The 4DN FISH Omics Format (FOF-CT)

FOF-CT is the 4DN Nucleome format for chromatin tracing: a core table of spots (Spot_ID, Trace_ID, X, Y, Z, Chrom, Chrom_Start, Chrom_End, optional Cell_ID and extra columns) under ## header lines, with optional companion tables of cells and of RNA spots.

Reading: ChromData.from_fofct

from chromdata import ChromData

cd = ChromData.from_fofct("core.csv", cell_table="cells.csv", rna_table="rna.csv")

Columns map as Spot_ID → spot_id, Trace_ID → trace_id, X/Y/Z → coords, Chrom, Chrom_Start, Chrom_End → the locus (bins), Cell_ID → cell_id. The cell table becomes cd.cells (gene counts as rna.<gene>; centroids Cent_ROI_x/y[/z] or cell_center_*_global are registered as cell positions), the RNA spot table cd.points["rna"]. out="x.chromdata.zarr" streams a large table into a store chunk by chunk instead of building it in memory.

from_fofct handles the quirks of real files:

  • ##Columns=(…) declared case-insensitively (some writers use lower case);

  • the CSV header row repeated after the ##Columns= line;

  • header lines wrapped in double quotes and padded with trailing commas;

  • extra columns (e.g. Readout) kept as spot columns;

  • ##XYZ_Unit and ##Genome_Assembly promoted to uns["xyz_unit"] / uns["genome_assembly"]; all header lines kept in uns["fofct_header"].

FOF-CT files are usually in µm; to use other units, scale cd.coords and set uns["xyz_unit"] so that plots are labelled correctly.

Writing: cd.to_fofct

cd.to_fofct(path, cell_table=None, rna_table=None) (or uchrom.io.write_fofct(cd, path, …)) is the inverse of from_fofct:

  • the core table: ##FOF-CT_version, ##Table_namespace, ##genome_assembly, ##XYZ_unit and the #key: value lines — from uns["fofct_header"] when the data came from FOF-CT, else from uns — then ##columns=(Spot_ID, Trace_ID, X, Y, Z, Chrom, Chrom_Start, Chrom_End, [Cell_ID, Sub_Cell_ROI_ID, Extra_Cell_ROI_ID], …extra spot columns, spot tracks), one row per spot;

  • cell_table=: cd.cells as a 4dn_FOF-CT_cell table (Cell_ID first; centroid_* → Cent_ROI_*, nucleus_area_um2 → area(um2), the rna. prefix removed);

  • rna_table=: points["rna"] as a 4dn_FOF-CT_rna table.

Coordinates are written with full precision and read back exactly, so from_fofct(to_fofct(cd)) gives back the same coordinates, ids, loci, extra columns, cell table and RNA spots. Spot tracks come back as spot columns; bin_tracks=True also writes the per-locus tracks, broadcast to spots. FOF-CT has no place for cellm, binm, layers, intervals, results or other uns keys.

cd.to_fofct("out_core.csv", cell_table="out_cell.csv", rna_table="out_rna.csv",
            header={"lab_name": "My lab"})

The tutorial Importing FOF-CT chromatin-tracing data does both on the Takei et al. 2021 tables.