Multiple and time-scheduled in situ DNA delivery mediated by beta-cyclodextrin embedded in a polyelectrolyte multilayer

The basic premise of gene therapy is that genes can be used to produce in situ therapeutic proteins. The controlled delivery of DNA complexes from biomaterials offers the potential to enhance gene transfer by maintaining an elevated concentration of DNA within the cellular microenvironment. Immobilization of the DNA to the substrate to which cells adhere maintains the DNA in the cell microenvironment for subsequent cellular internalization. Here, layer-by-layer (LBL) films made from poly(L-glutamic acid) (PLGA) and poly(L-lysine) (PLL) containing DNA were built in the presence of charged cyclodextrins. The biological activities of these polyelectrolyte films were tested by means of induced production of a specific protein in the nucleus or in the cytoplasm by cells in contact with the films. This type of coating offers the possibility for either simultaneous or sequential interfacial delivery of different DNA molecules aimed at cell transfection. These results open the route to numerous potential applications in patch vaccination, for example.

Heterochromatin formation in mammalian cells: interaction between histones and HP1 proteins

Members of the heterochromatin protein 1 (HP1) family are silencing nonhistone proteins. Here, we show that in P19 embryonal carcinoma (EC) nuclei, HP1 alpha, beta, and gamma form homo- and heteromers associated with nucleosomal core histones. In vitro, all three HP1s bind to tailed and tailless nucleosomes and specifically interact with the histone-fold of histone H3. Furthermore, HP1alpha interacts with the linker histone H1. HP1alpha binds to H3 and H1 through its chromodomain (CD) and hinge region, respectively. Interestingly, the Polycomb (Pc1/M33) CD also interacts with H3, and HP1alpha and Pc1/M33 binding to H3 is severely impaired by CD mutations known to abrogate HP1 and Polycomb silencing in Drosophila. These results define a novel function for the conserved CD and suggest that HP1 self-association and histone binding may play a crucial role in HP1-mediated heterochromatin assembly.

Differential expression of retinoic acid-inducible (Stra) genes during mouse placentation

Several retinoid binding proteins and nuclear receptors are specifically expressed in murine placenta. However, little is known about molecular events and target genes regulated by retinoids during placentation. Here, we report that several retinoic acid-inducible (Stra) genes, originally isolated by a differential screening procedure, exhibit specific expression patterns in mouse placental tissues. Three Stra genes, including the ephrinB1 receptor tyrosine kinase ligand, are prominently expressed in the regions of exchanges between maternal and embryonic circulations, i.e. the yolk sac and/or the labyrinthine zone of the mature placenta. The Meis2 homeobox gene appears to be specifically expressed in maternally-derived cell populations. Three other Stra genes, including the AP-2-related gene AP-2gamma, are differentially expressed in the trophoblastic cell lineage. Thus, retinoids may regulate various signaling pathways in specific placental cell-types.

Interaction with members of the heterochromatin protein 1 (HP1) family and histone deacetylation are differentially involved in transcriptional silencing by members of the TIF1 family

Mammalian TIF1alpha and TIF1beta (KAP-1/KRIP-1) are related transcriptional intermediary factors that possess intrinsic silencing activity. TIF1alpha is believed to be a euchromatic target for liganded nuclear receptors, while TIF1beta may serve as a co-repressor for the large family of KRAB domain-containing zinc finger proteins. Here, we report an association of TIF1beta with both heterochromatin and euchromatin in interphase nuclei. Co-immunoprecipitation of nuclear extracts shows that endogenous TIF1beta, but not TIF1alpha, is associated with members of the heterochromatin protein 1 (HP1) family. However, in vitro, both TIF1alpha and TIF1beta interact with and phosphorylate the HP1 proteins. This interaction involves a conserved amino acid motif, which is critical for the silencing activity of TIF1beta but not TIF1alpha. We further show that trichostatin A, an inhibitor of histone deacetylases, can interfere with both TIF1 and HP1 silencing. The silencing activity of TIF1alpha appears to result chiefly from histone deacetylation, whereas that of TIF1beta may be mediated via both HP1 binding and histone deacetylation.

Stra3/lefty, a retinoic acid-inducible novel member of the transforming growth factor-beta superfamily

We report the structure, chromosomal localization and expression features of Stra3, a novel mouse gene whose expression is upregulated by retinoic acid in P19 embryonal carcinoma cells. The Stra3 cDNA sequence, which encodes a novel member of the TGF-beta superfamily, corresponds to, but extends more 3' than the recently published lefty sequence (Meno et al., 1996, Nature 381:151-155). The Stra3/lefty protein, which exhibits characteristics of secreted proteins, is synthesized as a precursor of 42 kDa and secreted after cleavage, suggesting that it may function as an intercellular signaling molecule. There are four exons in the Stra3/lefty gene and its 5' flanking region contains, among other putative regulatory elements, an unusual retinoid response element consisting of two half sites arranged as a palindrome, with an 8 base pairs spacer. We also show that Stra3/lefty is ectopically induced in the endodermal and ectodermal layers following in vivo administration of retinoic acid to gastrulating mouse embryos.

Meis2, a novel mouse Pbx-related homeobox gene induced by retinoic acid during differentiation of P19 embryonal carcinoma cells

We report the cDNA cloning, partial genomic organization, and expression pattern of Stra10, a novel retinoic acid-inducible gene in P19 embryonal carcinoma cells. Four murine cDNA isoforms have been isolated, which are likely to result from alternative splicing. The predicted protein sequences exhibit approximately 85% identity with the Pbx-related Meis1 homeobox gene products, which are involved in myeloid leukemia in BXH-2 mice, and one of the Stra10 isoforms corresponds to the recently published Meis2 sequence (Nakamura et al. [1996] Oncogene 13:2235-2242). The Meis2 homeodomain is identical to that of Meis1, and is most closely related to those of the Pbx/TGIF homeobox gene products. By in situ hybridization analysis, we show that the Meis2 gene displays spatially restricted expression patterns in the developing nervous system, limbs, face, and in various viscera. In adult mice, Meis2 is mainly expressed in the brain and female genital tract, with a different distribution of the alternative splice forms in these organs.

Characterization of a premeiotic germ cell-specific cytoplasmic protein encoded by Stra8, a novel retinoic acid-responsive gene

The full-length cDNA corresponding to Stra8, a novel gene inducible by retinoic acid (RA) in P19 embryonal carcinoma cells, has been isolated and shown to encode a 45-kD protein. Both Stra8 mRNA and protein were induced in cells treated by all-trans and 9-cis retinoic acids. Two-dimensional gel analysis and dephosphorylation experiments revealed that the two stereoisomers of RA differentially regulate the phosphorylation status of the Stra8 protein, which was shown to exist in differently phosphorylated forms. Subcellular fractionation and immunocytochemistry studies showed that the Stra8 protein is cytoplasmic. During mouse embryogenesis, Stra8 expression was restricted to the male developing gonads, and in adult mice, the expression of Stra8 was restricted to the premeiotic germ cells. Thus, Stra8 protein may play a role in the premeiotic phase of spermatogenesis.

A new mouse member of the Wnt gene family, mWnt-8, is expressed during early embryogenesis and is ectopically induced by retinoic acid

We have identified a novel mouse Wnt genc using a cDNA differential screening procedure for retinoic-acid-induced transcripts in P19 embryonal carcinoma cells. Sequence analysis showed that this gene represents the first murine Wnt-8 (mWnt-8) gene reported to date. The expression of the mWnt-8 gene, which is rapidly induced by retinoic acid in P19 and embryonic stem cells, appears to be restricted to early stages of mouse embryogenesis. mWnt-8 transcripts are first detected in the posterior region of the epiblast of early primitive streak-stage embryos. As gastrulation proceeds, mWnt-8 expression spreads into the embryonic ectoderm up to a sharp rostral boundary at the base of the developing headfolds. mWnt-8 is also transiently expressed in the newly formed mesoderm. mWnt-8 expression is rapidly down-regulated during early somitogenesis, the latest detectable expression domains corresponding to the presumptive fourth rhombomere and the caudal region of the neural plate. The expression pattern of mWnt-8 is clearly distinct from those of other murine Wnt genes expressed during gastrulation, but shows striking similarities with that of the chicken Cwnt-8C gene. We also show that mWnt-8 expression is ectopically induced in the rostral neural plate in response to RA exposure of presumitic (7-7.5 days post coitum) cultured mouse embryos.

AP-2.2: a novel AP-2-related transcription factor induced by retinoic acid during differentiation of P19 embryonal carcinoma cells

A 2.8-kb cDNA encoding a new transcription factor (AP-2.2) has been cloned from mouse P19 embryonal carcinoma cells, in which the corresponding mRNA begins to accumulate 30 min after retinoic acid (RA) addition. The predicted protein is 449 amino acids long and exhibits approximately 65% overall identity with other AP-2-related proteins (human AP-2, mouse AP-2alpha and beta). A 96-amino-acid-long sequence, which is almost fully conserved between all these proteins, corresponds to the previously characterized human AP-2 DNA binding domain. Expression of AP-2.2 in Escherichia coli generated a protein that formed a specific complex with the AP-2 recognition site GCCN3GGC. AP-2.2 activated transcription from a reporter gene containing an AP-2 DNA binding site and acted synergistically with RARalpha to activate transcription from the CRABPII gene promoter. Transcriptional activation required the AP-2.2 amino-terminal region that contains a domain rich in proline and glutamine residues. The pattern of AP-2.2 expression in adult tissues, which is distinct from that of AP-2alpha, is essentially restricted to male and female gonads, to most if not all the squamous epithelia, and to several exocrine glands.

Restricted expression of a novel retinoic acid responsive gene during limb bud dorsoventral patterning and endochondral ossification

Using a differential substractive hybridization cloning procedure we have recently identified Stra6 as a novel retinoic acid-induced gene in murine P19 embryonal carcinoma cells. The putative amino acid sequence of Stra6 shows no similarity with previously characterised proteins. We report here the pattern of expression of Stra6 transcripts during mouse limb development as revealed by in situ hybridization. In 8.5-9.0 days post-coitum (dpc) embryos, Stra6 was expressed in the lateral plate mesenchyme prior to limb bud outgrowth. By 9.5 dpc, expression was restricted to the proximal and dorsal forelimb bud mesoderm. Over the next 2 gestational days, Stra6 expression was specific of the dorsal mesoderm of the undifferentiated forelimb and hindlimb buds with the exception of their distal-most region or progress zone. A novel proximal-ventral expression domain appeared, however, by 11.0-11.5 dpc. Stra6 also remained expressed in the flank mesoderm. From 11.5-13.5 dpc, Stra6 expression was restricted to the superficial mesenchyme surrounding the chondrogenic blastemas, and progressively extended until the distal extremities of the limbs upon disappearance of the progress zone. Progressive restriction of Stra6 expression to perichondrium and developing muscles was seen at 13.5-14.5 dpc. Upon the initiation of endochondral ossification (15.5-16.5 dpc), Stra6 expression was limited to the area of perichondrium opposing cells of high metabolic and proliferative activity (the elongation zone). We suggest that Stra6 may play a role in early dorsoventral limb patterning and later in the control of endochondral ossification.

AP-2.2, a novel gene related to AP-2, is expressed in the forebrain, limbs and face during mouse embryogenesis

Using a differential subtractive hybridization cloning procedure we have recently identified the AP-2.2 gene as a novel early retinoic acid-induced gene in murine P19 embryonal carcinoma cells. We have also shown that the AP-2.2 protein, which is highly related to the AP-2 transcription factor, can activate transcription when bound to an AP-2 consensus binding site [Oulad-Abdelghani et al. (1995) Mol. Cell. Biol., submitted]. We report here the in situ hybridization pattern of expression of AP-2.2 transcripts during mouse embryogenesis. At 7.5 days post-coitum, AP-2.2 transcripts were detected in the boundary region between neural plate and surface ectoderm, as well as in extra-embryonic tissues. By 8.0-8.5 gestational days, AP-2.2 transcripts appeared to be expressed in premigratory and migrating neural crest cells. Over the following days, the AP-2.2 gene displayed region-restricted expression in the facial mesenchyme, especially around the embryonic mouth cavity and the nasal cavities, as well as in the surface ectoderm, nasal and oral epithelia. AP-2.2 RNA was also specifically expressed in the presumptive cortical region of the forebrain vesicles. AP-2.2 transcripts were restricted to the distal mitotic area (the 'progress zone') of the limb buds and of the genital bud. AP-2.2 expression also appeared to be specific for primordial germ cells in the genital ridges. Thus, the AP-2.2 gene is expressed in several embryonic areas whose development can be affected by retinoids, such as the forebrain, face and limb buds.

Sequence and expression pattern of the Stra7 (Gbx-2) homeobox-containing gene induced by retinoic acid in P19 embryonal carcinoma cells

The cDNA sequence of Stra7, a retinoic acid (RA)-inducible gene in P19 embryonal carcinoma (EC) cells, was determined. The deduced Stra7 protein contains a homeodomain highly similar to that of the previously described chicken CHox7 gene product, and is highly conserved during evolution, from hemichordates to vertebrates. The mouse Stra7 cDNA corresponds to the full-length form of the 77 bp homeodomain-encoding cDNA fragment which was previously cloned and termed MMoxA or Gbx-2. Reverse-transcriptase-PCR analysis revealed the presence of Stra7/Gbx-2 transcripts in the adult brain, spleen, and female genital tract, whereas no expression could be observed in heart, liver, lung, kidney, or testes. In situ hybridization analysis showed a restricted expression pattern of Stra7/Gbx-2 in the three primitive germ layers during gastrulation. Restricted expression was also detected in the pharyngeal arches. Subsequently, there were specific expression domains in the developing central nervous system, at the midbrain/hindbrain boundary and later in the cerebellum anlage, in certain rhombomeres, in dorsal regions of the spinal cord, and in the developing dorsal thalamus and corpus striatum.

Efficient cloning of cDNAs of retinoic acid-responsive genes in P19 embryonal carcinoma cells and characterization of a novel mouse gene, Stra1 (mouse LERK-2/Eplg2)

Pluripotent mouse P19 embryonal carcinoma (EC) cells have been extensively used as a developmental model system because they can differentiate in the presence of retinoic acid (RA) into derivatives of all three germ layers depending on RA dosage and culture conditions. The expression of several genes has been shown to be induced in RA-treated P19 EC cells and, interestingly, some of these genes may play important roles during mouse embryogenesis. In view of the increasing evidence that RA is a crucial signaling molecule during vertebrate development, we have initiated a study aimed at the systematic isolation of genes whose expression is induced in P19 cells at various times after exposure to RA. We describe here an efficient differential subtractive hybridization cloning strategy which was used to identify additional RA-responsive genes in P19 cells. Fifty different cDNA fragments corresponding to RA-induced genes were isolated. Ten cDNAs represent known genes, 4 of which have already been described as RA-inducible, while the remaining 40 correspond to novel genes. Many of these cDNA sequences represent low-abundance mRNAs. Kinetic analysis of mRNA accumulation following RA treatment allowed us to characterize four classes of RA-responsive genes. We also report the sequence and expression pattern in mouse embryos and adult tissues of one of these novel RA-inducible genes, Stra1, and show that it corresponds to the mouse ligand for the Cek5 receptor protein-tyrosine kinase.

Phosphorylation of the retinoic acid receptor-alpha by protein kinase A

The phosphorylation of retinoic acid receptor-alpha 1 (RAR alpha 1) by PKA was investigated both in vitro and in vivo. We show that bacterially expressed RAR alpha 1 is phosphorylated in vitro by protein kinase A (PKA) at the unique serine residue 369 located in the C-terminal end of the E region. We also show that RAR alpha 1 overexpressed in COS-1 cells is phosphorylated on multiple serine residues and that phosphorylation at serine 369 occurs only when COS-1 cells are cotransfected with PKA or treated with forskolin. RAR alpha 1 mutants were constructed in which serine 369 was replaced by an alanine (S369A) or a glutamic acid (S369E) residue. Comparison of the tryptic phosphopeptide patterns of wild type and mutated RAR alpha 1 overexpressed in COS-1 cells allowed us to confirm that serine 369 is the unique phosphorylation site for PKA in cultured cells. The DNA-binding efficiency of RAR alpha/retinoid X receptor-alpha (RXR alpha) heterodimers was enhanced in vitro by the S369E mutation. However, in transfected RAC65 cells, the same S369E mutation did not affect the ligand-dependent transcriptional activation by RAR alpha 1 of reporter genes containing a retinoic acid (RA)-response element. In contrast, the S369A mutation slightly decreased both DNA binding and the efficiency of PKA to enhance RA-induced transactivation by RAR alpha 1. Finally, we show that endogenous RAR alpha is also phosphorylated in vivo at serine 369 in forskolin-treated F9 cells, supporting the idea that phosphorylation of RARs at this site is involved in the modulation of the RA-induced differentiation of F9 cells by (Bu)2cAMP.