A Study Planning Exercise Associated with Decreased Distraction Levels among Introductory Biology Students.

Students struggle to regulate their learning during independent study sessions. In this study, we ask whether an online behavioral intervention helped introductory students decrease distraction while studying. The intervention consisted of exam 1 reflection, exam 2 planning, and exam 2 reflection exercises. During planning, students formed a goal, mentally contrasted (MC) a positive outcome of their goal to their present reality, identified an obstacle, and formed an implementation intention (II) to overcome that obstacle. During reflection, students self-reported their distraction while studying. Distraction was the most frequently reported study obstacle, and decreasing distraction was the second most frequently reported study goal. While students who aimed to decrease distraction as a goal did not follow through, students who planned for distraction obstacles did follow through on decreasing distraction levels. Only about half of students generated an II that aligned with their study goal, which may provide one reason for the opposing follow-through of distraction framed as a goal versus as an obstacle. Lastly, we examined the specificity of students' II's and found no relationship with follow-through. Overall, MC with II holds promise as a self-regulatory technique to help introductory biology students change their behaviors while studying.

Imaging Epidermal Cell Rearrangement in the C. elegans Embryo.

The Caenorhabditis elegans embryo is well suited for analysis of directed cell rearrangement via modern microscopy, due to its simple organization, short generation time, transparency, invariant lineage, and the ability to generate engineered embryos expressing various fluorescent proteins. This chapter provides an overview of routine microscopy techniques for imaging dorsal intercalation, a convergent extension-like morphogenetic movement in the embryonic epidermis of C. elegans, including making agar mounts, low-cost four-dimensional (4D) Nomarski microscopy, laser microsurgery, and 4D fluorescence microscopy using actin and junctional fusion proteins, as well as tissue-specific promoters useful for studying dorsal intercalation.

To What Extent Do Study Habits Relate to Performance?

Students' study sessions outside class are important learning opportunities in college courses. However, we often depend on students to study effectively without explicit instruction. In this study, we described students' self-reported study habits and related those habits to their performance on exams. Notably, in these analyses, we controlled for potential confounds, such as academic preparation, self-reported class absences, and self-reported total study time. First, we found that, on average, students used approximately four active strategies to study and that they spent about half of their study time using active strategies. In addition, both the number of active strategies and the proportion of their study time using active strategies positively predicted exam performance. Second, on average, students started studying 6 days before an exam, but how early a student started studying was not related to performance on in-term (immediate) or cumulative (delayed) exams. Third, on average, students reported being distracted about 20% of their study time, and distraction while studying negatively predicted exam performance. These results add nuance to lab findings and help instructors prioritize study habits to target for change.

Biological Variation as a Threshold Concept: Can We Measure Threshold Crossing?

Threshold concepts are fundamental to a discipline and, once understood, transform students' understanding and perception of the subject. Despite the value of threshold concepts as a learning "portal" for heuristic purposes, there is limited empirical evidence of threshold crossing or achieving mastery. As a threshold concept, biological variation within species is fundamental to understanding evolution and provides a target for analyzing threshold crossing. We aimed to 1) examine student understanding of variation using four dimensions of a threshold concept (discursive, troublesome, liminal, and integrative), 2) measure "threshold crossing," and 3) investigate the utility of the threshold concept framework to curriculum design. We conducted semistructured interviews of 29 students affiliated with a "variation-enriched" curriculum in a cross-sectional design with precurriculum, current, and postcurriculum groups (Pre, Current, and Post) and an outgroup of three postbaccalaureate advanced learners (Outgroup). Interview transcripts revealed that Current students expand their "variation discourse," while the Post group and Outgroup displayed conformity in word choice about variation. The Post and Current groups displayed less troublesome and more integrative responses. Pre, Post, and Outgroup explanations' revealed liminality, with discomfort and uncertainty regardless of accuracy. When we combined all four threshold concept dimensions for each respondent, patterns indicative of threshold crossing emerged along with new insight regarding curricular design.

Participation in Voluntary Re-quizzing Is Predictive of Increased Performance on Cumulative Assessments in Introductory Biology.

Low-stakes testing, or quizzing, is a formative assessment tool often used to structure course work. After students complete a quiz, instructors commonly encourage them to use those quizzes again to retest themselves near exam time (i.e., delayed re-quizzing). In this study, we examine student use of online, ungraded practice quizzes that are reopened near exam time after a first graded attempt 1-3 weeks prior. We find that, when controlling for preparation (performance in a previous science, technology, engineering, and mathematics [STEM] course and incoming biology knowledge), re-quizzing predicts better performance on two cumulative exams in introductory biology: a course posttest and final exam. Additionally, we describe a preliminary finding that, for the final exam, but not the posttest, re-quizzing benefits students with lower performance in a previous STEM course more than their higher-performing peers. But unfortunately, these struggling students are also less likely to participate in re-quizzing. Together, these data suggest that a common practice, reopening quizzes for practice near exam time, can effectively benefit student performance. This study adds to a growing body of literature that suggests quizzing can be used as both an assessment tool and a learning tool by showing that the "testing effect" extends to delayed re-quizzing within the classroom.

CDC-42 Orients Cell Migration during Epithelial Intercalation in the Caenorhabditis elegans Epidermis.

Cell intercalation is a highly directed cell rearrangement that is essential for animal morphogenesis. As such, intercalation requires orchestration of cell polarity across the plane of the tissue. CDC-42 is a Rho family GTPase with key functions in cell polarity, yet its role during epithelial intercalation has not been established because its roles early in embryogenesis have historically made it difficult to study. To circumvent these early requirements, in this paper we use tissue-specific and conditional loss-of-function approaches to identify a role for CDC-42 during intercalation of the Caenorhabditis elegans dorsal embryonic epidermis. CDC-42 activity is enriched in the medial tips of intercalating cells, which extend as cells migrate past one another. Moreover, CDC-42 is involved in both the efficient formation and orientation of cell tips during cell rearrangement. Using conditional loss-of-function we also show that the PAR complex functions in tip formation and orientation. Additionally, we find that the sole C. elegans Eph receptor, VAB-1, functions during this process in an Ephrin-independent manner. Using epistasis analysis, we find that vab-1 lies in the same genetic pathway as cdc-42 and is responsible for polarizing CDC-42 activity to the medial tip. Together, these data establish a previously uncharacterized role for polarized CDC-42, in conjunction with PAR-6, PAR-3 and an Eph receptor, during epithelial intercalation.

Another morphogenetic movement on the map: Charting dorsal intercalation in C. elegans.

Dorsal intercalation is a coordinated cell migration event that rearranges hypodermal cells during C. elegans embryogenesis, and that resembles cell intercalation in many systems from flies to mice. Despite its conservation, the molecular mechanisms that govern dorsal intercalation in worms have remained elusive. Here, we comment on our recent publication, Walck-Shannon et al.,(1) which begins to spatially map the molecular requirements for intercalation. First, we provide a historical perspective on the factors that have previously hampered the study of dorsal intercalation. Next, we provide a summary of the molecular pathways identified in Walck-Shannon et al.,(1) pointing out surprises along the way. Finally, we consider the potential conservation of the molecular pathway we described and discuss future questions surrounding dorsal intercalation. Despite the challenges, dorsal intercalation is a process poised to advance our understanding of cell intercalation during morphogenesis throughout the animal kingdom.

Polarized Rac-dependent protrusions drive epithelial intercalation in the embryonic epidermis of C. elegans.

Cell intercalation is a fundamental, coordinated cell rearrangement process that shapes tissues throughout animal development. Studies of intercalation within epithelia have focused almost exclusively on the localized constriction of specific apical junctions. Another widely deployed yet poorly understood alternative mechanism of epithelial intercalation relies on basolateral protrusive activity. Using the dorsal embryonic epidermis of Caenorhabditis elegans, we have investigated this alternative mechanism using high-resolution live cell microscopy and genetic analysis. We find that as dorsal epidermal cells migrate past one another they produce F-actin-rich protrusions polarized at their extending (medial) edges. These protrusions are controlled by the C. elegans Rac and RhoG orthologs CED-10 and MIG-2, which function redundantly to polarize actin polymerization upstream of the WAVE complex and WASP, respectively. We also identify UNC-73, the C. elegans ortholog of Trio, as a guanine nucleotide exchange factor (GEF) upstream of both CED-10 and MIG-2. Further, we identify a novel polarizing cue, CRML-1, which is the ortholog of human capping Arp2/3 myosin I linker (CARMIL), that localizes to the nonprotrusive lateral edges of dorsal cells. CRML-1 genetically suppresses UNC-73 function and, indirectly, actin polymerization. This network identifies a novel, molecularly conserved cassette that regulates epithelial intercalation via basolateral protrusive activity.

Cell intercalation from top to bottom.

Animal development requires a carefully orchestrated cascade of cell fate specification events and cellular movements. A surprisingly small number of choreographed cellular behaviours are used repeatedly to shape the animal body plan. Among these, cell intercalation lengthens or spreads a tissue at the expense of narrowing along an orthogonal axis. Key steps in the polarization of both mediolaterally and radially intercalating cells have now been clarified. In these different contexts, intercalation seems to require a distinct combination of mechanisms, including adhesive changes that allow cells to rearrange, cytoskeletal events through which cells exert the forces needed for cell neighbour exchange, and in some cases the regulation of these processes through planar cell polarity.

Tropomodulin protects α-catenin-dependent junctional-actin networks under stress during epithelial morphogenesis.

α-catenin is central to recruitment of actin networks to the cadherin-catenin complex, but how such networks are subsequently stabilized against stress applied during morphogenesis is poorly understood. To identify proteins that functionally interact with α-catenin in this process, we performed enhancer screening using a weak allele of the C. elegans α-catenin, hmp-1, thereby identifying UNC-94/tropomodulin. Tropomodulins (Tmods) cap the minus ends of F-actin in sarcomeres. They also regulate lamellipodia, can promote actin nucleation, and are required for normal cardiovascular development and neuronal growth-cone morphology. Tmods regulate the morphology of cultured epithelial cells, but their role in epithelia in vivo remains unexplored. We find that UNC-94 is enriched within a HMP-1-dependent junctional-actin network at epidermal adherens junctions subject to stress during morphogenesis. Loss of UNC-94 leads to discontinuity of this network, and high-speed filming of hmp-1(fe4);unc-94(RNAi) embryos reveals large junctional displacements that depend on the Rho pathway. In vitro, UNC-94 acts in combination with HMP-1, leading to longer actin bundles than with HMP-1 alone. Our data suggest that Tmods protect actin filaments recruited by α-catenin from minus-end subunit loss, enabling them to withstand the stresses of morphogenesis.