Status of genomic imprinting in mouse spermatids

The advent of human round spermatid microinjection (ROSI) into oocytes as a treatment for severe male infertility raises the question of whether sperm atids have undergone all of the maturation processes necessary for normal d evelopment. It is particularly important to know whether spermatids have un dergone correct genomic imprinting, which results in the parent-of-origin-s pecific expression of only one allele of a gene. We assessed the imprinting status of three maternally and three paternally expressed genes in intersp ecific hybrid embryos generated by injecting Mus castaneus spermatids into Mus musculus oocytes. We used the single nucleotide primer extension (SNuPE ) assay to measure the relative expression of maternal and paternal alleles on the basis of sequence polymorphisms in the transcripts. Expression of i mprinted genes in mouse embryos derived by ROSI did not differ from control s, indicating that paternal genes have undergone proper imprinting by the r ound spermatid stage.