Tyrosine phosphatase inhibitor triggers rodlet cell discharge in sunfish scale epidermis cultures

Abstract

DePasquale, JA., 2014. Tyrosine phosphatase inhibitor triggers rodlet cell discharge in sunfish scale epidermis cultures. -Acta Zoologica (Stockholm) 95: 209-219.Epidermal rodlet cells were evaluated after treatment with the tyrosine phosphatase inhibitor pervanadate. Treatment of sunfish explant cell cultures with the inhibitor triggered a contraction of the rodlet cells and expulsion of cell contents. Time-lapse video differential interference contrast (DIC) microscopy was used to evaluate rodlet cell contraction and rodlet discharge. Three general steps in pervanadate triggered discharge were identified. First the rodlet cell undergoes a constriction of the midsection. Constriction is followed by a rapid forward movement of rodlets and sacs to the apical end of cell, culminating in discharge of rodlets and other cellular contents, including the nucleus. A ring-shaped structure around the apical pore was identified with DIC microscopy. Fluorescent-labeled phalloidin and antibodies to alpha-actinin and phosphotyrosine strongly stained the apical ring. A diffuse granular staining for both antibodies was also observed throughout the fibrous capsule. The results suggest that tyrosine kinases play a role in rodlet cell contraction. Alpha-actinin is a known substrate for tyrosine kinases and is a potential target for triggering rodlet cell contraction and rodlet ejection. Modification of alpha-actinin tyrosines could also be a mechanism for regulating the structural integrity of the fibrous capsule.

Tropomyosin and alpha‐actinin in teleost rodlet cells

“…Smooth muscle‐like arrangement of thin and thick filaments, likely actin and myosin, was first described in ultrastructural studies of the fibrous capsule (Leino, 1974, 2002) leading to the suggestion that the cortex undergoes a smooth muscle‐like contraction to expel rodlets (Barber et al., 1979; Kramer & Potter, 2002; Leino, 1974). Filamentous actin and alpha‐actinin were later directly localized to the cortex, supporting the idea that rodlet cells are enveloped by a layer of contractile proteins which are responsible for ejecting the cytoplasmic rodlets (DePasquale, 2014a,b). Indeed, the rodlets are ejected through an apical pore upon contraction of the cell cortex (DePasquale, 2014b; Schmachtenberg, 2007).…”

“…Filamentous actin and alpha‐actinin were later directly localized to the cortex, supporting the idea that rodlet cells are enveloped by a layer of contractile proteins which are responsible for ejecting the cytoplasmic rodlets (DePasquale, 2014a,b). Indeed, the rodlets are ejected through an apical pore upon contraction of the cell cortex (DePasquale, 2014b; Schmachtenberg, 2007).…”

“…F‐actin and alpha‐actinin are found in the cortex, while microtubules appear to be restricted to the cell interior (DePasquale, 2014a) or may be associated with the interior face of the capsule (Hawkins, 1984). Protein‐tyrosine kinases and phosphatases are also present in the cortex based on increased phosphotyrosine staining in the cell periphery in response to tyrosine phosphatase inhibition (DePasquale, 2014b). In the present study, rodlet cells in both whole scales or epidermal explants were examined for the presence of tropomyosin in the cortex.…”

“…In the present study, rodlet cells in both whole scales or epidermal explants were examined for the presence of tropomyosin in the cortex. In addition, the distribution of alpha‐actinin in rodlet cells (DePasquale, 2014b) was revisited using a modified immunostaining protocol. Alpha‐actinin was localized to the fibrous capsule predominantly in a partially fibrillar pattern reminiscent of smooth muscle dense plaques.…”

Microanalysis of Fish Ovarian Follicular Atresia: A Possible Synergic Action of Somatic and Immune Cells

“…These results indicated that these cells have a role in atresia. DePasquale (2014) reported that rodlet cells were enriched for phosphotyrosine, suggesting that active phosphatases and protein tyrosine kinases are found in this structure. Tyrosine kinase and phosphatase activity have been implicated in some aspects of smooth muscle contraction.…”