Complex Cell Type-Specific Transcriptional Regulation by the Promoter and an Intron of the Mouse P-Cadherin Gene. (P-cadherin/cell adhesion molecule/transcriptional regulation)

Analysis of mouse Cdh6 gene regulation by transgenesis of modified bacterial artificial chromosomes

Classic cadherins are cell adhesion molecules whose expression patterns are dynamically modulated in association with their diverse functions during morphogenesis. The large size and complexity of cadherin loci have made it a challenge to investigate the organization of cis-regulatory modules that control their spatiotemporal patterns of expression. Towards this end, we utilized bacterial artificial chromosomes (BACs) containing the Cdh6 gene, a mouse type II classic cadherin, to systematically identify cis-regulatory modules that govern its expression. By inserting a lacZ reporter gene into the Cdh6 BAC and generating a series of modified variants via homologous recombination or transposon insertions that have been examined in transgenic mice, we identified an array of genomic regions that contribute to specific regulation of the gene. These regions span approximately 350 kb of the locus between 161-kb upstream and 186-kb downstream of the Cdh6 transcription start site. Distinct modules independently regulate compartmental expression (i.e. forebrain, hindbrain rhombomeres, and spinal cord) and/or cell lineage-specific expression patterns (i.e. neural crest subpopulations such as Schwann cells) of Cdh6 at the early developmental stages. With respect to regulation of expression in neural crest cells, we have found that distinct regions contribute to different aspects of expression and have identified a short 79-bp region that is implicated in regulating expression in cells once they have emigrated from the neural tube. These results build a picture of the complex organization of Cdh6 cis-regulatory modules and highlight the diverse inputs that contribute to its dynamic expression during early mouse embryonic development.

Cadherin-4 expression in the zebrafish central nervous system and regulation by ventral midline signaling

In this study we show that zebrafish cadherin-4 (R-cadherin) transcript (cad4) and protein are expressed in several defined regions in the embryonic forebrain and in distinctive clusters in the hindbrain and spinal cord. This is the first report of a segmental pattern of expression of cadherin-4 in the hindbrain and spinal cord. Expression domains of cadherin-4 transcript and protein were compared with that of pax6.1. In the forebrain of zebrafish embryos, cad4 and pax6.1 expression domains overlapped extensively, although they were not completely coincident. Injection of pax6.1 mRNA resulted in an increase in cad4 expression, whereas overexpression of sonic hedgehog (shh), a midline signaling molecule that reduces pax6.1 expression, caused a reduction in cad4 expression throughout the brain. cad4 expression was increased in both forebrain and hindbrain in cyclops mutant embryos, which have a defect in midline signaling and an enlarged expression domain of pax6.1. These results suggest that zebrafish cadherin-4 may play a role in organization of neuronal architecture throughout the neural axis, and that its expression is regulated by a ventral midline signaling pathway that involves shh and pax6.1.

Vascular endothelial (VE)-cadherin: only an intercellular glue?

Data collected during the past years indicate that AJ- and more specifically VE-cadherin play an important role in endothelial cell biology. VE-cadherin may transfer information intracellularly through interaction with a complex network of cytoskeletal and signaling molecules. Expression of VE-cadherin is required for the control of vascular permeability and vascular integrity. In addition, the molecule may exert a morphogenetic role modulating the capacity of endothelial cells to organize into tubular-like structures. VE-cadherin presents many structural and sequence homologies to the other members of the family and apparently binds to the same intracellular molecules. However, remarkably, VE-cadherin may transfer specific signals to endothelial cells to modulate their functional reactivity.

Analysis of the E-cadherin and P-cadherin promoters in murine keratinocyte cell lines from different stages of mouse skin carcinogenesis

We previously isolated the 5' upstream sequences of the mouse P-cadherin gene, in which putative binding sites for several transcription factors were identified between nt-101 and +30. In the study reported here, the promoter activity of the postulated 5' cis-acting sequences of the P-cadherin promoter, and the activity of the proximal E-cadherin promoter were investigated in several murine keratinocyte cell lines showing different levels of P- and E-cadherin expression as well as different morphology and tumorigenic behavior. Cell-type specificity and optimal activity of P-cadherin expression in murine keratinocytes was conferred by 5' sequences located between nt -200 and +30, and the GC-rich region (nt -101 to +80) and a CCAAT box element (nt -65) had a major regulatory role. The cell-type specificity of the E-cadherin promoter, on the other hand, was mediated by a combination of positive regulatory elements, a GC-rich region (nt -58 to -24), and a CCAAT box (nt -65) and repressor elements inside the E-pal sequence. Interestingly, the maximum repressor effect of the E-pal element was observed in non-expressing undifferentiated spindle cells. In vitro binding studies indicated that the GC-rich region of the P-cadherin promoter was mainly recognized by Sp1-related nuclear factors, whereas both AP2- and Sp1-related factors were involved in the interaction of the GC-rich region of the E-cadherin promoter. Common factors (probably related to the CP1 family) seemed also to be involved in the recognition of the CCAAT-box element of both the E- and P-cadherin promoters, but additional specific factors participated in the interaction with the CCAAT box of the E-cadherin promoter. Our studies also support the hypothesis that loss or modification of some of the regulatory factors occurs during mouse skin tumor progression.

Sex-dependent expression of placental (P)-cadherin during mouse gonadogenesis

BACKGROUND

Placental (P)-cadherin is one of a family of cell adhesion molecules that participate in embryonic sorting and organogenesis. In previous work, P-cadherin was localized to Sertoli cells in the mouse testis as early as postnatal day 1. This early postnatal localization raised questions about when P-cadherin first appeared in the embryonic testis and whether P-cadherin was expressed differentially in the embryonic testis and ovary.

METHODS

The localization of P-cadherin, epithelial (E)-cadherin, and Müllerian inhibiting substance was determined in frozen sections of mouse gonads between embryonic days 10.5 and 18 using indirect immunohistochemistry. Alkaline phosphatase reactivity was used to identify germ cells.

RESULTS

The expression of P-cadherin was traced back to the indifferent stage of gonadogenesis where uniform distribution was observed in the indifferent gonad of both sexes. However, after sexual differentiation, the expression of P-cadherin in the testis was localized to Sertoli cells in the testicular cords, while its expression in the ovary fell below detectable levels.

CONCLUSIONS

The localization of P-cadherin in the male and female indifferent gonad is similar and cannot be used to distinguish the future testis and ovary. The localization of P-cadherin in the testis after sexual differentiation suggests a role for P-cadherin in testicular cord formation. The common temporal pattern of P-cadherin and Müllerian inhibiting substance expression in Sertoli cells is consistent with a shared regulatory mechanism.

Mechanisms identified in the transcriptional control of epithelial gene expression

Epithelium-specific gene expression is fundamental in both embryogenesis and the maintenance of adult tissues, and impairment of epithelial characteristics contributes to diseases such as cancer. We have here analyzed the 5'-region of the epithelial (E-) cadherin gene in order to understand mechanisms of epithelium-specific transcription and loss of expression during epithelial-mesenchymal transitions. The regulatory region of the mouse epithelial cadherin gene is composed of a promoter (from position -94 to the transcription start site) and a 150-base pair enhancer located in the first intron. The 5'-promoter consists of positive regulatory elements (a CCAAT-box and two AP-2 binding sites in a GC-rich region) and the palindromic element E-Pal that activates and represses transcription in epithelial and mesenchymal cells, respectively. The enhancer of the first intron stimulates the activity of heterologous promoters exclusively in epithelial cells. This epithelium-specific enhancer consists of three elements (E I to E III; E II and E III bind AP-2) that are necessary and sufficient for activity. We thus propose two regulatory mechanisms by which epithelial specificity of epithelial cadherin expression is determined: suppression of promoter activity in mesenchymal cells by E-Pal and enhancement of activity in epithelial cells by both E-Pal and the epithelium-specific enhancer.

Morphogenetic roles of classic cadherins

Classic cadherins, which are known to be crucial for homotypic cell-cell adhesion, have been found to be present not only in vertebrate but also in invertebrate species. Their three-dimensional structures, novel functions, and novel expression patterns were reported recently. These have been important steps towards a deeper understanding of the morphogenetic roles of this family of molecules.