Embryonic Precursor Cells from the Rhombic Lip Are Specified to a Cerebellar Granule Neuron Identity

AbstractThe specification of diverse classes of neurons is critical to the development of the cerebellar cortex. Here, we describe the purification of early embryonic precursors of cerebellar granule neurons from the rhombic lip, the dorsal aspect of the midbrain/hindbrain region. Isolation of rhombic lip cells reveals a homogenous population of precursor cells that express general neuronal markers and the granule cell marker RU49, but fail to extend neurites or express differentiation markers. Differentiation is induced by coculture with external germinal layer (EGL) cells, or their membranes, suggesting that a local inducing factor acts after formation of the EGL. Thus, proliferating precursors within the rhombic lip are specified to be granule cells very early, with the availability of an inducing factor increasing over the course of development

Decreased dyskerin levels as a mechanism of telomere shortening in X-linked dyskeratosis congenita

Dyskeratosis congenita (DC) is a premature ageing syndrome characterised by short telomeres. An X-linked form of DC is caused by mutations in DKC1 which encodes dyskerin, a telomerase component that is essential for telomerase RNA stability. However, mutations in DKC1 are identifiable in only half of X-linked DC families. A four generation family with pulmonary fibrosis and features of DC was identified. Affected males showed the classic mucocutaneous features of DC and died prematurely from pulmonary fibrosis. Although there were no coding sequence or splicing variants, genome wide linkage analysis of 16 individuals across four generations identified significant linkage at the DKC1 locus, and was accompanied by reduced dyskerin protein levels in affected males. Decreased dyskerin levels were associated with compromised telomerase RNA levels and very short telomeres. These data identify decreased dyskerin levels as a novel mechanism of DC, and indicate that intact dyskerin levels, in the absence of coding mutations, are critical for telomerase RNA stability and for in vivo telomere maintenance

Telomerase mutations in families with idiopathic pulmonary fibrosis

BACKGROUND: Idiopathic pulmonary fibrosis is progressive and often fatal; causes of familial clustering of the disease are unknown. Germ-line mutations in the genes hTERT and hTR, encoding telomerase reverse transcriptase and telomerase RNA, respectively, cause autosomal dominant dyskeratosis congenita, a rare hereditary disorder associated with premature death from aplastic anemia and pulmonary fibrosis. METHODS: To test the hypothesis that familial idiopathic pulmonary fibrosis may be caused by short telomeres, we screened 73 probands from the Vanderbilt Familial Pulmonary Fibrosis Registry for mutations in hTERT and hTR. RESULTS: Six probands (8%) had heterozygous mutations in hTERT or hTR; mutant telomerase resulted in short telomeres. Asymptomatic subjects with mutant telomerase also had short telomeres, suggesting that they may be at risk for the disease. We did not identify any of the classic features of dyskeratosis congenita in five of the six families. CONCLUSIONS: Mutations in the genes encoding telomerase components can appear as familial idiopathic pulmonary fibrosis. Our findings support the idea that pathways leading to telomere shortening are involved in the pathogenesis of this disease

Ancestral Mutation in Telomerase Causes Defects in Repeat Addition Processivity and Manifests As Familial Pulmonary Fibrosis

The telomerase reverse transcriptase synthesizes new telomeres onto chromosome ends by copying from a short template within its integral RNA component. During telomere synthesis, telomerase adds multiple short DNA repeats successively, a property known as repeat addition processivity. However, the consequences of defects in processivity on telomere length maintenance are not fully known. Germline mutations in telomerase cause haploinsufficiency in syndromes of telomere shortening, which most commonly manifest in the age-related disease idiopathic pulmonary fibrosis. We identified two pulmonary fibrosis families that share two non-synonymous substitutions in the catalytic domain of the telomerase reverse transcriptase gene hTERT: V791I and V867M. The two variants fell on the same hTERT allele and were associated with telomere shortening. Genealogy suggested that the pedigrees shared a single ancestor from the nineteenth century, and genetic studies confirmed the two families had a common founder. Functional studies indicated that, although the double mutant did not dramatically affect first repeat addition, hTERT V791I-V867M showed severe defects in telomere repeat addition processivity in vitro. Our data identify an ancestral mutation in telomerase with a novel loss-of-function mechanism. They indicate that telomere repeat addition processivity is a critical determinant of telomere length and telomere-mediated disease

Short Telomeres Compromise β-Cell Signaling and Survival

The genetic factors that underlie the increasing incidence of diabetes with age are poorly understood. We examined whether telomere length, which is inherited and known to shorten with age, plays a role in the age-dependent increased incidence of diabetes. We show that in mice with short telomeres, insulin secretion is impaired and leads to glucose intolerance despite the presence of an intact β-cell mass. In ex vivo studies, short telomeres induced cell-autonomous defects in β-cells including reduced mitochondrial membrane hyperpolarization and Ca2+ influx which limited insulin release. To examine the mechanism, we looked for evidence of apoptosis but found no baseline increase in β-cells with short telomeres. However, there was evidence of all the hallmarks of senescence including slower proliferation of β-cells and accumulation of p16INK4a. Specifically, we identified gene expression changes in pathways which are essential for Ca2+-mediated exocytosis. We also show that telomere length is additive to the damaging effect of endoplasmic reticulum stress which occurs in the late stages of type 2 diabetes. This additive effect manifests as more severe hyperglycemia in Akita mice with short telomeres which had a profound loss of β-cell mass and increased β-cell apoptosis. Our data indicate that short telomeres can affect β-cell metabolism even in the presence of intact β-cell number, thus identifying a novel mechanism of telomere-mediated disease. They implicate telomere length as a determinant of β-cell function and diabetes pathogenesis

Risk factors in child maltreatment: a meta-analytic review of the literature

This review presents the results of a series of meta-analyses identifying the relative strength of various risk factors for child physical abuse and neglect. Data from 155 studies examining 39 different risk factors were included in the review. Large effect sizes were found between child physical abuse and four risk factors (parent perceives child as problem, parent anger, family conflict and family cohesion). Large effect sizes were also found between child neglect and six risk factors (child social competence, parent-child relationship, parent perceives child as problem, parent’s level of stress, parent’s level of anger, and parent’s self-esteem)

Impact of Early and Concurrent Stunting on Cognition

Undernutrition is associated with poor cognitive development, late entry into school, decreased years of schooling, reduced productivity, and smaller adult stature. We use longitudinal data from 1674 Peruvian children participating in the Young Lives study to assess the relative impact of early stunting (stunted at 6-18 months of age) and concurrent stunting (stunted at 4.5-6 years of age) on cognitive ability. Anthropometric data were longitudinally collected for children at 6-18 months of age and 4.5-6 years of age at which time verbal and quantitative ability were also assessed. We estimate that an increase in concurrent height-for-age z-scores (HAZ) by one standard deviation was associated with an increase in a child’s score on the Peabody Picture Vocabulary Test (PPVT) by 2.35 points (CI: 1.55-3.15) and a 0.16 point increase on the Cognitive Development Assessment (CDA) (CI: 0.05-0.27). Further, we report that the estimate for concurrent HAZ and PPVT is significantly higher than the estimate for early stunting and PPVT. We found no significant difference between early and concurrent estimates for HAZ and CDA. Children from older mothers, children whose mothers had higher education levels, children living in urban areas, children who attended preschool, children with fewer siblings, and children from wealthier backgrounds scored higher on both assessments. Cognitive skills of children entering school were associated with early stunting but the strongest association was found with concurrent stunting suggesting that interventions preventing linear growth faltering should not only focus on the under twos but include children up to five years of age.© 2010 Blackwell Publishing Ltd. This is the peer reviewed version of the following article: Benjamin T. Crookston, Kirk A. Dearden, Stephen C. Alder, Christina A. Porucznik, Joseph B. Stanford, Ray M. Merrill, Ty T. Dickerson4, Mary E. Penny (2011) “Impact of Early and Concurrent Stunting on Cognition”, Maternal and Child Nutrition 7:397-409. DOI: 10.1111/j.1740-8709.2010.00255.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archiving

Impact of Early and Concurrent Stunting on Cognition

Undernutrition is associated with poor cognitive development, late entry into school, decreased years of schooling, reduced productivity, and smaller adult stature. We use longitudinal data from 1674 Peruvian children participating in the Young Lives study to assess the relative impact of early stunting (stunted at 6-18 months of age) and concurrent stunting (stunted at 4.5-6 years of age) on cognitive ability. Anthropometric data were longitudinally collected for children at 6-18 months of age and 4.5-6 years of age at which time verbal and quantitative ability were also assessed. We estimate that an increase in concurrent height-for-age z-scores (HAZ) by one standard deviation was associated with an increase in a child’s score on the Peabody Picture Vocabulary Test (PPVT) by 2.35 points (CI: 1.55-3.15) and a 0.16 point increase on the Cognitive Development Assessment (CDA) (CI: 0.05-0.27). Further, we report that the estimate for concurrent HAZ and PPVT is significantly higher than the estimate for early stunting and PPVT. We found no significant difference between early and concurrent estimates for HAZ and CDA. Children from older mothers, children whose mothers had higher education levels, children living in urban areas, children who attended preschool, children with fewer siblings, and children from wealthier backgrounds scored higher on both assessments. Cognitive skills of children entering school were associated with early stunting but the strongest association was found with concurrent stunting suggesting that interventions preventing linear growth faltering should not only focus on the under twos but include children up to five years of age.</p