Differential genomic imprinting regulates paracrine and autocrine roles of IGF2 in mouse adult neurogenesis.

Genomic imprinting is implicated in the control of gene dosage in neurogenic niches. Here we address the importance of Igf2 imprinting for murine adult neurogenesis in the subventricular zone (SVZ) and in the subgranular zone (SGZ) of the hippocampus in vivo. In the SVZ, paracrine IGF2 is a cerebrospinal fluid and endothelial-derived neurogenic factor requiring biallelic expression, with mutants having reduced activation of the stem cell pool and impaired olfactory bulb neurogenesis. In contrast, Igf2 is imprinted in the hippocampus acting as an autocrine factor expressed in neural stem cells (NSCs) solely from the paternal allele. Conditional mutagenesis of Igf2 in blood vessels confirms that endothelial-derived IGF2 contributes to NSC maintenance in SVZ but not in the SGZ, and that this is regulated by the biallelic expression of IGF2 in the vascular compartment. Our findings indicate that a regulatory decision to imprint or not is a functionally important mechanism of transcriptional dosage control in adult neurogenesis.

Adaptations in placental nutrient transfer capacity to meet fetal growth demands depend on placental size in mice.

Experimental reduction in placental growth often leads to increased placental efficiency measured as grams of fetus produced per gram of placenta, although little is known about the mechanisms involved. This study tested the hypothesis that the smallest placenta within a litter is the most efficient at supporting fetal growth by examining the natural intra-litter variation in placental nutrient transfer capacity in normal pregnant mice. The morphology, nutrient transfer and expression of key growth and nutrient supply genes (Igf2P0, Grb10, Slc2a1, Slc2a3, Slc38a1, Slc38a2 and Slc38a4) were compared in the lightest and heaviest placentas of a litter at days 16 and 19 of pregnancy, when mouse fetuses are growing most rapidly in absolute terms. The data show that there are morphological and functional adaptations in the lightest placenta within a litter, which increase active transport of amino acids per gram of placenta and maintain normal fetal growth close to term, despite the reduced placental mass. The specific placental adaptations differ with age. At E16, they are primarily morphological with an increase in the volume fraction of the labyrinthine zone responsible for nutrient exchange, whereas at E19 they are more functional with up-regulated placental expression of the glucose transporter gene, Slc2a1/GLUT1 and one isoform the System A family of amino acid transporters, Slc38a2/SNAT2. Thus, this adaptability in placental phenotype provides a functional reserve capacity for maximizing fetal growth during late gestation when placental growth is compromised.

Regulation of placental efficiency for nutrient transport by imprinted genes.

Intrauterine growth and development can impact upon the long-term health of an individual. The fetus is dependent upon the placenta for its supply of nutrients and oxygen from the mother. In turn, the functional capacity of the placenta to supply that demand is under the control of the fetal and maternal genomes. Recent evidence suggests that imprinted genes, a class of genes found in placental mammals whose expression depends on their parental origin, have multiple roles in the placenta. The imprinted genes regulate the growth and transport capacity of the placenta, thereby controlling the supply of nutrients. They may also regulate the growth rate of fetal tissues directly, thereby controlling nutrient demand by the fetus. Recent studies using mice with deletions or disruption of imprinted genes with an altered balance between placental and fetal growth and changes in placental efficiency are indicative of feto-placental signalling of fetal nutrient demand. We propose that signalling mechanisms involving growth demand signals and nutrient transporters are likely to occur and are important for fine tuning normal fetal growth.

[DNA repair pathways and their involvement in human diseases]. / Mecanismele de reparare a leziunilor ADN. Implicatii în patologia umana.

Integrity maintenance of the genome is crucial. Human DNA is vulnerable to damage arising from both endogenous and exogenous sources. Different DNA repair pathways counteract these potentially mutagenic accidents: damage reversal by methylguanine methyl transferase (MGMT), base nucleotide repair (BER), nucleotide excision repair (NER), mismatch repair (MMR) and repair of strand breaks. In some cases, DNA damage is not repaired but is instead bypassed by specialized DNA polymerases. The existence of human diseases associated with defects in DNA repair illustrates the importance of this process of quality control. Many of these human diseases have an increased susceptibility to cancer.

[Genetic susceptibility to cancer]. / Predispozitia genetica în cancer.

Hereditary predisposition is a common trait of many cancers. 15 to 20 percent of all cancers occur in individuals who have inherited a single gene alteration being members of families where multiple persons carry a high risk of developing cancer. Other than these so-called high penetrance genes which confer elevated risks of cancer development, there are many other genes that generate less dramatic but clinically important risks of cancer, often only if associated to specific exposures.

[Chaperone proteins--essential proteins for cellular activity]. / Proteinele chaperone--proteine esentiale pentru activitatea celulei.

Molecular chaperones are an ubiquitous, abundant and highly conserved group of proteins which bind and stabilize proteins at intermediate stages of folding, assembly, translocation across membranes and degradation. They first came to attention because of their specific induction during the cellular response of all organisms to heat shock, but are now known to be constitutively and abundantly expressed in the absence of any stress. Despite the obvious importance of stress responses, only recently has scrutiny focused on the role of heat shock proteins in the control of disease pathology. Knowledge about Hsp functions in bacteria is much further advanced than in eukaryotes, but already some hints of Hsp involvement in mammalian diseases have emerged.