Immunohistochemical localization of beta-endorphin-like material in the urodele and anuran amphibian tissues

Proteomic analysis of fibroblastema formation in regenerating hind limbs of Xenopus laevis froglets and comparison to axolotl

Background

To gain insight into what differences might restrict the capacity for limb regeneration in Xenopus froglets, we used High Performance Liquid Chromatography (HPLC)/double mass spectrometry to characterize protein expression during fibroblastema formation in the amputated froglet hindlimb, and compared the results to those obtained previously for blastema formation in the axolotl limb.

Results

Comparison of the Xenopus fibroblastema and axolotl blastema revealed several similarities and significant differences in proteomic profiles. The most significant similarity was the strong parallel down regulation of muscle proteins and enzymes involved in carbohydrate metabolism. Regenerating Xenopus limbs differed significantly from axolotl regenerating limbs in several ways: deficiency in the inositol phosphate/diacylglycerol signaling pathway, down regulation of Wnt signaling, up regulation of extracellular matrix (ECM) proteins and proteins involved in chondrocyte differentiation, lack of expression of a key cell cycle protein, ecotropic viral integration site 5 (EVI5), that blocks mitosis in the axolotl, and the expression of several patterning proteins not seen in the axolotl that may dorsalize the fibroblastema.

Conclusions

We have characterized global protein expression during fibroblastema formation after amputation of the Xenopus froglet hindlimb and identified several differences that lead to signaling deficiency, failure to retard mitosis, premature chondrocyte differentiation, and failure of dorsoventral axial asymmetry. These differences point to possible interventions to improve blastema formation and pattern formation in the froglet limb.

Proteomic analysis of blastema formation in regenerating axolotl limbs

BACKGROUND

Following amputation, urodele salamander limbs reprogram somatic cells to form a blastema that self-organizes into the missing limb parts to restore the structure and function of the limb. To help understand the molecular basis of blastema formation, we used quantitative label-free liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS)-based methods to analyze changes in the proteome that occurred 1, 4 and 7 days post amputation (dpa) through the mid-tibia/fibula of axolotl hind limbs.

RESULTS

We identified 309 unique proteins with significant fold change relative to controls (0 dpa), representing 10 biological process categories: (1) signaling, (2) Ca2+ binding and translocation, (3) transcription, (4) translation, (5) cytoskeleton, (6) extracellular matrix (ECM), (7) metabolism, (8) cell protection, (9) degradation, and (10) cell cycle. In all, 43 proteins exhibited exceptionally high fold changes. Of these, the ecotropic viral integrative factor 5 (EVI5), a cell cycle-related oncoprotein that prevents cells from entering the mitotic phase of the cell cycle prematurely, was of special interest because its fold change was exceptionally high throughout blastema formation.

CONCLUSION

Our data were consistent with previous studies indicating the importance of inositol triphosphate and Ca2+ signaling in initiating the ECM and cytoskeletal remodeling characteristic of histolysis and cell dedifferentiation. In addition, the data suggested that blastema formation requires several mechanisms to avoid apoptosis, including reduced metabolism, differential regulation of proapoptotic and antiapoptotic proteins, and initiation of an unfolded protein response (UPR). Since there is virtually no mitosis during blastema formation, we propose that high levels of EVI5 function to arrest dedifferentiated cells somewhere in the G1/S/G2 phases of the cell cycle until they have accumulated under the wound epidermis and enter mitosis in response to neural and epidermal factors. Our findings indicate the general value of quantitative proteomic analysis in understanding the regeneration of complex structures.

Distribution patterns of the paraneuronal endocrine cells in the skin, gills and the airways of fishes as determined by immunohistochemical and histological methods

The neuro-endocrine cells of fish skin and respiratory surfaces, and their bioactive secretion as far as is known, are reviewed, and compared with similar elements in tetrapods, particularly amphibians. In the skin of teleost fish, immunohistochemistry has shown that Merkel cells react for serotonin, neuron-specific enolase and enkephalins. The pharmacology is not established in dipnoans or lampreys. In some teleosts, neuromasts react for substance P and leu-enkephalins; substance P is also reported from some ampullary organs (electroreceptors). Taste buds of teleosts may react for enkephalin and substance P. Basal cells of taste buds react for serotonin and neuron-specific enolase. Some unicellular skin glands of teleosts express bioactive compounds, including serotonin and some peptides; this ectopic expression is paralleled in amphibian skin glands. The dipnoan Protopterus has innervated pulmonary neuro-endocrine cells in the pneumatic duct region with dense-cored vesicles. In Polypterus and Amia the lungs have serotonin-positive neuro-endocrine cells that are apparently not innervated. In fish gills, a closed type of neuro-endocrine cell reacts for serotonin, an open type for enkephalins and some calcium-binding proteins (calbindin, calmodulin and S-100 protein). The functions of neuro-endocrine cells in fishes await investigation, but it is assumed they are regulatory.

In vivo and in vitro studies on effects of beta-endorphin and naloxone on sex steroids in the water frog, Rana esculenta

The effects of beta-endorphin and its receptor antagonist, naloxone, on progesterone, androgens, and oestradiol-17 beta release in male and female Rana esculenta were studied in vivo and in vitro. In the in vivo experiments the frogs underwent hypophysectomy, gonadectomy or both, or were left intact; the animals were injected with beta-endorphin or naloxone and killed after 15, 30, 90 and 240 min. In the in vitro experiments inter-renal, testis and ovary, all with and without added pituitary, were incubated with beta-endorphin or naloxone for 10, 20, 40 and 80 min. The in vivo and in vitro data from males and females were in agreement. In vivo beta-endorphin increased progesterone in all experimental groups and oestradiol in intact and hypophysectomized frogs, while it decreased androgens in all experimental groups. In vitro beta-endorphin increased progesterone in inter-renal and gonadal tissue, and oestradiol in gonads only, while it decreased androgens in inter-renals and gonads. In vivo and in vitro naloxone induced opposite effects to beta-endorphin. These data suggest that in Rana esculenta, opioids are involved in the modulation of hypothalamo-pituitary-inter-renal and gonadal axes. In particular, the data indicate a direct effect of opioids on inter-renal and gonadal sex steroid production.

In vivo and in vitro effects of β-endorphin and naloxone on corticosterone and cortisol release in male and female water frog, Rana esculenta

1. beta-Endorphin and naloxone effects on corticosterone and cortisol production in male and female Rana esculenta, were studied in vivo and in vitro. 2. The in vivo and in vitro results were in agreement. 3. beta-Endorphin caused a decrease in corticosterone and cortisol release. 4. Naloxone induced an increase in the two corticosteroids at the same times as the decrease caused by beta-endorphin. 5. beta-Endorphin plus naloxone treatment did not change corticosterone and cortisol levels. 6. These results suggest that in Rana esculenta opioids are involved in the regulation of the hypothalamo-pituitary-interrenal axis; in particular, opioids directly modulated interrenal steroidogenesis.

Localization of beta-endorphin-like immunoreactivity in the nervous system of the adult newt, Notophthalmus viridescens

Using indirect immunofluorescence methods, we have localized for the first time in the newt, Notophthalmus viridescens, beta-endorphin (beta-ep)-like immunoreactivity in the neurons of spinal ganglia (SPG), spinal cord (SPC), as well as in the hypothalamic region of the brain. An examination of serially sectioned SPG showed that the beta-ep-positive neurons, cell bodies, and nerve fibers were distributed at all levels of SPG. Peripheral regions of the perikarya of beta-ep-positive SPG neurons exhibited intense staining for beta-ep, the central nuclear region remaining nonreactive. In SPC, brightly staining fibers were seen entering the afferent nociceptive input areas, namely the Lissauer's tracts, substantia gelatinosa, and the dorsal ascending columns. Dot-fiber immunofluorescence pattern was observed throughout the gray matter of SPC representing beta-ep-positive, secondary sensory neurons as well as interneurons. Also, discrete cluster of neurons located deep in the gray matter of SPC stained positively to beta-ep antisera. This study not only demonstrates for the first time the presence of beta-ep like material in the newt, more specifically in SPG and SPC, but also raises the question of a possible link between beta-ep and newt limb regeneration as previous work has shown that SPG support limb regeneration in a denervated-amputated newt forelimb.

Occurrence of immunoreactive Met- and Leu-enkephalin-like peptides in the ovary of the green frog, Rana esculenta

In the present study, we have localized for the first time Met- and Leu-enkephalin-like material in the ovary of the anuran, Rana esculenta, using the indirect immunofluorescence method. The ovaries were sampled during the main representative phases of the annual reproductive cycle of the frog, living in a mountain pond (Colfiorito, Umbria at 820 m a.s.l.). Strong immunoreactivity to Met- and Leu-enkephalin antisera was observed in the follicle cells of the granulosa layer of vitellogenic oocytes; moreover, during this phase, immunofluorescent materials were also radially localized in the cytoplasm and in the perinuclear zone. The mature oocytes showed Met- and Leu-enkephalin-like immunostaining in the thecal layer and in several granules scattered in the peripheral zone of the yolk. The different pattern of Leu- and Met-enkephalin-like immunoreactivity in the frog ovary parallels and complements the changes occurring in the reproductive (May) and in the vitellogenetic (September) phases during the ovarian cycle. Consequently, these findings strongly support the hypothesis for a local synthesis of these peptides in the ovary and suggest their possible involvement in the control of ovarian function.

A search for immunoreactive substance P and other neural peptides in the limb regenerate of the newt Notophthalmus viridescens

Immunochemical studies demonstrate that the undecapeptide substance P (SP) may be detected by radioimmunoassay in newt limb regenerates and that SP is localized in the blastemal epidermis by immunofluorescence and peroxidase-antiperoxidase staining. Immunoreactive SP is predominantly distributed at the periphery of epidermal cells, suggesting the presence of SP binding sites on the cell surface; the basal germinative layer of the epidermis and blastemal mesenchyme cells remain unreactive. The pattern of SP immunoreactivity in the blastema was compared with that of four other tachykinin-family peptides (eledoisin, kassinin, substance K, and neuromedin K) and with three non-tachykinin neural peptides (bombesin, neurotensin, and metenkephalin). With the exception of neurotensin, which showed weak staining in the basal layer but an absence in the peripheral layers of the epidermis, none of the peptides examined exhibited immunoreactivity in the blastema epidermis comparable to that of SP.