mTOR mutations in Smith-Kingsmore syndrome: Four additional patients and a review

Smith-Kingsmore syndrome (SKS) OMIM #616638, also known as MINDS syndrome (ORPHA 457485), is a rare autosomal dominant disorder reported so far in 23 patients. SKS is characterized by intellectual disability, macrocephaly/hemi/megalencephaly, and seizures. It is also associated with a pattern of facial dysmorphology and other non-neurological features. Germline or mosaic mutations of the mTOR gene have been detected in all patients. The mTOR gene is a key regulator of cell growth, cell proliferation, protein synthesis and synaptic plasticity, and the mTOR pathway (PI3K-AKT-mTOR) is highly regulated and critical for cell survival and apoptosis. Mutations in different genes in this pathway result in known rare diseases implicated in hemi/megalencephaly with epilepsy, as the tuberous sclerosis complex caused by mutations in TSC1 and TSC2, or the PIK3CA-related overgrowth spectrum (PROS). We here present 4 new cases of SKS, review all clinical and molecular aspects of this disorder, as well as some characteristics of the patients with only brain mTOR somatic mutations.

Overexpression of the crgA gene abolishes light requirement for carotenoid biosynthesis in Mucor circinelloides

This work describes the isolation and characterization of crgA, a Mucor circinelloides gene, which has a dominant-positive effect on light-regulated carotenogenesis. The crgA gene was originally identified in a transformation experiment as a 3'-truncated open reading frame which caused carotenoid overaccumulation in the dark. The complete cloning and sequencing of crgA revealed that its putative product presented several recognizable structural domains: a RING-finger zinc binding domain near the N-terminus, a putative nuclear localization signal, two stretches of acidic amino acids, glutamine-rich regions and a putative isoprenylation motif. The expression of exogenous copies of the complete crgA gene or two different 3'-truncated versions, produced a similar dominant-positive effect on the light-inducible carotenogenesis of M. circinelloides. The presence of these exogenous sequences also caused a missregulation of the endogenous crgA gene, resulting in its overexpression. Collectively, these observations suggest that crgA is involved in the regulation of carotenoid biosynthesis by light.

Prt1, an unusual retrotransposon-like sequence in the fungus Phycomyces blakesleeanus

This work reports the isolation and structural characterization of Prt1, a 4.7 kb retrotransposon-like sequence from the filamentous fungus Phycomyces blakesleeanus. Two open reading frames are found within Prt1. The first shows no similarity with known genes. The second encodes peptide stretches similar to the reverse transcriptase and RNaseH domains of the Ty3/gypsy family of LTR-retrotransposons. Prt1 lacks long terminal repeats, having instead short (54 bp) terminal inverted repeats. No target site duplication has been found. A single copy of Prt1 was detected in the genome of P. blakesleeanus. Adjacent to this sole copy of Prt1, a cluster of various short sequence repeats, both direct and inverted, is found. These sequences, which are reminiscent of defective, non-retroviral transposable elements, are also represented in other regions of the P. blakesleeanus genome.

PkpA, a novel Phycomyces blakesleeanus serine/threonine protein kinase

This work reports the cloning and sequencing of pkpA, a gene of the filamentous fungus Phycomyces blakesleeanus, whose expression seems to be coupled to vegetative growth. This gene encodes a putative serine/threonine-specific protein kinase, whose sequence is related to that of the yeast protein STE20, involved in pheromone-response pathways, and to a number of MAPK kinase proteins. However, detailed analysis of the kinase sequence suggests that PkpA is a novel serine/threonine protein kinase that probably participates as an intermediate in an intracellular system controlling nuclear proliferation in P. blakesleeanus.