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Peptidases have been implicated in the pathogenicity of fungi that cause disease in plants. Expression of the secreted aspartic peptidase gene (gcsap), of a Glomerella cingulata isolate pathogenic on apples, is induced during appressorium formation. To determine whether the secreted aspartic peptidase (GcSAP) is essential to pathogenicity, gcsap was disrupted using a vector containing a 637 bp fragment of genomic DNA that encodes the sequence spanning the two active site aspartic acid (Asp) residues. To ensure that the truncated gcsap gene products could not have residual peptidase activity the codons for the active site residues Asp112 and Asp297 were both mutated to histidine residues. Both PCR and Southern analysis confirmed disruption of gcsap. Neither gcsap mRNA nor GcSAP activity was detected in the disruption mutant. Pathogenicity tests on fruit from three apple cultivars showed that GcSAP was not required for pathogenicity. The disruption mutant grew on medium containing protein as the sole source of nitrogen because G. cingulata secretes a previously undetected peptidase(s). A serine peptidase that had a pH optimum between pH 7.0 and 8.0 and a K m of 0.25 mM for the synthetic substrate succinyl-Ala–Ala–Pro–Phe-p-nitroanilide was identified.

Germ-line events, such as paternal mutation or genomic imprinting, contribute to the early onset of childhood cancers such as retinoblastoma, Wilms tumors, and neuroblastoma. Given the high frequency of deletion involving chromosome 9p in childhood acute lymphoblastic leukemia (ALL), this study investigated whether 9p deletion might reflect preexisting germ-line gene inactivation. To do this the parental origin of deletion was determined in 10 cases of ALL with 9p21 loss of heterozygosity. Of these cases, 9 showed loss of the maternally derived allele, suggesting that a germ-line event involving a 9p gene may play a role in the onset of childhood ALL.

Mutations in PKD1 cause dominant polycystic kidney disease (PKD), characterized by large fluid-filled kidney cysts in adult life, but the molecular mechanism of cystogenesis remains obscure. Ostrom et al. [Dev. Biol., 219, 250-258 (2000)] showed that reduced dosage of Pax2 caused increased apoptosis, and ameliorated cystogenesis in Cpk mutant mice with recessive PKD. Pax2 is expressed in condensing metanephrogenic mesenchyme and arborizing ureteric bud, and plays an important role in kidney development. Transient Pax2 expression during fetal kidney mesenchyme-to-epithelial transition, as well as in nascent tubules, is followed by marked down-regulation of Pax2 expression. Here, we show that in humans with PKD, as well as in Pkd1(del34/del34) mutant mice, Pax2 was expressed in cyst epithelial cells, and facilitated cyst growth in Pkd1(del34/del34) mutant mice. In Pkd1(del34/del34) mutant kidneys, the expression of Pax2 persisted in nascent collecting ducts. In contrast, homozygous Pkd1(del34/del34) fetal mice carrying mutant Pax2 exhibited ameliorated cyst growth, although reduced cystogenesis was not associated with increased apoptosis. Pax2 expression was attenuated in nascent collecting ducts and absent from remnant cysts of Pkd1(del34/del34)/Pax2(1Neu/+) mutant mice. To investigate whether the Pkd1 gene product, Polycystin-1, regulates Pax2, MDCK cells were engineered constitutively expressing wild-type Pkd1; Pax2 protein levels and promoter activity were both repressed in MDCK cells over-expressing Pkd1, but not in cells without transgenic Pkd1. These data suggest that polycystin-1-deficient tubular epithelia persistently express Pax2 in ADPKD, and that Pax2 or its pathway may be an appropriate target for the development of novel therapies for ADPKD.

Loss of heterozygosity (LOH) studies are useful to detect tumor suppressor genes involved in human cancers. In childhood acute lymphoblastic leukemia (ALL), LOH has been reported for many chromosomal regions, including 11q23, close to the MLL gene. Previously in this journal, Webb and colleagues[1][