Summary The enterobactin system for iron transport in Escherichia coli is well characterized with the exception of the mechanism of enterobactin secretion to the extracellular environment. Escherichia coli membrane protein P43, encoded by ybdA in the chromosomal region of genes involved in enterobactin synthesis, shows strong homology to the 12‐transmembrane segment major facilitator superfamily of export pumps. A P43‐null mutation was created and siderophore nutrition assays, performed with a panel of E. coli strains expressing one or more outer membrane receptors for enterobactin‐related compounds, demonstrated that the P43 mutant was unable to secrete enterobactin efficiently. Products released from the mutant strain were identified with thin‐layer chromatography (TLC) and high‐performance liquid chromatography (HPLC), revealing that the P43 mutant secretes little, if any, enterobactin, but elevated levels of enterobactin breakdown products 2,3‐ dihydroxybenzoylserine (DHBS) monomer, dimer, and trimer. These data establish that P43 is a critical component of the E. coli enterobactin secretion machinery and provides a rationale for the designation of the previous genetic locus ybdA as entS to reflect its relevant biological function.

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A truncating mutation in canine ADAMTS17 causes PLL, a well-characterized veterinary disease, which can now be compared to a recently described rare WMS-like disease caused by truncating mutations of the human ADAMTS17 ortholog.

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage diseases characterized by progressive neurodegeneration and accumulation of autofluorescent storage granules. A 9 month old Miniature Dachshund presented with NCL-like signs that included disorientation, ataxia, weakness, visual impairment and behavioral changes. Neurons throughout the CNS contained autofluorescent lysosomal inclusions with granular osmiophilic deposit (GROD) ultrastructure characteristic of classical infantile NCL (INCL). Human INCL is an autosomal recessive disorder that results from mutations in PPT1, a gene that encodes the enzyme palmitoyl protein thioesterase 1 (PPT1; EC 3.1.22). Resequencing of PPT1 from the affected dog revealed that the dog was homozygous for a single nucleotide insertion in exon 8 (PPT1 c.736_737insC), upstream from the His289 active site. Brain tissue from this dog lacked PPT1 activity. The sire and dam of the propositus were heterozygous for the c.736_737insC mutation; whereas, 127 unrelated Dachshunds were homozygous for the wildtype allele. This is the first reported instance of canine NCL caused by a mutation in PPT1.

The childhood neuronal ceroid lipofuscinoses (NCLs) are inherited neurodegenerative diseases that are progressive and ultimately fatal. An Australian Shepherd that exhibited a progressive neurological disorder with signs similar to human NCL was evaluated. The cerebral cortex, cerebellum, and retina were found to contain massive accumulations of autofluorescent inclusions characteristic of the NCLs. Nucleotide sequence analysis of DNA from the affected dog identified a T to C variant (c.829T>C) in exon 7 of CLN6. Mutations in the human ortholog underlie a late-infantile form of NCL in humans. The T-to-C transition results in a tryptophan to arginine amino acid change in the predicted protein sequence. Tryptophans occur at homologous positions in the CLN6 proteins from all 13 other vertebrates evaluated. The c.829T>C transition is a strong candidate for the causative mutation in this NCL-affected dog. Dogs with this mutation could serve as a model for the analogous human disorder.

The neuronal ceroid lipofuscinoses (NCLs) are autosomal recessive lysosomal storage diseases characterized by progressive neurodegeneration and by accumulation of autofluorescent storage material in the central nervous system and other tissues. One of the most prominent clinical signs of NCL is progressive decline in cognitive function. We previously described a frame shift mutation of TPP1 in miniature long-haired Dachshunds which causes an early-onset form of NCL analogous to classical late-infantile onset NCL (CLN2) in children. Dogs homozygous for the TPP1 mutation exhibit progressive neurological signs similar to those exhibited by human patients. In order to establish biomarkers for evaluating the efficacy of ongoing therapeutic studies in this canine model, we characterized phenotypic changes in 13 dogs through 9 months of age. Cognitive function was assessed using a T-maze reversal learning task. Cognitive dysfunction was detected in affected dogs as early as 6 months of age and worsened as the disease progressed. Physical and neurological examination, funduscopy, and electroretinography (ERG) were performed at regular intervals. Only changes in ERG responses revealed signs of disease progression earlier than the reversal learning task. In the later stages of the disease clinical signs of visual and motor deficits became evident. The visual and motor deficits were not severe enough to affect the performance of dogs in the T-maze. Declining performance on the reversal learning task is a sensitive measure of higher order cognitive dysfunction which can serve as a useful biomarker of disease progression.

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