Worm Breeder's Gazette 11(3): 16

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A Type IV Collage Gene in Ascaris suum

Jonathan Pettitt and Barry Kingston

We have begun an analysis of the organization, structure and 
expression of collagen genes in Ascaris suum.  During the course of 
this work we have isolated a collagen containing clone (ucol-11) from 
a lambda genomic library of Ascaris DNA.  Specific fragments obtained 
from this clone during sequence analysis were found to hybridize to a 
transcript of about 5.5 kb in several Northern blots of RNA derived 
from different Ascaris adult tissues and developmental stages.  In 
order to further characterize the nature of the gene contained in the 
genomic clone, corresponding cDNA clones were isolated and sequence 
analysis of these revealed that the ucol-11 clone contained a type IV 
collagen gene.  A comparison of the NC-1 domain amino acid sequence 
with that of type IV collagen genes in other organisms showed that the 
gene specifically encoded the alpha 2 chain of Ascaris type IV 
collagen.  
Sequence analysis of the genomic clone revealed that although the 
gene constituted most of the insert, the clone did not contain the 
entire gene.  We have found that the reason for this is in part a 
consequence of the presence of large introns in the gene.  Such 
comparatively large introns have also been reported for two putative 
Ascaris cuticular collagen genes (Kingston et al), suggesting that 
Ascaris genes may generally have larger introns than those of C.  
elegans.  However, the intron/exon borders of the Ascaris genes are 
very similar to the C.  elegans consensus sequences for donor and 
acceptor splice sites.  
So far we have determined the sequence of about 9 kb of the genomic 
clone and have identified 15 exons which range in size from 
approximately 150 to 450 bp.  These are separated by introns whose 
sizes range from about 200 to 800 bp.  Since the clone does not 
contain the entire sequence there are likely to be more exons in the 
complete gene.  This organization is in contrast to the nine exons of 
the Drosophila alpha 1 chain gene, which are separated by relatively 
short introns, and the invertebrate genes, which although they have 
many exons, have much larger introns.  
We are currently using a cDNA clone as a probe to study the 
expression of the type IV collagen gene during embryogenesis, using 
runoff transcription in nuclei isolated from specific cell stages in 
Ascaris embryos.  There have been few studies of the synthesis of 
specific macromolecules in nematode embryos and we anticipate that 
because of the similarity between the embryonic lineages of different 
nematodes, the information gained from such studies on Ascaris embryos 
may also be applicable to C.  elegans.