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.
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Question: 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.

Answer: Cyclin A1 is required for meiosis in the male mouse

Question: To efficiently counteract pathogens, plants rely on a complex set of immune responses that are tightly regulated to allow the timely activation, appropriate duration and adequate amplitude of defense programs. The coordination of the plant immune response is known to require the activity of the ubiquitin/proteasome system, which controls the stability of proteins in eukaryotes. Here, we demonstrate that the N-end rule pathway, a subset of the ubiquitin/proteasome system, regulates the defense against a wide range of bacterial and fungal pathogens in the model plant Arabidopsis thaliana. We show that this pathway positively regulates the biosynthesis of plant-defense metabolites such as glucosinolates, as well as the biosynthesis and response to the phytohormone jasmonic acid, which plays a key role in plant immunity. Our results also suggest that the arginylation branch of the N-end rule pathway regulates the timing and amplitude of the defense program against the model pathogen Pseudomonas syringae AvrRpm1.

Answer: The N-end rule pathway regulates pathogen responses in plants.

Question: A classification of risk for developing breast cancer has been devised based solely on the appearance of the breast parenchyma by mammography. Four groups of patients were isolated. The study encompassed a five-year period and was done by reviewing the mammograms of all women over the age of 30 who had been examined at Hutzel Hospital, Detroit. The average time of followup would be approximately 2 1/2 years. Four groups had an incidence of developing breast cancer of 0.1, 0.4, 1.7, and 2.2. These parenchymal patterns are described and criteria for their identification are given.

Answer:
Risk for breast cancer development determined by mammographic parenchymal pattern.