May have a role in embryonic development. It is likely to provide a growth stimulus to target cells in maternal and fetal tissues during the development of the embryo at mid-gestation. May play a role during wound healing and in the hair follicle cycle as a growth factor and/or an angiogenesis factor. May play a role in microvilli formation and cell proliferation of neuroblastoma cells. Expressed in brain and cerebellum (PubMed:16876275). Expressed in placenta and hair follicles, with highest expression levels detected in the outer root sheath and no expression detected in bulb (PubMed:11316781, PubMed:10537154). Also expressed in body fluids such as plasma and amniotic fluid (PubMed:10537154). Expressed in embryonic fibroblasts and at low levels in keratinocytes (PubMed:11316781). Isoform 1: Expressed in brain and Neuro-2a cells (PubMed:16876275). Isoform 2: Expressed in brain (PubMed:16876275). Expressed at low levels during hair follicle morphogenesis, with highest expression levels detected at late anagen stage of the hair follicle cycle (PubMed:11316781). Expressed in developing brain from embryo to adult (PubMed:16876275). In placenta, detected at 8 dpc, peaks at 10 dpc and declines thereafter (PubMed:10537154). N-glycosylated and sialylated. Belongs to the somatotropin/prolactin family.