Generation of basal radial glia in the embryonic mouse dorsal telencephalon

The human brain, as much as it is “unaccountable” in the eyes of Virginia Woolf, is a marvel. It is the evolutionary increase in brain size, especially in the cerebral cortex, that both allowed Mrs Woolf to create and us to perceive the beautiful imagery that exists in her fictional world. The evolutionary increase in brain size in part reflects the increase in the number of neurons generated during neocortical development. This in turn reflects two principal features of cortical expansion, namely, an increase in the number of neural stem and progenitor cells (from here on referred to as progenitor cells) and their neurogenic potential. Strikingly, in order to cater for this increase in progenitor cells and neurogenic potential, there is a significant expansion and diversification of basal progenitors in the subventricular zone (SVZ). Basal progenitors can be divided into three types: basal intermediate progenitors (bIPs), basal radial glias (bRGs) and transit-amplifying progenitors (TAPs). bIPs are the most abundant progenitors in the mouse SVZ. These cells are non-polar and are Pax6 and Sox2 negative, but Tbr2 positive. They have limited proliferative capacity as they can divide only once to produce two neurons. bRGs and TAPs, on the other hand, are able to undergo multiple rounds of division and exist in higher abundance in gyrencephalic brains (for bRG, in humans up to 50% versus mouse 5% at mid-neurogenesis). The morphology of bRGs are reported to be dynamic (fluctuating between states of having process(es) to none), whereas TAPs are generally described to be non-polar during mitosis. bRGs are known to express Pax6 and Sox2 but not Tbr2 while TAPs are known to express both Pax6 and Tbr2. The increase in the proportion of these self-renewing basal progenitors (more specifically bRGs) might allow for cortical expansion. Hence, the main objective of this doctoral work was to generate more bRGs in the mouse dorsal telencephalon, the region that ultimately develops to become the cerebral cortex. To achieve this objective, two approaches were used– (i) a general approach by microinjecting a pool of ferret poly-A+ RNA and (ii) a candidate approach by conditionally expressing the transcription factor Pax6. In the general approach, the microinjection technique was first established and validated in an organotypic slice culture of the mouse dorsal telencephalon. A pool of ferret poly-A¬+ RNA extracted at P1, the developmental stage corresponding to the peak of bRG production, was then microinjected into the dorsal telencephalon. We hypothesized that at the peak of bRG production, the “instructive” messages on how to generate bRG would be at their peak. Hence, by introducing these “instructive” messages into a apical radial glia (aRG), these cells would thus “know” how to generate bRGs. At 24 h after microinjection, only aRGs, the predominant progenitor residing in the ventricular zone during mid-neurogenesis were recovered. At 48 h after microinjection, however, 75% of cells that translated the ferret poly-A¬+ RNA had a morphology reminiscent of bRG. These cells were located away from the ventricular surface and had a basal but not apical process. We conclude from these experiments that we did indeed generate bRG-like cells in the mouse dorsal telencephalon via microinjection of the ferret poly-A¬+ RNA. In the candidate approach, this work aimed to conditionally express Pax6, a transcription factor that has been linked to proliferation and neurogenesis in aRG. More specifically, as there is a significant increase in the number of Pax6 positive cells (bRGs) in the SVZ of gyrencephalic animals during mid-neurogenesis, we wanted to recapitulate this phenomenon in the mouse dorsal telencephalon, where Pax6 is normally downregulated. To achieve this, the Tis21–CreERT2 mouse was used. Tis21 is a pan-neurogenic marker that is switched on once aRG switches from a proliferative division (i.e. 1 aRG⇒2aRG) to a neurogenic division (i.e. 1aRG⇒1aRG+1bIP). Consequently, the neurogenic aRGs and its progeny, bIPs would thus be Tis21 positive. By conditionally expressing Pax6 in Tis21 positive aRGs, the ectopic expression of Pax6 was successfully induced in the SVZ of the mouse dorsal telencephalon. Interestingly, conditional expression of Pax6 increased the percentage of proliferating cells in the SVZ. However, instead of producing more bIPs as predicted by the neurogenic division of Tis21 positive aRGs, these cells had the cell morphology, transcription factor expression profile, and division-type of bRGs and/or TAPs. Thus, using the conditional expression of Pax6 we were able to generate more bRG-like progenitors in the mouse dorsal telencephalon. The fate of these conditionally expressing Pax6 progenitors at a later stage was then investigated. A phenotypic change in the behaviour of neurons generated was observed. Instead of migrating into the cortical plate, cells that were highly expressing Pax6 formed a heterotopia at the SVZ or intermediate zone, suggestive of Pax6 interfering with neuronal migration. Interestingly, of those lowly expressing Pax6 cells that successfully migrated to the CP, a disproportionate majority became upper layer neurons. As the fate of neurons are dependent on their date of birth (i.e early born neurons are normally found in the deep layer while late born neurons are normally found in the upper layer), the increase in the upper layer neurons is consistent with the fact that conditionally expressing Pax6 delayed the birth of these neurons by delaying neurogenesis in order to increase the number of proliferative divisions. Interestingly, this increase in upper layer neurons is consistent with the difference between small- and large-brained species. In conclusion, through this work more bRGs was successfully generated in the mouse dorsal telencephalon through two distinct but complementary approaches

Effect of neuroinflammation on cognition and potential mechanisms involved

Master'sMASTER OF SCIENC

HRM and KM as catalysts of environmental performance: A conceptual framework

The purpose of this paper is to develop a theoretical framework to investigate the relationships among human resource management (HRM), knowledge management (KM) and environmental performance (EP).Environmental friendly business activities demand high level of human resource competency in terms of knowledge, skills and capabilities in order to better firm performance. This paper serves to establish the link among HRM, KM, and EP to fill the gap in the current literature.The research model is proposed based on reviews of the literature on HR and KM perspectives on environmental management and performance.Both theoretical and practical implications are discussed in this paper.With new knowledge gained on the associations among HRM, KM and EP, manufacturing firm managers can focus their effort and resources on HRM and KM to deliver better environmental management effectiveness.It is anticipated that this paper will contribute towards sustainability development for a better living environment

Harmony and discord:Development of political parties and social fragmentation in Hong Kong, 1980-2017

This paper seeks to examine why political parties in Hong Kong are fragmented and how the development of political parties in Hong Kong leads to social discord. Political parties started to emerge in Hong Kong in the 1980s. They had a golden opportunity to develop in the 1990s due to political reform, but why are political parties in Hong Kong still small, weak, with poor reputations and weak support? The author points out five factors that lead to the malfunction of political parties in Hong Kong. Although some factors are caused by the political parties themselves, the author argues that they are, all in all, constitutional or institutional factors, as they are long-term restraints directly set by the government since the colonial era. Due to the failure of party development in Hong Kong caused by constitutional and institutional restraints, the author will also discuss how this failure has lead to the political and social discord in the past two decades since the handover and the future

Breastfeeding and weaning practices among Hong Kong mothers: a prospective study

<p>Abstract</p> <p>Background</p> <p>Breastfeeding provides optimal and complete nutrition for newborn babies. Although new mothers in Hong Kong are increasingly choosing to breastfeed their babies, rates of exclusive breastfeeding are low and duration remains short. The purpose of this study was to describe the breastfeeding and weaning practices of Hong Kong mothers over the infant's first year of life to determine the factors associated with early cessation.</p> <p>Methods</p> <p>A cohort of 1417 mother-infant pairs was recruited from the obstetric units of four public hospitals in Hong Kong in the immediate post-partum period and followed prospectively for 12 months or until weaned. We used descriptive statistics to describe breastfeeding and weaning practices and multiple logistic regression to investigate the relationship between maternal characteristics and breastfeeding cessation.</p> <p>Results</p> <p>At 1 month, 3 months, 6 months and 12 months only 63%, 37.3%, 26.9%, and 12.5% of the infants respectively, were still receiving any breast milk; approximately one-half of breastfeeding mothers were exclusively breastfeeding. Younger mothers, those with a longer duration of residence in Hong Kong, and those returning to work postpartum were more likely to wean before 1 month. Mothers with higher education, previous breastfeeding experience, who were breastfed themselves and those who were planning to exclusively breastfeed and whose husbands preferred breastfeeding were more likely to continue breastfeeding beyond 1 month. The introduction of infant formula before 1 month and returning to work postpartum were predictive of weaning before 3 months.</p> <p>Conclusions</p> <p>Breastfeeding promotion programs have been successful in achieving high rates of breastfeeding initiation but the focus must now shift to helping new mothers exclusively breastfeed and sustain breastfeeding for longer.</p

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts