This tutorial will walk you through the process of finding data in the HCA Data Explorer, generating an expression matrix in loom format, and then loading these data into Scanpy via a Jupyter notebook for exploration.
This work leverages data from the study Single-Cell Analysis of Human Pancreas Reveals Transcriptional Signatures of Aging and Somatic Mutation Patterns by Enge, et al. and attempts to provide examples of the type of analysis found in this paper.
While the techniques shown in this Jupyter notebook can be used generally when analyzing single cell data there are a few caveats. First, this notebook is not an attempt to perfectly recreate the results of this paper, there are additional analysis and filtering steps that are omitted here. Second, this notebook leverages key gene lists for coloring clusters and these lists will change depending on a given study's experimental design. To work with projects other than the Enge et al. study, you will need to modify this notebook. This notebook it is designed to be a starting point for your own research not a general use tool.
The notebook presented here is based on a Data Consumer Vignette created by Genevieve Haliburton and other members of the HCA DCP team. You can find other vignettes in this GitHub repo and more will be adapted into tutorials over time.
Since you're reading this tutorial on our DCP Data Portal site we are going to assume you are at least generally familiar with the portal. To find data, use the Data Explorer which can be reached by clicking "Explore" at the top of the page.
This is the faceted browser that let's you explore the data available in the HCA. Take a look at the facets (which are represented as pull downs) at the top of the page. These let you perform a text search or select any number of Donor, Tissue Type, Specimen, Method, or File attributes through drop down search fields. When you select multiple values within a given facet your choices are OR'd together. When you select values across facets the query is AND'd together. While this may sound confusing, once you practice and try a few queries you will understand better how this works.
Below the search facets, you will see tabs for Project, Samples, and Files. When performing your query, you can switch between these tabs to see the Projects, Samples, and Files that match your search criteria.
Let's get started by searching for all the data from the Enge et al. study. First choose the Tissue Type facet and then choose the Organ to be pancreas. You'll see the project list automatically filter down to just the 3 projects that contain samples from pancreas. Next, limit the results down to just the Enge et al. study, the easiest way to do this is to select the study with the checkbox to the left of the project name. You can see a few things when you do this. First, the number of projects, donors, specimens, estimated cell count, files, and file size all automatically update. Second, you see you can request either a File Manifest or an Expression Matrix. We'll use the latter in the next step and you can use the former if you want to download files to your system and/or want to see metadata on these files that correspond to the facets you can search on in the Data Explorer. Another important feature in this page is the Metadata link in the table. This allows you to download an easy-to-parse TSV file that contains all of the metadata available for each project.
Figure 1: The Data Explorer offers a faceted-browser that allows you to quickly search for projects, samples, and files. Here we are searching for all projects that have data from pancreas cells and further refining our search to focus on the Enge et al. study.
Now that you've done the very simple query in the previous step to find all data from the Enge et al. study let's go ahead and generate a cell by gene matrix of expression values for all ~2.5K cells available for this project. With your search entered, all you now have to do is click the "Request Expression Matrix" button, you should see a dialog asking what format you'd like. We'll use "loom" format for this tutorial.
Figure 2: The request matrix option gives a summary of the number of files processed to return the gene by cell matrix you requested along with other statistics. You have the option of 3 different formats, we'll use the loom format for this tutorial.
The matrix generation can take some time to complete, recent tests show this project takes approximately 1.5 minutes to complete. In that time do not click away or close your browser window since that will prevent you from getting your matrix URL that we need for the next step. You can, of course, continue to explore the portal in another tab while waiting for your matrix.
Eventually, you will be presented with a result dialog that allows you to download or copy the URL for your matrix result.
Figure 3: The download options for the resulting matrix.
Make sure you copy the URL starting with https://s3... for the next step.
There are many different ways to launch Jupyter Notebooks including:
Since there are many different ways to get a functioning Juptyer Notebook server up and running this tutorial is going to focus on using Jupyter Notebook rather than how to set it up in different ways. Instead, see the much more detailed README in our Data Consumer Vignettes GitHub repository for a quick rundown of how to setup Jupyter locally. That should provide enough guidance to get started locally and also how you might run the notebook in other systems as well. The environment we used for this tutorial was Terra but Juptyer Notebooks will look the same running locally, on Binder, or on Terra regardless.
Here's a quick rundown of the steps you might use to launch this notebook locally, please see the README above for more details:
$ git clone https://github.com/HumanCellAtlas/data-consumer-vignettes.git $ cd may2019_demo $ pip install -r requirements.txt $ jupyter notebook --notebook-dir=`pwd`
Once you have the notebook server running you can navigate to:
To interact with the Jupter Notebook environment. You can then
notebooks_hca_demo_scanpy.ipynb notebook from the
Go ahead and open it up, you should something like Figure 4, which includes results
from a previous run of the notebook.
Figure 4: The Jupyter notebook opened and running in Terra. Running a Jupyter Notebook locally will look almost identical to the Terra interface presented here.
Now that you have 1) a URL for the matrix from the Data Explorer for the Enge et al. study and 2)
notebooks_hca_demo_scanpy.ipynb notebook opened in a Jupyter notebook environment,
the next step is to actually re-run the notebook on this matrix.
Since this is likely the first time you've executed the notebook you need to begin
from the first code cell and execute one by one to reproduce the analysis in the notebook.
Start by clicking on the first two code cells and running one after the other. At the end, you should
now see a field that currently contains the value
Replace that with the URL you got from the matrix on the Data Explorer. For example,
Your address will be different of course. You don't need (or want) to rerun this cell again after
you paste in your URL to the text field, the variable will be updated for other cells as soon as you paste your URL in the field.
Figure 5: Fill in the URL you got from the data explorer.
Now that you have your matrix URL pasted into the field run the 3rd, 4th, etc code blocks one by one
until you reach the end. Notice, a running code cell will show as
In [*] as it's running.
Make sure you let each code cell finish running before you move onto the next cell.
In the end, you should get a figure in the final code cell that looks almost identical to Figure 6.
Figure 6: The final cell clusters.
If you followed this tutorial this far and got a result similar to the final figure above then you are in a great position! You have successfully searched for data in the DCP using the Data Explorer, generated a cell by gene matrix for use by Scanpy, and you replicated (in a very basic way) the results of the Enge et al. study. The next step is really up to you, adapt this Jupyter notebook for your own use and explore the data in the HCA DCP in new and interesting ways. For some inspiration, you can check out the Scanpy examples gallery.