A large class of mammalian genes is not completely shared throughout sperm development and differentiation, according to a new study of sperm in organisms including mice, macaques and men. The findings provide an explanation to why testis gene expression patterns often appear as an outlier relative to all other tissues. In mammals, spermatogenesis includes a long stage of haploid gene expression, which could lead to variation between individual sperm cells, resulting in sperm-level natural selection and trait inheritance. However, during differentiation, maturing haploid spermatids remain connected to neighboring cells by cytoplasmic bridges and can share gene products with one another and effectively erase phenotypic differences linked to the haploid genome. There are a few known exceptions, but, while previous research has shown that not all gene products are shared between cells, the total range of allele-specific biases in mammalian spermatids remains unknown. Kuanal Bhutani and colleagues performed single-cell RNA sequencing on sperm from mice, cattle and humans, and found that a large class of mammalian genes is not completely shared across the cytoplasmic bridges connecting spermatids. Some of these genes, which the authors dub "genoinformative markers," can act as selfish genetic elements and spread alleles unevenly through a population, revealing a mechanism for sperm-level natural selection.
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Science