cpgplot

 

Function

Plot CpG rich areas

Description

CpG refers to a C nucleotide immediately followed by a G. The 'p' in 'CpG' refers to the phosphate group linking the two bases.

Detection of regions of genomic sequences that are rich in the CpG pattern is important because such regions are resistant to methylation and tend to be associated with genes which are frequently switched on. Regions rich in the CpG pattern are known as CpG islands.

It has been estimated that about half of all mammalian genes have a CpG-rich region around their 5' end. It is said that all mammalian house-keeping genes have a CpG island!

Non-mammalian vertebrates have some CpG islands that are associated with genes, but the association gets equivocal in the farther taxonomic groups.

Finding a CpG island upstream of predicted exons or genes is good contributory evidence.

By default, this program defines a CpG island as a region where, over an average of 10 windows, the calculated % composition is over 50% and the calculated Obs/Exp (i.e. Observed/Expected) ratio is over 0.6 and the conditions hold for a minimum of 200 bases. These conditions can be modified by setting the values of the appropriate parameters.

The Observed number of CpG patterns in a window is simply the count of the number of times a 'C' is found followed immediately by a 'G'.

The Expected number of CpG patterns is calculated for each window as the number of CpG dinucleotides you would expect to see in that window based on the frequency of C's and G's in that window. Thus, the Expected frequency of CpG's in a window is calculated as the number of 'C's in the window multiplied by the number of 'G's in the window, divided by the window length. 

	Expected = (number of C's  * number of G's) / window length

This program reads in one or more sequences and calculates the Obs/Exp ratio, the percentage CpG over a window which is moved along the sequence. These calculated values can be plotted, together with the regions which match this program's definition of a CpG island.

Usage

Here is a sample session with cpgplot 


% cpgplot tembl:rnu68037 -graph cps 
Plot CpG rich areas
Window size [100]: 
Minimum length of an island [200]: 
Minimum observed/expected [0.6]: 
Minimum percentage [50.]: 
Output file [rnu68037.cpgplot]: 
Output features [rnu68037.gff]: 

Created cpgplot.ps

Go to the input files for this example
Go to the output files for this example

Command line arguments 

   Standard (Mandatory) qualifiers:
  [-sequence]          seqall     Sequence database USA
   -window             integer    The percentage CG content and the Observed
                                  frequency of CG is calculated within a
                                  window whose size is set by this parameter.
                                  The window is moved down the sequence and
                                  these statistics are calculated at each
                                  postition that the window is moved to.
   -minlen             integer    This sets the minimum length that a CpG
                                  island has to be before it is reported.
   -minoe              float      This sets the minimum average observed to
                                  expected ratio of C plus G to CpG in a set
                                  of 10 windows that are required before a CpG
                                  island is reported.
   -minpc              float      This sets the minimum average percentage of
                                  G plus C a set of 10 windows that are
                                  required before a CpG island is reported.
  [-outfile]           outfile    This sets the name of the file holding the
                                  report of the input sequence name, CpG
                                  island parameters and the output details of
                                  any CpG islands that are found.
  [-graph]             xygraph    Graph type
  [-outfeat]           featout    File for output features

   Additional (Optional) qualifiers: (none)
   Advanced (Unprompted) qualifiers:
   -[no]obsexp         boolean    If this is set to true then the graph of the
                                  observed to expected ratio of C plus G to
                                  CpG within a window is displayed.
   -[no]cg             boolean    If this is set to true then the graph of the
                                  regions which have been determined to be
                                  CpG islands is displayed.
   -[no]pc             boolean    If this is set to true then the graph of the
                                  percentage C plus G within a window is
                                  displayed.

   Associated qualifiers:

   "-sequence" associated qualifiers
   -sbegin1            integer    Start of each sequence to be used
   -send1              integer    End of each sequence to be used
   -sreverse1          boolean    Reverse (if DNA)
   -sask1              boolean    Ask for begin/end/reverse
   -snucleotide1       boolean    Sequence is nucleotide
   -sprotein1          boolean    Sequence is protein
   -slower1            boolean    Make lower case
   -supper1            boolean    Make upper case
   -sformat1           string     Input sequence format
   -sdbname1           string     Database name
   -sid1               string     Entryname
   -ufo1               string     UFO features
   -fformat1           string     Features format
   -fopenfile1         string     Features file name

   "-outfile" associated qualifiers
   -odirectory2        string     Output directory

   "-graph" associated qualifiers
   -gprompt3           boolean    Graph prompting
   -gtitle3            string     Graph title
   -gsubtitle3         string     Graph subtitle
   -gxtitle3           string     Graph x axis title
   -gytitle3           string     Graph y axis title
   -goutfile3          string     Output file for non interactive displays
   -gdirectory3        string     Output directory

   "-outfeat" associated qualifiers
   -offormat4          string     Output feature format
   -ofopenfile4        string     Features file name
   -ofextension4       string     File name extension
   -ofdirectory4       string     Output directory
   -ofname4            string     Base file name
   -ofsingle4          boolean    Separate file for each entry

   General qualifiers:
   -auto               boolean    Turn off prompts
   -stdout             boolean    Write standard output
   -filter             boolean    Read standard input, write standard output
   -options            boolean    Prompt for standard and additional values
   -debug              boolean    Write debug output to program.dbg
   -verbose            boolean    Report some/full command line options
   -help               boolean    Report command line options. More
                                  information on associated and general
                                  qualifiers can be found with -help -verbose
   -warning            boolean    Report warnings
   -error              boolean    Report errors
   -fatal              boolean    Report fatal errors
   -die                boolean    Report deaths

Standard (Mandatory) qualifiers Allowed values Default
[-sequence]
(Parameter 1)		 Sequence database USA Readable sequence(s) Required
-window The percentage CG content and the Observed frequency of CG is calculated within a window whose size is set by this parameter. The window is moved down the sequence and these statistics are calculated at each postition that the window is moved to. Integer 1 or more 100
-minlen This sets the minimum length that a CpG island has to be before it is reported. Integer 1 or more 200
-minoe This sets the minimum average observed to expected ratio of C plus G to CpG in a set of 10 windows that are required before a CpG island is reported. Number from 0.000 to 10.000 0.6
-minpc This sets the minimum average percentage of G plus C a set of 10 windows that are required before a CpG island is reported. Number from 0.000 to 100.000 50.
[-outfile]
(Parameter 2)		 This sets the name of the file holding the report of the input sequence name, CpG island parameters and the output details of any CpG islands that are found. Output file <sequence>.cpgplot
[-graph]
(Parameter 3)		 Graph type EMBOSS has a list of known devices, including postscript, ps, hpgl, hp7470, hp7580, meta, colourps, cps, xwindows, x11, tektronics, tekt, tek4107t, tek, none, null, text, data, xterm, png, xml EMBOSS_GRAPHICS value, or x11
[-outfeat]
(Parameter 4)		 File for output features Writeable feature table unknown.gff
Additional (Optional) qualifiers Allowed values Default
(none)
Advanced (Unprompted) qualifiers Allowed values Default
-[no]obsexp If this is set to true then the graph of the observed to expected ratio of C plus G to CpG within a window is displayed. Boolean value Yes/No Yes
-[no]cg If this is set to true then the graph of the regions which have been determined to be CpG islands is displayed. Boolean value Yes/No Yes
-[no]pc If this is set to true then the graph of the percentage C plus G within a window is displayed. Boolean value Yes/No Yes

Input file format

Any DNA sequence USA.

Input files for usage example

'tembl:rnu68037' is a sequence entry in the example nucleic acid database 'tembl'

Database entry: tembl:rnu68037

ID   RNU68037   standard; RNA; ROD; 1218 BP.
XX
AC   U68037;
XX
SV   U68037.1
XX
DT   23-SEP-1996 (Rel. 49, Created)
DT   04-MAR-2000 (Rel. 63, Last updated, Version 2)
XX
DE   Rattus norvegicus EP1 prostanoid receptor mRNA, complete cds.
XX
KW   .
XX
OS   Rattus norvegicus (Norway rat)
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia;
OC   Eutheria; Rodentia; Sciurognathi; Muridae; Murinae; Rattus.
XX
RN   [1]
RP   1-1218
RA   Abramovitz M., Boie Y.;
RT   "Cloning of the rat EP1 prostanoid receptor";
RL   Unpublished.
XX
RN   [2]
RP   1-1218
RA   Abramovitz M., Boie Y.;
RT   ;
RL   Submitted (26-AUG-1996) to the EMBL/GenBank/DDBJ databases.
RL   Biochemistry & Molecular Biology, Merck Frosst Center for Therapeutic
RL   Research, P. O. Box 1005, Pointe Claire - Dorval, Quebec H9R 4P8, Canada
XX
DR   SWISS-PROT; P70597; PE21_RAT.
XX
FH   Key             Location/Qualifiers
FH
FT   source          1..1218
FT                   /db_xref="taxon:10116"
FT                   /organism="Rattus norvegicus"
FT                   /strain="Sprague-Dawley"
FT   CDS             1..1218
FT                   /codon_start=1
FT                   /db_xref="SWISS-PROT:P70597"
FT                   /note="family 1 G-protein coupled receptor"
FT                   /product="EP1 prostanoid receptor"
FT                   /protein_id="AAB07735.1"
FT                   /translation="MSPYGLNLSLVDEATTCVTPRVPNTSVVLPTGGNGTSPALPIFSM
FT                   TLGAVSNVLALALLAQVAGRLRRRRSTATFLLFVASLLAIDLAGHVIPGALVLRLYTAG
FT                   RAPAGGACHFLGGCMVFFGLCPLLLGCGMAVERCVGVTQPLIHAARVSVARARLALALL
FT                   AAMALAVALLPLVHVGHYELQYPGTWCFISLGPPGGWRQALLAGLFAGLGLAALLAALV
FT                   CNTLSGLALLRARWRRRRSRRFRENAGPDDRRRWGSRGLRLASASSASSITSTTAALRS
FT                   SRGGGSARRVHAHDVEMVGQLVGIMVVSCICWSPLLVLVVLAIGGWNSNSLQRPLFLAV
FT                   RLASWNQILDPWVYILLRQAMLRQLLRLLPLRVSAKGGPTELSLTKSAWEASSLRSSRH
FT                   SGFSHL"
XX
SQ   Sequence 1218 BP; 162 A; 397 C; 387 G; 272 T; 0 other;
     atgagcccct acgggcttaa cctgagccta gtggatgagg caacaacgtg tgtaacaccc        60
     agggtcccca atacatctgt ggtgctgcca acaggcggta acggcacatc accagcgctg       120
     cctatcttct ccatgacgct gggtgctgtg tccaacgtgc tggcgctggc gctgctggcc       180
     caggttgcag gcagactgcg gcgccgccgc tcgactgcca ccttcctgtt gttcgtcgcc       240
     agcctgcttg ccatcgacct agcaggccat gtgatcccgg gcgccttggt gcttcgcctg       300
     tatactgcag gacgtgcgcc cgctggcggg gcctgtcatt tcctgggcgg ctgtatggtc       360
     ttctttggcc tgtgcccact tttgcttggc tgtggcatgg ccgtggagcg ctgcgtgggt       420
     gtcacgcagc cgctgatcca cgcggcgcgc gtgtccgtag cccgcgcacg cctggcacta       480
     gccctgctgg ccgccatggc tttggcagtg gcgctgctgc cactagtgca cgtgggtcac       540
     tacgagctac agtaccctgg cacttggtgt ttcattagcc ttgggcctcc tggaggttgg       600
     cgccaggcgt tgcttgcggg cctcttcgcc ggccttggcc tggctgcgct ccttgccgca       660
     ctagtgtgta atacgctcag cggcctggcg ctccttcgtg cccgctggag gcggcgtcgc       720
     tctcgacgtt tccgagagaa cgcaggtccc gatgatcgcc ggcgctgggg gtcccgtgga       780
     ctccgcttgg cctccgcctc gtctgcgtca tccatcactt caaccacagc tgccctccgc       840
     agctctcggg gaggcggctc cgcgcgcagg gttcacgcac acgacgtgga aatggtgggc       900
     cagctcgtgg gcatcatggt ggtgtcgtgc atctgctgga gccccctgct ggtattggtg       960
     gtgttggcca tcgggggctg gaactctaac tccctgcagc ggccgctctt tctggctgta      1020
     cgcctcgcgt cgtggaacca gatcctggac ccatgggtgt acatcctgct gcgccaggct      1080
     atgctgcgcc aacttcttcg cctcctaccc ctgagggtta gtgccaaggg tggtccaacg      1140
     gagctgagcc taaccaagag tgcctgggag gccagttcac tgcgtagctc ccggcacagt      1200
     ggcttcagcc acttgtga                                                    1218
//

Output file format

Output files for usage example

File: rnu68037.cpgplot



CPGPLOT islands of unusual CG composition
RNU68037 from 1 to 1218

     Observed/Expected ratio > 0.60
     Percent C + Percent G > 50.00
     Length > 200

 Length 406 (104..509)

 Length 329 (596..924)

File: rnu68037.gff

##gff-version 2.0
##date 2005-07-15
##Type DNA RNU68037
RNU68037	cpgplot	misc_feature	104	509	0.000	+	.	Sequence "RNU68037.1"
RNU68037	cpgplot	misc_feature	596	924	0.000	+	.	Sequence "RNU68037.2"

Graphics File: cpgplot.ps

[cpgplot results]

Notes

None.

References

The original program was described in:
  1. Larsen F, Gundersen G, Lopez R, Prydz H "CpG islands as gene markers in the human genome." Genomics 1992 Aug;13(4):1095-107

Warnings

None.

Diagnostic Error Messages

None.

Exit status

0 if successful.

Known bugs

None.

See also

Program nameDescription
cpgreportReports all CpG rich regions
geeceeCalculates fractional GC content of nucleic acid sequences
newcpgreportReport CpG rich areas
newcpgseekReports CpG rich regions

As there is no official definition of what is a cpg island is, and worst where they begin and end, we have to live with 2 definitions and thus two methods. These are:

1. newcpgseek and cpgreport - both declare a putative island if the score is higher than a threshold (17 at the moment). They now also displaying the actual CpG count, the % CG and the observed/expected ration in the region where the score is above the threshold. This scoring method based on sum/frequencies overpredicts islands but finds the smaller ones around primary exons. newcpgseek uses the same method as cpgreport but the output is different and more readable.

2. newcpgreport and cpgplot use a sliding window within which the Obs/Exp ratio of CpG is calculated. The important thing to note in this method is that an island, in order to be reported, is defined as a region that satisfies the following contraints: 

   Obs/Exp ratio > 0.6
   % C + % G > 50%
   Length > 200.

For all practical purposes you should probably use newcpgreport. It is actually used to produce the human cpgisland database you can find on the EBI's ftp server as well as on the EBI's SRS server.

geecee measures CG content in the entire input sequence and is not to be used to detect CpG islands. It can be usefull for detecting sequences that MIGHT contain an island.

Author(s)

Alan Bleasby (ajb © ebi.ac.uk)
European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK

History

Completed 23rd March 1999.

Target users

This program is intended to be used by everyone and everything, from naive users to embedded scripts.

Comments

None