Hematopoietic stem cells emerge from a specialized subset of endothelial cells in the midgestation mouse aorta. This subset, the so-called hemogenic endothelium (HE), undergoes a morphological and molecular change to a hematopoietic cell type, as part of the endothelial-to- hematopoietic transition (EHT). Previously, lack of specific markers prevented mechanistic studies of HE, as well as studies into its developmental origin. Runx1 is a critical regulator of developmental hematopoiesis and is expressed in all cell intermediates of EHT. Identification of the Runx1 +23 enhancer led to the development of enhancer-reporter tools in order to isolate HE for further analysis. Here, I investigated the cell-type specific activity of another Runx1 enhancer, located 204 kb downstream of the ATG in exon 1. I generated a novel enhancer-reporter mouse line (204GFP) and determined the expression pattern and lineage potential of 204GFP+ cells. It was established that the +204 enhancer marks all HE and part of the HSCs. Hematopoietic progenitor cells, in contrast, were not marked by the 204GFP transgene. Interestingly, the 204GFP reporter also marks part of the Runx1- expressing sub-aortic mesenchyme. To test whether the 204GFP reporter could enrich for HE when combined with a Runx1 +23 enhancer-reporter transgene, I generated and characterized a 23Cherry transgenic mouse line. Expression analysis of aortic endothelial cells marked by both the 204GFP and 23Cherry transgenes using the Fluidigm platform indicated an enrichment of cells with a HE expression signature. This enrichment will facilitate further analysis of the molecular networks active in HE using whole genome expression profiling. The Runx1 enhancer-reporter models are also valuable tools to track the developmental origin of HE, which remains to be established in the mouse embryo. To this end, I mapped the precise spatio-temporal expression pattern of the 23GFP transgene in pre- somitic embryos and established lineage tracing experiments. This provides the basis to revisit fate mapping of the primitive streak to determine the origin(s) of the HE lineage.

The mammalian neocortex comprises a diverse population of excitatory neurons that perform distinct roles in the neocortical circuit. These neurons are born from a heterogeneous population of progenitor cells during embryonic development and it is increasingly being recognised that individual progenitors can impart specific functional characteristics to their offspring. For example, clonally-related sister neurons in mouse neocortex are biased to form gap junctions with one another early in development, to form synaptic connections with one another as they mature, and to show similar response properties in the adult. This highlights a fundamental role for neuronal lineage in the formation of precise neocortical connectivity. However, the extent to which neuronal phenotype is determined by lineage, and the process by which this arises, is not fully understood. Nor is it known whether similar lineage relationships exist in the human neocortex. Deciphering neocortical lineage relationships has been limited by the techniques available to identify and manipulate clonally-related neurons. In this thesis I have developed novel molecular tools for the identification and manipulation of clonally-related neurons and refined their use by in utero surgery in mice. I first developed a retrovirus encoding Cre recombinase and demonstrated that this can be successfully combined with reporter mice to capitalise on optogenetics for functional studies. In an effort to establish a reliable and unequivocal method of identifying clonally-related neurons, I then constructed a retrovirus encoding genetically-distinct RNA barcodes. I confirmed that the RNA barcode could be reliably retrieved from single neurons and used to determine clonal relationships in mouse neocortex and in an in vitro model of human neocortex derived from induced pluripotent stem cells (iPSCs). By comparing the dendritic morphology of barcoded mouse neocortical neurons, I was able to demonstrate that the dendritic arbor of clonally-related neurons is more similar than control neurons derived from different progenitors. This may contribute to specific patterns of synaptic connectivity amongst clonally-related neurons. Within the iPSC system, I demonstrate the utility of the retroviral RNA barcode and revealed that clonally-related human neocortical cells exhibit a higher probability of being gap-junction coupled. These studies advance our understanding of lineage relationships in neocortical excitatory neurons in mouse and provide the first evidence that human neocortical clones exhibit similar functional relationships to those observed in the rodent neocortex.

Curiosity can be defined as the “urge to know more” that manifests behaviorally in questioning and exploration. Curiosity is associated with a host of positive youth outcomes, including academic achievement, school engagement, and deeper learning, yet studies indicate that few teachers foster curiosity in their classrooms, possibly due to a lack of pedagogical techniques focused on inspiring student curiosity. Many scholars suggest directly teaching questioning to cultivate student curiosity; yet, relatively few empirical studies on the role of questioning in fostering curiosity have been conducted. Accordingly, the present study conducted a quasi-experimental, longitudinal investigation to examine the relationship between exposure to the Question Formulation Technique (QFT), a classroom-based intervention that seeks to teach students how to ask their own questions, and scores on curiosity and related strengths in a sample of Northeast high school students. Participating English/Language Arts faculty at four high schools (N = 2,217 students; 42 teachers) were randomly assigned to either a fall or spring start condition. The study utilized student self-report questionnaires and teacher fidelity checks at three time points (fall, winter, and spring) across schools in order to consider the potential impact of the QFT on students’ curiosity, divergent thinking, school engagement, and self-efficacy. In light of prior research, it was hypothesized that the QFT would have a significant positive treatment effect on the study constructs, and would positively impact growth in these attributes. In addition, higher teacher fidelity of implementation of the intervention was expected to lead to greater growth in these attributes. Furthermore, positive and reciprocal mediational paths between curiosity, cognitive engagement, and self-efficacy were proposed. Multilevel modeling revealed the QFT to have a positive absolute treatment effect on students’ curiosity, but not an impact on students’ curiosity growth. In addition, high teacher fidelity, but not dosage, led to increases in students’ curiosity growth over the school year. No other overall positive treatment effects were found, although fidelity and dosage were related positively to growth on several variables. In addition, multiple-group structural equation path models revealed several complex indirect and direct pathways between the four variables of interest. Most surprising, cognitive engagement served as predictors of all other variables in the model. Qualitatively, teachers discussed the impact of the QFT on student responsiveness, described adaptations they made to the intervention, and noted the need for professional development. Limitations of the current study and implications for future research are discussed.

Bioelectricity refers to differential membrane voltage and cytoplasmic ion concentrations in tissues or cells which persist over long periods of time. Differences in these steady-state ionic conditions are responsible for large-scale axial patterning and morphogenesis in developing embryos. The sea urchin embryo is an excellent model organism for studying embryonic development, yet a comprehensive study of bioelectricity in sea urchin development has not been reported. Differential ion channel activity is a primary means by which bioelectricity is controlled; thus, we hypothesized that disrupting ion channel activity would reveal the requirements for bioelectricity in the sea urchin embryo. We performed a screen of ion channel inhibitors and discovered that their activities are required for many processes in sea urchin development. We chose two interesting phenotypes to investigate further. First, we demonstrate that H+/K+ ATPase (HKA) activity is required for biomineralization of the sea urchin larval skeleton. We determined that embryos raised with HKA inhibitors initially exhibit voltage and pH changes, then revert to normal voltage and pH during biomineralization via compensatory changes in sodium and chloride ions; it is likely that these compensatory changes lead to defects in transport of carbonate ions, that in turn, inhibit biomineralization of the calcium carbonate skeleton. We hypothesize that similar mechanisms are at play in human patients on long-term HKA inhibitors to treat acid reflux, in whom biomineralization is also decreased. Next, we demonstrate that V-type H+ ATPase (VHA) activity is required for specification of the dorsal-ventral (DV) axis, for the normal inactivation of p38 MAPK in the presumptive dorsal region, and for the subsequent asymmetric onset of expression of the TGFβ family member Nodal, that locally specifies the ventral territory. Embryos treated with VHA inhibitors exhibit global p38 MAPK activity and Nodal expression, and are ventralized. We describe previously unknown gradients of voltage and pH across the DV axis, the sharpness of which requires VHA activity. We propose that the voltage and pH gradients encode spatial information which confers asymmetry on p38 MAPK activity. Overall, we demonstrate that bioelectrical changes are essential for development of the sea urchin embryo, specifically via roles in biomineralization and DV axis specification. / 2019-01-25

abstract: Organized activity participation is associated with a wide array of positive developmental outcomes. Latinos are one of the largest and fastest growing ethnic groups in the U.S., yet are less likely to participate in organized activities than their peers. Theoretically, the alignment or fit between adolescents' and their activities' characteristics is critical to support youths' use and engagement in organized activities. Using qualitative data in Study 1, I examined parents' and adolescents' perspectives and experiences related to several indicators of ethnicity and culture in their activities. Results suggested that alignment on Spanish-language use was critical for participation. However, some Latino families did not prefer aspects of ethnicity and culture in their activities because adolescents learned about their culture with family or because adolescents wanted to fit in with their majority White peers. Study 2 tested quantitatively whether features of ethnicity and culture in the activity mattered for Latino adolescents' experiences during activities. Ethnic and cultural features in activities, particularly respect for one's ethnicity and culture, fostered positive experiences during activities. Unexpectedly, some ethnic and cultural features were detrimental, such that overt teaching about ethnicity and culture was related to negative feelings during the activity. There was little evidence that the relation between ethnic and cultural features in activities and concurrent experiences varied by Latino cultural orientation. Integrating the findings across these two studies, there was mixed evidence for the traditional theoretical notions that optimal development occurs in environments that fit with individual's characteristics. Complementary fit was optimal when adolescents' needs were considered across the many contexts in which their lives are embedded, including their families and neighborhoods. I recommend that practitioners should take care in learning about the specific families and youth that their activity serves to best understand how to meet their needs. Some aspects of culture, such as Spanish-language use may be critical for participation; other aspects may require special attention from activity leaders, such as teaching about ethnicity and culture. This dissertation is an important step in understanding how to best design activities that promote the recruitment and retention of Latino youth in organized activities. / Dissertation/Thesis / Doctoral Dissertation Family and Human Development 2014

abstract: In two complementary studies, I used an innovative ecological momentary assessment (EMA) design to examine associations between adolescents’ daily interactions with parents and peers and their mood states during two developmentally normative, yet demanding contexts: romantic relationships and the transition to college. The first study examined how adolescents’ daily romantic relationship experiences (e.g., romantic emotionality, conflict, affiliation) were related to negative affective states. Eighty-eight adolescent romantic couples (Mage = 16.74 , SD = 0.96; 44% Latina/o, 42% White) completed short electronic surveys twice-weekly for 12 weeks, which assessed their affective states and their relationship processes (24 total possible surveys). Results indicated that greater conflict and negative romantic emotionality predicted greater within-person fluctuations in same-day negative affect. Greater daily affiliation with a romantic partner predicted slightly lower levels of same-day negative affect; positive romantic emotionality did not significantly predict negative affect. Study 2 examined first-year college students’ growth trajectories in positive and negative affect across the transition to college (i.e., spanning the entire first semester), predicted said trajectories and daily affective states. Participants were 146 first-year college students from a large southwestern university entering their first semester of college (Mage = 17.8, SD = 0.5). Electronic diary surveys were administered to students twice weekly between July and December of 2014, so as to span the transition to college and the entire first semester, and assessed daily affective states and interpersonal interactions. Results indicated that students decreased in their positive affect gradually across the first semester, but remained stable in their negative affect. Significant variability emerged around these average trends, and was predicted by indices of conflict and involvement with parents and friends. Generally, greater involvement with friends and parents was associated with greater positive and less negative affect, whereas greater conflict with these important social groups predicted greater negative affect. Together, these studies underscore the importance of positive attachments during developmentally-challenging contexts experienced in adolescence. / Dissertation/Thesis / Doctoral Dissertation Family and Human Development 2017

abstract: The primary goals of this study were to empirically identify subgroups of socially withdrawn youth in late childhood using latent profile analysis and to examine profiles of students' scholastic adjustment. Further, comparisons of the academic functioning for different subtypes of withdrawn children, with particular emphasis on socially disinterested and socially avoidant youth, were made. Participants were 358 fifth grade children. Results indicated that theoretical subtypes of socially withdrawn youth emerge among fifth grade students (i.e., shy, socially disinterested, socially avoidant, and nonwithdrawn). Additionally, associations among subtype membership and various indices of academic engagement and achievement demonstrated unique academic profiles depending on subgroup classification. In particular, youth who were identified as socially avoidant were at greatest risk for academic difficulties compared to their peers. Findings also emerged for socially disinterested youth indicating some degree of academic maladjustment associated with a preference for solitude. These findings have implications for students exhibiting different forms of social withdrawal for their academic functioning in later childhood. / Dissertation/Thesis / M.S. Family and Human Development 2012

abstract: This dissertation used an evolutionary approach to examine the antecedents and outcomes to early pubertal development in girls in four major ethnic groups (i.e., European American, African American, Hispanic American, and Asian American). In the first study, logistic regressions were conducted to investigate the links between socioeconomic status (SES), parenting behaviors, and father absence to pubertal development across and within ethnic groups. SES and father absence predicted earlier pubertal development among European, African, and Hispanic Americans but not for Asian Americans. In the second study, growth curves were estimated for sexual outcomes across ethnic groups. Early developing European and African American girls had higher levels of sexual risk and pregnancy into adulthood. Puberty did not predict outcomes for Hispanic and Asian American girls. Overall, the findings from both studies revealed the importance of investigating childhood environmental contexts, puberty, and sexual health outcomes using an evolutionary perspective. / Dissertation/Thesis / Ph.D. Family and Human Development 2013

abstract: The current study expands prior work on children's coping with peer victimization by employing person-centered analyses to identify discrete classes of coping behavior, associations with children's maladjustment, and patterns of stability and change over time. Specifically, data were collected at two longitudinal time points from 515 middle school children who reported experiencing at least occasional peer victimization (284 girls, 231 boys; Mage = 8 years, 5 months, SDage = 10.38 months). Three active, behavioral coping strategies were examined: support seeking from teachers, support seeking from friends, and retaliation. A series of cross-sectional latent profile analyses suggested that coping styles may be characterized by 3 distinct classes: (1) support seeking, (2) retaliation, or (3) a combination of these strategies, labeled mixed strategy coping. Peer victimization, depression, and loneliness were included as concurrent covariates of class membership and results indicate that mixed strategy coping may put children at greater social and emotional risk, whereas both support seeking and retaliation may pose potential benefits in the face of victimization. Further, longitudinal latent transition analyses were conducted to examine the stability and change in coping over time, indicating that coping is largely dispositional, though has the potential to change, particularly among children who experience shifts towards greater maladjustment over time. Results emphasize mixed strategy coping - a coping style that is underrepresented in the current research - as both an important factor that may contribute to greater social and emotional difficulties and also as a potential transitioning point during which change in children's coping may be addressed. / Dissertation/Thesis / Ph.D. Family and Human Development 2013

abstract: Although anxiety may be developmentally appropriate, it can become problematic in some youth. From an ecological perspective, social systems, like family and friendships, are theorized to influence developmental trajectories toward (mal)adjustment, but empirical evidence is scant with regard to the relative impact of subjective satisfaction with family and friendship on anxiety problem development. This thesis study used a subsample of approximately 50% Hispanic/Latino clinic-referred youth (n = 71, ages 6-16 years). Overall, results suggest that the effect of friendship satisfaction on anxiety varied as a function of age but not ethnicity, such that there was a significant negative relationship between child-reported friendship satisfaction and anxiety levels for older children (approx. 9 years and older) but not for younger children. The effect of family satisfaction on anxiety also varied as a function of age, such that older children showed a positive relation between child reported family satisfaction and parent reported anxiety. Furthermore, a positive relation between family satisfaction and anxiety was found only for the H/L children. Post hoc analyses regarding cultural underpinnings of this finding and implications for future research are discussed, as are the results regarding differences between parent and child reports of anxiety. / Dissertation/Thesis / M.A. Psychology 2013