Another way that flies sense temperature

If you remember your (bio-)physical chemistry, you’ll remember that most proteins are temperature sensitive. But which ones acts as the sensors that drive behavior in higher organisms? The Garrity Lab at Brandeis has been working on thermosensation in Drosophila, and previous work has implicated the channel protein TRPA1 as a key mediator of temperature preference and thermotaxis,  In a new paper in Nature, members of the Garrity lab working in collaboration with the Griffith and Theobald have have identified another protein, GR28B(D), a member of the family of gustatory receptor proteins, as another behaviorally important temperature sensor, involved in rapid avoidance of high temperatures. Authors on the paper include postdocs Lina Ni (lead author) and Peter Bronk, grad students April Lowell (Mol. Cell Biology) and Vincent Panzano (PhD ’13, Neuroscience), undergraduate Juliette Flam ’12, and technician Elaine Chang ’08.

  • Ni L, Bronk P, Chang EC, Lowell AM, Flam JO, Panzano VC, Theobald DL, Griffith LC, Garrity PA. A gustatory receptor paralogue controls rapid warmth avoidance in Drosophila. Nature. 2013.
  • story at BrandeisNOW


How does the brain decide whether you like what you eat?

When we encounter a taste, we appreciate both its chemosensory properties and its palatability—the degree to which the taste is pleasurable or aversive. Recent work suggests that the processing of this complex taste experience may involve coordination between multiple brain areas. Dissecting these interactions help understand the organization and working of the taste system.

F4.largeThe lateral hypothalamus (LH) is a region of the brain important for feeding. In a rodent, damage the LH, and the rodent may starve itself to death; stimulate it, and you get a curious mix of voracious eating and expressions of disgust over what is being eaten. Such data suggest that LH plays a complex game of balancing escape and avoidance, palatability and aversion, during the evaluation of a taste stimulus. Little is known, however, about how neurons in LH actually respond to tastes of different valences.

Brandeis postdocs Jennifer Li and Takashi Yoshida. undergraduate Kevin Monk ’13, and Associate Professor of Psychology Don Katz have recently published a study of neuronal reponses in LH in the Journal of Neuroscience. They have shown that taste-responsive neurons in LH break neatly down into two groups–one that responds preferentially to palatable tastes and one to aversive tastes. Virtually every taste neuron in LH could be identified as a palatable- or aversive-preferring neuron. In addition, even without considering the specific tastes to which a particular neuron responded, these two groups of neurons could be differentiated according to their baseline firing rate, shape of response, and tuning width. While these neurons were spatially intermingled, several pieces of data (functional connectivity analysis, relationship to responses in amygdala and cortex) suggest that they are parts of distinct neural circuits. These results offer insights into the multiple feeding-related processes that LH manages, and how the hypothalamus’ role in these processes might be related to its connection to other parts of the taste system.

Li JX, Yoshida T, Monk KJ, Katz DB. Lateral Hypothalamus Contains Two Types of Palatability-Related Taste Responses with Distinct Dynamics. J Neurosci. 2013;33(22):9462-73.

Cryo-electron tomography and the structure of doublet microtubules

In a new paper in PNAS entitled “Cryo-electron tomography reveals conserved features of doublet microtubules“, Assistant Professor of Biology Daniela Nicastro and coworkers describe in striking new detail the structure and organization of the doublet microtubules (DMTs), the most conserved feature of eukaryotic cilia and flagella.

Cilia and flagella are thin, hair-like appendages on the surface of most animal and lower plant cells, which use these organelles to move, and to sense the environment. Defects in cilia and flagella are known to cause disease and developmental disorders, including polycystic kidney disease, respiratory disease, and neurological disorders. An essential feature of these organelles is the presence of nine outer DMTs (hollow protein tubes) that form the cylindrical core of the structure known as the axoneme. The doublet microtubule is formed by tubulin protofilaments and other structural proteins, which provide a scaffold for the attachment of dynein motors (that drive ciliary and flagellar motility) and regulatory components in a highly specific and ordered manner.

To address long-standing questions and controversies about the assembly, stability, and detailed structure of DMTs , the Nicastro lab used a high-resolution imaging technique, cryo-electron microscope tomography (cryo-ET), to probe the structure of DMTs from Chlamydomonas (single-celled algae) and sea urchin sperm flagella. Cryo-ET involves:

  1. rapid freezing of the sample to cryo-immobilize the molecules without forming ice crystals,
  2. tilting the specimen in the electron microscope to collect ~70 different views from +65° to –65°,
  3. computational alignment of the views to calculate a tomogram (a three-dimensional reconstruction of the imaged sample), and
  4. computational averaging of repeating structures in the tomogram to reduce noise and increase resolution.

Cryo-ET provided the necessary resolution to show that the B-tubules of DMTs are composed of 10 protofilaments, not 11, and that the inner and outer junctions between the A- and B-tubules are fundamentally different (see figure). The outer junction, crucial for the initial formation of the DMT, appears to be formed by interactions between the tubulin subunits of three protofilaments with unusual tubulin interfaces, but one of these protofilaments does not fit with the conventionally accepted orientation for tubulin protofilaments. This outer junction is important physiologically, as shown by mutations affecting the usual pattern of posttranslational modifications of tubulin. In contrast, the inner junction is not formed by direct interactions between tubulin protofilaments. Instead, a ladder-like structure that is clearly thinner than tubulin connects protofilaments of the A- and B-tubules.

The level of detail also allowed the Nicastro lab to show that the recently discovered microtubule inner proteins (MIPs) located within the A- and B-tubules are more complex than previously thought. MIPs 1 and 2 are both composed of alternating small and large subunits recurring every 16 and/or 48 nm along the inner A-tubule wall. MIP 3 forms small protein arches connecting the two B-tubule protofilaments closest to the inner junction, but does not form the inner junction itself. MIP 4 is associated with the inner surface of the A-tubule along the partition protofilaments, i.e., the five protofilaments of the A-tubule bounded by the two junctions with the B-tubule.

The Nicastro lab plans to build on this foundation in future work on the molecular assembly and stability of the doublet microtubule and axoneme, and hope to use it to elucidate molecular mechanisms of ciliary and flagellar motility and signal transduction in normal and disease states.

Other authors on the paper include Brandeis postdocs Xiaofeng Fu and Thomas Heuser, Brandeis undergrad Alan Tso (’10), and collaborators Mary Porter and Richard Linck from the University of Minnesota.

Older Adults are Better at Spotting Fake Smiles

Studies of aging and the ability to recognize others’ emotional states tend to show that older adults are worse than younger adults at recognizing facial expressions of emotion, a pattern that parallels findings on non-social types of perception. Most of the previous research focused on the recognition of negative emotions such as anger and fear. In a study “Recognition of Posed and Spontaneous Dynamic Smiles in Young and Older Adults” recently published in Psychology and Aging, Derek Isaacowitz’s Emotion Laboratory set out to investigate possible aging effects in recognizing positive emotions; specifically, the ability to discriminate between posed or “fake” smiles and genuine smiles. They video-recorded different types of smiles (posed and genuine) from younger adults (mean age = 22) and older adults (mean age = 70). Then we showed those smiles to participants who judged whether the smiles were posed or genuine.

Across two studies, older adults were actually better at discriminating between posed and genuine smiles compared to younger adults. This is one of the only findings in the social perception literature suggesting an age difference favoring older individuals. One plausible reason why older adults may be better at distinguishing posed and spontaneous smiles is due to their greater experience in making these nuanced social judgments across the life span; this may then be a case where life experience can offset the effects of negative age-related change in cognition and perception.

This was the first known study to present younger and older adult videotaped smiles to both younger and older adult participants; using dynamic stimuli provides a more ecologically valid method of assessing social perception than using static pictures of faces. The findings are exciting because they suggest that while older adults may lose some ability to recognize the negative emotions of others, their ability to discriminate posed and genuine positive emotions may remain intact, or even improve.

The Emotion Laboratory is located in the Volen Center at Brandeis. First author Dr. Nora Murphy (now Assistant Professor of Psychology at Loyola Marymount University) conducted the research as a postdoctoral research fellow, under the supervision of Dr. Isaacowitz, and second author Jonathan Lehrfeld (Brandeis class of 2008) completed his Psychology senior honors thesis as part of the project. The research was funded by the National Institute of Aging.

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