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The article explains the various symptoms and causes of spinocerebellar ataxia type 31 (SCA31), an adult-onset autosomal-dominant neurodegenerative disorder. The numerous insertions containing the complex penta-nucleotide repeats including a long [(TGGAA).sub.n] stretch are shown to be highly associated with the onset of the disorder.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.07.025 Byline: Eleanor Ager (a), Shunsuke Suzuki (b), Andrew Pask (a), Geoff Shaw (a), Fumitoshi Ishino (b), Marilyn B. Renfree (a) Keywords: Tammar wallaby; Chorio-vitelline placenta; Yolk sac; INS; Genomic imprinting; Evolution Abstract: Therian mammals (marsupials and eutherians) rely on a placenta for embryo survival. All mammals have a yolk sac, but while both chorio-allantoic and chorio-vitelline (yolk sac) placentation can occur, most marsupials only develop a yolk sac placenta. Insulin (INS) is unusual in that it is the only gene that is imprinted exclusively in the yolk sac placenta. Marsupials, therefore, provide a unique opportunity to examine the conservation of INS imprinting in mammalian yolk sac placentation. Marsupial INS was cloned and its imprint status in the yolk sac placenta of the tammar wallaby, Macropus eugenii, examined. In two informative individuals of the eight that showed imprinting, INS was paternally expressed. INS protein was restricted to the yolk sac endoderm, while insulin receptor, IR, protein was additionally expressed in the trophoblast. INS protein increased during late gestation up to 2 days before birth, but was low the day before and on the day of birth. The conservation of imprinted expression of insulin in the yolk sac placenta of divergent mammalian species suggests that it is of critical importance in the yolk sac placenta. The restriction of imprinting to the yolk sac suggests that imprinting of INS evolved in the chorio-vitelline placenta independently of other tissues in the therian ancestor of marsupials and eutherians. Author Affiliation: (a) Department of Zoology, The University of Melbourne, Melbourne, Victoria, 3010, Australia (b) Department of Epigenetics, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kandasurugadai, Chiyoda-ku, Tokyo 101-0062, Japan Article History: Received 10 May 2007; Revised 19 July 2007; Accepted 20 July 2007

We produced XX [left and right arrow] XY chimeras by using embryos whose X chromosomes were tagged with EGFP ([X.sup.*]), making the fluorescent green female (X[X.sup.*]) germ cells easily distinguishable from their nonfluorescent male (XY) counterparts. Taking advantage of tagging with EGFP, the X[X.sup.*] 'prospermatogonia' were isolated from the testes, and the status of their genomic imprinting was examined. It was shown that these XX cells underwent a paternal imprinting, despite their chromosomal constitution. As previously indicated in sex-reversal XXsxr testes, we also found a few green X[X.sup.*] germ cells developed as 'eggs' within the seminiferous tubules of X[X.sup.*] [left and right arrow] XY chimeric testes. These cells were indistinguishable from X[X.sup.*] prospermatogonia at birth but resumed oogenesis in a testicular environment. The biological nature of the 'testicular eggs' was examined by recovering the eggs from chimeric testes. The testicular eggs not only formed an egg-specific structure, the zona pellucida, but also were able to fuse with sperm. The collected testicular eggs were indicated to undergo maternal imprinting, despite the testicular environment. The genomic imprinting did not always follow the environmental conditions of where the germ cells resided; rather, it was defined by the sex that was chosen by the germ cells at early embryonic stage. sex differentiation | XX prospermatogonia | EGFP | XX [left and right arrow] XY chimera | genomic imprinting

Germline cells that can form different embryonic stem (ES) as well as embryonic germ (EG) cells are obtained only from embryonic tissues, hence tests were conducted to obtain such cells from other sources. Researchers conducted tests to obtain similar ES-like cells from neonatal mouse testis and these cells were similar to the ES/EG cells except that in their genomic imprinting pattern.