DNA repair synthesis-related enzymes during spermatogenesis in the mouse

Characterization of dUTPase expression in mouse postnatal development and adult neurogenesis

The enzyme dUTPase has an essential role in maintaining genomic integrity. In mouse, nuclear and mitochondrial isoforms of the enzyme have been described. Here we present the isoform-specific mRNA expression levels in different murine organs during development using RT-qPCR. In this study, we analyzed organs of 14.5-day embryos and of postnatal 2-, 4-, 10-week- and 13-month-old mice. We demonstrate organ-, sex- and developmental stage-specific differences in the mRNA expression levels of both isoforms. We found high mRNA expression level of the nuclear isoform in the embryo brain, and the expression level remained relatively high in the adult brain as well. This was surprising, since dUTPase is known to play an important role in proliferating cells, and mass production of neural cells is completed by adulthood. Thus, we investigated the pattern of the dUTPase protein expression specifically in the adult brain with immunostaining and found that dUTPase is present in the germinative zones, the subventricular and the subgranular zones, where neurogenesis occurs and in the rostral migratory stream where neuroblasts migrate to the olfactory bulb. These novel findings suggest that dUTPase may have a role in cell differentiation and indicate that accurate dTTP biosynthesis can be vital, especially in neurogenesis.

New insights into the rat spermatogonial proteome: identification of 156 additional proteins

Despite the essential role played by spermatogonia in testicular function, little is known about these cells. To improve our understanding of their biology, our group recently identified a set of 53 spermatogonial proteins using two-dimensional (2-D) gel electrophoresis and mass spectrometry. To continue this work, we investigated a subset of the spermatogonial proteome using narrow range immobilized pH gradients to favor the detection of less abundant proteins. A 2-D reference map of spermatogonia in the pH range 4-9 was created, and protein entities fractionated in a pH 5-6 2-D gel were further processed for protein identification. A new set of 156 polypeptides was identified by peptide mass fingerprinting and tandem mass spectrometry. These polypeptides corresponded to 102 different proteins, which reflect the complexity of post-translational modifications. Seventy-nine of these proteins were identified for the first time in spermatogonia. All identified proteins were classified into functional groups. This work represents a first step toward the establishment of a systematic spermatogonia protein database.

Misincorporation of uracil into DNA as possible contributor to neuronal aging and abiotrophy

Neuronal aging and abiotrophy may be related to the abnormal presence of uracil in DNA. Evidence which could support this hypothesis exists: 1) DNA polymerase beta, the only nuclear DNA polymerase present in adult neurons which is able to repair damaged DNA, incorporates dUTP or dTTP with the same efficiency. This suggests that in adult neurons the incorporation of dUTP into DNA is solely dependent on the relative intracellular concentration of dUTP; 2) uracil into DNA also arises from cytosine deamination; 3) at birth, when neurons stop proliferating, uracil DNA-glycosylase, the enzyme responsible of the removal of uracil from DNA, nearly disappears; 4) a significant replacement of thymine by uracil in DNA could produce genetic instability which in turn could affect the recognition of DNA sequences by enzymes and/or by regulatory DNA binding proteins. Thus enzymatic defects which might alter the intracellular dUTP pool, in different neuronal systems, could account for the multiplicity of the clinical manifestations of aging and neurodegenerative disorders. The increase of the age-specific rate of abiotrophic diseases may be due to accumulation with time of uracil containing DNA.

Replicating premeiotic germ cells of the mouse contain a novel DNA primase stimulatory factor

A protein factor that stimulates DNA primase activity associated with DNA polymerase alpha has been identified in mouse germ cell populations enriched in spermatogonia and preleptotene spermatocytes. The partially purified factor enhances DNA primase activity from homologous cell types as well as DNA primase activity from Xenopus laevis oocytes in a poly dT or M 13 directed reaction. The factor does not stimulate DNA polymerase alpha activity in a gapped salmon sperm or poly dT-rA directed reaction. The DNA primase stimulating factor is identified in a male mouse germ cell population enriched in premeiotic cells; it is not detectable in middle-late pachytene spermatocytes, spermatids, Sertoli cells or fibroblasts.

Biochemical changes in testicular varicocele

The precise mechanism of the hypospermatogenesis associated with varicocele has remained uncertain, although there have been a number of speculations on the etiology of the associated infertility. The altered spermatogenesis has been attributed to the reflux of toxic metabolites from either adrenal or renal origin, disturbed hormone status, spermatic venous hypertension, testicular hypoxia secondary to stasis, and abnormal temperature regulation. However, the biochemical changes of the testicular tissue with varicocele have been only partially explored. This overview includes the available information on the biochemical change in the testes associated with varicocele as well as the introduction of basic biochemical aspects on the testes, which may give new insights into the possible pathophysiological mechanism of male infertility.

The DNA-repair enzyme uracil-DNA glycosylase in the human hematopoietic system

The expression of the DNA base-excision-repair enzyme uracil-DNA glycosylase in the human hematopoietic system followed a tightly regulated pattern: high enzyme activities were recorded in proliferating bone marrow progenitor cells and in peripheral blood T- and B-cells, both groups of cells requiring the integrity of their genetic information for their proper function. The blood quiescent immunocompetent cells retained their DNA-uracil exclusion capacity, even in the oldest age groups. Peripheral blood mature end cells, granulocytes, platelets and red cells had little activity, consistent with the fact that these cells are anuclear or short-lived, so that no template-primer functions of their DNA are required. Uracil-DNA glycosylase expression is high in all types of human leukemia, providing a selective advantage for survival of leukemic cells. Overall results show that a deficiency of this DNA base-excision-repair pathway is not likely to be an etiopathogenetic factor in the formation of non-random or other chromosomal abnormalities or in the leukemogenesis itself.

DNA repair synthesis in mouse spermatogenesis involves DNA polymerase beta activity

The role of DNA polymerase alpha-DNA primase complex and DNA polymerase beta in DNA replication and ultraviolet-induced DNA repair synthesis has been analyzed in mouse spermatogenesis. Autoradiographic experiments with germ cells in culture, indicating an involvement of DNA polymerase alpha and/or delta in DNA replication, and of DNA polymerase beta in DNA repair synthesis, have been confirmed by studying partially purified enzymes. These findings support the idea that, different from other biological systems, in meiotic and post meiotic male mouse germ cells DNA polymerase beta is the main DNA polymerase form needed for DNA repair.

DNA repair: relationship to drug and radiation resistance, metastasis and growth factors

DNA repair mechanisms are important for the recovery of both normal and malignant tissues from radiation and chemotherapy. Drug 'resistance' may merely reflect the similarity of cancer to normal tissues. Investigating the normal repair mechanisms by cloning human DNA repair genes will permit a much better comparison. Therapeutic inhibition of DNA repair may be possible with poly-ADP-ribose polymerase inhibitors. A differential effect may be obtained since less-differentiated cells have a higher poly-ADP-ribose polymerase activity. Clinical application of repair inhibitors can be achieved by using antimetabolites such as high-dose hydroxyurea which produces levels of 1-3 mmol litre -1/24 hours. The whole cell and tissue response to DNA damage is more complex than removal of adducts and joining strand breaks. DNA damage can result in an increase in growth-factor receptors, the release of soluble mediators that affect undamaged cells and stimulation of plasminogen activator. These changes may enhance growth and recovery as well as bypass or repair the damage. The generation of heterogeneity in a tumour population may be mediated by DNA rearrangements. Genetic instability is much higher in metastatic clones and a comparison of DNA strand-break repair in a metastatic and a non-metastatic line showed more rapid repair in the former. Aberrant use of DNA repair stimulated by growth factors may mediate tumour progression and heterogeneity as well as drug resistance.