随着单细胞数据的不断积累和转化，拿一个组织画个图谱的草莽时代已经基本一去不复返了。往深了做的一个方面就是做某个细胞类型的图谱。特别是对那些异质性较高的细胞类型。
例如，我们熟悉的fibroblast 就是这样的一类细胞，先来看看科普级的介绍：
https://www.britannica.com/science/fibroblast
成纤维细胞，结缔组织的主要活性细胞。成纤维细胞是大的、扁平的、细长的(纺锤形)细胞，具有从细胞体末端延伸出来的突起。细胞核呈扁平椭圆形。成纤维细胞产生胶原蛋白的前身胶原蛋白和基质，基质是一种无定形凝胶状基质，填充在结缔组织的细胞和纤维之间。
成纤维细胞似乎在伤口愈合中起着重要的作用，而这种活性被认为是由位于组织基质中的纤维细胞调节的。在组织损伤后，成纤维细胞迁移到损伤部位，在那里沉积新的胶原蛋白，促进愈合过程。
纤维细胞是指细胞处于不活跃状态，参与组织的维护和代谢。一些研究人员用成纤维细胞来表示这两种细胞状态，但“blast”一词通常指干细胞或细胞的激活状态。
成纤维细胞最初来源于原始间充质，因此显示出丝蛋白波形蛋白，作为中胚层起源的标记。在某些情况下，上皮细胞也可以产生成纤维细胞，这个过程被称为上皮-间充质转化(EMT)。相反，成纤维细胞有时会发生间充质-上皮转变(MET)产生上皮细胞，这一过程见于发育、组织修复和肿瘤生长。
https://www.news-medical.net/health/What-are-Fibroblasts.aspx
下面我们走马观花似的，看几篇案例。
这就，能写一段，就是写哪个marker在哪些cluster里表达了，好处是，我们可以从这里面copy marker list：
Cancer-associated fibroblasts (CAFs) are a prominent stromal cell type in solid tumors and molecules secreted by CAFs play an important role in tumor progression and metastasis.
Feature plots showing the expression of CAF markers Acta2, Ly6c1, Cdk1, Cd74, Crabp1and Cd53intheCAF clusters identified with 1000 most variable genes。
Cells in cluster 4 had high levels of Thy1, Pdpn and Pdgfra [25] and were identified as CAFs。
Fibroblast Activation Protein (FAP) marker
monocle2 用的可以啊，中规中矩的一篇文章，分群，差异，go
、kegg富集。
- Distinct MC subtypes were defined by single-cell transcriptome analysis
- Lipofibroblasts were identified
- Fibrotic Pdgfrb high MC subtype emerges post-injury
- Integrative analysis of MC trajectories was constructed by machine learning
We found that these Adrp and Pparg highly expressing MCs were clustered together to form a distinct subpopulation, and at the same time, this cluster also expresses considerable levels of Fabp1,4,5, Lpl, and Lipa. Therefore, we referred to this cluster as lipofibroblasts。
It is interesting that M2 macrophage-like signature genes , together with mesenchymal genes (Mlc1, Plek, CD44, Ptpn12, and Slpi), are expressed in the lipofibroblast subtype
Seven clusters comprised the two key cell types of the skin, keratinocytes and fibroblasts. Keratinocytes were detected in three clusters (#5, #7 and #15) and their diversity was mainly due to their degree of differentiation. While epidermal stem cells (EpSC) and other undifferentiated progenitors (#7 and #15) expressed markers such as KRT5, KRT14, TP63, ITGA6, and ITGB1, differentiated keratinocytes (#5) were defined by KRT1, KRT10, SBSN, and KRTDAP expression33 (Fig. 1c and Supplementary Fig. 1c). Fibroblasts were identified by their archetypal markers LUM, DCN, VIM, PDGFRA, and COL1A227, constituted the most abundant skin cell type (5948 cells in total), and were represented by four clusters (#1, #2, #3, and #9, Fig. 1c and Supplementary Fig. 1c). Despite the lower amount of cells, the individual analysis of each sample generated a similar number of clusters and identified the same major cell types (Supplementary Fig. 2).
