstream of other genes expressed in the pineal gland, suggesting that it may play an important role in governing pineal expression. Our data establish that PERE is a novel cis-acting element contributing to pineal-specific gene expression and to Otx target gene regulation.

Temporal and spatial delineation of mouse Otx2 functions by conditional self-knockout

To identify the independent spatial and temporal activities of the essential developmental gene the Otx2, the germline mutation of which is lethal at embryonic day 8.5, we floxed one allele and substituted the other with an inducible CreER recombinase gene. This makes 'trans' self-knockout possible at any developmental stage. The transient action of tamoxifen pulses allows time-course mutation. We demonstrate efficient temporal knockout and demarcate spatio-temporal windows in which Otx2 controls the head, brain structures and body development.

Molecular dissection reveals decreased activity and not dominant negative effect in human OTX2 mutants

The paired-type homeodomain transcription factor Otx2 is essential for forebrain and eye development. Severe ocular malformations in humans have recently been associated with heterozygous OTX2 mutations. To document the molecular defects in human mutants, Otx2 structural characterization was carried out. A collection of deletion and point mutants was created to perform transactivation, DNA binding, and subcellular localization analyses. Transactivation was ascribed to both N- and C-termini of the protein, and DNA binding to the minimal homeodomain, where critical amino acid residues were identified. Acute nuclear localization appeared controlled by a nuclear localization sequence located within the homeodomain which acts in conjunction with a novel nuclear retention domain that we unraveled located in the central part of the protein. This region, which is poorly conserved among Otx proteins, was also endowed with dominant negative activity suggesting that it might confer unique properties to Otx2. Molecular diagnostic of human mutant OTX2 proteins discriminates hypomorphic and loss of function mutations from other mutations that may not be relevant to ocular pathology.

Alternative usage ofOtx2 promoters during mouse development

Our previous structural analysis of mouse Otx2 transcripts has revealed the existence of three different promoters and suggested that the corresponding mRNAs could exhibit specific expression patterns. Here, we analyze the precise dynamics of their expression throughout mouse development. Their spatial distribution was determined by isoform-specific in situ hybridization and their relative abundance by real-time reverse transcriptase-polymerase chain reaction. Although the three promoters may be used in the same areas, we show that transcription preferentially occurs from the proximal promoter at onset of gene activity in early embryogenesis, and switches to the more distal one in most of the sites of expression in the adult brain. During gestation, their relative utilization becomes inverted. The third promoter, which shows no activity in embryonic stem cells and is moderately expressed during embryogenesis, is mostly used in specific areas derived from the rostral part of the neural tube.

New Otx2 mRNA isoforms expressed in the mouse brain

The mouse Otx2 gene is essential throughout head and brain development, from anterior-posterior polarity determination and neuroectoderm induction to post-natal sensory organ maturation. These numerous activities must rely on a very finely tuned regulation of expression. In order to understand the molecular control of the Otx2 gene, we set out to isolate its promoter. During this quest, we identified three remote transcription start sites, two defining two new upstream exons and one mapping within the previously reported first exon. The three transcripts differed in their 5' non-coding region but encoded the same protein. The transcription start nucleotides of each mRNA species have been mapped by RNase protection assays and by an RNA circularization technique. We have demonstrated that they are all used and linked to functional promoters. In addition to leader versatility, we also detected alternative splicing within the coding sequence that gives rise to a new protein endowed with an 8 amino-acid insertion upstream of the homeodomain. Combined analysis of the relative abundance of Otx2 mRNA isoforms in representative tissues and in situ hybridization studies revealed distinct spatial and temporal, although partially overlapping, expression patterns of the mRNA isoforms. These findings provide new clues to a better understanding of the relationships between Otx2 gene architecture and its complex regulatory requirements.

A pituitary cell-restricted T box factor, Tpit, activates POMC transcription in cooperation with Pitx homeoproteins

The pituitary gland has provided unique insight into molecular mechanisms and regulatory factors controlling both differentiation and gene transcription. We identified Tpit, a novel T box factor only present in the two pituitary POMC-expressing lineages, the corticotrophs and melanotrophs, and apparently in no other tissue, including hypothalamic POMC neurons. In pituitary cells, Tpit activation of POMC gene transcription requires cooperation with Pitx1, the two factors binding to contiguous sites within the same regulatory element. In gain-of-function experiments, Tpit induces POMC expression in undifferentiated pituitary cells, indicating that it can initiate differentiation into POMC-expressing lineages. TPIT gene mutations were found in patients with isolated deficiency of pituitary POMC-derived ACTH, in support of an essential role of Tpit for differentiation of the pituitary POMC lineage.

The PTX family of homeodomain transcription factors during pituitary developments

A subfamily of bicoid-related homeodomain factors was recently discovered through its involvement in transcription of pituitary-specific genes. We isolated the first member of this family, Ptxl (pituitary homeobox 1), through its DNA binding properties whereas a second related gene, Ptx2 (RIEG), was identified by positional cloning as the causative gene for Rieger's syndrome. The mechanisms of Ptx action on its target genes as well as its putative roles during development are reviewed with particular emphasis on its role in pituitary function.

Ptx1, a bicoid-related homeo box transcription factor involved in transcription of the pro-opiomelanocortin gene

The pituitary gland contains six distinct hormone-producing cell types that arise sequentially during organogenesis. The first cells to differentiate are those that express the pro-opiomelanocortin (POMC) gene in the anterior pituitary lobe. The other lineages, which appear later, include cells that are dependent on the POU factor Pit-1 and another POMC-expressing lineage in the intermediate pituitary lobe. Using AtT-20 cells as a model for early expression of POMC in the anterior pituitary, we have defined a regulatory element conferring cell specificity of transcription and cloned a cognate transcription factor. This factor, Ptx1 (pituitary homeo box 1), contains a homeo box related to those of the anterior-specific genes bicoid and orthodenticle in Drosophila, and Otx-1 and Otx-2 in mammals. Ptx1 activates transcription upon binding a sequence related to the Drosophila bicoid target sites. Ptx1 is the only nuclear factor of this DNA-binding specificity that is detected in AtT-20 cells, and it is expressed at high levels in a subset of adult anterior pituitary cells that express POMC. However, Ptx1 is expressed in most cells of Rathke's pouch at an early time during pituitary development and before final differentiation of hormone-producing cells. Thus, Ptx1 may have a role in differentiation of pituitary cells, and its early expression pattern suggests that it may have a role in pituitary formation. In the adult pituitary gland, Ptx1 appears to be recruited for cell-specific transcription of the POMC gene.

IGF-2 autocrine stimulation in tumorigenic clones of a human colon-carcinoma cell line

Clonal analysis has shown that the SW613-S human colon-carcinoma cell line is heterogeneous: some cell clones display a high level of amplification of the c-myc gene and are tumorigenic in nude mice, whereas others have a small number of copies of this gene and are non-tumorigenic. Tumorigenic clones can proliferate in a chemically defined serum-free medium, whereas non-tumorigenic clones cannot. Suramin, like anti-insulin-like growth factor (IGF) or anti-IGF-I receptor antibodies, efficiently inhibits the growth of tumorigenic clones in defined medium. Inhibition by suramin or by anti-IGF antibodies can be reversed by pure IGF-I or IGF-2. Pure IGF-1 or IGF-2 or culture medium conditioned by tumorigenic clones can stimulate DNA synthesis in cells of non-tumorigenic clones. Co-culture with cells of tumorigenic clones sustains the growth of non-tumorigenic clones in defined medium. Cells of both tumorigenic and non-tumorigenic clones express high-affinity IGF-1 receptors at their surface but tumorigenic clones produce on average 5 times more IGF-1 and 25 times more IGF-2 than non-tumorigenic ones. These results indicate that autocrine growth stimulation of tumorigenic clones by IGFs through the IGF-1 receptor is essential for their ability to grow in defined medium. Since cells of tumorigenic clones produce IGF-2 at levels 80 times higher than IGF-1 and since an antibody strictly specific for IGF-1 has no effect on DNA synthesis in cells of tumorigenic clones grown in defined medium, IGF-2 is very likely the main effector in the autocrine loop.

Constitutive or inducible overexpression of the IGF-2 gene in cells of a human colon carcinoma cell line

Two types of clones have been isolated from the SW613-S human colon carcinoma cell line. Clones with a high level of amplification of the c-myc gene are tumorigenic in nude mice and can proliferate in chemically defined, serum-free medium, whereas clones with a low level of amplification are nontumorigenic and cannot multiply in defined medium. The expression level of the insulin-like growth factor type 1 (IGF-1) gene is low in tumorigenic clones and undetectable in nontumorigenic clones. Tumorigenic clones produce high levels of IGF-2 (and IGF-binding proteins), compared to nontumorigenic clones. This is the consequence of a differential transcriptional regulation of the IGF-2 gene between the two types of clones. This regulation consists of a modulation of the activity of promoters P3 and P4. Overexpression of the IGF-2 gene is constitutive in tumorigenic clones: it is stably maintained during in vitro propagation of the cells. Tumorigenic cell lines obtained after transfer of c-myc gene copies into the cells of nontumorigenic clones exhibit a high level of expression of the IGF-2 gene when they are grown in vivo, as subcutaneous tumors in nude mice. This high level of expression is lost in most of these cell lines when they are returned to in vitro culture conditions indicating that, in these cells, IGF-2 overexpression is not constitutive but inducible by in vivo growth conditions. We had previously shown that tumorigenic clones use the overproduced IGF-2 as an autocrine growth factor. The results reported here suggest than IGF-2 overexpression has an important role in the tumorigenic phenotype of these cells.

TGF-alpha production correlates with tumorigenicity in clones of the SW613-S human colon carcinoma cell line

The c-myc gene is amplified and the c-Ki-ras gene is mutated in the SW613-S human colon carcinoma cell line. Two cell types with different levels of c-myc amplification are present in the SW613-S cell population and representative cell clones can be isolated. The clones with a high level of amplification and expression of the c-myc gene are tumorigenic in nude mice whereas those with a low level are not. The tumorigenic clones secrete transforming growth factor alpha (TGF-alpha) in the culture medium whereas the non-tumorigenic clones do not produce any detectable amount. Accordingly the level of TGF-alpha mRNA is higher and the transcription rate of the gene is increased in the tumorigenic clones. The acquisition of the tumorigenic phenotype by cells of non-tumorigenic clones, following introduction of c-myc gene copies by transfection, is accompanied by an increase in the steady-state level of TGF-alpha mRNA. These findings suggest a role for an elevated level of TGF-alpha production in the tumorigenic phenotype of SW613-S cells. The possibility that this role is indirect is discussed.

The human breast carcinoma cell line SW 613-S: an experimental system to study tumor heterogeneity in relation to c-myc amplification, growth factor production and other markers (review)

Amplification of the c-myc gene has been frequently reported in breast carcinomas. However the precise function of the c-myc protein is still unknown and the nature of the selective advantage offered to a cell by an overexpression of such a protein is unclear. We are addressing this question using the SW 613-S human breast carcinoma cell line as a model system. This cell line harbours an amplified c-myc gene and a mutated c-Ki-ras gene. By various criteria the amplified c-myc gene of SW613-S cells appears undistinguishable from a normal human c-myc gene. The SW613-S cell line is heterogeneous: it contains cells with a high level of amplification and carrying the extra copies of the c-myc gene in double minute chromosomes (DMs) and cells with few c-myc genes integrated into chromosomes. DM-containing cells are progressively lost upon in vitro cultivation but are selected for during in vivo growth, as tumors in nude mice, or by cultivating the cells in a chemically defined, serum-free medium or under conditions preventing anchorage. Clones with different levels of amplification and different chromosomal localization of the c-myc copies were isolated from the SW 613-S cell population. Those with a high level of amplification and expression of the c-myc gene are tumorigenic in nude mice, whereas those with a low level are not. Introduction of c-myc gene copies by transfection confers tumorigenicity to the nontumorigenic clones, indicating that a high level of amplification of the c-myc gene contributes to the tumorigenic phenotype of SW 613-S cells. Tumorigenic clones grow unattached, are able to proliferate in a chemically defined medium, and produce high levels of several growth factors (e.g. TGF-alpha, IGF2). Nontumorigenic clones are more dependent upon anchorage for growth, show a restricted growth in defined medium, and produce low or undetectable level of the growth factors tested. We have identified several genes, besides c-myc, the expression level of which is markedly different in the two types of clones. TGF-alpha, IGF2, PDGF-A, int-2, cytokeratins K8 and K18 and ferritin H chain are overexpressed in tumorigenic clones. In contrast, c-erbB1 (EGF receptor), c-jun, vimentin and p53 are expressed at a higher level in the nontumorigenic clones. Finally the major histocompatibility class I antigens, ferritin L chain, TGF-beta and c-Ki-ras, are examples of genes expressed at the same level in both types of clones.(ABSTRACT TRUNCATED AT 400 WORDS)