placentaspecific

Placenta-specific, or placental-specific, describes genes, transcripts, proteins, or regulatory elements whose expression is largely confined to the placenta, particularly in trophoblast lineages, during pregnancy in mammals. The term is used to distinguish these placental products from those expressed in other tissues.

In placental biology, placenta-specific expression underpins endocrine, immunomodulatory, and structural functions essential for fetal development. Placenta-specific genes often encode hormones, cytokines, and surface or secreted proteins that mediate maternal-fetal communication, nutrient transfer, and immune tolerance. Expression patterns can be developmentally regulated and may vary across species, reflecting different placental structures and strategies of reproduction.

Examples commonly described as placenta-specific include PLAC1 (placenta-specific 1), a conserved gene expressed by placental trophoblasts; pregnancy-specific glycoproteins (PSGs), a family predominantly produced by the human placenta with roles in immune modulation and maternal adaptation to pregnancy; and the chorionic somatomammotropin/human placental lactogen (CSH/hPL) gene family, which encodes hormones controlling maternal metabolism to support fetal growth. Other placenta-associated genes may exhibit placental-restricted but not absolutely exclusive expression, and some show coexpression in related tissues or developmental stages.

Placenta-specific expression is a subject of study in evolutionary biology, reproductive genetics, and placental pathology. It highlights how the placenta has evolved specialized molecular programs to sustain pregnancy, and it is often used in gene annotation and comparative genomics. Because placental expression can be stage- and species-specific, researchers avoid assuming absolute tissue exclusivity and consider contextual factors in interpretation.