Thérèse Bassez

EDEN and EDEN-BP, a cis element and an associated factor that mediate sequence-specific mRNA deadenylation in Xenopus embryos

During Xenopus early development, gene expression is regulated mainly at the translational level by the length of the poly(A) tail of mRNAs. The Eg family and c‐mos maternal mRNAs are deadenylated rapidly and translationally repressed after fertilization. Here, we characterize a short sequence element (EDEN) responsible for the rapid deadenylation of Eg5 mRNA. Determining the core EDEN sequence permitted us to localize the c‐mos EDEN sequence. The c‐mos EDEN confered a rapid deadenylation to a reporter gene. The EDEN‐specific RNA‐binding protein (EDEN‐BP) was purified and a cDNA obtained. EDEN‐BP is highly homologous to a human protein possibly involved in myotonic dystrophy. Immunodepleting EDEN‐BP from an egg extract totally abolished the EDEN‐mediated deadenylation activity, but did not affect the default deadenylation activity. Therefore, EDEN‐BP constitutes the first trans‐acting factor for which an essential role in the specificity of mRNA deadenylation has been directly demonstrated.

EDEN-dependent translational repression of maternal mRNAs is conserved between Xenopus and Drosophila

Translational control is a key level in regulating gene expression in oocytes and eggs because many mRNAs are synthesized and stored during oogenesis for latter use at various stages of oocyte maturation and embryonic development. Understanding the molecular mechanisms that underlie this translational control is therefore crucial. Another important issue is the evolutionary conservation of these mechanisms—in other words the determination of their universal and specific aspects. We report here a comparative analysis of a translational repression mechanism that depends on the EDEN (embryo deadenylation element) element. This small cis-acting element, localized in the 3′ untranslated region of c-mos and Eg mRNAs, was shown to be involved in a deadenylation process. We demonstrate here that in Xenopus embryos, mRNAs that contain an EDEN are translationally repressed. Next, transgenic flies were used to study the effect of the EDEN motif on translation in Drosophila oocytes. We show that this element also causes the translational repression of a reporter gene in Drosophila demonstrating that the EDEN-dependent translational repression is functionally conserved between Xenopus and Drosophila.

Seasonal variations of androgens, estrogens, and progesterone in the different lobules of the testis and in the plasma of Salamandra salamandra

Progesterone, 4-androstenedione, testosterone, dihydrotestosterone, 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-diol), 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-diol), estrone, and estradiol levels were determined by radioimmunoassay in the different lobules of the testis of Salamandra salamandra throughout the year according to the seasonal cycle. 3 beta-diol levels were not detectable. High levels of steroids were found in the grandular tissue (enlarged pericystic cells after spermiation) and large variations were showed for progesterone, 4-androstenedione, testosterone, 3 alpha-diol, and estrone. In the mature lobule (formed by cysts with mature spermatozoa), only testosterone showed seasonal variations and in the immature lobule (with early stages of meiosis), 3 alpha-diol showed fluctuations. The major estrogen found in the testis of Salamandra was estrone; estradiol stayed at a low level throughout the cycle. The steroids fluctuation seems to be related to the histological evolution of the testis throughout the cycle. The present data were the first on steroid seasonal variations in the testis of an urodele.

DNA ligases in human leukemia

Following partial purification on sucrose gradient and/or phosphocellulose chromatography, DNA ligase was tested in peripheral white blood and bone marrow cells of nearly 100 patients with various kinds of leukemias, mainly acute leukemias. Terminal deoxynucleotidyl transferase (TdT) was tested in parallel. DNA ligase of acute myeloblastic leukemia (AML) was extracted with the same sedimentation coefficient (5.5S) on sucrose gradient, and eluted with the same KCl molarity (0.3 M) than the one extracted from normal lymphocytes. Acute lymphoblastic leukemias (ALL) were characterized by no detectable DNA ligase activity--in most T or non T-non B-ALL, or a low activity in pre-B and B (Burkitt type) ALL, with levels similar to the one observed in chronic lymphocytic leukemia (CLL). An inverse relationship was observed between DNA-ligase and TdT in ALL, ligase being undetectable in cells positive for TdT and being present in some T or non T-non B, and in all pre-B and B-ALL negative for TdT. AML and chronic myelocytic leukemia (CML) were characterized by a markedly higher DNA-ligase activity. This activity was higher in the most differentiated subtypes--M2, M3 and M4 subtypes of FAB classification--and in CML. Moreover a high degree of correlation was observed in AML between the DNA ligase activity and the S phase fraction measured by 3 H-thymidine autoradiography or flow cytophotometry on the total cell sampling. Besides their clinical interest, these results are discussed in relation with the role of DNA-ligase in DNA replication and repair.

Effects of antileukemic agents on the activity of terminal deoxynucleotidyl transferase from human normal thymic and leukemic cells “in vitro”

Several widely used and experimental antileukemic drugs have been tested on the activity of Terminal deoxynucleotidyl Transferase (TdT) purified from normal human thymocytes and T-derived acute lymphoblastic leukemia peripheral blood lymphoblasts. The majority of these inhibitors were equally potent inhibitors of the enzyme from thymocytes or leukemic lymphocytes. Adriamycine and etoposide were more potent inhibitors of the enzyme purified from thymocytes. Vincristine was a more potent inhibitor of TdT extracted from leukemic lymphocytes than from thymocytes. These results are discussed in terms of possible functions for TdT in the two types of cells and on the value of TdT as an indicator for clinical treatment.