The bHLH/PAS transcription factor singleminded 2s promotes mammary gland lactogenic differentiation

Noncanonical role of singleminded-2s in mitochondrial respiratory chain formation in breast cancer

Dysregulation of cellular metabolism is a hallmark of breast cancer progression and is associated with metastasis and therapeutic resistance. Here, we show that the breast tumor suppressor gene SIM2 promotes mitochondrial oxidative phosphorylation (OXPHOS) using breast cancer cell line models. Mechanistically, we found that SIM2s functions not as a transcription factor but localizes to mitochondria and directly interacts with the mitochondrial respiratory chain (MRC) to facilitate functional supercomplex (SC) formation. Loss of SIM2s expression disrupts SC formation through destabilization of MRC Complex III, leading to inhibition of electron transport, although Complex I (CI) activity is retained. A metabolomic analysis showed that knockout of SIM2s leads to a compensatory increase in ATP production through glycolysis and accelerated glutamine-driven TCA cycle production of NADH, creating a favorable environment for high cell proliferation. Our findings indicate that SIM2s is a novel stabilizing factor required for SC assembly, providing insight into the impact of the MRC on metabolic adaptation and breast cancer progression.

SIM2s directed Parkin-mediated mitophagy promotes mammary epithelial cell differentiation

The functionally differentiated mammary gland adapts to extreme levels of stress from increased demand for energy by activating specific protective mechanisms to support neonatal health. Here, we identify the breast tumor suppressor gene, single-minded 2 s (SIM2s) as a novel regulator of mitophagy, a key component of this stress response. Using tissue-specific mouse models, we found that loss of Sim2 reduced lactation performance, whereas gain (overexpression) of Sim2s enhanced and extended lactation performance and survival of mammary epithelial cells (MECs). Using an in vitro model of MEC differentiation, we observed SIM2s is required for Parkin-mediated mitophagy, which we have previously shown as necessary for functional differentiation. Mechanistically, SIM2s localizes to mitochondria to directly mediate Parkin mitochondrial loading. Together, our data suggest that SIM2s regulates the rapid recycling of mitochondria via mitophagy, enhancing the function and survival of differentiated MECs.

TF-Prioritizer: a Java pipeline to prioritize condition-specific transcription factors

BACKGROUND

Eukaryotic gene expression is controlled by cis-regulatory elements (CREs), including promoters and enhancers, which are bound by transcription factors (TFs). Differential expression of TFs and their binding affinity at putative CREs determine tissue- and developmental-specific transcriptional activity. Consolidating genomic datasets can offer further insights into the accessibility of CREs, TF activity, and, thus, gene regulation. However, the integration and analysis of multimodal datasets are hampered by considerable technical challenges. While methods for highlighting differential TF activity from combined chromatin state data (e.g., chromatin immunoprecipitation [ChIP], ATAC, or DNase sequencing) and RNA sequencing data exist, they do not offer convenient usability, have limited support for large-scale data processing, and provide only minimal functionality for visually interpreting results.

RESULTS

We developed TF-Prioritizer, an automated pipeline that prioritizes condition-specific TFs from multimodal data and generates an interactive web report. We demonstrated its potential by identifying known TFs along with their target genes, as well as previously unreported TFs active in lactating mouse mammary glands. Additionally, we studied a variety of ENCODE datasets for cell lines K562 and MCF-7, including 12 histone modification ChIP sequencing as well as ATAC and DNase sequencing datasets, where we observe and discuss assay-specific differences.

CONCLUSION

TF-Prioritizer accepts ATAC, DNase, or ChIP sequencing and RNA sequencing data as input and identifies TFs with differential activity, thus offering an understanding of genome-wide gene regulation, potential pathogenesis, and therapeutic targets in biomedical research.

Inhibitor of Differentiation 4 (ID4) represses mammary myoepithelial differentiation via inhibition of HEB

Inhibitor of differentiation (ID) proteins dimerize with basic HLH (bHLH) transcription factors, repressing transcription of lineage-specification genes across diverse cellular lineages. ID4 is a key regulator of mammary stem cells; however, the mechanism by which it achieves this is unclear. Here, we show that ID4 has a cell autonomous role in preventing myoepithelial differentiation of basal cells in mammary organoids and in vivo. ID4 positively regulates proliferative genes and negatively regulates genes involved in myoepithelial function. Mass spectrometry reveals that ID4 interacts with the bHLH protein HEB, which binds to E-box motifs in regulatory elements of basal developmental genes involved in extracellular matrix and the contractile cytoskeleton. We conclude that high ID4 expression in mammary basal stem cells antagonizes HEB transcriptional activity, preventing myoepithelial differentiation and allowing for appropriate tissue morphogenesis. Downregulation of ID4 during pregnancy modulates gene regulated by HEB, promoting specialization of basal cells into myoepithelial cells.

Autophagy regulates functional differentiation of mammary epithelial cells

Mitochondria operate as a central hub for many metabolic processes by sensing and responding to the cellular environment. Developmental cues from the environment have been implicated in selective autophagy, or mitophagy, of mitochondria during cell differentiation and tissue development. Mitophagy occurring in this context, termed programmed mitophagy, responds to cell state rather than mitochondrial damage and is often accompanied by a metabolic transition. However, little is known about the mechanisms that engage and execute mitophagy under physiological or developmental conditions. As the mammary gland undergoes post-natal development and lactation challenges mitochondrial homeostasis, we investigated the contribution of mitochondria to differentiation of mammary epithelial cells (MECs). Using lactogenic differentiation of the HC11 mouse MEC line, we demonstrated that HC11 cells transition to a highly energetic state during differentiation by engaging both oxidative phosphorylation and glycolysis. Interestingly, this transition was lost when autophagy was inhibited with bafilomycin A₁ or knockdown of Atg7 (autophagy related 7). To evaluate the specific targeting of mitochondria, we traced mitochondrial oxidation and turnover in vitro with the fluorescent probe, pMitoTimer. Indeed, we found that differentiation engaged mitophagy. To further evaluate the requirement of mitophagy during differentiation, we knocked down the expression of Prkn/parkin in HC11 cells. We found that MEC differentiation was impaired in shPrkn cells, implying that PRKN is required for MEC differentiation. These studies suggest a novel regulation of MEC differentiation through programmed mitophagy and provide a foundation for future studies of development and disease associated with mitochondrial function in the mammary gland.Abbreviations: AA: antimycin A; ATG5: autophagy related 5; BAF: bafilomycin A₁; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; COX8A: cytochrome c oxidase subunit 8A; CQ: chloroquine; CSN2: casein beta; ECAR: extracellular acidification rate; FCCP: trifluoromethoxy carbonylcyanide phenylhydrazone; FUNDC1: FUN14 domain containing 1; HIF1A: hypoxia inducible factor 1 subunit alpha; L1: lactation day 1; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MEC: mammary epithelial cell; mitoQ: mitoquinol; mROS: mitochondrial reactive oxygen species; OCR: oxygen consumption rate; P: priming; P16: pregnancy day 16; PARP1: poly(ADP-ribose) polymerase 1; PINK1: PTEN induced kinase 1; PPARGC1A: PPARG coactivator 1 alpha; PRKN: parkin RBR E3 ubiquitin protein ligase; shNT: short hairpin non-targeting control; SQSTM1: sequestosome 1; STAT3: signal transducer and activator of transcription 3; TEM: transmission electron microscopy; TFAM: transcription factor A, mitochondrial; U: undifferentiated.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Loss of SIM2s inhibits RAD51 binding and leads to unresolved replication stress

Background

Mutations in genes associated with homologous recombination (HR) increase an individual’s risk of developing triple-negative breast cancer (TNBC). Although known for their role in repairing dsDNA breaks, HR repair elements also stabilize and restart stalled replication forks. Essential to these functions are RAD51 and its paralogs, each of which has a unique role in preventing replication fork collapse and restart. However, progress toward understanding the regulation of these factors has been slow. With such a pivotal role in the maintenance of genomic integrity, furthering our understanding of this pathway through the discovery of new factors involved in HR is important. Recently, we showed that singleminded-2s (SIM2s) is stabilized in response to dsDNA breaks and is required for effective HR.

Methods

Initial analysis of the effect loss of SIM2s has on replication stress resolution was conducted using DNA combing assays in established breast cancer cell lines. Further analysis was conducted via immunostaining to determine the effect loss of SIM2s has on factor recruitment. In vivo confirmation was achieved through the use of a mammary epithelial cell conditional knockout mouse model before SIM2s’ role in RAD51 recruitment was determined by immunoblotting.

Results

Here, we show loss of SIM2s decreases replication fork stability, leading to fork collapse in response to genotoxic stress. Furthermore, loss of SIM2s results in aberrant separation of sister chromatids during mitosis, which has been previously shown to result in chromosomal fragmentation and aneuploidy. Interestingly, loss of SIM2s was shown to result in failure of RAD51 to localize to sites of replication stress in both breast cancer cell lines and primary mammary epithelial cells. Finally, we observed SIM2 is stabilized in response to genotoxic stress and interacts with RAD51, which is necessary for RAD51-DNA binding.

Conclusions

Together, these results show a role for SIM2s in the resolution of replication stress and further characterize the necessity of SIM2s for effective RAD51 loading in response to DNA damage or stress, ultimately promoting genomic integrity and thus preventing the accumulation of cancer-promoting mutations.

ATM-dependent activation of SIM2s regulates homologous recombination and epithelial-mesenchymal transition

There is increasing evidence that genomic instability is a prerequisite for cancer progression. Here we show that SIM2s, a member of the bHLH/PAS family of transcription factors, regulates DNA damage repair through enhancement of homologous recombination (HR), and prevents epithelial-mesenchymal transitions (EMT) in an Ataxia-telangiectasia mutated (ATM)-dependent manner. Mechanistically, we found that SIM2s interacts with ATM and is stabilized through ATM-dependent phosphorylation in response to IR. Once stabilized, SIM2s interacts with BRCA1 and supports RAD51 recruitment to the site of DNA damage. Loss of SIM2s through the introduction of shSIM2 or the mutation of SIM2s at one of the predicted ATM phosphorylation sites (S115) reduces HR efficiency through disruption of RAD51 recruitment, resulting in genomic instability and induction of EMT. The EMT induced by the mutation of S115 is characterized by a decrease in E-cadherin and an induction of the basal marker, K14, resulting in increased invasion and metastasis. Together, these results identify a novel player in the DNA damage repair pathway and provides a link in ductal carcinoma in situ progression to invasive ductal carcinoma through loss of SIM2s, increased genomic instability, EMT, and metastasis.

In Vitro Models for Studying Invasive Transitions of Ductal Carcinoma In Situ

About one fourth of all newly identified cases of breast carcinoma are diagnoses of breast ductal carcinoma in situ (DCIS). Since we cannot yet distinguish DCIS cases that would remain indolent from those that may progress to life-threatening invasive ductal carcinoma (IDC), almost all women undergo aggressive treatment. In order to allow for more rational individualized treatment, we and others are developing in vitro models to identify and validate druggable pathways that mediate the transition of DCIS to IDC. These models range from conventional two-dimensional (2D) monolayer cultures on plastic to 3D cultures in natural or synthetic matrices. Some models consist solely of DCIS cells, either cell lines or primary cells. Others are co-cultures that include additional cell types present in the normal or cancerous human breast. The 3D co-culture models more accurately mimic structural and functional changes in breast architecture that accompany the transition of DCIS to IDC. Mechanistic studies of the dynamic and temporal changes associated with this transition are facilitated by adapting the in vitro models to engineered microfluidic platforms. Ultimately, the goal is to create in vitro models that can serve as a reproducible preclinical screen for testing therapeutic strategies that will reduce progression of DCIS to IDC. This review will discuss the in vitro models that are currently available, as well as the progress that has been made using them to understand DCIS pathobiology.

Multiple roles of single-minded 2 in esophageal squamous cell carcinoma and its clinical implications

Degree of histological differentiation is an important characteristic of cancers and may be associated with malignant potential. However, in squamous cell carcinomas, a key transcriptional factor regulating tumor differentiation is largely unknown. Chemoradiotherapy (CRT) is a standard treatment for locally advanced esophageal squamous cell carcinoma; however, the survival rate is still below 40%. From microarray data, single‐minded 2 (SIM2) was overexpressed in the epithelial subtype. Here, we investigated the correlation between SIM2 expression and its clinical implication, and in vitro and in vivo functions of SIM2 in tumor differentiation and in CRT sensitivity. Although SIM2 was suppressed in cancerous tissues, SIM2‐high ESCC showed a favorable prognosis in CRT. Transient SIM2 expression followed by 3D culture induced expression of differentiation markers and suppressed epithelial‐mesenchymal transition‐ and basal‐cell markers. Levels of PDPN‐high tumor basal cells and of expression of genes for DNA repair and antioxidant enzymes were reduced in stable transfectants, and they showed high CDDP and H₂O₂ sensitivities, and their xenografts showed a well‐differentiated histology. Reduction of tumor basal cells was restored by knockdown of aryl hydrocarbon receptor nuclear translocator (ARNT) that interacted with SIM2. Together, SIM2 increases CRT sensitivity through tumor differentiation by cooperation with ARNT.

Hypothyroidism advances mammary involution in lactating rats through inhibition of PRL signaling and induction of LIF/STAT3 mRNAs

Thyroid diseases have deleterious effects on lactation, litter growth and survival, and hinder the suckling-induced hormone release, leading in the case of hyperthyroidism, to premature mammary involution. To determine the effects of hypothyroidism (HypoT) on late lactation, we analyzed the effect of chronic 6-propyl-2-thiouracil (PTU)-induced HypoT on mammary histology and the expression of members of the JAK/STAT/SOCS signaling pathway, milk proteins, prolactin (PRLR), estrogen (ER), progesterone (PR) and thyroid hormone (TR) receptors, markers of involution (such as stat3, lif, bcl2, BAX and PARP) on lactation (L) day 21. HypoT mothers showed increased histological markers of involution compared with control rats, such as adipose/epithelial ratio, inactive alveoli, picnotic nuclei and numerous detached apoptotic cells within the alveolar lumina. We also found decreased PRLR, β-casein and α-lactoalbumin mRNAs, but increased SOCS1, SOCS3, STAT3 and LIF mRNAs, suggesting a decrease in PRL signaling and induction of involution markers. Furthermore, Caspase-3 and 8 and PARP labeled cells and the expression of structural proteins such as β-Actin, α-Tubulin and Lamin B were increased, indicating the activation of apoptotic pathways and tissue remodelation. HypoT also increased PRA (mRNA and protein) and erβ and decreased erα mRNAs, and increased strongly TRα1, TRβ1, PRA and ERα protein levels. These results show that lactating HypoT rats have premature mammary involution, most probably induced by the inhibition of prolactin signaling along with the activation of the LIF-STAT3 pathway.

Dioxin exposure blocks lactation through a direct effect on mammary epithelial cells mediated by the aryl hydrocarbon receptor repressor

In mammals, lactation is a rich source of nutrients and antibodies for newborn animals. However, millions of mothers each year experience an inability to breastfeed. Exposure to several environmental toxicants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been strongly implicated in impaired mammary differentiation and lactation. TCDD and related polyhalogenated aromatic hydrocarbons are widespread industrial pollutants that activate the aryl hydrocarbon receptor (AHR). Despite many epidemiological and animal studies, the molecular mechanism through which AHR signaling blocks lactation remains unclear. We employed in vitro models of mammary differentiation to recapitulate lactogenesis in the presence of toxicants. We demonstrate AHR agonists directly block milk production in isolated mammary epithelial cells. Moreover, we define a novel role for the aryl hydrocarbon receptor repressor (AHRR) in mediating this response. Our mechanistic studies suggest AHRR is sufficient to block transcription of the milk gene β-casein. As TCDD is a prevalent environmental pollutant that affects women worldwide, our results have important public health implications for newborn nutrition.

bHLH-PAS proteins in cancer

Mammalian basic HLH (helix-loop-helix)-PER-ARNT-SIM (bHLH-PAS) proteins are heterodimeric transcription factors that sense and respond to environmental signals (such as pollutants) or to physiological signals (for example, hypoxia and circadian rhythms) through their two PAS domains. PAS domains form a generic three-dimensional fold, which commonly contains an internal cavity capable of small-molecule binding and outer surfaces adept at protein-protein interactions. These proteins are important in several pro-tumour and antitumour pathways and their activities can be modulated by both natural metabolites and oncometabolites. Recently determined structures and successful small-molecule screening programmes are now providing new opportunities to discover selective agonists and antagonists directed against this multitasking family of transcription factors.

Epigenetic modifications unlock the milk protein gene loci during mouse mammary gland development and differentiation

BACKGROUND

Unlike other tissues, development and differentiation of the mammary gland occur mostly after birth. The roles of systemic hormones and local growth factors important for this development and functional differentiation are well-studied. In other tissues, it has been shown that chromatin organization plays a key role in transcriptional regulation and underlies epigenetic regulation during development and differentiation. However, the role of chromatin organization in mammary gland development and differentiation is less well-defined. Here, we have studied the changes in chromatin organization at the milk protein gene loci (casein, whey acidic protein, and others) in the mouse mammary gland before and after functional differentiation.

METHODOLOGY/PRINCIPAL FINDINGS

Distal regulatory elements within the casein gene cluster and whey acidic protein gene region have an open chromatin organization after pubertal development, while proximal promoters only gain open-chromatin marks during pregnancy in conjunction with the major induction of their expression. In contrast, other milk protein genes, such as alpha-lactalbumin, already have an open chromatin organization in the mature virgin gland. Changes in chromatin organization in the casein gene cluster region that are present after puberty persisted after lactation has ceased, while the changes which occurred during pregnancy at the gene promoters were not maintained. In general, mammary gland expressed genes and their regulatory elements exhibit developmental stage- and tissue-specific chromatin organization.

CONCLUSIONS/SIGNIFICANCE

A progressive gain of epigenetic marks indicative of open/active chromatin on genes marking functional differentiation accompanies the development of the mammary gland. These results support a model in which a chromatin organization is established during pubertal development that is then poised to respond to the systemic hormonal signals of pregnancy and lactation to achieve the full functional capacity of the mammary gland.

Regulation of DCIS to invasive breast cancer progression by Singleminded-2s (SIM2s)

Singleminded-2s (SIM2s) is a member of the bHLH/PAS family of transcription factors and a key regulator of mammary epithelial cell differentiation. SIM2s is highly expressed in mammary epithelial cells and down regulated in human breast cancer. Loss of Sim2s causes aberrant mouse mammary ductal development with features suggestive of malignant transformation, whereas over-expression of SIM2s promotes precocious alveolar differentiation in nulliparous mouse mammary glands, suggesting that SIM2s is required for establishing and enhancing mammary gland differentiation. To test the hypothesis that SIM2s regulates tumor cell differentiation, we analyzed SIM2s expression in human primary breast ductal carcinoma in situ (DCIS) samples and found that SIM2s is lost with progression from DCIS to invasive ductal cancer (IDC). Utilizing a MCF10DCIS.COM progression model, we have shown that SIM2s expression is decreased in MCF10DCIS.COM cells compared to MCF10A cells and reestablishment of SIM2s in MCF10DCIS.COM cells significantly inhibits growth and invasion in vitro and in vivo. Analysis of SIM2s-MCF10DCIS.com tumors showed that SIM2s promoted a more differentiated tumor phenotype including the expression of a broad range of luminal markers (CSN2 (β-casein), CDH1 (E-cadherin), and KER18 (keratin-18)) and suppressed genes associated with stem cell maintenance and a basal phenotype (SMO (smoothened), p63, SLUG (snail-2), KER14 (keratin-14) and VIM (vimentin)). Furthermore, loss of SIM2s expression in MCF10DCIS.COM xenografts resulted in a more invasive phenotype and increased lung metastasis likely due to an increase in hedgehog signaling and matrix metalloproteinase expression. Together, these exciting new data support a role for SIM2s in promoting human breast tumor differentiation and maintaining epithelial integrity.

Sim2 prevents entry into the myogenic program by repressing MyoD transcription during limb embryonic myogenesis

The basic helix-loop-helix transcription factor MyoD is a central actor that triggers the skeletal myogenic program. Cell-autonomous and non-cell-autonomous regulatory pathways must tightly control MyoD expression to ensure correct initiation of the muscle program at different places in the embryo and at different developmental times. In the present study, we have addressed the involvement of Sim2 (single-minded 2) in limb embryonic myogenesis. Sim2 is a bHLH-PAS transcription factor that inhibits transcription by active repression and displays enhanced expression in ventral limb muscle masses during chick and mouse embryonic myogenesis. We have demonstrated that Sim2 is expressed in muscle progenitors that have not entered the myogenic program, in different experimental conditions. MyoD expression is transiently upregulated in limb muscle masses of Sim2(-/-) mice. Conversely, Sim2 gain-of-function experiments in chick and Xenopus embryos showed that Sim2 represses MyoD expression. In addition, we show that Sim2 represses the activity of the mouse MyoD promoter in primary myoblasts and is recruited to the MyoD core enhancer in embryonic mouse limbs. Sim2 expression is non-autonomously and negatively regulated by the dorsalising factor Lmx1b. We propose that Sim2 represses MyoD transcription in limb muscle masses, through Sim2 recruitment to the MyoD core enhancer, in order to prevent premature entry into the myogenic program. This MyoD repression is predominant in ventral limb regions and is likely to contribute to the differential increase of the global mass of ventral muscles versus dorsal muscles.

The role of the transcription factor SIM2 in prostate cancer

BACKGROUND

Recent reports have suggested a possible involvement of Single-minded homolog 2 (SIM2) in human solid cancers, including prostate cancer. However, the exact role of SIM2 in cancer in general, and in prostate cancer in particular, remains largely unknown. This study was designed to elucidate the role of SIM2 in prostate cancer using a shRNA-based approach in the PC3 prostate cancer cell line.

METHODS

Lentiviral shRNAs were used to inhibit SIM2 gene and protein levels in PC3 cells. Quantitative RT-PCR and branched DNA were performed to evaluate transcript expression. SIM2 protein expression level was measured by western blot. Profiling of gene expression spanning the whole genome, as well as polar metabolomics of several major metabolic pathways was performed to identify major pathway dysregulations.

RESULTS

SIM2 gene and protein products were significantly downregulated by lenti-shRNA in PC3 cell line. This low expression of SIM2 affected gene expression profile, revealing significant changes in major signaling pathways, networks and functions. In addition, major metabolic pathways were affected.

CONCLUSION

Taken together, our results suggest an involvement of SIM2 in key traits of prostate tumor cell biology and might underlie a contribution of this transcription factor to prostate cancer onset and progression.

Molecular cloning and its expression of trachealess gene (As-trh) during development in brine shrimp, Artemia sinica

Basic helix-loop-helix-PAS (bHLH-PAS) family transcription factors are implicated in multiple developmental and physiological regulatory processes. Herein, a full-length cDNA encoding a bHLH-PAS domain transcription factor trachealess gene (designated as As-trh) was cloned and characterized from brine shrimp (Artemia sinica) for the first time. The full-length cDNA of As-trh was 2,698 bp with a 2,319 bp open reading frame encoding a deduced protein of 772 amino acid polypeptide with a calculated molecular mass of 86.02 kDa and an isoelectric point of 5.87. Sequence alignment revealed that As-trh had high homology with other species trh gene, including the D-trh gene in Drosophila melanogaster and Bm-trh in Bombyx mori. The early and persistent expression of As-trh in the naupliar stages by whole-mount embryonic in situ hybridization and immunohistochemistry suggest that As-trh functions very early in the salt gland and may be required continuously in this tissue. Later in development, expression of As-trh begins to decrease and disappear in salt gland of the older nauplius and appears in the thoracic epipods of the sub-adult Artemia. These results indicated that As-trh might play an important role in osmoregulatiory organ development from the larvae stages through adult stages.

Singleminded-2s (Sim2s) promotes delayed involution of the mouse mammary gland through suppression of Stat3 and NFκB

Postlactational involution of the mammary gland provides a unique model to study breast cancer susceptibility and metastasis. We have shown that the short isoform of Singleminded-2s (Sim2s), a basic helix loop helix/PAS transcription factor, plays a role in promoting lactogenic differentiation, as well as maintaining mammary epithelial differentiation and malignancy. Sim2s is dynamically expressed during mammary gland development, with expression peaking during lactation, and decreasing in early involution. To determine the role of SIM2S in involution, we used transgenic mice expressing SIM2S under the mouse mammary tumor virus-Sim2s promoter. Overexpression of Sim2s in the mouse mammary gland resulted in delayed involution, indicated by a lower proportion of cleaved caspase-3-positive cells and slower reestablishment of the mammary fat pad. Immunohistochemical and quantitative RNA analysis showed a decrease in apoptotic markers and inflammatory response genes, and an increase in antiapoptotic genes, which were accompanied by inhibition of signal transducer and activator of transcription 3 activity. Microarray analysis confirmed that genes in the signal transducer and activator of transcription 3 signaling pathway were repressed by SIM2S expression, along with nuclear factor-κB and other key pathways involved in mammary gland development. Multiparous mouse mammary tumor virus-Sim2s females displayed a more differentiated phenotype compared with wild-type controls, characterized by enhanced β-casein expression and alveolar structures. Together, these results suggest a role for SIM2S in the normal involuting gland and identify potential downstream pathways regulated by SIM2S.