Aging alters the epigenetic asymmetry of HSC division

Hematopoietic stem cells (HSCs) balance self-renewal and differentiation to maintain homeostasis. With aging, the frequency of polar HSCs decreases. Cell polarity in HSCs is controlled by the activity of the small RhoGTPase cell division control protein 42 (Cdc42). Here we demonstrate—using a comprehensive set of paired daughter cell analyses that include single-cell 3D confocal imaging, single-cell transplants, single-cell RNA-seq, and single-cell transposase-accessible chromatin sequencing (ATAC-seq)—that the outcome of HSC divisions is strongly linked to the polarity status before mitosis, which is in turn determined by the level of the activity Cdc42 in stem cells. Aged apolar HSCs undergo preferentially self-renewing symmetric divisions, resulting in daughter stem cells with reduced regenerative capacity and lymphoid potential, while young polar HSCs undergo preferentially asymmetric divisions. Mathematical modeling in combination with experimental data implies a mechanistic role of the asymmetric sorting of Cdc42 in determining the potential of daughter cells via epigenetic mechanisms. Therefore, molecules that control HSC polarity might serve as modulators of the mode of stem cell division regulating the potential of daughter cells.

Stem cells are unique cells that can differentiate to produce more stem cells or other types of cells and can divide both symmetrically (to produce daughter cells with the same fate) and asymmetrically (to produce one daughter cell that retains stem cell potential and one that differentiates). The mechanisms that control the outcome of stem cell divisions have been the focus of many studies; however, they remain mainly unknown. Here, we have analyzed these mechanisms in murine hematopoietic stem cells (HSCs) by directly comparing the epigenetic signature, the transcriptome, and the function of the two daughter cells stemming from the first division of either a young or an aged HSC. We observe that, while young HSCs divide mainly asymmetrically, aged HSCs divide primarily symmetrically. We find that the mode of division is tightly linked to stem cell polarity and is regulated by the activity level of the small RhoGTPase cell division control protein 42 (Cdc42). In addition, we show that the potential of daughter cells is further linked to the amount of the epigenetic mark H4K16ac and also to the amount of open chromatin allocated to a daughter cell, but it is not linked to its transcriptome. In summary, our study suggests that HSC polarity linked to Cdc42 activity drives the mode of division, while epigenetic mechanisms determine the functional outcome of the stem cell division.

A heterozygous mutation in tubulin, beta 2B ( Tubb2b ) causes cognitive deficits and hippocampal disorganization

Development of the mammalian forebrain requires a significant contribution from tubulin proteins to physically facilitate both the large number of mitoses in the neurogenic brain (in the form of mitotic spindles) as well as support cellular scaffolds to guide radial migration (radial glial neuroblasts). Recent studies have identified a number of mutations in human tubulin genes affecting the forebrain, including TUBB2B . We previously identified a mouse mutation in Tubb2b and we show here that mice heterozygous for this missense mutation in Tubb2b have significant cognitive defects in spatial learning and memory. We further showed reduced hippocampal long-term potentiation consistent with these defects. In addition to the behavioural and physiological deficits, we show here abnormal hippocampal morphology. Taken together, these phenotypes suggest that heterozygous mutations in tubulin genes result in cognitive deficits not previously appreciated. This has implications for design and interpretation of genetic testing for humans with intellectual disability disorders.

A mutation in FRIZZLED2 impairs Wnt signaling and causes autosomal dominant omodysplasia

Autosomal dominant omodysplasia is a rare skeletal dysplasia characterized by short humeri, radial head dislocation, short first metacarpals, facial dysmorphism and genitourinary anomalies. We performed next-generation whole-exome sequencing and comparative analysis of a proband with omodysplasia, her unaffected parents and her affected daughter. We identified a de novo mutation in FRIZZLED2 (FZD2) in the proband and her daughter that was not found in unaffected family members. The FZD2 mutation (c.1644G>A) changes a tryptophan residue at amino acid 548 to a premature stop (p.Trp548*). This altered protein is still produced in vitro, but we show reduced ability of this mutant form of FZD2 to interact with its downstream target DISHEVELLED. Furthermore, expressing the mutant form of FZD2 in vitro is not able to facilitate the cellular response to canonical Wnt signaling like wild-type FZD2. We therefore conclude that the FRIZZLED2 mutation is a de novo, novel cause for autosomal dominant omodysplasia.

Headache in the emergency department

OBJECTIVE

To perform an observational study of the demographics, clinical factors, and therapeutic efficacy in patients presenting to the emergency department with a chief complaint of headache.

BACKGROUND

Acute headache presentations to the emergency department are a therapeutic dilemma for physicians.

METHODS

Patients presenting with nontraumatic headache to the emergency department of Hermann Hospital in Houston, Texas, during a 16-month period were prospectively ascertained by active and passive surveillance. The medical record was abstracted. Demographic and clinical information are presented with descriptive statistics. Relative benefit of individual therapies are compared with odds ratios (95% confidence intervals).

RESULTS

Of the 38 730 patients who were prospectively screened, 455 presented with a chief complaint of headache. Seventy-six percent were women, and the mean age was 37 years. Non-Hispanic whites were more likely diagnosed with migraine compared with Hispanics or African Americans (P<.001). Three percent had subarachnoid hemorrhage. Neurologist follow-up was ordered in 10%. The median time in the emergency department was 265 minutes. With the initial treatment, 44% resolved, 47% improved, and 9% had no change; none worsened. In comparison with all other therapies used, there was a trend suggesting the superiority of antiemetics (odds ratio, 2.66; 95% confidence interval, 0.81 to 8.61). Acetaminophen was less helpful (odds ratio, 0.27; 95% confidence interval, 0.10 to 0.70). When comparing specific agents to therapies which could be used at home, antiemetics led to headache resolution most often (odds ratio, 3.18; 95% confidence interval, 1.40 to 7.22); ketorolac showed a similar trend (odds ratio, 2.05; 95% confidence interval, 0.86 to 4.89).

CONCLUSIONS

Headache in the emergency department is a phenomena of young women who spend a long time waiting and receive many tests. A variety of therapies are used. Antiemetics may be especially useful for headache resolution.

Axenic culture and characterization of Giardia ardeae from the great blue heron (Ardea herodias)

Trophozoites of Giardia ardeae were obtained from the great blue heron (Ardea herodias) and established in axenic culture using the TYI-S-33 medium. The generation time in culture for G. ardeae was 22-25 hr, which was 3-fold longer than for Giardia duodenalis (WB strain). A morphological comparison of trophozoites in the original intestinal isolate to those grown in culture revealed that they were identical for the following characteristics: a pyriform-shaped body, a ventral adhesive disc with a deep notch in the posterior border, teardrop-shaped nuclei, pleomorphism in median body structure ranging from a round-oval appearance (Giardia muris type) to that of a clawhammer (G. duodenalis type), and a single caudal flagellum on the right side (as viewed dorsally) with the left one being rudimentary. Analysis of the chromosomal migration patterns was performed by orthogonal-field-alternation gel electrophoresis and demonstrated that the pattern for G. ardeae was distinctly different from that for G. duodenalis (Portland 1-CCW strain). Bacterial symbionts were seen attached to trophozoites in the original isolate but could not be detected in cultured trophozoites using scanning electron microscopy, fluorescence light microscopy using the Hoechst 33258 dye for DNA localization, or by standard microbiological techniques using nonselective media for growing aerobic or anaerobic bacteria. This study demonstrated that avian-derived Giardia could be grown in axenic culture; based on morphological criteria and chromosomal migration patterns, that G. ardeae should be considered a distinct species; and that rationale for determining Giardia spp., based on median body structure alone, should no longer be considered adequate for classification at the species level.

The health consequences of multiple morbidity in the elderly. The Alameda County study

Longitudinal data from the Alameda County Study are used to examine three health consequences of multiple or co-morbidity, defined as the coexistence of two or more chronic conditions and/or symptoms. Age-adjusted analyses of the consequences of baseline co-morbidity show significant associations in both age groups with 17-year mortality, and with the development of multiple new conditions and the occurrence of depression over a 9-year follow-up. After adjustments for sociodemographic characteristics and health behaviors, all associations with multiple new conditions remain significant. The association with depressive symptoms, however, remains significant for the younger age group only and the association with mortality become nonsignificant in both age groups.