Worm Breeder's Gazette 15(3): 40 (June 1, 1998)

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.

An Alternative Tale of UNC-52/Perlecan

Teresa Rogalski, Greg Mullen, Don Moerman

Department of Zoology, University of British Columbia, Vancouver, B.C. Canada

     Mammalian perlecan, the major heparan sulfate proteoglycan of the
extracellular matrix has five domains with similarity to the
LDL-receptor (domain II), laminin (domains III & V) and the neural cell
adhesion molecule (domain IV).  We have previously shown that the unc-52
gene in C. elegans encodes several large proteins structurally
homologous to perlecan but lacking the C-terminal domain V (Rogalski et
al., 1993, Genes and Dev. 7:1471-1484).  Our analysis of this gene
identified 26 exons covering almost 15 kb of genomic DNA and revealed
the presence of several alternatively spliced transcripts.  Two
different poly(A) addition sites located 8.5 kb apart are utilized to
generate a number of large polypeptides containing domains I, II, III &
IV or a shortened polypeptide(s) containing only domains I, II & III.

     Recently, we discovered that the unc-52 gene actually spans over 20
kb of genomic DNA and consists of 37 exons.   Eleven additional exons
were identified downstream of exon 26 when the C. elegans genome
consortium provided the sequence and annotation of cosmid C38C6.   We
have confirmed the intron-exon boundaries in this region by sequencing a
cDNA clone obtained from Y. Kohara that extends from exon 27 to  ~200 bp
downstream of the putative stop codon in exon 37.  In addition, several
RT-PCR fragments were generated and sequenced to confirm that the newly
identified exons were part of the unc-52 gene and to identify the splice
sites used to join exon 26 to exon 27.

     The longest potential open reading frame of the unc-52 gene now
encodes a 3375 amino acid protein with a molecular weight of
approximately 370 kD consisting of a putative signal sequence and five
distinct domains.  The newly identified exons encode sequences that are
very similar to domain V of  the mouse and human perlecan polypeptides,
confirming our earlier conclusion that the UNC-52 proteins are the
nematode orthologs of these mammalian proteoglycans.  Curiously, domain
V of the nematode protein contains a region of approximately 180 amino
acids that is not found in the mammalian proteins.  This region is
extremely rich in threonine (45/180) and serine (19/180) residues and
also contains 12 repeats of the amino acid sequence EEP.

     In summary, the unc-52 gene uses three separate transcriptional
stop regions to produce three general classes of  protein isoforms:
short (domains I, II & III), medium (domains I, II, III & IV) and long
(domains I, II, III, IV & V).  At least some of  these UNC-52
polypeptides function in the basement membranes of muscle cells and are
essential for the assembly and attachment of the myofilament lattice.