Trophoblast cell-specific carcinoembryonic antigen cell adhesion molecule 9 is not required for placental development or a positive outcome of allotypic pregnancies

Widespread divergence of the CEACAM/PSG genes in vertebrates and humans suggests sensitivity to selection

In mammals, carcinoembryonic antigen cell adhesion molecules (CEACAMs) and pregnancy-specific glycoproteins (PSGs) play important roles in the regulation of pathogen transmission, tumorigenesis, insulin signaling turnover, and fetal–maternal interactions. However, how these genes evolved and to what extent they diverged in humans remain to be investigated specifically. Based on syntenic mapping of chordate genomes, we reveal that diverging homologs with a prototypic CEACAM architecture–including an extracellular domain with immunoglobulin variable and constant domain-like regions, and an intracellular domain containing ITAM motif–are present from cartilaginous fish to humans, but are absent in sea lamprey, cephalochordate or urochordate. Interestingly, the CEACAM/PSG gene inventory underwent radical divergence in various vertebrate lineages: from zero in avian species to dozens in therian mammals. In addition, analyses of genetic variations in human populations showed the presence of various types of copy number variations (CNVs) at the CEACAM/PSG locus. These copy number polymorphisms have 3–80% frequency in select populations, and encompass single to more than six PSG genes. Furthermore, we found that CEACAM/PSG genes contain a significantly higher density of nonsynonymous single nucleotide polymorphism (SNP) compared to the chromosome average, and many CEACAM/PSG SNPs exhibit high population differentiation. Taken together, our study suggested that CEACAM/PSG genes have had a more dynamic evolutionary history in vertebrates than previously thought. Given that CEACAM/PSGs play important roles in maternal–fetal interaction and pathogen recognition, these data have laid the groundwork for future analysis of adaptive CEACAM/PSG genotype-phenotypic relationships in normal and complicated pregnancies as well as other etiologies.

Carcinoembryonic Antigen and Related Molecules in Normal and Transformed Trophoblast

Carcinoembryonic antigen (CEA, CD66e) and CEA-related cell adhesion molecules (CEACAMs) are important mediators in remodeling of diverse human tissues, and modulators of cell proliferation and differentiation. Expression by normal and transformed trophoblast of gestational trophoblastic diseases (GTDs), isolated cytotrophoblast and choriocarcinoma cell lines is presented here. Immunocyto/histochemistry of normal placenta (n=9), invasive mole (n=8), choriocarcinoma (n=7), a placental site trophoblastic tumor, cytotrophoblast in primary culture and JAr and JEG-3 cells was performed using polyclonal anti-CEA and specific monoclonal anti-CEA antibodies. Data were analyzed and scored using Mann-Whitney Test. CEA and CEA-related molecules were identified by Western blot and immunoaffinity chromatography in JAr and JEG-3 cells and extracts of 1st and 3rd trimester of pregnancy tissue and cytotrophoblast cell lysates. CEA is expressed throughout pregnancy, in first trimester predominantly in syncytiotrophoblast, but also in villous cytotrophoblast and extravillous trophoblast. Data presented here demonstrate that CEA is significantly increased in transformed trophoblast of GTDs (p<0.05). Both cytotrophoblast in primary culture and choriocarcinoma cell lines express CEA, with staining of granular deposits in JAr and cell membrane in JEG-3. The results suggest that CEA (CD66e) and other CEA-related protein(s) could be involved in trophoblast differentiation.

Identification of a novel group of evolutionarily conserved members within the rapidly diverging murine Cea family

The carcinoembryonic antigen (CEA) family comprises a still actively evolving populous group of proteins that are involved in controlling tissue homeostasis, immune responses, and host/pathogen interactions. The genes identified to date in rodents and primates exhibit low sequence similarity and an extremely variable domain composition. Among the 22 murine Cea-related genes, only for Ceacam1 has an ortholog been assigned. To identify all CEA-related genes in mouse, rat, and human we undertook genome-wide analyses. Eight of 9 new expressible genes (Ceacam12-Ceacam20) could be located within the approximately 6.5-Mb murine Cea locus. Five of the genes were rodent-specific (Ceacam12-Ceacam15 and Ceacam17). Surprisingly, for the remaining 4 (Ceacam16 and Ceacam18-Ceacam20) orthologs could be detected in all three genomes at syntenic locations. Gene-specific reverse transcription/PCR analyses of total RNA from 31 murine adult, placental, and embryonic tissues as well as tumors revealed very distinct expression patterns, suggesting diversified functions within the CEA family.

Two Variable Regions in Carcinoembryonic Antigen-related Cell Adhesion Molecule1 N-terminal Domains Located in or Next to Monoclonal Antibody and Adhesion Epitopes Show Evidence of Recombination in Rat but Not in Human

In this paper, we have characterized the structure, evolutionary origin, and function of rat and human carcinoembryonic antigen-related cell adhesion molecule1 (CEACAM1) multifunctional Ig-like cell adhesion proteins that are expressed by many epithelial tissues. Restriction enzyme digestion reverse transcriptase-PCR analysis identified three cDNAs encoding novel CEACAM1 N-domains. Comparative sequence analysis showed that human and rat CEACAM1 N-domains segregated into two groups differing in similarity to rat CEACAM1(a)-4L and human CEACAM1. Sequence variability analysis indicated that both human and rat N-domains possessed two variable regions, and one contained a major adhesive epitope. Recombination analysis showed that the group of rat but not human N-domains with high sequence similarity was derived at least in part by recombination. Binding assays revealed that three monoclonal antibodies with strong reactivity for the CEACAM1(a)-4L N-domain showed no reactivity with CEACAM1(b)-4S, an allele with a different N-domain sequence. CEACAM1(b)-4S displayed adhesive activity efficiently blocked by a synthetic peptide corresponding to the adhesive epitope in CEACAM1(a)-4L. Blocking analysis also showed that the adhesive epitope for rat CEACAM1 was located downstream from the equivalent human and mouse epitopes. Glycosylation analysis demonstrated O-linked sugars on rat CEACAM1(b)-4S from COS-1 cells. However, this was not the alteration responsible for the lack of monoclonal antibody reactivity. When considered together with previous studies, our findings suggest an inverse relationship between functionality and amino acid sequence similarity to CEACAM1. Like IgG, the N-domain of CEACAM1 appears to tolerate 10-15% sequence diversification without loss of function but begins to show either altered specificity or diminished functionality at higher levels.

Carcinoembryonic antigen-related cell adhesion molecule 10 expressed specifically early in pregnancy in the decidua is dispensable for normal murine development

The carcinoembryonic antigen (CEA) family consists of a large group of evolutionarily and structurally divergent glycoproteins. The murine CEACAM9 and CEACAM11-related proteins as well as the pregnancy-specific glycoproteins (PSG) are secreted members of the CEA family which are differentially expressed in fetal trophoblast cell populations during placental development. PSG are essential for a successful pregnancy, possibly by protecting the semiallotypic fetus from the maternal immune system. In contrast, Ceacam10 mRNA, coding for a protein identical in structure with CEACAM11-related proteins, is expressed in the maternal decidua surrounding the implantation site of the conceptus only during early stages of gestation between day 6.5 and day 10.5 postcoitum. To determine its role during murine development, we inactivated Ceacam10. Ceacam10(-/-) mice developed, like the previously established Ceacam9(-/-) mice, indistinguishably from wild-type littermates with respect to sex ratio, weight gain, and fertility. However, a small but significant reduction of the litter size by 23% was observed in Ceacam10(-/-) matings. Furthermore, combining the Ceacam9 and Ceacam10 null alleles, both located on chromosome 7, by meiotic recombination and subsequent mating of heterozygotes carrying both knockout alleles on one chromosome yielded wild-type and double knockout offspring at the expected Mendelian ratio. Taken together, both Ceacam10 and Ceacam9, alone or in combination, are not essential for either murine placental and embryonic development or for adult life.

Secreted CEACAM1 splice variants in rat cell lines and in vivo in rat serum

The widely expressed adhesion receptor CEACAM1 is a member of the carcinoembryonic antigen (CEA) family within the immunoglobulin (Ig) superfamily of glycoproteins. While the expression of transmembrane isoforms has been described in detail, only little is known about soluble isoforms. By RT-PCR characterization of rat pheochromocytoma PC12 and mammary adenocarcinoma MTC cell lines, two novel splice variants, designated CEACAM1-4C1 and CEACAM1-4C2, lacking the transmembrane region, were identified. In addition, we demonstrate the expression of transmembrane CEACAM1-4L and CEACAM1-4S with a truncated cytoplasmic domain. The C-termini of CEACAM1-4C2 and CEACAM1-L are identical, which allowed the specific in vitro and in vivo detection of the soluble CEACAM1-4C2 protein by an antiserum generated against the CEACAM1-L cytoplasmic part. Functionally, soluble CEACAM1 could inhibit CEACAM1-mediated aggregation of CHO cells. In conclusion, our data define a new mechanism for the appearance of functionally active rat CEACAM1 protein in body fluids.

A new panoptic stain for developmental biology--the mouse placenta paradigm

A panoptic histological stain, PHTA, is introduced for routine use in developmental biology. The protocol is based on three dyes, hematoxylin and, after tannic acid treatment, phloxine B and azure B. It was optimized for differential staining of extracellular matrix, cytoplasm and chromatin. The method is quick, inexpensive and well-reproducible. The mouse placenta is used here to demonstrate the excellent suitability of PHTA for routine morphology.