MACC1 Regulates LGR5 to Promote Cancer Stem Cell Properties in Colorectal Cancer

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths worldwide. The high mortality is directly associated with metastatic disease, which is thought to be initiated by colon cancer stem cells, according to the cancer stem cell (CSC) model. Consequently, early identification of those patients who are at high risk for metastasis is crucial for improved treatment and patient outcomes. Metastasis-associated in colon cancer 1 (MACC1) is a novel prognostic biomarker for tumor progression and metastasis formation independent of tumor stage. We previously showed an involvement of MACC1 in cancer stemness in the mouse intestine of our MACC1 transgenic mouse models. However, the expression of MACC1 in human CSCs and possible implications remain elusive. Here, we explored the molecular mechanisms by which MACC1 regulates stemness and the CSC-associated invasive phenotype based on patient-derived tumor organoids (PDOs), patient-derived xenografts (PDXs) and human CRC cell lines. We showed that CD44-enriched CSCs from PDO models express significantly higher levels of MACC1 and LGR5 and display higher tumorigenicity in immunocompromised mice. Similarly, RNA sequencing performed on PDO and PDX models demonstrated significantly increased MACC1 expression in ALDH1(+) CSCs, highlighting its involvement in cancer stemness. We further showed the correlation of MACC1 with the CSC markers CD44, NANOG and LGR5 in PDO models as well as established cell lines. Additionally, MACC1 increased stem cell gene expression, clonogenicity and sphere formation. Strikingly, we showed that MACC1 binds as a transcription factor to the LGR5 gene promoter, uncovering the long-known CSC marker LGR5 as a novel essential signaling mediator employed by MACC1 to induce CSC-like properties in human CRC patients. Our in vitro findings were further substantiated by a significant positive correlation of MACC1 with LGR5 in CRC cell lines as well as CRC patient tumors. Taken together, this study indicates that the metastasis inducer MACC1 acts as a cancer stem cell-associated marker. Interventional approaches targeting MACC1 would potentially improve further targeted therapies for colorectal cancer patients to eradicate CSCs and prevent cancer recurrence and distant metastasis formation.

Identification of a Neural Development Gene Expression Signature in Colon Cancer Stem Cells Reveals a Role for EGR2 in Tumorigenesis

Recent evidence demonstrates that colon cancer stem cells (CSCs) can generate neurons that synapse with tumor innervating fibers required for tumorigenesis and disease progression. Greater understanding of the mechanisms that regulate CSC driven tumor neurogenesis may therefore lead to more effective treatments. RNA-sequencing analyses of ALDH^Positive CSCs from colon cancer patient-derived organoids (PDOs) and xenografts (PDXs) showed CSCs to be enriched for neural development genes. Functional analyses of genes differentially expressed in CSCs from PDO and PDX models demonstrated the neural crest stem cell (NCSC) regulator EGR2 to be required for tumor growth and to control expression of homebox superfamily embryonic master transcriptional regulator HOX genes and the neural stem cell and master cell fate regulator SOX2. These data support CSCs as the source of tumor neurogenesis and suggest that targeting EGR2 may provide a therapeutic differentiation strategy to eliminate CSCs and block nervous system driven disease progression.

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Colon cancer stem cells (CSCs) are enriched for nervous system development genes

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Colon cancer cells express nerve cell markers

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EGR2 is required for CSC survival and tumor growth and regulates SOX2 and HOX genes

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Targeting EGR2 may block cancer neurogenesis and stop disease progression

Protocol for isolation and functional validation of label-retaining quiescent colorectal cancer stem cells from patient-derived organoids for RNA-seq

Quiescent cancer stem cells (qCSCs) are a major source of posttreatment relapse, but methods to identify molecular targets for qCSC elimination are limited. Here, we present a protocol using the fluorescent dye PKH26 to isolate label-retaining qCSCs from colorectal cancer (CRC) patient-derived organoids (PDOs). We describe processing of organoids to single cells, followed by PKH26 labeling and FACS-based cell isolation. We then detail steps for functional assays and RNA sequencing. This protocol can also be applied to normal tissue-derived organoids.

For complete details on the use and execution of this protocol, please refer to Regan et al. (2021).

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Protocol for the isolation of PKH26 label-retaining cells from CRC organoids

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Processing organoids to single cells, PKH26 labeling, and FACS

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Functional validation and RNA sequencing of quiescent cancer stem cells

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Applicable to normal tissue-derived and patient-derived organoids

RNA sequencing of long-term label-retaining colon cancer stem cells identifies novel regulators of quiescence

Recent data suggest that therapy-resistant quiescent cancer stem cells (qCSCs) are the source of relapse in colon cancer. Here, using colon cancer patient-derived organoids and xenografts, we identify rare long-term label-retaining qCSCs that can re-enter the cell cycle to generate new tumors. RNA sequencing analyses demonstrated that these cells display the molecular hallmarks of quiescent tissue stem cells, including expression of p53 signaling genes, and are enriched for transcripts common to damage-induced quiescent revival stem cells of the regenerating intestine. In addition, we identify negative regulators of cell cycle, downstream of p53, that we show are indicators of poor prognosis and may be targeted for qCSC abolition in both p53 wild-type and mutant tumors. These data support the temporal inhibition of downstream targets of p53 signaling, in combination with standard-of-care treatments, for the elimination of qCSCs and prevention of relapse in colon cancer.

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Colon tumors contain therapy-resistant quiescent cancer stem cells (qCSCs)

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qCSC gene expression mirrors that of quiescent stem cells of the regenerating gut

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qCSCs are enriched for p53 signaling genes

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qCSC elimination may be achieved by inhibiting downstream targets of p53 signaling

Generation of Patient-Derived Colorectal Cancer Organoids for RAS Studies

Human cell line models have been widely used for testing of novel anticancer compounds and for predicting clinical response to monotherapies and combinatorial therapies. For many years, standard monolayer culture conditions were used as gold standard, only surpassed by in vivo testing of mouse models. Recently, the incorporation of three-dimensional culture has been shown to further improve predictive compound testing. In view of the renewed interest in anti-RAS cancer therapy, we provide a protocol for establishing colorectal cancer organoids which are characterized by a high prevalence of KRAS mutations.

Integrating single-cell RNA-sequencing and functional assays to decipher mammary cell states and lineage hierarchies

The identification and molecular characterization of cellular hierarchies in complex tissues is key to understanding both normal cellular homeostasis and tumorigenesis. The mammary epithelium is a heterogeneous tissue consisting of two main cellular compartments, an outer basal layer containing myoepithelial cells and an inner luminal layer consisting of estrogen receptor-negative (ER⁻) ductal cells and secretory alveolar cells (in the fully functional differentiated tissue) and hormone-responsive estrogen receptor-positive (ER⁺) cells. Recent publications have used single-cell RNA-sequencing (scRNA-seq) analysis to decipher epithelial cell differentiation hierarchies in human and murine mammary glands, and reported the identification of new cell types and states based on the expression of the luminal progenitor cell marker KIT (c-Kit). These studies allow for comprehensive and unbiased analysis of the different cell types that constitute a heterogeneous tissue. Here we discuss scRNA-seq studies in the context of previous research in which mammary epithelial cell populations were molecularly and functionally characterized, and identified c-Kit⁺ progenitors and cell states analogous to those reported in the recent scRNA-seq studies.

Cell fate in colon cancer stem cells: To GLI or not to GLI?

Colon cancer is a heterogeneous tumor driven by subpopulations of cancer stem cells (CSCs). We recently used patient-derived organoids (PDOs) to demonstrate that CSC survival is regulated by autocrine non-canonical Hedgehog signaling, which acts as a positive regulator of Wnt signaling to block CSC differentiation.

Abstract 1715: Whole transcriptome analysis of patient-derived 3D in vitro and xenograft models of colon cancer identifies placental genes required for the survival of cancer stem cells

Growing evidence supports a subpopulation of cancer stem cells (CSCs) as both the drivers of tumor growth and the source of relapse following treatment. The identification of genes and pathways required for the survival of CSCs may therefore lead to better treatment outcomes. Here, as part of the OncoTrack* consortium, we report the use of 3D in vitro and xenograft models of patient-derived colon cancer for the identification of novel regulators of CSCs.

Increased aldehyde dehydrogenase (ALDH) activity has been demonstrated to be a marker of normal intestinal stem cells and colon CSCs. We therefore isolated and functionally tested ALDH+ cells for CSC properties using 3D in vitro models and xenografts of patient derived colon cancer. These studies revealed ALDH+ cells to be highly enriched for CSCs. In addition, there was a positive correlation between CSC frequency in the models and tumor grade at time of surgical resection.

ALDH+ CSCs were subjected to RNA sequencing for whole transcriptome analysis. These analyses demonstrated ALDH+ CSCs to be enriched for stem cell associated genes (ALDH1A1, BMI1, LGR5, CD44, CD166), signaling pathways (Wnt, Hedgehog) and developmental (embryonic, placental, tissue development, EMT) and metabolic processes (retinol metabolism, drug metabolism, hypoxia).

Lentivirus mediated gene knockdown was carried out on a panel of genes that were differentially expressed in ALDH+ cells from 3D in vitro models and xenografts. These studies led to the identification of genes required for the self-renewal and survival of colon CSCs. Interestingly, these genes have been reported as important regulators of early embryonic and placental development but have not previously been reported in the regulation of cancer stem cells.

*The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under grant agreement n°115234.

Citation Format: Joseph L. Regan, Stephanie Staudte, Dirk Schumacher, Ulrich Keilholz, Johannes Haybaeck, Hans Lehrach, Marie-Laure Yaspo, David Henderson, Andreas Steffen, Joern Toedling, Ralf Lesche, Reinhold Schaefer, Christian R. Regenbrecht, Dominik Mumberg, Martin Lange. Whole transcriptome analysis of patient-derived 3D in vitro and xenograft models of colon cancer identifies placental genes required for the survival of cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1715.

Abstract 1714: The role of Hedgehog signaling in the regulation of human colon cancer stem cells

Recent data support a hierarchical model of colon cancer in which tumor growth is driven by a subpopulation of cancer stem cells (CSCs) that may also be the source of relapse following treatment. Elucidation of the cellular heterogeneity within a tumor would therefore facilitate better characterization of patient subtypes and lead to more personalized and effective treatments. Here, as part of the OncoTrack* consortium, we report the use of Matrigel-based 3D in vitro models of patient-derived colon cancer for the characterization of molecular pathways important in the regulation of CSC self-renewal and survival.

Cellular subpopulations were isolated from patient-derived 3D-culture models based on expression of the CSC marker aldehyde dehydrogenase (ALDH) and then functionally tested for tumor initiation and self-renewal capacity by limiting dilution serial xenotransplantation. These studies demonstrate CSCs to be ALDH+. ALDH+ and ALDH- cells from 3D-culture and xenograft models were then subjected to RNA sequencing for whole transcriptome analysis.

These analyses demonstrated ALDH+ CSCs cells to be enriched for stem cell associated genes (ALDH1A1, LGR5, BMI1, CD44, CD166), developmental processes (embryonic, tissue development, EMT) and signaling pathways (Wnt signaling). In particular, the Hedgehog signaling pathway was found to be enriched in both 3D in vitro and xenograft models.

The role of Hedgehog signaling in colon cancer remains controversial. It has been reported as a negative regulator of Wnt signaling and to be inactive in colon cancer cells lines. Here, using small molecule inhibitors and lentivirus mediated gene knockdown, we report on the role of Hedgehog signaling in the regulation of colon CSC self-renewal and identify non-canonical Hedgehog signaling as a positive regulator of Wnt signaling.

*The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under grant agreement n°115234.

Citation Format: Joseph L. Regan, Stephanie Staudte, Dirk Schumacher, Ulrich Keilholz, Johannes Haybaeck, Hans Lehrach, Marie-Laure Yaspo, David Henderson, Andreas Steffen, Joern Toedling, Ralf Lesche, Reinhold Schaefer, Christian R. Regenbrecht, Dominik Mumberg, Martin Lange. The role of Hedgehog signaling in the regulation of human colon cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1714.

Abstract 977: 3D-models of patient-derived colon tumors for the identification of genetic factors important in the regulation of cancer stem cells

Colon cancer is a heterogeneous tumour entity. Growing evidence supports a subpopulation of cancer stem cells (CSCs) as both the drivers of tumour growth and the source of relapse following treatment. Elucidation of the cellular heterogeneity within a tumour would therefore facilitate better characterization of patient subtypes and lead to more personalized and effective treatments. Here, as part of the OncoTrack* consortium, we report the use of a Matrigel-based 3D in vitro model for the identification of genetic factors important in the regulation of CSCs.

The identity and frequency of CSCs within each patient-derived culture model was determined by separating cells using fluorescence assisted cell sorting (FACS) based on expression of previously defined markers of colon CSCs (ALDH+ CD44+ CD166+). Isolated subpopulations of cells are functionally tested for CSC properties in vitro (limiting dilution serial passage and population dynamics analysis) and in vivo (limiting dilution serial xenotransplantation). These studies reveal ALDH+ colon cancer cells to be highly enriched for CSCs and demonstrate large levels of variation in CSC frequency between patients.

To identify genes and pathways that could be used to specifically target CSC function, ALDH+ tumour cell subpopulations were subjected to genome-wide analyses using next-generation sequencing for detailed characterization at the level of the transcriptome and methylome. To date, genes important in the regulation of normal stem cells and CSCs, such as BMI1, EPHB2 and the WNT signalling pathway, were found to be highly expressed in CSCs. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) mediated gene technology was used to knock out genes of interest and their role in regulating CSC function was confirmed using established functional assays.

These studies provide insight into the relationship between variable tumour composition and the variable response of tumours to treatment. Ultimately, these studies will facilitate the more accurate classification and personalized treatment of colon tumours.

*The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under grant agreement n°115234.

Citation Format: Joseph L. Regan, Dirk Schumacher, Stephanie Staudte, Karsten Boehnke, Ulrich Keilholz, Johannes Haybaeck, Hans Lehrach, David Henderson, Reinhold Schaefer, Christian R. Regenbrecht, Dominik Mumberg, Martin Lange. 3D-models of patient-derived colon tumors for the identification of genetic factors important in the regulation of cancer stem cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 977. doi:10.1158/1538-7445.AM2015-977

Abstract 3875: Functional and molecular characterization of colon cancer stem cells in tumor heterogeneity and disease relapse using a 3D-model of patient-derived tumors

Colon cancer is a heterogeneous disease. Growing evidence supports a subpopulation of cancer stem cells (CSCs) as both the drivers of tumour growth and the source of relapse following treatment. Elucidation of the cellular heterogeneity within a tumour would therefore facilitate better characterization of patient subtypes and lead to more personalized and effective treatments. Here we report the use of a Matrigel-based 3D in vitro model for the study of tumour heterogeneity and therapeutic resistance in patient derived colon tumours. To date, this system has enabled the establishment and long term culture of more than 53 patient-specific primary and metastasis derived colon tumours.

Tumour heterogeneity and the prospective isolation of CSCs within each patient-derived culture model is determined by separating cells using fluorescence assisted cell sorting (FACS) based on expression of previously defined markers of colon CSCs (e.g. ALDH+, CD133+, CD44+, CD166+, EpCAMHigh). To date, these analyses have been performed on ten of the patient derived tumour models and demonstrate both inter- and intra- tumour heterogeneity as each tumour contains varying subpopulations of cells either positive or negative for expression of CSC markers. In addition, immunofluorescence staining and 3D confocal analysis of genes important in the regulation of both normal and CSCs (e.g. Notch, Wnt and Hedgehog signalling genes) has also revealed heterogeneity of expression.

Functional characterization using in vitro and in vivo assays to determine the tumorigenic and differentiation capacity of the separated subpopulations are currently underway. Validated CSC subpopulations will be subjected to genome-wide analyses using next-generation sequencing for detailed characterization at the level of the transcriptome and methylome.

To study the effect of drug treatment on CSCs we have determined the IC50 values for standard of care drugs (e.g. 5-fluorouracil, oxaliplatin, irinotecan, receptor tyrosine kinase inhibitors) for each patient derived colon tumour. Tumour cells were treated for 72 - 96 hrs after which time treatment was terminated and the cells were allowed to recover. Surviving cells were then analyzed by FACS to determine the effect of treatment on the frequency of CSCs. Molecular characterization of the therapy resistant CSCs was then used to identify possible biomarkers and targets for more effective treatments.

These studies will provide insight into the relationship between variable tumour composition and the variable response of tumours to treatment. Ultimately, these studies will facilitate the more accurate classification and personalized treatment of colon tumours. OncoTrack is a project funded by the Innovative Medicines Initiative Joint Undertaking (IMI JU).

Citation Format: Joseph L. Regan, Dirk Schumacher, Karsten Boehnke, Cathrin Davies, Ulrich Keilholz, Johannes Haybaeck, Christoph Reinhard, Hans Lehrach, David Henderson, Reinhold Schaefer, Christian Regenbrecht, Martin Lange. Functional and molecular characterization of colon cancer stem cells in tumor heterogeneity and disease relapse using a 3D-model of patient-derived tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3875. doi:10.1158/1538-7445.AM2014-3875

Aurora A kinase regulates mammary epithelial cell fate by determining mitotic spindle orientation in a Notch-dependent manner

Cell fate determination in the progeny of mammary epithelial stem/progenitor cells remains poorly understood. Here, we have examined the role of the mitotic kinase Aurora A (AURKA) in regulating the balance between basal and luminal mammary lineages. We find that AURKA is highly expressed in basal stem cells and, to a lesser extent, in luminal progenitors. Wild-type AURKA expression promoted luminal cell fate, but expression of an S155R mutant reduced proliferation, promoted basal fate, and inhibited serial transplantation. The mechanism involved regulation of mitotic spindle orientation by AURKA and the positioning of daughter cells after division. Remarkably, this was NOTCH dependent, as NOTCH inhibitor blocked the effect of wild-type AURKA expression on spindle orientation and instead mimicked the effect of the S155R mutant. These findings directly link AURKA, NOTCH signaling, and mitotic spindle orientation and suggest a mechanism for regulating the balance between luminal and basal lineages in the mammary gland.

Isolation of mouse mammary epithelial subpopulations: a comparison of leading methods

Isolation of mammary epithelial subpopulations, including stem and progenitor cells, has become a standard technique in recent years. However, a number of methods and approaches for this have developed and the relative benefits of the different approaches, and the reason for their development, have not always been clear. Here, three of the leading laboratories working on the separation of mammary cell subpopulations have summarised their methods, highlighted their differences and similarities and also discussed the reasoning behind the approaches they have taken. This article will assist workers establishing mammary cell separation protocols in their laboratories to make informed choices about the methods they should use.

Pregnancy in the mature adult mouse does not alter the proportion of mammary epithelial stem/progenitor cells

Introduction

In humans, an early full-term pregnancy reduces lifetime breast cancer risk by up to 50% whereas a later pregnancy (>35 years old) can increase lifetime risk. Several mechanisms have been suggested, including changes in levels of circulating hormones, changes in the way the breast responds to these hormones, changes in gene expression programmes which may alter susceptibility to transformation and changes to mammary stem cell numbers or behaviour. Previous studies have shown that the mammary tissue isolated from both virgin and parous mice has the ability to repopulate a cleared mammary fat pad in transplant experiments. Limited dilution transplant assays have demonstrated that early pregnancy (at 5 weeks of age) reduces stem/progenitor cell numbers in the mouse mammary epithelium by twofold. However, the effects on stem/progenitor cell numbers in the mammary epithelium of a pregnancy in older animals have not yet been tested.

Methods

Mice were put through a full-term pregnancy at 9 weeks of age, when the mammary epithelium is mature. The total mammary epithelium was purified from parous 7-week post-lactation and age-matched virgin mice and analysed by flow cytometry and limiting dilution cleared fat pad transplants.

Results

There were no significant differences in the proportions of different mammary epithelial cell populations or numbers of CD24^+/Low Sca-1^- CD49f^High cells (stem cell enriched basal mammary epithelial compartment). There was no significant difference in stem/progenitor cell frequency based on limiting dilution transplants between the parous and age-matched virgin epithelium.

Conclusions

Although differences between parous and virgin mammary epithelium at later time points post lactation or following multiple pregnancies cannot be ruled out, there are no differences in stem/progenitor cell numbers between mammary epithelium isolated from parous animals which were mated at 9 weeks old and virgin animals. However, a recent report has suggested that animals that were mated at 5 weeks old have a twofold reduction in stem/progenitor cell numbers. This is of interest given the association between early, but not late, pregnancy and breast cancer risk reduction in humans. However, a mechanistic connection between stem cell numbers and breast cancer risk remains to be established.

Transcriptome analysis of mammary epithelial subpopulations identifies novel determinants of lineage commitment and cell fate

Background

Understanding the molecular control of cell lineages and fate determination in complex tissues is key to not only understanding the developmental biology and cellular homeostasis of such tissues but also for our understanding and interpretation of the molecular pathology of diseases such as cancer. The prerequisite for such an understanding is detailed knowledge of the cell types that make up such tissues, including their comprehensive molecular characterisation. In the mammary epithelium, the bulk of the tissue is composed of three cell lineages, namely the basal/myoepithelial, luminal epithelial estrogen receptor positive and luminal epithelial estrogen receptor negative cells. However, a detailed molecular characterisation of the transcriptomic differences between these three populations has not been carried out.

Results

A whole transcriptome analysis of basal/myoepithelial cells, luminal estrogen receptor negative cells and luminal estrogen receptor positive cells isolated from the virgin mouse mammary epithelium identified 861, 326 and 488 genes as highly differentially expressed in the three cell types, respectively. Network analysis of the transcriptomic data identified a subpopulation of luminal estrogen receptor negative cells with a novel potential role as non-professional immune cells. Analysis of the data for potential paracrine interacting factors showed that the basal/myoepithelial cells, remarkably, expressed over twice as many ligands and cell surface receptors as the other two populations combined. A number of transcriptional regulators were also identified that were differentially expressed between the cell lineages. One of these, Sox6, was specifically expressed in luminal estrogen receptor negative cells and functional assays confirmed that it maintained mammary epithelial cells in a differentiated luminal cell lineage.

Conclusion

The mouse mammary epithelium is composed of three main cell types with distinct gene expression patterns. These suggest the existence of a novel functional cell type within the gland, that the basal/myoepithelial cells are key regulators of paracrine signalling and that there is a complex network of differentially expressed transcription factors controlling mammary epithelial cell fate. These data will form the basis for understanding not only cell fate determination and cellular homeostasis in the normal mammary epithelium but also the contribution of different mammary epithelial cell types to the etiology and molecular pathology of breast disease.

Regulator of G-protein signalling 2 mRNA is differentially expressed in mammary epithelial subpopulations and over-expressed in the majority of breast cancers

Introduction

To understand which signalling pathways become deregulated in breast cancer, it is necessary to identify functionally significant gene expression patterns in the stem, progenitor, transit amplifying and differentiated cells of the mammary epithelium. We have previously used the markers 33A10, CD24 and Sca-1 to identify mouse mammary epithelial cell subpopulations. We now investigate the relationship between cells expressing these markers and use gene expression microarray analysis to identify genes differentially expressed in the cell populations.

Methods

Freshly isolated primary mouse mammary epithelial cells were separated on the basis of staining with the 33A10 antibody and an α-Sca-1 antibody. The populations identified were profiled using gene expression microarray analysis. Gene expression patterns were confirmed on normal mouse and human mammary epithelial subpopulations and were examined in a panel of breast cancer samples and cell lines.

Results

Analysis of the separated populations demonstrated that Sca-1^- 33A10^High stained cells were estrogen receptor α (Esr1)^- luminal epithelial cells, whereas Sca-1⁺ 33A10^Low/- stained cells were a mix of nonepithelial cells and Esr1⁺ epithelial cells. Analysis of the gene expression data identified the gene Rgs2 (regulator of G-protein signalling 2) as being highly expressed in the Sca-1^- 33A10^Low/- population, which included myoepithelial/basal cells. RGS2 has previously been described as a regulator of angiotensin II receptor signalling. Gene expression analysis by quantitative real-time RT-PCR of cells separated on the basis of CD24 and Sca-1 expression confirmed that Rgs2 was more highly expressed in mouse myoepithelial/basal mammary cells than luminal cells. This expression pattern was conserved in normal human breast cells. Functional analysis demonstrated RGS2 to be a modulator of oxytocin receptor signalling. The potential significance of RGS2 expression in breast cancer was demonstrated by semi-quantitative RT-PCR analysis, data mining and quantitative real-time RT-PCR approaches, which showed that RGS2 was expressed in the majority of solid breast cancers at much higher levels than in normal human mammary cells.

Conclusion

Molecular analysis of prospectively isolated mammary epithelial cells identified RGS2 as a modulator of oxytocin receptor signalling, which is highly expressed in the myoepithelial cells. The RGS2 gene, but not the oxytocin receptor, was also shown to be over-expressed in the majority of breast cancers, identifying the product of this gene, or the pathway(s) it regulates, as potentially significant therapeutic targets.

A direct experimental test of founder-flush effects on the evolutionary potential for assortative mating

Founder-flush speciation models propose that population bottlenecks can enhance evolutionary potential for reproductive isolation. To test this prediction, we subjected bottlenecked (three-pair founder-flush) and nonbottlenecked populations of the housefly to 18 generations of selection for assortative mating. After the selection regime, we analysed videotaped courtship bouts in these lines to identify correlated responses to the selection protocol. The realized heritabilities for assortative mating for both the bottlenecked and nonbottlenecked treatments were very low, but still significant. The founder-flush populations had thus responded to selection as well as the nonbottlenecked populations, although not significantly greater (i.e. total increases in assortative mating were 9.6 and 8.6%, respectively). Multivariate analyses on the courtship repertoires found that, although both bottlenecked and nonbottlenecked treatments attained similar levels of assortative mating, the treatments exhibited different evolutionary solutions in their correlated responses. Specifically, the bottlenecked lines demonstrated a significantly more diverse set of evolutionary trajectories (i.e. significant shifts along the second principal component for courtship). This suggests that the bottlenecked lines had greater potential for the evolution of novel phenotypes as predicted by founder-induced speciation models. Our results, however, cannot distinguish whether the more variable evolutionary responses resulted from increased heritabilities in courtship components, reduced potential to follow the convergent evolutionary trajectories noted for the nonbottlenecked lines, or some combination of both general processes in determining the resultant multivariate phenotype.