# 4.10 实战十 | CEL-seq | 小鼠造血干细胞

## 1 前言

数据来自[Grun et al. 2016](https://pubmed.ncbi.nlm.nih.gov/27345837/)的小鼠造血干细胞 haematopoietic stem cell (HSC) ，使用的技术是CEL-seq

### **数据准备**

```r
library(scRNAseq)
sce.grun.hsc <- GrunHSCData(ensembl=TRUE)
sce.grun.hsc
# class: SingleCellExperiment 
# dim: 21817 1915 
# metadata(0):
#   assays(1): counts
# rownames(21817): ENSMUSG00000109644
# ENSMUSG00000007777 ... ENSMUSG00000055670
# ENSMUSG00000039068
# rowData names(3): symbol chr originalName
# colnames(1915): JC4_349_HSC_FE_S13_
# JC4_350_HSC_FE_S13_ ...
# JC48P6_1203_HSC_FE_S8_
# JC48P6_1204_HSC_FE_S8_
# colData names(2): sample protocol
# reducedDimNames(0):
#   altExpNames(0):

table(sce.grun.hsc$sample)
# 
# JC20   JC21   JC26   JC27   JC28   JC30   JC32 
# 87     96     85     91     80     96     93 
# JC35   JC36   JC37   JC39    JC4   JC40   JC41 
# 96     80     87     93     84     96     94 
# JC43   JC44   JC45   JC46 JC48P4 JC48P6 JC48P7 
# 92     94     90     96     95     96     94
```

### **ID转换**

```r
library(AnnotationHub)
ens.mm.v97 <- AnnotationHub()[["AH73905"]]
anno <- select(ens.mm.v97, keys=rownames(sce.grun.hsc), 
               keytype="GENEID", columns=c("SYMBOL", "SEQNAME"))

# 这里全部对应
> sum(is.na(anno$SYMBOL))
[1] 0
> sum(is.na(anno$SEQNAME))
[1] 0

# 接下来只需要匹配顺序即可
rowData(sce.grun.hsc) <- anno[match(rownames(sce.grun.hsc), anno$GENEID),]

sce.grun.hsc
## class: SingleCellExperiment 
## dim: 21817 1915 
## metadata(0):
## assays(1): counts
## rownames(21817): ENSMUSG00000109644 ENSMUSG00000007777 ...
##   ENSMUSG00000055670 ENSMUSG00000039068
## rowData names(3): GENEID SYMBOL SEQNAME
## colnames(1915): JC4_349_HSC_FE_S13_ JC4_350_HSC_FE_S13_ ...
##   JC48P6_1203_HSC_FE_S8_ JC48P6_1204_HSC_FE_S8_
## colData names(2): sample protocol
## reducedDimNames(0):
## altExpNames(0):
```

## 2 质控

**依然是备份一下，把unfiltered数据主要用在质控的探索上**

```r
unfiltered <- sce.grun.hsc
```

**发现这个数据既没有MT也没有ERCC**

```r
grep('MT',rowData(sce.grun.hsc)$SEQNAME)
# integer(0)
```

能用的数据只有其中的`protocol`了，它表示细胞提取方法

```r
table(sce.grun.hsc$protocol)
# 
# micro-dissected cells 
# 1546 
# sorted hematopoietic stem cells 
# 369 

# 再看一下各个样本与提取方法的对应关系
table(sce.grun.hsc$protocol,sce.grun.hsc$sample)
```

![](https://jieandze1314-1255603621.cos.ap-guangzhou.myqcloud.com/blog/2020-07-21-111940.png)

根据背景知识，**大部分显微操作（micro-dissected）得到的细胞很多质量都较低**，和我们的质控假设相违背，于是这里就不把它们纳入过滤条件

```r
library(scater)
stats <- perCellQCMetrics(sce.grun.hsc)
# 只用sorted hematopoietic stem cells 计算过滤条件
qc <- quickPerCellQC(stats, batch=sce.grun.hsc$protocol,
    subset=grepl("sorted", sce.grun.hsc$protocol))

colSums(as.matrix(qc))
##   low_lib_size low_n_features        discard 
##            465            482            488

sce.grun.hsc <- sce.grun.hsc[,!qc$discard]
```

**做个图看看**

```r
colData(unfiltered) <- cbind(colData(unfiltered), stats)
unfiltered$discard <- qc$discard

gridExtra::grid.arrange(
    plotColData(unfiltered, y="sum", x="sample", colour_by="discard", 
        other_fields="protocol") + scale_y_log10() + ggtitle("Total count") +
        facet_wrap(~protocol),
    plotColData(unfiltered, y="detected", x="sample", colour_by="discard",
        other_fields="protocol") + scale_y_log10() + 
        ggtitle("Detected features") + facet_wrap(~protocol),
    ncol=1
)
```

可以看到，大多数的显微操作技术得到的细胞文库都比较小，相比于细胞分选方法，它在提取过程中对细胞损伤较大

![](https://jieandze1314-1255603621.cos.ap-guangzhou.myqcloud.com/blog/2020-07-21-112248.png)

## 3 归一化

使用去卷积方法

```r
library(scran)
set.seed(101000110)
clusters <- quickCluster(sce.grun.hsc)
sce.grun.hsc <- computeSumFactors(sce.grun.hsc, clusters=clusters)
sce.grun.hsc <- logNormCounts(sce.grun.hsc)
```

## 4 找表达量高变化基因

这里没有指定任何的批次，因为想保留这两种技术产生的任何差异

```r
set.seed(00010101)
dec.grun.hsc <- modelGeneVarByPoisson(sce.grun.hsc) 
top.grun.hsc <- getTopHVGs(dec.grun.hsc, prop=0.1)
```

做个图

```r
plot(dec.grun.hsc$mean, dec.grun.hsc$total, pch=16, cex=0.5,
    xlab="Mean of log-expression", ylab="Variance of log-expression")
curfit <- metadata(dec.grun.hsc)
curve(curfit$trend(x), col='dodgerblue', add=TRUE, lwd=2)
```

**看到这个线有点“太平缓”**，和之前见过的都不一样，感觉“中间少了一个峰”。**这是因为细胞中的基因表达量都比较低**，差别也不大【大家一起贫穷，于是贫富差距很小】，所以大部分细胞在纵坐标（衡量变化的方差）上体现不出来差距，也就导致了拟合的曲线不会有“峰”

> 可能会想，那为什么不是大家表达量都很高呢（大家都很富有，贫富差距不是也很小吗）？因为横坐标可以看到，从0-3.5，这个范围对于表达量来说确实很小，之前做的图有的都大于10、15

![](https://jieandze1314-1255603621.cos.ap-guangzhou.myqcloud.com/blog/2020-07-21-113627.png)

## 5 降维聚类

### **降维就采取最基础的方式：**

```r
set.seed(101010011)
sce.grun.hsc <- denoisePCA(sce.grun.hsc, technical=dec.grun.hsc, subset.row=top.grun.hsc)
sce.grun.hsc <- runTSNE(sce.grun.hsc, dimred="PCA")

# 检查PC的数量
ncol(reducedDim(sce.grun.hsc, "PCA"))
## [1] 9
```

### **聚类**

```r
snn.gr <- buildSNNGraph(sce.grun.hsc, use.dimred="PCA")
colLabels(sce.grun.hsc) <- factor(igraph::cluster_walktrap(snn.gr)$membership)

table(colLabels(sce.grun.hsc))
## 
##   1   2   3   4   5   6   7   8   9  10  11  12 
## 259 148 221 103 177 108  48 122  98  63  62  18
```

### **作图**

```r
short <- ifelse(grepl("micro", sce.grun.hsc$protocol), "micro", "sorted")
gridExtra:::grid.arrange(
    plotTSNE(sce.grun.hsc, colour_by="label"),
    plotTSNE(sce.grun.hsc, colour_by=I(short)),
    ncol=2
)
```

由于没有去除两个技术批次的差异，所以这里分的很开

![](https://jieandze1314-1255603621.cos.ap-guangzhou.myqcloud.com/blog/2020-07-21-114640.png)

## 6 找marker基因

```r
markers <- findMarkers(sce.grun.hsc, test.type="wilcox", direction="up",
    row.data=rowData(sce.grun.hsc)[,"SYMBOL",drop=FALSE])
```

检查一下cluster6的marker基因

```r
chosen <- markers[['6']]
best <- chosen[chosen$Top <= 10,]
length(best)
# [1] 16

# 将cluster6与其他clusters对比的AUC结果提取出来
aucs <- getMarkerEffects(best, prefix="AUC")
rownames(aucs) <- best$SYMBOL

library(pheatmap)
pheatmap(aucs, color=viridis::plasma(100))
```

看到溶菌酶相关基因（LYZ家族）、Camp、 Lcn2、 Ltf 都上调，表明**cluster6可能是神经元起源细胞**

![](https://jieandze1314-1255603621.cos.ap-guangzhou.myqcloud.com/blog/2020-07-21-115323.png)