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Clustering 3K PBMCs with Scanpy

Authors: AvatarMehmet Tekman

last_modification Updated:

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Requirements

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question Questions

  • What are the main steps of scRNA-seq?

  • What kind of variation can confound an analysis?

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objectives Objectives

  • Learn the main stages of an scRNA-seq analysis

  • Understand the methods and concepts underlying scRNA-seq

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Single Cell RNA Pre-processing

fig01

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  1. Barcode Extraction
  2. Mapping
  3. Gene Annotation
  4. Batch count matrices

Single Cell RNA Downstream Analysis

fig10

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  1. Filtering
  2. Normalising
    • Confounder Removal
  3. Dimension Reduction
  4. Clustering
    • Annotation

Barcoding Cells

fig1

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Filtering: Cell and Gene

fig2

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Normalisation: Technical Variation

fig3

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Normalisation: Biological Variation

fig4

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Dimension Reduction: Relatedness of Cells

fig5

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Build a KNN graph from distance matrix:

  • If P and q share distance which is

Dimension Reduction: Projection

fig6

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  • Can use tSNE, PCA, UMAP

Community Clustering: Louvain

Aim: Maximise internal links and minimise external links

fig7

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Community Clustering: Louvain

Pick a cell, place in neighbour, and accept if internal:external increases

fig8

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Cell Type: Identifying Cluster Types

fig9 fig10

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Clustering: Hard vs Soft


fig11

Hard

  • Big spaces between clusters
  • Cell types are well defined and the clustering reflects that
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Clustering: Hard vs Soft


fig11

Hard

  • Big spaces between clusters
  • Cell types are well defined and the clustering reflects that

fig12

Soft

  • Clusters bleed into one another
  • Cell types seem to intermingle with one another.
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Why? Why would there be clusters so close to one another?

Continuous Phenotypes:

fig13

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  • Cells aren't discrete, they transition

  • Continuously changing over time from a less mature type to more mature type

Interactive Environments: live.usegalaxy.eu


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What is Differential Expression in scRNA-seq?

CellxGene Local Test

  • We can probe clusters to see how they are so differentially expressed

    pip3 install cellxgene
    cellxgene launch https://cellxgene-example-data.czi.technology/pbmc3k.h5ad
  • Launch locally: http://127.0.0.1:5005

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keypoints Key points

  • Understanding the purpose of barcoding

  • Knowing the difference between hard and soft clustering

  • A KNN graph can be generated from a count matrix.

  • Community clustering can be generated from a KNN graph.

  • Interpreting scRNA-seq plots

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Thank You!

This material is the result of a collaborative work. Thanks to the Galaxy Training Network and all the contributors!

Authors: AvatarMehmet Tekman
Galaxy Training Network

This material is licensed under the Creative Commons Attribution 4.0 International License.

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Requirements

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