RESUMO
X chromosome dosage compensation in female eutherian mammals is regulated by the noncoding Xist RNA and is associated with the differential acquisition of active and repressive histone modifications, resulting in repression of most genes on one of the two X chromosome homologs. Marsupial mammals exhibit dosage compensation; however, they lack Xist, and the mechanisms conferring epigenetic control of X chromosome dosage compensation remain elusive. Oviparous mammals, the monotremes, have multiple X chromosomes, and it is not clear whether they undergo dosage compensation and whether there is epigenetic dimorphism between homologous pairs in female monotremes. Here, using antibodies against DNA methylation, eight different histone modifications, and HP1, we conduct immunofluorescence on somatic cells of the female Australian marsupial possum Trichosurus vulpecula, the female platypus Ornithorhynchus anatinus, and control mouse cells. The two marsupial X's were different for all epigenetic features tested. In particular, unlike in the mouse, both repressive modifications, H3K9me3 and H4K20Me3, are enriched on one of the X chromosomes, and this is associated with the presence of HP1 and hypomethylation of DNA. Using sequential labeling, we determine that this DNA hypomethylated X correlates with histone marks of inactivity. These results suggest that female marsupials use a repressive histone-mediated inactivation mechanism and that this may represent an ancestral dosage compensation process that differs from eutherians that require Xist transcription and DNA methylation. In comparison to the marsupial, the monotreme exhibited no epigenetic differences between homologous X chromosomes, suggesting the absence of a dosage compensation process comparable to that in therians.
Assuntos
Evolução Biológica , Mecanismo Genético de Compensação de Dose/genética , Epigênese Genética/genética , Ornitorrinco/genética , Trichosurus/genética , Cromossomo X/genética , Animais , Coloração Cromossômica , Metilação de DNA/genética , Feminino , Imunofluorescência , Histonas/genética , Camundongos , Microscopia de Fluorescência , Especificidade da EspécieRESUMO
Increasing evidence suggests that there may be a causal relationship between the development of donor-specific alloantibodies and chronic allograft vasculopathy (CAV). PVG.RT1(u) rat heart allografts spontaneously undergo chronic rejection when transplanted into unmodified PVG.R8 congenic recipients that differ only at the classical MHC class I RT1.A locus. Here we show that development of vasculopathy in this experimental model is associated with production of a strong anti-A(u) antibody response. Perioperative intravenous administration of recombinant soluble RT1.A(u) heavy chain that is sequence identical to donor MHC class I, or chimaeric A(u/a) (donor/recipient) protein had a variable effect resulting generally in either sensitisation and accelerated rejection, or abrogation of alloantibody and attenuation of chronic rejection. These findings highlight the potential for soluble donor MHC class I alloantigen given at the time of heart transplantation to influence alloantibody production and graft outcome.