Arne Christensen, PhD
Associate Professor of Biology
Anna Maria College
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Christensen research group, 2018

Current areas of research:
1) Cellular biology of the integument of the Cladocera (water fleas)
2) Osmoregulatory physiology of euryhaline fishes

Students interested in collaborating on research projects (see below) should email
Dr. Christensen - achristensen "at"

F-actin bundles in the carapace epithelia of Daphnia magna.
In the left panels F-actin is shown in white, in the right panels F-actin (red) is shown with DNA (blue) and membranous organelles (green). Upper panels are an enface view, lower panels are confocal 3D reconstructions. Click image for higher resolution.
Examples of ongoing, or potential, projects focusing on the integument of the Cladocera

1. Pharmacological characterization of large filamentous actin (F-actin) bundles in the carapace of Daphnia magna.
This project will examine the impacts of actin depolymerizing drugs, cytochalasin D and latrunculin A, on the F-actin bundles, thereby shedding light on their structure and function.

2. Cell cycle dynamics during development in the carapace of D. magna.
This project will use time-lapse microscopy of histone H2B-GFP transgenic D. magna to characterize cell cycle dynamics in D. manga carapace epithelia, which are thought to be composed of diploid and polyploid cells.

Fish osmoregulatory physiology

Fish in freshwater or seawater face different physiological challenges. In freshwater, diffusive ion loss and water gain must be counteracted by active ion uptake and retention, and dilute urine production. Conversely, in seawater, diffusive ion gain and water loss must be countered by active ion extrusion and increased water consumption. For fishes that remain in freshwater or seawater, the mechanisms that maintain ion homeostasis may be relatively static. On the other hand, fish which can adapt to freshwater and seawater, termed euryhaline, must do so by regulating the expression of proteins important for ion-transport and trans-epithelial resistance in tissues that are critical for maintaining ion-homeostasis, such as the gill.
Ionocytes (see top panels, white/orange cells) are a class of highly specialized cells found in the gill and larval integument. These cells are a major site of ion transport between a fish and the aqueous environment. The morphology, arrangement (see left, freshwater-FW vs. seawater-SW) and expression profiles of these cells are dependent on environmental salinity. We are interested in developing a clearer understanding of how environmental factors, such as salinity, impact the origin and fate of these cells, as well the expression profiles of proteins important for ion-homeostasis, such as the Na+/K+-ATPase and Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). The more we understand about how cells, and in turn, animals maintain ion-homeostasis, the better equipped we will be to determine how these processes may be impaired by environmental contaminants and changing environmental conditions.
Site by: Arne Christensen, PhD
Anna Maria College
50 Sunset Lane - Box 84
Paxton, MA 01612