2 research outputs found
Two Heparanase Splicing Variants with Distinct Properties Are Necessary in Early Xenopus Development*
Heparanase is an endoglycosidase that cleaves heparan sulfate (HS) side
chains from heparan sulfate proteoglycans (HSPGs) present in extracellular
matrix and cell membranes. Although HSPGs have many functions during
development, little is known of the role of the enzyme that degrades HS,
heparanase. We cloned and characterized the expression of two heparanase
splicing variants from Xenopus laevis and studied their function in
early embryonic development. The heparanase gene (termed xHpa) spans
over 15 kb and consists of at least 12 exons. The long heparanase (XHpaL) cDNA
encodes a 531-amino acid protein, whereas the short splicing variant (XHpaS)
results in a protein with the same open reading frame but missing 58 amino
acids as a consequence of a skipped exon 4. Comparative studies of both
isoforms using heterologous expression systems showed: 1) XHpaL is
enzymatically active, whereas XHpaS is not; 2) XHpaL and XHpaS interact with
heparin and HS; 3) both proteins traffic through the endoplasmic reticulum and
Golgi apparatus, but XHpaL is secreted into the medium, whereas XHpaS remains
associated with the membrane as a consequence of the loss of three
glycosylation sites; 4) overexpression of XHpaS but not XHpaL increases cell
adhesion of glioma cells to HS-coated surfaces; 5) XHpaL and XHpaS mRNA and
protein levels vary as development progresses; 6) specific antisense
knock-down of both XHpaL and XHpaS, but not XHpaL alone, results in failure of
embryogenesis to proceed. Interestingly, rescue experiments suggest that the
two heparanases regulate the same developmental processes, but via different
mechanisms
Recommended from our members
3D genome mapping identifies subgroup-specific chromosome conformations and tumor-dependency genes in ependymoma
Ependymoma is a tumor of the brain or spinal cord. The two most common and aggressive molecular groups of ependymoma are the supratentorial ZFTA-fusion associated and the posterior fossa ependymoma group A. In both groups, tumors occur mainly in young children and frequently recur after treatment. Although molecular mechanisms underlying these diseases have recently been uncovered, they remain difficult to target and innovative therapeutic approaches are urgently needed. Here, we use genome-wide chromosome conformation capture (Hi-C), complemented with CTCF and H3K27ac ChIP-seq, as well as gene expression and DNA methylation analysis in primary and relapsed ependymoma tumors, to identify chromosomal conformations and regulatory mechanisms associated with aberrant gene expression. In particular, we observe the formation of new topologically associating domains ('neo-TADs') caused by structural variants, group-specific 3D chromatin loops, and the replacement of CTCF insulators by DNA hyper-methylation. Through inhibition experiments, we validate that genes implicated by these 3D genome conformations are essential for the survival of patient-derived ependymoma models in a group-specific manner. Thus, this study extends our ability to reveal tumor-dependency genes by 3D genome conformations even in tumors that lack targetable genetic alterations