Intracisternal A-particle (IAP)-mediated leukemogenesis: levels and stability of IAP mRNA in FDC-P1 cells exposed to the conditions of an irradiated environment

Factors regulating endogenous retroviral sequences in human and mouse

Endogenous retroviruses (ERVs) are stably integrated in the genome of vertebrates and inherited as Mendelian genes. The several human ERV (HERV) families and related elements represent up to 5-8% of the DNA of our species. ERVs may be involved in the regulation of adjacent genomic loci, especially promoting the tissue-specific expression of genes; some HERVs may have functional roles, e.g., coding for the placental fusogenic protein, syncytin. This paper reviews the growing evidence about factors that may modulate ERVs, including: cell and tissue types (with special attention to placenta and germ cells), processes related to differentiation and aging, cytokines, agents that disrupt cell functions (e.g., DNA hypomethylating agents) and steroids. Special attention is given to HERVs, due to their possible involvement in autoimmunity and reproduction, as well as altered expression in some cancer types; moreover, different HERV families may deserve specific attention, due to remarkable differences concerning, e.g., expression in tissues. A comparison with factors interacting with murine ERV-related sequences indicates that the mouse may be a useful model for studying some patterns of HERV regulation. Overall, the available evidence identifies the diverse, potential interactions with endogenous or exogenous factors as a promising field for investigating the roles of ERVs in physiology and disease.

Expression of an intracisternal A-particle-like element in rat ovary

We have isolated a rat intracisternal-A particle element (IAP)-like element (IAP-LE) from ovarian granulosa cells that appears to be identical to the rat EST clone AA964260. The compiled cDNA sequences contain several putative in-frame translation initiation codons with the largest capable of encoding a 365 amino acid protein with a reverse transcriptase domain in the N-terminus as well as a bipartite nuclear localization signal sequence in the middle. Northern blotting shows a major approximately 7 Kb transcript and a minor approximately 5 Kb transcript that are abundantly expressed in the ovary. In situ hybridization histochemistry using ovaries from gonadotropin-treated immature rats and regularly cycling adult rats show that this transcript is predominantly localized to granulosa cells of all healthy follicles, including primary follicles, and to newly-formed and healthy corpora lutea. This cell-specific expression pattern of the IAP-LE gene is distinct from those of the several known retroviral elements, suggesting the potentially novel functional importance of the IAP-LE gene. Taken together, our results demonstrate abundant and cell-specific expression of a novel IAP-LE in rat granulosa cells.