During the breast-feeding period, infants undergo remarkable changes, including rapid physiological and developmental growth. However, little is known about gene expression features and sex-specific gene expression in breast-feeding infants. In this study, we sequenced 32 blood transcriptomes from 16 breast-feeding rhesus macaque(Macaca mulatta) infants and their lactating mothers. We identified 218 differentially expressed genes(DEGs) between infants and mothers, including 91 up-regulated and 127 down-regulated DEGs in the infant group. Functional enrichment analysis of the up-regulated DEGs and unique hub genes in infants showed primary enrichment in immunity, growth, and development. Protein-protein interaction analysis also revealed that genes at key positions in infants were mainly related to development and immunity. However, we only detected 23 DEGs between female and male infants, including three DEGs located on chromosome X and 14 DEGs located on chromosome Y. Of these DEGs, TMF1 regulated nuclear protein 1 (Trnp1), which was highly expressed in female infants, is crucial for controlling the tangential and radial expansion of the cerebral cortex in mammals. Thus, our study provides novel insight into the gene expression features of breast-feeding infants in non-human primates(NHPs) and reveals sex-specific gene expression between these infants. During the breast-feeding period, breast milk provides the first source of immune protection for infants and also activates the development of an infant’s own immune system (Rogier et al., 2014). Moreover, breast-feeding infants also experience significant changes in growth, metabolism, and neurobehavioral development during this period (Feldman & Eidelman, 2003; Shoji & Shimizu, 2019). Therefore, the expression levels of genes related to such functions or pathways in infants may show significant differences to that found in adults.

Although male and female genomes share much of the same genetic information, previous studies have found sexspecific gene expression in various species and tissues (Gershoni & Pietrokovski, 2017; Ronen & Benvenisty, 2014; Tower, 2017; Villa et al., 2018). For example, males and females exhibit differences in brain anatomy and development (Collaer & Hines, 1995; Giedd et al., 1997), women consistently exhibit greater longevity than men (Tower, 2017), and sex differences are pervasive in metabolic and cardiovascular traits (Chella Krishnan et al., 2018). Rhesus macaques exhibit a close evolutionary relationship to humans and are thus widely used in biomedical studies (Rhesus Macaque Genome Sequencing and Analysis Consortium et al., 2007). They are also considered an ideal animal model for human infant nutritional research (Lönnerdal, 2012). To date, however, little is known about the gene expression features in breast-feeding rhesus macaques, or the differences between infants and their mothers. Furthermore, whether breast-feeding female and male infants exhibit differences in gene expression remains unclear. In this study, we sequenced the blood transcriptomes of 16 breastfeeding rhesus macaque infants (eight males and eight females) and their lactating mothers to determine the:(1) transcriptional profiles of these infants;(2) gene expression differences between infants and their mothers; and(3) sexspecific gene expression in breast-feeding infants. Peripheral whole blood samples were collected during a routine examination of 32 captive rhesus macaques in September 2019. All libraries were sequenced using the Illumina NovaSeq 6000 platform with a paired-end sequencing length of 150 bp (PE150) at …