In this task, you are given an abstract of article. Your task is to generate title for this article. Preferred titles are under thirty words.

Q: The mammalian A-type cyclin family consists of two members, cyclin A1 (encoded by Ccna1) and cyclin A2 (encoded by Ccna2). Cyclin A2 promotes both G1/S and G2/M transitions, and targeted deletion of Ccna2 in mouse is embryonic lethal. Cyclin A1 is expressed in mice exclusively in the germ cell lineage and is expressed in humans at highest levels in the testis and certain myeloid leukaemia cells. To investigate the role of cyclin A1 and possible redundancy among the cyclins in vivo, we generated mice bearing a null mutation of Ccna1. Ccna1-/- males were sterile due to a block of spermatogenesis before the first meiotic division, whereas females were normal. Meiosis arrest in Ccna1/ males was associated with increased germ cell apoptosis, desynapsis abnormalities and reduction of Cdc2 kinase activation at the end of meiotic prophase. Cyclin A1 is therefore essential for spermatocyte passage into the first meiotic division in male mice, a function that cannot be complemented by the concurrently expressed B-type cyclins.

A: Cyclin A1 is required for meiosis in the male mouse
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Q: Werner's syndrome (WS) and Bloom's syndrome (BS) are cancer predisposition disorders caused by loss of function of the RecQ helicases WRN or BLM, respectively. BS and WS are characterized by replication defects, hyperrecombination events and chromosomal aberrations, which are hallmarks of cancer. Inefficient replication of the G-rich telomeric strand contributes to chromosome aberrations in WS cells, demonstrating a link between WRN, telomeres and genomic stability. Herein, we provide evidence that BLM also contributes to chromosome-end maintenance. Telomere defects (TDs) are observed in BLM-deficient cells at an elevated frequency, which is similar to cells lacking a functional WRN helicase. Loss of both helicases exacerbates TDs and chromosome aberrations, indicating that BLM and WRN function independently in telomere maintenance. BLM localization, particularly its recruitment to telomeres, changes in response to replication dysfunction, such as in WRN-deficient cells or after aphidicolin treatment. Exposure to replication challenge causes an increase in decatenated deoxyribonucleic acid (DNA) structures and late-replicating intermediates (LRIs), which are visible as BLM-covered ultra-fine bridges (UFBs) in anaphase. A subset of UFBs originates from telomeric DNA and their frequency correlates with telomere replication defects. We propose that the BLM complex contributes to telomere maintenance through its activity in resolving LRIs.

A: The BLM helicase contributes to telomere maintenance through processing of late-replicating intermediate structures
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Q: Ex-FABP, an extracellular fatty acid binding lipocalin, is physiologically expressed by differentiating chicken chondrocytes and myoblasts. Its expression is enhanced after cell treatment with inflammatory stimuli and repressed by anti-inflammatory agents, behaving as an acute phase protein. Chicken liver fragments in culture show enhanced protein expression after bacterial endotoxin treatment. To investigate the biological role of Ex-FABP, we stably transfected proliferating chondrocytes with an expression vector carrying antisense oriented Ex-FABP cDNA. We observed a dramatic loss of cell viability and a strong inhibition of cell proliferation and differentiation. When chondrocytes were transfected with the antisense oriented Ex-FABP cDNA we observed that Ex-FABP down-modulation increased apoptotic cell number. Myoblasts transfected with the same expression vector showed extensive cell death and impaired myotube formation. We suggest that Ex-FABP acts as a constitutive survival protein and that its expression and activation are fundamental to protect chondrocytes from cell death.

A:
Inhibition of cell proliferation and induction of apoptosis by ExFABP gene targeting.
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