皮膚是動物最大的器官，在保護生物體免受病原體和水分流失等外部因素影響方面發揮 著至關重要的作用。 網脊是一種特殊的上皮結構，存在於皮膚緊密的動物(例如鯨魚、豬和 人類)中，以增加上皮與真皮黏附的表面積。 令人驚訝的是，很少有研究探網脊的三維結構。 因此，為了更了解這項特徵，我們利用兩種不同的方法來建構蘭嶼豬網脊的 3D 模型。 第一 種方法是將連續的石蠟切片合併成一個結構連貫的重組模型。 第二種方法為使用細胞角質蛋 白 5 (K5) 和整合素 α6 (ITG α6) 標記物進行全組織免疫染色，這些標記在會基底層表現出 陽性訊號。 接著透過共軛焦顯微鏡掃描 z 軸堆疊影像，以視覺化網狀脊的三維形態。 透過 K5 的全組織染色，網脊形態呈現通道狀結構，有趣的是，通道從毛囊向外輻射。在 ITG α6 全組織染色中，網狀脊形態表現為相互連接的通道。 兩種方法都顯示蘭嶼豬的網脊形成通道 狀結構，錯綜複雜地交織在一起。 而不是 2D 石蠟切片所顯示的手指狀壓痕型態。
此外，我們研究了人類不同區域標本的網脊三維形態。 我們的研究結果表示，人類的網脊不僅表現出通道狀結構，而且還表現出區域特異性的特徵。 我們的 K5 和 ITG α6 全組 織免疫染色數據顯示人類皮膚標本每個區域都有不同的形態模式。 具體而言，人類上背部皮 膚表皮的網脊呈現分支網絡般的型態，而人類腳趾皮膚表皮則呈現出具有較小網脊連接的深 色水平平行線性條紋。 相較之下，人類足背皮膚表皮顯示出深色水平波浪狀條紋，網脊之間 偶爾有連接。
鹼性磷酸鹽 (ALP) 全組織染色結果顯示與網脊形態一致的網狀圖案。 值得注意的是， 與基底上層相比，覆蓋網脊基底角質形成細胞層底部的 ALP 強度增加。總而言之，我們假設 人類網脊具有區域特異性的特徵。揭示這種新穎且區域特異性的 3D 網脊結構將有助於為再 生醫學領域提供新的視角。

Skin is the largest organ in animals and plays a crucial role in protecting organisms from external factors for example pathogens and water loss. The rete ridge is a specialized epithelial structure present in tight-skinned animals, for example, whales, pigs, and humans, to increase surface area for adherence of the epithelium to the dermis. Surprisingly, there is a paucity of research exploring the three-dimensional structure of the rete ridge. Thus, to understand this feature more, we utilized two distinct methodologies to construct 3D models of rete ridges in Lanyu pig. The first approach involved amalgamating serial paraffin sections into a coherent structure. The second method involved whole- mount immunostaining with cytokeratin 5 (K5) and integrin α6 (ITG α6) markers, which exhibit positive signals at the basal layer or basal lamina. The samples were then scanned via confocal microscopy z-stacking to visualize the three-dimensional morphology of the rete ridge. With K5 whole-mount staining, the rete ridge morphology displayed an interconnected lattice/channel-like structure. Interestingly, these channels radiate out from hair follicles. In the ITG α6 whole-mount staining, the rete ridge morphology appeared as interconnected channels. Both methodologies revealed that the rete ridges in Lanyu pig form channel-like structures, intricately interwoven and interconnected. In general, they do not form finger-like indentations as suggested by 2D paraffin sections.
Furthermore, we investigated the three-dimensional morphology of human rete ridges from multiple regions. Our results revealed that human rete ridges exhibited an interconnected lattice/channel-like structures with regional-specific characteristics. Our whole-mount immunostaining data for K5 and ITG α6 showed distinct morphological patterns for each region of human skin specimens. Specifically, human upper back skin epidermis exhibited a branching network of rete ridges, while human toe skin epidermis displayed dark horizontal parallel linear striations with minor connections of rete ridges. In contrast, human dorsal foot skin epidermis showed dark horizontal wavy striations with occasional connections between rete ridges.
Alkaline phosphates (ALP) staining exhibited a network-like pattern in the rete ridge channels that mimicked the whole mount IHC patterns. Of note, the ALP intensity overlying the bottom of rete ridge basal keratinocyte layer was increased versus the suprabasal layers. We hypothesize rete ridges exhibit regional-specific morphology. Unraveling this novel regional-specific 3D rete ridge structure will help contribute new perspectives to the field of regenerative medicine.

1. Monavarian M, Kader S, Moeinzadeh S, Jabbari E. Regenerative Scar-Free Skin Wound Healing. Tissue Eng Part B Rev. Aug 2019;25(4):294-311.
2. Rittié L. Cellular mechanisms of skin repair in humans and other mammals. J Cell Commun Signal. Jun 2016;10(2):103-120.
3. Regional Specific Human Skin Rete Ridges Characterization: National Cheng Kung University Institute of Clinical Medicine; 2023.
4. Lin CH, Chiu PY, Hsueh YY, et al. Regeneration of rete ridges in Lanyu pig (Sus scrofa): Insights for human skin wound healing. Exp Dermatol. Apr 2019;28(4):472-479.
5. Yamamura T, Kobayashi S, Yoshida I, Kuriyama KI. Enlarged rete pegs with excessive accumulation of melanosomes leading to darker aging spots revealed by histomorphological measurements of internal structures of the epidermis. Int J Cosmet Sci. Jun 2023;45(3):387- 399.
6. Newton VL, Bradley RS, Seroul P, et al. Novel approaches to characterize age-related remodelling of the dermal-epidermal junction in 2D, 3D and in vivo. Skin Res Technol. May 2017;23(2):131-148.
7. Szabó G. The regional anatomy of the human integument with special reference to the distribution of hair follicles, sweat glands and melanocytes. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 1967;252:447 - 485.
8. Penrose LS, Ohara PT. The development of the epidermal ridges. J Med Genet. Sep 1973;10(3):201-208.
9. Wertheim K, Maceo A. The Critical Stage of Friction Ridge and Pattern Formation2002.
10. Ashbaugh DR, Section RCMPFIS. Ridgeology: Modern Evaluative Friction Ridge
Identification: Royal Canadian Mounted Police, Forensic Identification Support Section; 1989.
11. Hirobe T, Enami H, Nakayama A. The human melanocyte and melanoblast populations per unit area of epidermis in the rete ridge are greater than in the inter-rete ridge. Int J Cosmet Sci.
Apr 2021;43(2):211-217.
12. Díaz-García D, Filipová A, Garza-Veloz I, Martinez-Fierro ML. A Beginner's Introduction to
Skin Stem Cells and Wound Healing. Int J Mol Sci. Oct 13 2021;22(20).
13. Inoue K, Aoi N, Sato T, et al. Differential expression of stem-cell-associated markers in human
hair follicle epithelial cells. Lab Invest. Aug 2009;89(8):844-856.
14. Shen Z, Sun L, Liu Z, et al. Rete ridges: Morphogenesis, function, regulation, and
reconstruction. Acta Biomater. Jan 1 2023;155:19-34.
15. Štefková K, Procházková J, Pacherník J. Alkaline phosphatase in stem cells. Stem Cells Int. 2015;2015:628368.
16. Yang R, Liu F, Wang J, Chen X, Xie J, Xiong K. Epidermal stem cells in wound healing and their clinical applications. Stem Cell Res Ther. Jul 29 2019;10(1):229.