cDNA subtraction cloning reveals novel genes whose temporal and spatial expression indicates association with trophoblast invasion

Identification of placenta-specific protein 1 (PLAC-1) expression on human PC-3 cell line-derived prostate cancer stem cells compared to the tumor parental cells

Placenta-specific protein 1 (PLAC-1) is a gene primarily expressed in the placenta and the testis. Interestingly, it is also found to be expressed in many solid tumors, and it is involved in malignant cell features. However, no evidence has been reported regarding the relationship between PLAC-1 and cancer stem cells (CSCs). In the current research, we explored the expression of the PLAC-1 molecule in prostate cancer stem cells (PCSCs) derived from the human PC-3 cell line. The enrichment of PCSCs was achieved using a three-dimensional cell culture technique known as the sphere-formation assay. To confirm the identity of PCSCs, we examined the expression of genes associated with stemness and pluripotency, such as SOX2, OCT4, Nanog, C-Myc, and KLF-4, as well as stem cell differentiation molecules like CD44 and CD133. These evaluations were conducted in both the PCSCs and the original tumor cells (parental cells) using real-time PCR and flow cytometry. Subsequently, we assessed the expression of the PLAC-1 molecule in both enriched cells and parental tumor cells at the gene and protein levels using the same techniques. The tumor cells from the PC-3 cell line formed spheroids with CSC characteristics in a non-adherent medium. The expression of SOX2, OCT4, Nanog, and C-Myc genes (p < 0.01), and the molecules CD44 and CD133 (p < 0.05) were significantly elevated in PCSCs compared to the parental cells. The expression of the PLAC-1 molecule in PCSCs showed a significant increase compared to the parental cells at both gene (p < 0.01) and protein (p < 0.001) levels. In conclusion, it was indicated for the first time that PLAC-1 is up-regulated in PCSCs derived from human PC-3 cell line. This study may propose PLAC-1 as a potential target in targeted therapies, which should be confirmed through further studies.

Effects of Maternal Diabetes and Diet on Gene Expression in the Murine Placenta

Adverse exposures during pregnancy have been shown to contribute to susceptibility for chronic diseases in offspring. Maternal diabetes during pregnancy is associated with higher risk of pregnancy complications, structural birth defects, and cardiometabolic health impairments later in life. We showed previously in a mouse model that the placenta is smaller in diabetic pregnancies, with reduced size of the junctional zone and labyrinth. In addition, cell migration is impaired, resulting in ectopic accumulation of spongiotrophoblasts within the labyrinth. The present study had the goal to identify the mechanisms underlying the growth defects and trophoblast migration abnormalities. Based upon gene expression assays of 47 candidate genes, we were able to attribute the reduced growth of diabetic placenta to alterations in the Insulin growth factor and Serotonin signaling pathways, and provide evidence for Prostaglandin signaling deficiencies as the possible cause for abnormal trophoblast migration. Furthermore, our results reinforce the notion that the exposure to maternal diabetes has particularly pronounced effects on gene expression at midgestation time points. An implication of these findings is that mechanisms underlying developmental programming act early in pregnancy, during placenta morphogenesis, and before the conceptus switches from histiotrophic to hemotrophic nutrition.

Breaching the Bacterial Envelope: The Pivotal Role of Perforin-2 (MPEG1) Within Phagocytes

The membrane attack complex (MAC) of the complement system and Perforin-1 are well characterized innate immune effectors. MAC is composed of C9 and other complement proteins that target the envelope of gram-negative bacteria. Perforin-1 is deployed when killer lymphocytes degranulate to destroy virally infected or cancerous cells. These molecules polymerize with MAC-perforin/cholesterol-dependent cytolysin (MACPF/CDC) domains of each monomer deploying amphipathic β-strands to form pores through target lipid bilayers. In this review we discuss one of the most recently discovered members of this family; Perforin-2, the product of the Mpeg1 gene. Since their initial description more than 100 years ago, innumerable studies have made macrophages and other phagocytes some of the best understood cells of the immune system. Yet remarkably it was only recently revealed that Perforin-2 underpins a pivotal function of phagocytes; the destruction of phagocytosed microbes. Several studies have established that phagocytosed bacteria persist and in some cases flourish within phagocytes that lack Perforin-2. When challenged with either gram-negative or gram-positive pathogens Mpeg1 knockout mice succumb to infectious doses that the majority of wild-type mice survive. As expected by their immunocompromised phenotype, bacterial pathogens replicate and disseminate to deeper tissues of Mpeg1 knockout mice. Thus, this evolutionarily ancient gene endows phagocytes with potent bactericidal capability across taxa spanning sponges to humans. The recently elucidated structures of mammalian Perforin-2 reveal it to be a homopolymer that depends upon low pH, such as within phagosomes, to transition to its membrane-spanning pore conformation. Clinical manifestations of Mpeg1 missense mutations further highlight the pivotal role of Perforin-2 within phagocytes. Controversies and gaps within the field of Perforin-2 research are also discussed as well as animal models that may be used to resolve the outstanding issues. Our review concludes with a discussion of bacterial counter measures against Perforin-2.

PLAC1: biology and potential application in cancer immunotherapy

The emergence of immunotherapy has revolutionized medical oncology with unprecedented advances in cancer treatment over the past two decades. However, a major obstacle in cancer immunotherapy is identifying appropriate tumor-specific antigens to make targeted therapy achievable with fewer normal cells being impaired. The similarity between placentation and tumor development and growth has inspired many investigators to discover antigens for effective immunotherapy of cancers. Placenta-specific 1 (PLAC1) is one of the recently discovered placental antigens with limited normal tissue expression and fundamental roles in placental function and development. There is a growing body of evidence showing that PLAC1 is frequently activated in a wide variety of cancer types and promotes cancer progression. Based on the restricted expression of PLAC1 in testis, placenta and a wide variety of cancers, we have designated this molecule with new terminology, cancer-testis-placenta (CTP) antigen, a feature that PLAC1 shares with many other cancer testis antigens. Recent reports from our lab provide compelling evidence on the preferential expression of PLAC1 in prostate cancer and its potential utility in prostate cancer immunotherapy. PLAC1 may be regarded as a potential CTP antigen for targeted cancer immunotherapy based on the available data on its promoting function in cancer development and also its expression in cancers of different histological origin. In this review, we will summarize current data on PLAC1 with emphasis on its association with cancer development and immunotherapy.

Single-cell RNA-seq reveals cell type-specific transcriptional signatures at the maternal-foetal interface during pregnancy

Growth and survival of the mammalian embryo within the uterine environment depends on the placenta, a highly complex vascularized organ comprised of both maternal and foetal tissues. Recent experiments demonstrate that the zinc finger transcriptional repressor Prdm1/Blimp1 is essential for specification of spiral artery trophoblast giant cells (SpA-TGCs) that invade and remodel maternal blood vessels. To learn more about functional contributions made by Blimp1+ cell lineages here we perform the first single-cell RNA-seq analysis of the placenta. Cell types of both foetal and maternal origin are profiled. Comparisons with microarray datasets from mutant placenta and in vitro differentiated trophoblast stem cells allow us to identify Blimp1-dependent transcripts enriched in SpA-TGCs. Our experiments provide new insights into the functionally distinct cell types present at the maternal–foetal interface and advance our knowledge of dynamic gene expression patterns controlling placental morphogenesis and vascular mimicry.

The zinc finger transcriptional repressor Prdm1/Blimp1 is essential for remodelling maternal blood vessels in a subset of trophoblast cells. Here, the authors perform single-cell RNA-seq analysis on this Blimp1+ lineage, identifying functionally distinct cell types present at the maternal–foetal interface.

Perforin-2/Mpeg1 and other pore-forming proteins throughout evolution

Development of the ancient innate immune system required not only a mechanism to recognize foreign organisms from self but also to destroy them. Pore-forming proteins containing the membrane attack complex Perforin domain were one of the first triumphs of an innate immune system needing to eliminate microbes and virally infected cells. Membrane attack complex of complement and Perforin domain proteins is unique from other immune effector molecules in that the mechanism of attack is strictly physical and unspecific. The large water-filled holes created by membrane attack complex of complement and Perforin domain pore formation allow access for additional effectors to complete the destruction of the foreign organism via chemical or enzymatic attack. Perforin-2/macrophage-expressed protein 1 is one of the oldest membrane attack complexes of complement and Perforin domain protein involved in immune defense, and it is still functional today in vertebrates. Here, we trace the impact of Perforin-2/macrophage-expressed protein 1 from the earliest multicellular organisms to modern vertebrates, as well as review the development of other membrane attack complexes of complement and Perforin domain member proteins.

Macrophage-expressed perforins mpeg1 and mpeg1.2 have an anti-bacterial function in zebrafish

Macrophage-expressed gene 1 (MPEG1) encodes an evolutionarily conserved protein with a predicted membrane attack complex/perforin domain associated with host defence against invading pathogens. In vertebrates, MPEG1/perforin-2 is an integral membrane protein of macrophages, suspected to be involved in the killing of intracellular bacteria by pore-forming activity. Zebrafish have 3 copies of MPEG1; 2 are expressed in macrophages, whereas the third could be a pseudogene. The mpeg1 and mpeg1.2 genes show differential regulation during infection of zebrafish embryos with the bacterial pathogens Mycobacterium marinum and Salmonella typhimurium. While mpeg1 is downregulated during infection with both pathogens, mpeg1.2 is infection inducible. Upregulation of mpeg1.2 is partially dependent on the presence of functional Mpeg1 and requires the Toll-like receptor adaptor molecule MyD88 and the transcription factor NFκB. Knockdown of mpeg1 alters the immune response to M. marinum infection and results in an increased bacterial burden. In Salmonella typhimurium infection, both mpeg1 and mpeg1.2 knockdown increase the bacterial burdens, but mpeg1 morphants show increased survival times. The combined results of these two in vivo infection models support the anti-bacterial function of the MPEG1/perforin-2 family and indicate that the intricate cross-regulation of the two mpeg1 copies aids the zebrafish host in combatting infection of various pathogens.

Role of placenta-specific protein 1 in trophoblast invasion and migration

Placenta-specific protein 1 (PLAC1), a placenta-specific gene, is known to be involved in the development of placenta in both humans and mice. However, the precise role of PLAC1 in placental trophoblast function remains unclear. In this study, the localization of PLAC1 in human placental tissues and its physiological significance in trophoblast invasion and migration are investigated by technical studies including real-time RT-PCR, in situ hybridization, immunohistochemistry, and functional studies by utilizing cell invasion and migration assays in the trophoblast cell line HTR8/SVneo as well as the primary inducing extravillous trophoblasts (EVTs). The results show that PLAC1 is mainly detected in the trophoblast columns and syncytiotrophoblast of the first-trimester human placental villi, as well as in the EVTs that invade into the maternal decidua. Knockdown of PLAC1 by RNA interference significantly suppresses the invasion and migration of HTR8/SVneo cells and shortens the distance of the outgrowth of the induced EVTs from the cytotrophoblast column of the explants. All the above data suggests that PLAC1 plays an important role in human placental trophoblast invasion and migration.

The placental specific gene, PLAC1, is induced by the Epstein-Barr virus and is expressed in human tumor cells

BACKGROUND

The Epstein-Barr virus (EBV) is a causal agent in a number of malignancies in humans including hematopoietic tumors and non-hematopoietic tumors. Burkitt's lymphoma cell lines containing the Epstein-Barr virus have been shown to form tumors in nude mice while clonal derivatives of such cell lines in which the viral genome has been lost do not (JID 177: 1194-1201, 1998; JV 72: 9150-9156, 1998; JV 68: 6069-6073, 1994). The re-introduction of EBV into these EBV negative BLs reconstitutes the tumor phenotype. Thus, EBV-induced cellular genes play critical role in EBV-related tumors.

METHODS AND RESULTS

In an attempt to identify cellular genes regulated by EBV that may contribute to its tumorigenic properties, we have enforced genome loss in the Burkitt's lymphoma (BL) line, MutuI, by introducing a dominant negative form of the episomal replication factor, EBNA1 and carried out gene array analysis. One of the genes identified by this analysis is PLAC1, a gene originally identified as being expressed exclusively in placental tissue. Real time RT-PCR analysis verified higher expression in EBV positive vs. EBV negative Mutu clones. Analysis of a panel of RNAs from 20 normal tissues demonstrated the highest level of expression in placenta but significant expression was also observed in testis and brain cerebellum. PLAC1 expression was also observed in non-BL tumor cell lines derived from breast, ovary, and prostate. Lastly, expression of PLAC1 was found to be higher in some primary breast tumors compared to normal adjacent tissues.

CONCLUSION

This data suggests that the EBV-induced PLAC1 is a member of the cancer/testis group of tumor antigens.

Distribution of MACPF/CDC proteins

Membrane Attack Complex/Perforin (MACPF) and Cholesterol-Dependent Cytolysins (CDC) form the MACPF/CDC superfamily of important effector proteins widespread in nature. MACPFs and CDCs were discovered separately with no sequence similarity at that stage being apparent between the two protein families such that they were not, until recently, considered evolutionary related. The breakthrough showing they are came with recent structural work that also shed light on the molecular mechanism of action of various MACPF proteins. Similarity in structural properties and conserved functional features indicate that both protein families have the same evolutionary origin. We will describe the distribution of MACPF/CDC proteins in nature and discuss briefly their similarity and functional role in different biological processes.

Blimp1/Prdm1 governs terminal differentiation of endovascular trophoblast giant cells and defines multipotent progenitors in the developing placenta

Developmental arrest of Blimp1/Prdm1 mutant embryos at around embryonic day 10.5 (E10.5) has been attributed to placental disturbances. Here we investigate Blimp1/Prdm1 requirements in the trophoblast cell lineage. Loss of function disrupts specification of the invasive spiral artery-associated trophoblast giant cells (SpA-TGCs) surrounding maternal blood vessels and severely compromises the ability of the spongiotrophoblast layer to expand appropriately, secondarily causing collapse of the underlying labyrinth layer. Additionally, we identify a population of proliferating Blimp1(+) diploid cells present within the spongiotrophoblast layer. Lineage tracing experiments exploiting a novel Prdm1.Cre-LacZ allele demonstrate that these Blimp1(+) cells give rise to the mature SpA-TGCs, canal TGCs, and glycogen trophoblasts. In sum, the transcriptional repressor Blimp1/Prdm1 is required for terminal differentiation of SpA-TGCs and defines a lineage-restricted progenitor cell population contributing to placental growth and morphogenesis.

The structure and function of mammalian membrane-attack complex/perforin-like proteins

The membrane-attack complex (MAC) of complement pathway and perforin (PF) are important tools deployed by the immune system to target pathogens. Both perforin and the C9 component of the MAC contain a common 'MACPF' domain and form pores in the cell membrane as part of their function. The MAC targets gram-negative bacteria and certain pathogenic parasites, while perforin, released by natural killer cells or cytotoxic T lymphocytes (CTLs), targets virus-infected and transformed host cells (1). Remarkably, recent structural studies show that the MACPF domain is homologous to the pore-forming portion of bacterial cholesterol-dependent cytolysins; these data have provided important insight into the mechanism of pore-forming MACPF proteins. In addition to their role in immunity, MACPF family members have been identified as animal venoms, factors required for pathogen migration across host cell membranes and factors that govern developmental processes such as embryonic patterning and neuronal guidance (2). While most MACPF proteins characterized to date either form pores or span lipid membranes, some do not (e.g. the C6 component of the MAC). A current challenge is thus to understand the role, pore forming or otherwise, of MACPF proteins in developmental biology. This review discusses structural and functional diversity of the mammalian MACPF proteins.

Protein processing by the placental protease, cathepsin P

Cathepsin P is a member of a family of placentally expressed cathepsins (PECs). The closest human homolog of cathepsin P is cathepsin L, a broad specificity enzyme that has functions in many tissues in addition to placenta. The gene duplications that gave rise to the PECs provide a rare opportunity to define proteolytic functions in placenta, a transient organ unique to mammals. Peptidyl substrate and inhibitor libraries have shown that cathepsin P has evolved an unusually restricted preference for substrates containing hydrophobic amino acids. Proteomic techniques were used to probe for substrates of this enzyme. Recombinant cathepsin P was incubated with rat choriocarcinoma (Rcho-1) cell proteins to identify substrates using two-dimensional difference gel electrophoresis. Substrate proteins were excised from gels and characterized by trypsin digestion and MALDI MS/MS. Two endoplasmic reticulum (ER) proteins, gp96 and calreticulin, emerged as potential substrates, and western blotting showed that these proteins are processed by cathepsin P from their C-terminus, removing the KDEL ER retention signal. Immunohistochemistry showed that a portion of cathepsin P co-localizes with calreticulin in Rcho-1 cells. Extracellular calreticulin induces differentiation of Rcho-1 cells, indicating a potential role of cathepsin P in processing and secretion of calreticulin during differentiation of trophoblast giant cells.

Cathepsin proteases have distinct roles in trophoblast function and vascular remodelling

Trophoblast giant cells are instrumental in promoting blood flow towards the mouse embryo by invading the uterine endometrium and remodelling the maternal vasculature. This process involves the degradation of the perivascular smooth muscle layer and the displacement of vascular endothelial cells to form trophoblast-lined blood sinuses. How this vascular remodelling is achieved at the molecular level remains largely elusive. Here, we show that two placenta-specific cathepsins, Cts7 and Cts8, are expressed in distinct but largely overlapping subsets of giant cells that are in direct contact with maternal arteries. We find that Cts8, but not Cts7, has the capacity to mediate loss of smooth muscle alpha-actin and to disintegrate blood vessels. Consequently, conditional ubiquitous overexpression of Cts8 leads to midgestational embryonic lethality caused by severe vascularization defects. In addition, both cathepsins determine trophoblast cell fate by inhibiting the self-renewing capacity of trophoblast stem cells when overexpressed in vitro. Similarly, transgenic overexpression of Cts7 and Cts8 affects trophoblast proliferation and differentiation by prolonging mitotic cell cycle progression and promoting giant cell differentiation, respectively. We also show that the cell cycle effect is directly caused by some proportion of CTS7 localizing to the nucleus, highlighting the emerging functional diversity of these typically lysosomal proteases in distinct intracellular compartments. Our findings provide evidence for the highly specialized functions of closely related cysteine cathepsin proteases in extra-embryonic development, and reinforce their importance for a successful outcome of pregnancy.

The MACPF/CDC family of pore-forming toxins

Pore-forming toxins (PFTs) are commonly associated with bacterial pathogenesis. In eukaryotes, however, PFTs operate in the immune system or are deployed for attacking prey (e.g. venoms). This review focuses upon two families of globular protein PFTs: the cholesterol-dependent cytolysins (CDCs) and the membrane attack complex/perforin superfamily (MACPF). CDCs are produced by Gram-positive bacteria and lyse or permeabilize host cells or intracellular organelles during infection. In eukaryotes, MACPF proteins have both lytic and non-lytic roles and function in immunity, invasion and development. The structure and molecular mechanism of several CDCs are relatively well characterized. Pore formation involves oligomerization and assembly of soluble monomers into a ring-shaped pre-pore which undergoes conformational change to insert into membranes, forming a large amphipathic transmembrane β-barrel. In contrast, the structure and mechanism of MACPF proteins has remained obscure. Recent crystallographic studies now reveal that although MACPF and CDCs are extremely divergent at the sequence level, they share a common fold. Together with biochemical studies, these structural data suggest that lytic MACPF proteins use a CDC-like mechanism of membrane disruption, and will help understand the roles these proteins play in immunity and development.

Emerging functions of placental cathepsins

A series of tandem duplications of an ancestral cathepsin L gene has given rise to a family of eight placenta-specific cathepsins in mice. These genes are differentially regulated both spatially and temporally and thus each can perform unique placental functions. Analysis of the function and expression of these genes is yielding new insights into gene regulation and proteolytic processes in placenta, and may dissect critical placental roles of the single human functional ortholog, cathepsin L.

Molecular cloning and responsive expression of macrophage expressed gene from small abalone Haliotis diversicolor supertexta

The complete cDNA sequence of macrophage expressed gene (saMpeg1), a perforin-like molecule, was isolated from small abalone (Haliotis diversicolor supertexta) by homology cloning and rapid amplification of cDNA ends (RACE). The full-length cDNA of saMpeg1 was 2781 bp, consisting of a 5'-terminal untranslated region (UTR) of 252 bp, a 3'-terminal UTR of 342 bp with a signal sequence TAA and a poly (A) tail, and an open reading frame of 2184 bp. The deduced protein (saMpeg1) was composed of 728 amino acids, and contains the cytolytic "helix-turn-helix" domain of perforin (residues 171-218), of which the alpha-helices are amphipathic as are those of perforin. A putative single transmembrane domain is located at residues 667-689, and a modified furin cleavage site (KRRRK; residues 689-693) immediately follows. The result of real time quantitative PCR showed that saMpeg1 was highly expressed at 8h and 96 h post-injection of the Gram-negative bacterium Vibrio parahaemolyticus, but there was no change after TBT exposure. The structural similarity to mammalian perforin and the different gene expression level to bacterial infection and TBT exposure suggest that saMpeg1 may play a role in the immune response against microorganisms in small abalone.

Diverse subtypes and developmental origins of trophoblast giant cells in the mouse placenta

Trophoblast giant cells (TGCs) are the first terminally differentiated subtype to form in the trophoblast cell lineage in rodents. In addition to mediating implantation, they are the main endocrine cells of the placenta, producing several hormones which regulate the maternal endocrine and immune systems and promote maternal blood flow to the implantation site. Generally considered a homogeneous population, TGCs have been identified by their expression of genes encoding placental lactogen 1 or proliferin. In the present study, we have identified a number of TGC subtypes, based on morphology and molecular criteria and demonstrated a previously underappreciated diversity of TGCs. In addition to TGCs that surround the implantation site and form the interface with the maternal deciduas, we demonstrate at least three other unique TGC subtypes: spiral artery-associated TGCs, maternal blood canal-associated TGCs and a TGC within the sinusoidal spaces of the labyrinth layer of the placenta. All four TGC subtypes could be identified based on the expression patterns of four genes: Pl1, Pl2, Plf (encoded by genes of the prolactin/prolactin-like protein/placental lactogen gene locus), and Ctsq (from a placental-specific cathepsin gene locus). Each of these subtypes was detected in differentiated trophoblast stem cell cultures and can be differentially regulated; treatment with retinoic acid induces Pl1/Plf+ TGCs preferentially. Furthermore, cell lineage tracing studies indicated unique origins for different TGC subtypes, in contrast with previous suggestions that secondary TGCs all arise from Tpbpa+ ectoplacental cone precursors.

Expression of cathepsin P mRNA, protein and activity in the rat choriocarcinoma cell line, Rcho-1, during giant cell transformation

Lysosomal proteases perform critical functions in protein turnover and are essential for normal growth and development. Cathepsin P is a member of a newly discovered family of lysosomal cysteine proteases uniquely expressed in rodent placenta (PECs), and is closely related to human cathepsin L. Using the rat choriocarcinoma cell line model, Rcho-1, mRNA for the PECs cathepsins P, M, Q, R, 1, 2 was found to increase in expression during differentiation into a trophoblast giant cell phenotype. By contrast, expression of cathepsin L was not regulated. A specific enzyme assay was developed to show that activity of cathepsin P mirrored mRNA expression during differentiation. Cathepsin P protein co-localizes with cathepsin B, indicating that the enzyme probably functions in the endosomal-lysosomal compartment. This study demonstrates that the PEC genes produce functional proteases that can perform specific placental roles that are probably performed by broader specificity proteases in human placenta.

Expression and Functional Analysis of Fibulin-1 (Fbln1) During Normal and Abnormal Placental Development of the Mouse

The extracellular matrix protein fibulin-1 (FBLN1) is an important component of blood vessel walls, as shown by the lethality of mice with homozygous targeted deletion of the Fbln1 gene. Here, we show that a murine placental overgrowth phenotype is associated with elevated Fbln1 transcript levels, suggesting that the gene and its product have a functional role in placentation. Fbln1 exhibits a specific expression pattern in the mouse placenta. Transcripts could not be detected prior to day 12. In subsequent stages, Fbln1 was expressed strongly in the spongiotrophoblast. Other sites of expression were endothelia of large fetal blood vessels, a tissue type reported to not express this gene. In addition, a subset of giant cells expressed the gene. This giant cell specific expression was strongly increased in hyperplastic placentas. Analysis of the placentation in fibulin null mice did not show any abnormality. Attempts to rescue the placental phenotypes of a congenic model of interspecies hybrid placental dysplasia (IHPD) by normalizing expression of Fbln1 proved that Fbln1 alone is not the key cause of phenotypes in these models of placental hyperplasia.

The PLAC1-homology region of the ZP domain is sufficient for protein polymerisation

Background

Hundreds of extracellular proteins polymerise into filaments and matrices by using zona pellucida (ZP) domains. ZP domain proteins perform highly diverse functions, ranging from structural to receptorial, and mutations in their genes are responsible for a number of severe human diseases. Recently, PLAC1, Oosp1-3, Papillote and CG16798 proteins were identified that share sequence homology with the N-terminal half of the ZP domain (ZP-N), but not with its C-terminal half (ZP-C). The functional significance of this partial conservation is unknown.

Results

By exploiting a highly engineered bacterial strain, we expressed in soluble form the PLAC1-homology region of mammalian sperm receptor ZP3 as a fusion to maltose binding protein. Mass spectrometry showed that the 4 conserved Cys residues within the ZP-N moiety of the fusion protein adopt the same disulfide bond connectivity as in full-length native ZP3, indicating that it is correctly folded, and electron microscopy and biochemical analyses revealed that it assembles into filaments.

Conclusion

These findings provide a function for PLAC1-like proteins and, by showing that ZP-N is a biologically active folding unit, prompt a re-evaluation of the architecture of the ZP domain and its polymers. Furthermore, they suggest that ZP-C might play a regulatory role in the assembly of ZP domain protein complexes.

The importance of cysteine cathepsin proteases for placental development

The typically lysosomal family of cysteine cathepsin proteases has been implicated in the development of the placenta in particular, from studies in the mouse. Here, we analysed overall expression, regulation and presence of transcript isoforms of cysteine cathepsins during human extra-embryonic development. All 11 family members are expressed in human placental tissues, and many are differentially regulated during gestation. Several cysteine cathepsins exhibit deregulated expression levels in placentas from pregnancies complicated by pre-eclampsia. The localization of cathepsin B predominantly in placental and decidual macrophages suggests a role in the physiological functions of these cells in mediating villous angiogenesis and decidual apoptosis. Cathepsin L levels are highest in a subpopulation of invasive cytotrophoblasts. Reflecting the expression pattern of two murine cathepsins, these data give insights into the evolutionary conservation of cathepsin function that is not necessarily exhibited by gene pairs defined by highest sequence similarity. Furthermore, cathepsin L protein localization in uterine epithelial cells demonstrates the in vivo occurrence of intranuclear cathepsin L isoforms. The zonally restricted expression of cathepsin in the syncytiotrophoblast may be important for the metabolic breakdown of maternal nutrients. Overall, the distribution and abnormal expression levels in pre-eclamptic placentas indicate that cysteine cathepsins may play important roles during normal placentation and in the etiology of pre-eclampsia.

Placental cathepsin M is alternatively spliced and exclusively expressed in the spongiotrophoblast layer

Cathepsin M and cathepsin-3 are cysteine peptidases expressed exclusively in the murine placenta. Their expression increases continuously from 11.5 dpc until the end of gestation. The cathepsin M gene consists of 8 exons and 7 introns covering 6 kb of genomic DNA on mouse chromosome 13. Multiple variants of CTSM were identified which display alternative splicing of exon 2 or exon 7. Alternative splicing of exon 2 does not affect the translated region of CTSM whereas aberrant splicing of exon 7 will results in enzymatically inactive versions of CTSM which still might retain inhibitory activity towards cysteine peptidases. Besides two defined major transcription start sites the putative promoter region comprises of a TATA-box and a relatively low (41%) G+C content reflecting its highly specific spatial and temporal expression pattern. Similar features are found within the promoter region of CTS3 which is highly homologous to CTSM. Both cathepsin M and -3 expression are confined to the spongiotrophoblast layer of the mouse placenta an expression pattern which is unique among cysteine peptidases located within the cluster of cathepsin J-like peptidases on mouse chromosome 13.

Parietal endoderm secreted SPARC promotes early cardiomyogenesis in vitro

Cardiomyogenesis proceeds in the presence of signals emanating from extra-embryonic lineages emerging before and during early eutherian gastrulation. In embryonic stem cell derived embryoid bodies, primitive endoderm gives rise to visceral and parietal endoderm. Parietal endoderm undergoes an epithelial to mesenchymal transition shortly before first cardiomyocytes start to contract rhythmically. Here, we demonstrate that Secreted Protein, Acidic, Rich in Cysteine, SPARC, predominantly secreted by mesenchymal parietal endoderm specifically promotes early myocardial cell differentiation in embryoid bodies. SPARC enhanced the expression of bmp2 and nkx2.5 in embryoid bodies and fetal cardiomyocytes. Inhibition of either SPARC or Bmp2 attenuated in both cases cardiomyogenesis and downregulated nkx2.5 expression. Thus, SPARC directly affects cardiomyogenesis, modulates Bmp2 signaling, and contributes to a positive autoregulatory loop of Bmp2 and Nkx2.5 in cardiomyocytes.

Zona pellucida domain proteins

Many eukaryotic proteins share a sequence designated as the zona pellucida (ZP) domain. This structural element, present in extracellular proteins from a wide variety of organisms, from nematodes to mammals, consists of approximately 260 amino acids with eight conserved cysteine (Cys) residues and is located close to the C terminus of the polypeptide. ZP domain proteins are often glycosylated, modular structures consisting of multiple types of domains. Predictions can be made about some of the structural features of the ZP domain and ZP domain proteins. The functions of ZP domain proteins vary tremendously, from serving as structural components of egg coats, appendicularian mucous houses, and nematode dauer larvae, to serving as mechanotransducers in flies and receptors in mammals and nonmammals. Generally, ZP domain proteins are present in filaments and/or matrices, which is consistent with the role of the domain in protein polymerization. A general mechanism for assembly of ZP domain proteins has been presented. It is likely that the ZP domain plays a common role despite its presence in proteins of widely diverse functions.

Determinants of trophoblast lineage and cell subtype specification in the mouse placenta

Cells of the trophoblast lineage make up the epithelial compartment of the placenta, and their rapid development is essential for the establishment and maintenance of pregnancy. A diverse array of specialized trophoblast subtypes form throughout gestation and are responsible for mediating implantation, as well as promotion of blood to the implantation site, changes in maternal physiology, and nutrient and gas exchange between the fetal and maternal blood supplies. Within the last decade, targeted mutations in mice and the study of trophoblast stem cells in vitro have contributed greatly to our understanding of trophoblast lineage development. Here, we review recent insights into the molecular pathways regulating trophoblast lineage segregation, stem cell maintenance, and subtype differentiation.

How to make a placenta: Mechanisms of trophoblast cell differentiation in mice – A Review

The word placenta is derived from the Latin term meaning 'flat cake'. Despite the rather humble name, the placenta is an amazing organ that forms both the interface for selective delivery of nutrients from the mother to the fetus and also re-directs maternal metabolic, endocrine, cardiovascular and immune functions to promote fetal survival and growth. These two functions are fulfilled by different specialized trophoblast cell subtypes, and my laboratory has been studying how their formation and functions are regulated during placental development. Through molecular studies in cultured cells and tissues, genetic studies in mice, and comparative analysis of placentas from humans, rodents and farm animals, it is now possible to describe molecular pathways that control the development of all major trophoblast cell subtypes and structures of the placenta. The work has revealed an intricate complexity of cell-cell interactions, environmental factors, and molecular networks that control normal development.

C2360, a nuclear protein expressed in human proliferative cytotrophoblasts, is a representative member of a novel protein family with a conserved coiled coil–helix–coiled coil–helix domain

In this study, we describe the identification of nine novel genes isolated from a unique human first-trimester cDNA library generated from the placental bed. One of these clones, called C2360 and located on chromosome 10q22, was selected as it showed restricted expression in placental bed tissue as well as in JEG3 choriocarcinoma cells with absent expression in adult tissues. We show that the expression is restricted to first-trimester proliferative trophoblasts of the proximal column and show that C2360 is a nuclear protein. No detectable transactivation potential was observed for different domains of the protein. Secondary structure prediction showed that C2360 is a representative member of a eukaryotic family of proteins with a low conservation at the amino acid level, but with strong conservation at the structural level, sharing the general domain (coiled coil 1)-(helix 1)-(coiled coil 2)-(helix 2), or CHCH domain. Each alpha-helix within this domain contains two cysteine amino acids, and these intrahelical cysteines are separated by nine amino acids (C-X(9)-C motif). The fixed position within each helix indicated that both helices could form a hairpin structure stabilized by two interhelical disulfide bonds. Other proteins belonging to the family include estrogen-induced gene 2 and the ethanol-induced 6 protein. The conserved motif was found in yeast, plant, Drosophila, Caenorhabditis elegans, mouse, and human proteins, indicating that the ancestor of this protein family is of eukaryotic origin. These results indicate that C2360 is a representative member of a multifamily of proteins, sharing a protein domain that is conserved in eukaryotes.

A perforin-like protein from a marine mollusk

Abalone (gastropod mollusks) express a protein, abMpeg1, which is a homolog of two mammalian proteins that share homology with mammalian perforin, a cytolytic and immune-regulatory protein of lymphocytes. One of the mammalian proteins, Mpeg1, is expressed in mature macrophage and prion-infected mouse brains, while the other, Epcs50, is expressed in ectoplacental cone cells of the invading placenta. Although the functions of these three proteins remain unknown, their structural similarity to mammalian perforin suggests that they may be involved in cell killing, the inflammatory response or tissue invasion. Consistent with these proposed functions, the Mpeg1 gene family shows the signature of positive Darwinian selection (adaptive evolution). The perforin-homology domain of abMpeg1 contains the cytolytic "helix-turn-helix" domain of perforin, supporting the idea that abMpeg1 is a cytolytic protein of the abalone innate immune system. The alpha-helices of abMpeg1 are amphipathic as are those of perforin. The conservation among abMpeg1, mammalian Mpeg1, and Epcs50 shows that Mpeg1 proteins represent a novel, ancient protein family of probable immunological function.

Phylogeny of Antigen-Processing Enzymes: Cathepsins of a Cephalochordate, an Agnathan and a Bony Fish

Cathepsins are enzymes that have been cleaving peptide bonds of lysosomal proteins probably since lysosomes appeared in early eucaryotes. When the adaptive system emerged in gnathostomes, cathepsins were recruited to produce peptides for loading onto the major histocompatibility complex class II molecules and for degrading the class II-associated invariant chain just before the loading. The circumstances under which this recruitment took place are unclear because the knowledge about vertebrate cathepsins is limited largely to mammals. To shed light on the recruitment, 10 amphioxus, one lamprey and one cichlid fish cathepsin cDNA clone were characterized and analysed phylogenetically. Disregarding cathepsin O, whose phylogenetic position is uncertain, the analysis confirms the existence of two old lines of descent, the B and the L lineages of cathepsins, which diverged from each other early in the evolution of eucaryotes. The B lineage encompasses cathepsins B, C and Z (X). The L lineage splits off sublineages encompassing cathepsins F and W before the plant-animal separation and cathepsin H early in the evolution of the metazoa. The remaining cathepsins belonging to the L lineage diverged from one another during the evolution of vertebrates: S, K and L before the emergence of bony fishes, and the group of rodent placentally expressed cathepsins [J (P), M, Q, R, 3, 6, 7 and 8] as well as the testis/ova-expressed cathepsins (testins) probably after the divergence of rodents from primates. The part possibly played by the adaptive immune system in some of these divergences is discussed.

Plac8 and Plac9, novel placental-enriched genes identified through microarray analysis

Microarray expression profiling of a collection of 15,000 mouse genes with placental and embryonic RNAs revealed candidates for placental-enriched genes, three of which we have confirmed and further characterized. One, Plac1, strongly expressed in all trophoblast-derived cells in the placenta, has been described earlier (Genomics 68 (2000) 305). Here we report that of the other two, Plac8 expression is restricted to the spongiotrophoblast layer during development, whereas Plac9 is weakly expressed though highly enriched in placenta. For both, cDNAs with complete open reading frames were recovered and exon-intron structures inferred from comparisons of mouse cDNA and genomic sequence. The predicted proteins (112 and 108 amino acids) both contain putative signal peptides, with a coiled-coil segment of mPLAC9 as the only other detected motif. Genomic sequence comparisons reveal that in addition to an apparent pseudogene on chromosome 1, Plac8 is expressed at mouse cytoband 5e3. It is tightly conserved in human in a syntenically equivalent ortholog at 4q21.23. Plac9 is present in a single copy on chromosome 14, with a syntenically equivalent human ortholog at 10q22.3. Putative promoter regions up to 10 kb 5' of the transcription units for Plac1, Plac8, and Plac9 contain sites for widely-expressed transcription factors which, by analogy to other instances, may be sufficient to explain placental enrichment.

IF3, a novel cell-differentiation factor, highly expressed in murine liver and ovary

The IF3 gene was isolated by expression cloning from a cDNA library of mouse oocytes. This gene was revealed to have no homology to any known gene and its cDNA encodes a 202-amino acid protein that contains a signal-peptide sequence. Moreover, an IF3 isoform, IF3(2), was expressed in both liver and ovary. Its cDNA encoded a 92-amino acid protein contains a signal-peptide sequence, which may be an alternative splice and frameshift form of IF3. The mRNA of IF3s was expressed in oocytes, ovary, and liver. Moreover, the gene expression of IF3s was regulated in a development-dependent manner in preimplantation-embryo and liver. Both IF3(1) and IF3(2) isoforms induced the differentiation of 2T3 and ATDC5 cells to the osteogenic and chondrogenic phenotype, respectively, suggesting that IF3s may modulate the differentiation status. Our findings suggest that IF3 may be one of the secreted factors that regulate oogenesis and certain liver functions.

Evolution of placental proteases

The placenta is a critical organ in mammals required for the transport of nutrients from the mother to the fetus during gestation. Other critical functions of the placenta include hormone regulation and immune regulation. The origin of the mammals and early placenta is relatively recent in evolutionary terms, and consequently there are few placenta-specific genes. In two separate branches of mammalian evolution, gene duplications have given rise to two large families of protease genes that are expressed only by placental tissues. A family of aspartic protease genes is expressed only in artiodactyls, and a family of cysteine protease genes is expressed only in rodents. These genes have probably evolved to perform specific functions in the placenta that are carried out by broader specificity proteases in mammalian species that do not express these proteases.

Hoxa 11 is upstream of Integrin alpha8 expression in the developing kidney

Mutation of the functionally redundant Hoxa 11/Hoxd 11 genes gives absent or rudimentary kidneys resulting from a dramatic reduction of the growth and branching of the ureteric bud. To understand better the molecular mechanisms of Hoxa 11/Hoxd 11 function in kidney development, it is necessary to identify the downstream target genes regulated by their encoded transcription factors. To this end, we conducted a screen for Hoxa 11-responsive genes in two kidney cell lines. HEK293 cells, which usually do not express Hoxa 11, were modified to allow inducible Hoxa 11 expression. The mK10 cells, derived specifically for this study from Hoxa 11/Hoxd 11 double-mutant mice, were also modified to give cell populations with and without Hoxa 11 expression. Differential display, Gene Discovery Arrays, and Affymetrix genechip probe arrays were used to screen for genes up- or down-regulated by Hoxa 11. Nine genes, PDGF A, Cathepsin L, annexin A1, Mm.112139, Est2 repressor factor, NrCAM, ZNF192, integrin-associated protein, and GCM1, showed reproducible 3-fold or smaller changes in gene expression in response to Hoxa 11. One gene, the Integrin alpha8, was up-regulated approximately 20-fold after Hoxa 11 expression. The Integrin alpha8 gene is expressed together with Hoxa 11 in metanephric mesenchyme cells, and mutation of Integrin alpha8 gives a bud-branching morphogenesis defect very similar to that observed in Hoxa 11/Hoxd 11 mutant mice. In situ hybridizations showed a dramatic regional reduction in Integrin alpha8 expression in the developing kidneys of Hoxa 11/Hoxd 11 mutant mice. This work suggests that the Integrin alpha8 gene may be a major effector of Hoxa 11/Hoxd 11 function in the developing kidney.

Evolution of placentally expressed cathepsins

Species and strain variants of a family of placentally expressed cathepsins (PECs) were cloned and sequenced in order to identify evolutionary conserved structural characteristics of this large family of cysteine proteases. Cathepsins M, P, Q, and R, are conserved in mice and rats but homologs of these genes are not found in human or rabbit placenta, showing that this family of proteases are probably restricted to rodents. Species-specific gene duplications have given rise to variants of cathepsin M in mice, and cathepsin Q in rats. Although the PECs have diverged at a greater rate than the other lysosomal cathepsins, residues around the specificity sub-sites of the individual enzymes are conserved. Strain-specific polymorphisms show that the evolutionary rate of divergence of cathepsins M and 3, the most recently duplicated pair of mouse genes, is even higher than the other PECs. In human placenta, critical functions of the PECs are probably performed by broader specificity proteases such as cathepsins B and L.

Identification and characterization of a dense cluster of placenta-specific cysteine peptidase genes and related genes on mouse chromosome 13

Genes encoding novel murine cysteine peptidases of the papain family C1A and related genes were cloned and mapped to mouse chromosome 13, colocalizing with the previously assigned cathepsin J gene. We constructed a <460-kb phage artificial chromosome (PAC) contig and characterized a dense cluster comprising eight C1A cysteine peptidase genes, cathepsins J, M, Q, R, -1, -2, -3, and -6; three pseudogenes of cathepsins M, -1, and -2; and four genes encoding putative cysteine peptidase inhibitors related to the proregion of C1A peptidases (trophoblast-specific proteins alpha and beta and cytotoxic T-lymphocyte-associated proteins 2alpha and -beta). Because of sequence homologies of 61.9-72.0% between cathepsin J and the other seven putative cysteine peptidases of the cluster, these peptidases are classified as "cathepsin J-like". The absence of cathepsin J-like peptidases and related genes from the human genome suggests that the cathepsin J cluster arose by partial and complete gene duplication events after the divergence of primate and rodent lineages. The expression of cathepsin J-like peptidases and related genes in the cluster is restricted to the placenta only. Clustered genes are induced at specific time points, and their expression increases toward the end of gestation. The specific expression pattern and high expression level suggest an essential role of cathepsin J-like peptidases and related genes in formation and development of the murine placenta.

Differential activity of cathepsin L in human placenta at two different stages of gestation

The implantation of blastocyst depends on the invasiveness of the syncytiotrophoblast, which penetrates the maternal decidua to establish the placenta. Cathepsin L, a lysosomal cysteine protease over-expressed in a variety of human malignancies, has been implicated in tumour invasion and metastasis. Specific inhibitors of cathepsin L inhibit the invasion of amnion by murine tumour cells. Previous studies have revealed that tumour and trophoblast invasiveness are mediated by shared factors, like metalloproteinases and laminin. Several proteases closely related to cathepsin L have recently been reported in the placentae of different species. In the present study, we demonstrate the expression of cathepsin L in human placenta by immunohistochemical analysis and RT-PCR followed by Southern hybridization. The activity of cathepsin L against the synthetic dipeptidyl substrate, Cbz-Phe-Arg-N-Methylcoumarin, was assayed. E-64, a specific inhibitor of cathepsin L was used to confirm that the enzyme activity being measured was due to cathepsin L. We observed the specific activity of cathepsin L in first trimester placenta to be significantly higher as compared to the term placenta. However, the levels of placental cathepsin L mRNA were comparable at these two stages of gestation. The increased enzymatic activity of cathepsin L in the invasive phase of placentation taken together with its previously established role in tumour invasion and metastasis indicates the involvement of this protease in trophoblast invasion.

UniGene cDNA array-based monitoring of transcriptome changes during mouse placental development

The placenta is a highly specialized organ essential for embryonic growth and development. Here, we have applied cDNA subtraction between extraembryonic tissues of early- (day 7.5 of gestation) and late-stage embryos (day 17.5) to generate stage-specific cDNA pools that were used for screening of high-density mouse UniGene cDNA arrays containing 25,000 clones. A total of 638 clones were identified, 488 with the e7.5-specific probe and 150 with the e17.5-specific probe. Importantly, 363/638 (56.9%) of the hybridizing clones were not known to be expressed during placental development before. Differential regulation was confirmed by Northern blot and in situ hybridization for a total of 44/44 of positive clones. Thus, this combination of cDNA subtraction and array hybridization was highly successful for identification of genes expressed and regulated during placental development. These included growth factors and receptors, components of the transcriptional and translational machinery, cell cycle regulators, molecular chaperones, and cytoskeletal elements. The extensive in situ hybridization analysis revealed extraembryonic structures with a high density of differentially expressed genes, most strikingly the ectoplacental cone and the spongiotrophoblast. This large-scale identification of genes regulated during placentogenesis is extremely useful to further elucidate the molecular basis of extraembryonic development.

Oosp1 encodes a novel mouse oocyte-secreted protein

Oocyte-somatic cell communication is necessary for normal ovarian function. However, the identities of the majority of oocyte-secreted proteins remain unknown. A novel cDNA encoding mouse oocyte-secreted protein 1 (OOSP1) was identified using a modified subtractive hybridization screen. The Oosp1 cDNA encodes a 202-amino acid protein that contains a 21-amino acid signal peptide sequence, 5 putative N-linked glycosylation consensus sequences, and 6 cysteines that are predicted to form 3 disulfide bonds. OOSP1 shares amino acid identity with placental-specific protein 1 (PLAC1), a secreted protein expressed in the placenta and the ectoplacental cone. The Oosp1 mRNA is approximately 1.0 kb and is present at high levels in the oocytes of adult ovaries and at lower levels in the spleen. The mouse Oosp1 gene is 5 exons, spans greater than 16.4 kb, and localizes to chromosome 19 at a position that shares synteny with human chromosome 11q12-11q13. The identification of OOSP1 as a new oocyte-secreted protein permits future in vitro and in vivo functional analyses to define its role in ovarian folliculogenesis.