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Background Sheep milk is a nutritional and health-promoting food source for humans. The DEATH superfamily is a conserved protein family, and some of its members are closely related to lactation. Systematic studies of the members of the DEATH superfamily are important for further understanding its functions in the mammary gland during lactation; however, there studies are currently lacking. Results Herein, 74 members of the DEATH superfamily were identified in sheep, and phylogenetic analyses indicated that four subfamilies were strongly correlated in evolution. The Ka/Ks calculations demonstrated that negative selection was the primary pressure acting on DEATH members; however, the immune-related gene IFI203 was undergoing strong positive selection in sheep. Furthermore, in the late pregnancy and lactation period, these DEATH genes exhibited similar expression patterns under different nutritional conditions in the mammary gland, and four subfamilies were positively correlated in expression patterns. Additionally, half or more DEATH genes were upregulated in the lactation period, which implied their crucial roles in the lactation of sheep. Conclusions The current research contributes to a better understanding of the evolutionary characteristics of the DEATH superfamily and their roles in sheep lactation, and it also provides potential target genes for the molecular breeding of dairy sheep. Graphical Abstract

Background Sheep milk is an attractive nutritional and functional food source. Some Dishevelled, Egl-10 and pleckstrin (DEP) domain-containing proteins can regulate lactation performance in mammals. However, systematic study of the role of sheep DEP family members in regulating lactation is currently lacking. This study aimed to reveal the roles of sheep DEP family members in lactation by exploring their genetic characteristics and functional features at the whole genome-wide level. Results Twenty DEP family members were identified in the sheep genome, and they can be divided into four major groups. Ka/Ks calculations suggest that the purifying selection is the main pressure acting on DEP genes. In the late pregnancy and lactation periods, the expression levels of eight DEP genes exhibited significant differences in the mammary gland. In addition, nutritional conditions have a great influence on the expression of DEP family members, and the DEP gene family underwent more expansion than the average gene family in the early stages of biological evolution. The Mirrortree assays indicated that the DEP family members coevolved in biological evolution. Conclusions Our research provides a better understanding of the characters of the DEP domain-containing protein family and their potential roles in regulating lactation in sheep. Moreover, these results of our study may contribute to the genetic improvement of milk performance in dairy sheep breed. Graphical Abstract