Genes flanking Xist in mouse and human are separated on the X chromosome in American marsupials

X inactivation, the transcriptional silencing of one of the two X chromosomes in female mammals, achieves dosage compensation of X-linked genes relative to XY males. In eutherian mammals X inactivation is regulated by the X-inactive specific transcript (Xist), a cis-acting non-coding RNA that triggers silencing of the chromosome from which it is transcribed. Marsupial mammals also undergo X inactivation but the mechanism is relatively poorly understood. We set out to analyse the X chromosome in Monodelphis domestica and Didelphis virginiana, focusing on characterizing the interval defined by the Chic1 and Slc16a2 genes that in eutherians flank the Xist locus. The synteny of this region is retained on chicken chromosome 4 where other loci belonging to the evolutionarily ancient stratum of the human X chromosome, the so-called X conserved region (XCR), are also located. We show that in both M. domestica and D. virginiana an evolutionary breakpoint has separated the Chic1 and Slc16a2 loci. Detailed analysis of opossum genomic sequences revealed linkage of Chic1 with the Lnx3 gene, recently proposed to be the evolutionary precursor of Xist, and Fip1, the evolutionary precursor of Tsx, a gene located immediately downstream of Xist in eutherians. We discuss these findings in relation to the evolution of Xist and X inactivation in mammals

Out of Mind, Out of Sight: Language Affects Perceptual Vividness in Memory

We examined whether language affects the strength of a visual representation in memory. Participants studied a picture, read a story about the depicted object, and then selected out of two pictures the one whose transparency level most resembled that of the previously presented picture. The stories contained two linguistic manipulations that have been demonstrated to affect concept availability in memory, i.e., object presence and goal-relevance. The results show that described absence of an object caused people to select the most transparent picture more often than described presence of the object. This effect was not moderated by goal-relevance, suggesting that our paradigm tapped into the perceptual quality of representations rather than, for example, their linguistic availability. We discuss the implications of these findings within a framework of grounded cognition

Post-meiotic transcription of phosphoglycerate-kinase 2 in mouse testes

We have used a human phosphoglycerate kinase-1 (PGK-1) cDNA clone to study expression of PGK-2 during mouse spermatogenesis. Hybrid selection, in vitro translation with product identification by 2-D gel electrophoresis demon-strated that the PGK-1 cDNA clone hybridized to PGK-2 mRNA in mouse testes. Northern analyses of RNA purified from separated spermatogenic cells demonstrated a large increase in abundance of PGK-2 mRNA in post-meiotic cells. Thus, post-meiotic transcription of PGK-2 mRNA is demonstrable with cloned DNA probes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44192/1/10540_2005_Article_BF01119630.pd

Evolution from XIST-Independent to XIST-Controlled X-Chromosome Inactivation: Epigenetic Modifications in Distantly Related Mammals

X chromosome inactivation (XCI) is the transcriptional silencing of one X in female mammals, balancing expression of X genes between females (XX) and males (XY). In placental mammals non-coding XIST RNA triggers silencing of one X (Xi) and recruits a characteristic suite of epigenetic modifications, including the histone mark H3K27me3. In marsupials, where XIST is missing, H3K27me3 association seems to have different degrees of stability, depending on cell-types and species. However, the complete suite of histone marks associated with the Xi and their stability throughout cell cycle remain a mystery, as does the evolution of an ancient mammal XCI system. Our extensive immunofluorescence analysis (using antibodies against specific histone modifications) in nuclei of mammals distantly related to human and mouse, revealed a general absence from the mammalian Xi territory of transcription machinery and histone modifications associated with active chromatin. Specific repressive modifications associated with XCI in human and mouse were also observed in elephant (a distantly related placental mammal), as was accumulation of XIST RNA. However, in two marsupial species the Xi either lacked these modifications (H4K20me1), or they were restricted to specific windows of the cell cycle (H3K27me3, H3K9me2). Surprisingly, the marsupial Xi was stably enriched for modifications associated with constitutive heterochromatin in all eukaryotes (H4K20me3, H3K9me3). We propose that marsupial XCI is comparable to a system that evolved in the common therian (marsupial and placental) ancestor. Silent chromatin of the early inactive X was exapted from neighbouring constitutive heterochromatin and, in early placental evolution, was augmented by the rise of XIST and the stable recruitment of specific histone modifications now classically associated with XCI

Testis-specific glyceraldehyde-3-phosphate dehydrogenase: origin and evolution

<p>Abstract</p> <p>Background</p> <p>Glyceraldehyde-3-phosphate dehydrogenase (GAPD) catalyses one of the glycolytic reactions and is also involved in a number of non-glycolytic processes, such as endocytosis, DNA excision repair, and induction of apoptosis. Mammals are known to possess two homologous GAPD isoenzymes: GAPD-1, a well-studied protein found in all somatic cells, and GAPD-2, which is expressed solely in testis. GAPD-2 supplies energy required for the movement of spermatozoa and is tightly bound to the sperm tail cytoskeleton by the additional N-terminal proline-rich domain absent in GAPD-1. In this study we investigate the evolutionary history of GAPD and gain some insights into specialization of GAPD-2 as a testis-specific protein.</p> <p>Results</p> <p>A dataset of GAPD sequences was assembled from public databases and used for phylogeny reconstruction by means of the Bayesian method. Since resolution in some clades of the obtained tree was too low, syntenic analysis was carried out to define the evolutionary history of GAPD more precisely. The performed selection tests showed that selective pressure varies across lineages and isoenzymes, as well as across different regions of the same sequences.</p> <p>Conclusions</p> <p>The obtained results suggest that GAPD-1 and GAPD-2 emerged after duplication during the early evolution of chordates. GAPD-2 was subsequently lost by most lineages except lizards, mammals, as well as cartilaginous and bony fishes. In reptilians and mammals, GAPD-2 specialized to a testis-specific protein and acquired the novel N-terminal proline-rich domain anchoring the protein in the sperm tail cytoskeleton. This domain is likely to have originated by exonization of a microsatellite genomic region. Recognition of the proline-rich domain by cytoskeletal proteins seems to be unspecific. Besides testis, GAPD-2 of lizards was also found in some regenerating tissues, but it lacks the proline-rich domain due to tissue-specific alternative splicing.</p

Specific patterns of histone marks accompany X chromosome inactivation in a marsupial

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Husbandry Of Monodelphis Domestica In The Study Of Mammalian Embryogenesis

Monodelphis domestica, commonly called the laboratory opossum, is a useful laboratory animal for studying marsupial embryogenesis and mammalian development. Females breed year-round and the animals can be sustainably bred indoors. The authors draw on their own laboratory\u27s experience to supplement previously published research on laboratory opossums. They describe a breeding protocol that reliably produces timed-pregnant M. domestica. Additionally, the authors discuss general laboratory opossum husbandry techniques and describe how to collect, handle and culture embryos