FGF7 and FGF10 Promote Fate Transition of Human Epidermal Cell-derived Organoids to an Eccrine Gland Phenotype

Epidermal appendages play a key role in thermoregulation, which is crucial in maintaining the equilibrium of body temperature. The normality of eccrine sweat glands (SwGs) and hair follicles (HFs) assures homeostatic thermoregulation. However, the fate commitments of SwGs and HFs development and their key regulators are still poorly understood. To elucidate the regulatory networks and the major regulators in SwGs and HFs development, we generated a transcriptomic atlas within three tissues (dorsal back skin, front and hinder ventral foot skin) across four early development stages (embryonic (E) days E15.5 and E17.5, postnatal (P) days P1 and P3) of Mus musculus. We then applied a second-order polynomial model to fit time-course expression of genes and used likelihood ratio test (LRT) to identify temporal dynamic expressed genes. We further constructed temporal regulatory networks to investigate the master regulators during different developmental stages. We found the distinct temporally developmental patterns between dorsal back and ventral foot skin. Eight temporally dynamic expression modes were inferred, which are comprised of over 90% of the dynamic genes. Shh, Eda, Bmp2 and other previously identified factors were noted in our dominant dynamic patterns as well and temporally dynamic expressed in dorsal back and ventral foot. Combined with differentially expressed genes analysis, we highlighted 501 genes that were common in front and hinder foot, albeit uniquely enrich or depleted in dorsal back. Moreover, the integration of temporal expression models and genes regulatory networks accentuated master transcription factors functioning at specific stages in different tissues. Our findings demonstrated the temporally dynamic determinants during SwGs and HFs fate commitments and can contribute to restoring impaired SwGs and HFs clinically after hypohidrosis or burn injury. Overall design: To understand the early fate determination of hair follicles (HFs) and eccrine sweat glands (ESGs), we performed RNA-sequencing on mice dorsal back tissues and ventral front/hinder foot tissue at two embryonic (E) days 15.5 and 17.5 and two postnatal (P) days P1 and P3.

皮肤附属器在体温调节中发挥关键作用，而体温稳态的维持离不开正常的体温调节功能。外泌汗腺（eccrine sweat glands，SwGs）与毛囊（hair follicles，HFs）的正常状态是实现稳态体温调节的重要保障。然而，目前对于外泌汗腺与毛囊发育的命运决定过程及其关键调控因子，我们仍缺乏深入认知。
为阐明外泌汗腺与毛囊发育过程中的调控网络及核心调控因子，我们针对小家鼠（Mus musculus）的三种组织——背部皮肤、前脚掌腹侧皮肤及后脚掌腹侧皮肤，在四个早期发育阶段（胚胎期E15.5、E17.5，出生后P1、P3）构建了转录组图谱。
随后，我们采用二阶多项式模型拟合基因的时序表达谱，并通过似然比检验（likelihood ratio test，LRT）识别时序动态表达基因。我们进一步构建时序调控网络，以探究不同发育阶段的核心调控因子。
研究发现，背部皮肤与脚掌腹侧皮肤呈现出截然不同的时序发育模式。我们共推断出8种时序动态表达模式，覆盖了超过90%的动态表达基因。Shh、Eda、Bmp2等已被报道的调控因子也出现在我们的优势动态表达模式中，且在背部皮肤与脚掌组织中呈现时序动态表达特征。结合差异表达基因分析，我们筛选出501个在前脚掌与后脚掌中共有、但在背部皮肤中呈现独特富集或缺失的基因。此外，整合时序表达模型与基因调控网络，我们进一步明确了在不同组织的特定发育阶段发挥功能的核心转录因子。
本研究揭示了外泌汗腺与毛囊命运决定过程中的时序动态调控机制，可为临床中少汗症或烧伤损伤后受损的外泌汗腺与毛囊修复提供理论参考。
总体实验设计：为解析毛囊与外泌汗腺的早期命运决定机制，我们对小家鼠在两个胚胎期（E15.5、E17.5）与两个出生后期（P1、P3）的背部皮肤组织以及前/后脚掌腹侧组织进行了RNA测序（RNA-sequencing）。