Fig. 1: Rete ridges form perinatally in human and pig skin.
From: Rete ridges form via evolutionarily distinct mechanisms in mammalian skin
a, Epidermal placodes form continuously through early-to-mid gestation, but rete ridges do not. Representative H&E stains from human GW12, GW13.5, GW17 and GW19 trunk skin are shown. b, Rete ridges have formed and are maintained in adult human skin. Representative H&E stains of samples from trunk and face skin of adult male humans are shown. In a and b, the dashed box indicates the region of the zoomed-in inlay. c,d, Quantification of human trunk skin histology at GW7–9 (n = 1), GW12–13 (n = 1), GW13–14 (n = 1), GW14–15 (n = 1), GW16–17 (n = 7) and GW18–20 (n = 5), and trunk or face skin of 21–39-year-old (21–39 yo, n = 1), 40–59 yo (n = 3), 60–79 yo (n = 11) and 80 yo+ (n = 8) individuals for rete ridge density (c), epidermal thickness (d, left), and the ratio of rete ridge (RR) to inter-ridge (IR) thickness (d, right). Sample sizes in c and d are the same as in a and b. e, Graphical representation of human gestation compared with pig gestation. Coloured boxes indicate general availability of tissue samples. f,g, Rete ridges begin to form perinatally in pig skin (f) and rete ridge formation peaks postnatally alongside increased epidermal thickness and dermal vascularization (g). Representative H&E stains from skin across fetal (f) and postnatal (g) pig development from mixed backgrounds are shown (see Methods for full details). h,i, Quantification of pig histology for rete ridge density, showing rete ridges form continuously across perinatal life in pigs (h); epidermal thickness, showing rete ridge formation and maturation drives postnatal epidermal thickening (i, left); and the ratio of RR to IR thickness (i, right) at GW6–8 (n = 7), GW9–11 (n = 6), GW12–14 (n = 14), GW15–16 (n = 4), P1–2 (n = 3), P3–4 (n = 7), P5 (n = 5), P10 (n = 2) and P25 (n = 2) and in 1 month old (mo; n = 9), 1.5 mo (n = 2), 2mo (n = 2), 6 mo (n = 7), 7 mo (n = 3) and >1 yo (n = 4) individuals. Sample sizes in h and i are the same as in f and g. Scale bars, 100 μm. BB, basal bud/epithelial placode; HF, hair follicle; BV, blood vessel; pap, papillary dermis; ret, reticular dermis; Sw, sweat gland; Sb, sebaceous gland; PC, panniculus carnosus; APM, arrector pili muscle. Error bars in line plots in c, d, h and i represent s.e.m. Illustrations in c–i were created using BioRender. Thompson, S. (2026) https://BioRender.com/8rd8cz9.
