Worm Breeder's Gazette 9(2): 26

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Update of MSP Gene Organization

S. Ward, D. Burke, E. Hogan, J. Sulston, A. Coulson, D. Albertson, M. Klass, and D. Ammons

We are continuing to study the genomic organization of expressed MSP 
genes and MSP pseudogenes by physical mapping of cloned genes (WBG Vol.
8,3 p.  61).  We have now examined a total of 39 different MSP genes.
Thirty of these genes are grouped into 5 clusters of 3 to 6 genes 
each.  The other 9 genes are isolated on small contigs.  The MSP genes 
of a given cluster are grouped within about 50 Kb of DNA but are not 
in tandem arrays; they are separated by 2-10 Kb of DNA.  The clusters 
are surrounded by DNA free of MSP genes .  Genes with similar 3' 
untranslated sequences are found in the same cluster.  Four of the 
five clusters have been mapped to chromosomes by overlap with known 
genes or in situ hybridization.  One cluster of six genes is adjacent 
to col-2 on chromosome IV.  Another cluster of 5 genes maps on the 
left side of IV.  Two other clusters map to the same location on the 
left side of chromosome II perhaps near dpy-10.  In addition to the 
MSP genes in the gene cluster near col-2, three genomic lambda clones 
which may contain other sperm-specific genes map within this cluster.  
This suggests that this may be a general cluster of sperm-specific 
genes, perhaps reflecting common functional or regulatory interactions.

It is unlikely that the multiple clusters of MSP genes arose by 
duplication of an initial cluster.  It is more likely that genes have 
duplicated themselves nearby.  The similarity in sequence of nearby 
genes could represent evolutionarily recent duplication or gene 
conversion of nearby genes.  Further sequence analysis may distinguish 
these possibilities.
Of the sequenced or carefully probed genes, about half are 
incomplete pseudogenes missing their 5' or 3' ends or containing 
insertions in the coding sequences.  These are intermingled among the 
expressed genes in the two clusters analyzed.  The coding sequences 
remaining in these pseudogenes are still highly homologous to complete 
MSP genes suggesting that the defects in these genes are of recent 
We are presently mapping the contigs containing MSP gene clusters on 
chromosome II and the contig containing col-2 on chromosome IV by 
trying to find overlaps between cosmids and known deletion breakpoints.
If anyone else has identified clones which overlap deletion 
breakpoints in these regions please let us know.