Involvement of the proto-oncogene c-ets 1 and the urokinase plasminogen activator during mouse implantation and placentation.

Many of the Ets proteins have been shown to be transcription activators. In vitro, Ets 1 proteins are involved in the transcriptional induction of genes such as stromelysin 1, collagenase 1 or urokinase type plasminogen activator, which are proteases responsible for extracellular matrix degradation. In vivo, c-ets 1 is expressed in a wide variety of embryonic tissues in migrating cells, especially in endothelial cells during blood vessel formation. C-ets 1 is also expressed in stromal cells of invasive carcinomas. In the present work, we have investigated the expression of both c-ets 1 and u-PA, a putative target gene of the Ets 1 proteins, within a biological model which includes both embryonic and tumoral aspects. Implantation and placentation of the mouse embryo display migration of the trophoblastic cells, which invade the stroma of the uterine endometrium and trigger the establishment of a new vascular frame. Using in situ hybridization, we show that the overlapping of expression of c-ets 1 and u-PA is restricted to some maternal cell populations from the invasive front and to the endothelial cells of the endometrial vasculature. C-ets 1 is never expressed in trophoblasts. In contrast, u-PA expression in trophoblasts is strong and coincides with the embryo invasive phase. In the embryo proper, c-ets 1 displays a spatio-temporal expression pattern similar to that described in the chick embryo. Until E 10.5, u-PA is expressed neither in embryonic nor in extra-embryonic structures. The respective roles of c-ets 1 and u-PA and their relationship during mammalian placentation are discussed.

Structure and organization of the mouse elk1 gene.

In the ets gene family of transcription factors, elk1 belongs to the subfamily of Ternary Complex Factors (TCFs) which bind to the Serum Response Element (SRE) in conjunction with a dimer of Serum Response Factors (SRFs). In this communication we report the isolation of cDNAs from the mouse elk1 gene, containing the full coding sequence homologous (87% identical) to the human gene, and the structure and organization of 22 kb of the mouse elk1 locus. The coding sequence is spread through 5 exons (numbered 1 to 5): exons 1 to 4 range from 102 bp to 447 bp and exon 5 is at least 620 bp. Exon 0 was not found in the 8.5 kb sequence upstream of exon 1. The intron between exons 1 and 2 is 4 kb long and the 3 other introns are less than 500 bp long. This information will be useful to engineer targeted mutations of this gene in mice and to determine the genomic structure of the other TCF genes.

Pax-QNR/Pax-6, a paired- and homeobox-containing protein, recognizes Ets binding sites and can alter the transactivating properties of Ets transcription factors.

We have previously isolated a cDNA clone encoding a protein with a paired- and homeodomain from MC29-transformed quail neuroretina cells that we have termed Pax-QNR. Pax-QNR is homologous to the murine Pax-6, which is mutated in the autosomal dominant mutation small eye (Sey) of the mouse and aniridia in man. The 46 kDa Pax-QNR protein binds specifically to the e5 DNA recognition sequence present upstream of the Drosophila even-skipped gene. The Pax-QNR paired and homeobox domains expressed separately in bacteria are both able to recognize this sequence. The core sequence recognized by the paired domain of Pax genes is TTCC (GGAA), and this sequence is also present in the core recognition site bound specifically by Ets family-encoded proteins. Ets proteins are a family of transcription factors sharing a highly conserved 85 amino acid DNA binding domain. In this article we demonstrate that Pax-QNR/Pax-6 expressed in reticulocyte lysate is able to specifically recognize several Ets binding sites. In addition, we found that the transactivation mediated by the p68c-ets-1 pr p55erg through the Polyomavirus enhancer sequence is specifically inhibited by the p46kDaPax-QNR in transient transfection assay.

Structure and DNA-binding properties of Pax-QNR, a paired box- and homeobox-containing gene.

After differential screening of a complementary DNA library constructed from quail neuroretina cells (QNR) infected with the v-myc-containing avian retrovirus MC29, we have isolated a complementary DNA clone which identifies a mRNA essentially expressed in the neuronal layer of the retina. This complementary DNA encodes a protein containing paired box and homeobox domains. This gene, called Pax-QNR, is homologous to the murine Pax-6 and human AN genes, which are mutated in the autosomal dominant mutation small eye (Sey) of the mouse and aniridia in humans. Here, we report the genomic exon-intron organization, as well as the existence of alternative splicing events taking place at both the 5' end and the middle part of the gene. A Pax-QNR clone translated in reticulocyte lysate directed the synthesis of a 46 kilodalton protein able to bind specifically to the e5 sequence present upstream of the Drosophila even-skipped gene and target of the Drosophila paired protein. The Pax-QNR paired and homeobox domains individually expressed in bacteria are both able to recognize the e5 sequence.

Increased T-cell apoptosis and terminal B-cell differentiation induced by inactivation of the Ets-1 proto-oncogene.

The Ets-1 proto-oncogene is a member of a transcription factor family characterized by homology to the v-ets oncogene. In adult mice, Ets-1 is expressed predominantly in lymphoid cells where it has been implicated in regulating transcription of lymphocyte-specific genes. Following T-cell activation, the specific DNA binding activity of Ets-1 is inactivated by transient phosphorylation, suggesting a function in the transition from the resting to activated state. Ets-1 has also been suggested to cooperate with the AP-1 transcription factor complex to mediate cellular growth factor responses. Here we show, by using RAG-2-deficient blastocyst complementation, that Ets-1 deficiency has dramatic, but different, effects on development and function of T- and B-lineage cells. Ets-1-deficient T cells were present in reduced numbers and were highly susceptible to cell death in vitro. In contrast, Ets-1-deficient B cells were present in normal numbers but a large proportion were IgM plasma cells. Our data demonstrate that Ets-1 is essential for maintenance of the normal pool of resting T- and B-lineage cells.