Tail Fin Tissue Research Articles

A New Investigation to Discriminate Sexes in Alive Nile Tilapia (Oreochromis niloticus) Using Cyp19a1a and Dmrt1 Gene Expression in Tail Fin Tissues

The Nile Tilapia (Oreochromis niloticus), a gonochoristic teleost fish with a XX/XY sex-determination system, is an ideal model for investigating gonadal sex differentiation. During gonadal differentiation, the expression of cyp19a1a in XX gonads and dmrt1 in XY gonads are required for undifferentiated tissues to develop into ovary or testis. In this study, quantitative real-time RT-PCR assessed the expression of cyp19a1a and dmrt1 genes in gonads and tail fin tissues. Differences in gene expression mean among sexually differentiated fish were analyzed using two-way analysis of variance (ANOVA) and validation of mixed model using discriminant analysis (DA) for morphometric traits and the gene expression in gonads and tail fin tissues used to validate and utilize them in discriminating sexes in sex-differentiated Nile Tilapia fish. The results revealed that, cyp19a1a gene expression in female ovaries was more significant than dmrt1 in male testis. In the other hand, the dmrt1 gene expression in the tail fin was higher in males than females. Both, cyp19a1a and dmrt1 genes, can discriminate fish sexes by 100% by using their expression in tail fin tissues. In conclusion, the cyp19a1a and dmrt1 genes could be used as a genetic marker to discriminate between the Nile Tilapia sexes, whereas used as an indicator for ovarian or testis differentiation in sexually differentiated Nile Tilapia using tail fin tissues. It is worth mentioning that this is the first investigation for using cyp19a1a and dmrt1 genes from Nile Tilapia tail fin tissues in sex determination.

A Novel Investigation for Early Sex Determination in Alive Adult European Seabass (Dicentrarchus labrax) Using cyp19a1a, dmrt1a, and dmrt1b Genes Expression in Tail Fin tissues

This study is the first investigation for using sex-related gene expression in tail fin tissues of seabass as early sex determination without killing the fish. The European seabass (Dicentrarchus labrax) is gonochoristic and lacks distinguishable sex chromosomes, so, sex determination is referred to molecular actions for some sex-related genes on autosomal chromosomes which are well known such as cyp19a1a, dmrt1a, and dmrt1b genes which play crucial role in gonads development and sex differentiation. cyp19a1a is expressed highly in females for ovarian development and dmrt1a and dmrt1b are for testis development in males. In this study, we evaluated the difference in the gene expression levels of studied genes by qPCR in tail fins and gonads. We then performed discriminant analysis (DA) using morphometric traits and studied gene expression parameters as predictor tools for fish sex. The results revealed that cyp19a1a gene expression was significantly higher in future females’ gonads and tail fins (p ≥ 0.05). Statistically, cyp19a1a gene expression was the best parameter to discriminate sex even the hit rate of any other variable by itself could not correctly classify 100% of the fish sex except when it was used in combination with cyp19a1a. In contrast, Dmrt1a gene expression was higher in males than females but there were difficulties in analyzing dmrt1a and dmrt1b expressions in the tail because levels were low. So, it could be used in future research to differentiate and determine the sex of adult fish using the cyp19a1a gene expression marker without killing or sacrificing fish.

Biocompatible recombinant type III collagen enhancing skin repair and anti-wrinkle effects.

Treating sunburn and other UV-induced skin damage issues remains a significant challenge in the field of dermatology. In this study, we synthesized a highly bioactive recombinant type III collagen (rCol III) to accelerate the healing of UV-damaged skin. The high-purity rCol III demonstrated excellent biocompatibility and bioactivity, significantly promoting the adhesion, proliferation, and migration of HFF-1 cells. In a mouse UV-damage model, Combo evaluations demonstrated that rCol III contributed to restore transepidermal water loss (TEWL) values of UV-damaged skin to normal levels. Histological analysis further confirmed that rCol III substantially accelerated skin repair by enhancing collagen regeneration. Additionally, rCol III facilitated the regeneration of zebrafish tail fin tissue and alleviated shrinkage caused by excessive UV exposure. The biocompatible and bioactive rCol III offers a novel strategy for treating UV-induced skin damage, holding immense potential for applications in skin tissue engineering.

Using Zebrafish to Dissect the Interaction of Mycobacteria with the Autophagic Machinery in Macrophages.

Existing drug treatment against tuberculosis is no match against the increasing number of multi-drug resistant strains of its causative agent, Mycobacterium tuberculosis (Mtb). A better understanding of how mycobacteria subvert the host immune defenses is crucial for developing novel therapeutic strategies. A potential approach is enhancing the activity of the autophagy machinery, which can direct bacteria to autophagolysosomal degradation. However, the interplay specifics between mycobacteria and the autophagy machinery must be better understood. Here, we analyzed live imaging data from the zebrafish model of tuberculosis to characterize mycobacteria-autophagy interactions during the early stages of infection in vivo. For high-resolution imaging, we microinjected fluorescent Mycobacterium marinum (Mm) into the tail fin tissue of zebrafish larvae carrying the GFP-LC3 autophagy reporter. We detected phagocytosed Mm clusters and LC3-positive Mm-containing vesicles within the first hour of infection. LC3 associations with these vesicles were transient and heterogeneous, ranging from simple vesicles to complex compound structures, dynamically changing shape by fusions between Mm-containing and empty vesicles. LC3-Mm-vesicles could adopt elongated shapes during cell migration or alternate between spacious and compact morphologies. LC3-Mm-vesicles were also observed in cells reverse migrating from the infection site, indicating that the autophagy machinery fails to control infection before tissue dissemination.

Dioctyl Sodium Sulfosuccinate as a Potential Endocrine Disruptor of Thyroid Hormone Activity in American bullfrog, Rana (Lithobates) catesbeiana, Tadpoles.

The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are required to regulate complex developmental processes in vertebrates and are highly sensitive to endocrine-disrupting compounds. Previous studies demonstrate that dioctyl sodium sulfosuccinate (DOSS), a common constituent of pharmaceuticals, cosmetics, and food products, disrupts canonical signaling of adipocyte differentiation by binding a nuclear hormone receptor in the same superfamily as thyroid hormone (TH) receptors. The present study was designed to determine whether DOSS is capable of disrupting TH signaling using the American bullfrog, Rana (Lithobates) catesbeiana-a cosmopolitan frog species that undergoes TH-dependent metamorphosis to transition from an aquatic tadpole to a terrestrial juvenile frog. Premetamorphic R. catesbeiana tadpoles were injected with 2pmol/g body weight T3 or 10pmol/g body weight T4 to induce precocious metamorphosis, then exposed for 48h to environmentally or clinically relevant DOSS concentrations (0.5, 5, and 50mg/L). Gene expression of three classical TH-responsive targets (thra, thrb, and thibz) was measured in tadpole liver and tail fin tissue through reverse transcription quantitative polymerase chain reaction (RT-qPCR). DOSS disrupted gene expression in liver and tail fin tissue at all three concentrations tested but the patterns of expression differed by tissue, gene transcript, and TH treatment status. To our knowledge, this is the first demonstration that DOSS can alter TH signaling. Further exploration into DOSS disruption of TH signaling is warranted, because exposure may affect other TH-dependent processes, such as salmon smoltification and perinatal human development.

Human health risk assessment of heavy metals via consumption of commercial marine fish (Thunnus albacares, Euthynnus affinis, and Katsuwonus pelamis) in Oman Sea

This study was performed to determine the concentrations of copper (Cu), zinc (Zn), and lead (Pb) in the gill, liver, muscle, and tail fin tissues of Euthynnus affinis, Katsuwonus pelamis, and Thunnus albacares from Oman Sea. All samples were analyzed using a flame atomic absorption spectrophotometer and the results were expressed as μgg-1 dry weight. Metal concentrations were significantly higher in the liver than other tissues in three species (with some exceptions) (p < 0.05). The concentrations of metal accumulation in tissues of tuna species followed the Zn > Cu > Pb. Correlation matrix and principal component analysis (PCA) revealed that Zn and Pb have anthropogenic sources. Estimated daily intake (EDI) in three tuna species for heavy metals were below the tolerable daily intake (TDI). Also, the mean target hazard quotient (THQ) based on studied metals in three tuna species was below 1, which suggests that consumption of these fish can be safe for human health in the Oman Sea. Graphical Abstract .

HDAC Regulates Transcription at the Outset of Axolotl Tail Regeneration

Tissue regeneration is associated with complex changes in gene expression and post-translational modifications of proteins, including transcription factors and histones that comprise chromatin. We tested 172 compounds designed to target epigenetic mechanisms in an axolotl (Ambystoma mexicanum) embryo tail regeneration assay. A relatively large number of compounds (N = 55) inhibited tail regeneration, including 18 histone deacetylase inhibitors (HDACi). In particular, romidepsin, an FDA-approved anticancer drug, potently inhibited tail regeneration when embryos were treated continuously for 7 days. Additional experiments revealed that romidepsin acted within a very narrow, post-injury window. Romidepsin treatment for only 1-minute post amputation inhibited regeneration through the first 7 days, however after this time, regeneration commenced with variable outgrowth of tailfin tissue and abnormal patterning. Microarray analysis showed that romidepsin altered early, transcriptional responses at 3 and 6-hour post-amputation, especially targeting genes that are implicated in tumor cell death, as well as genes that function in the regulation of transcription, cell differentiation, cell proliferation, pattern specification, and tissue morphogenesis. Our results show that HDAC activity is required at the time of tail amputation to regulate the initial transcriptional response to injury and regeneration.

Comparative Analysis of Tissue and Cell Cycle on the Far Eastern Catfish, Silurus asotus between Diploid and Triploid.

ABSTRACTThe influence of triploidization on histological characteristics of retina, trunk kidney, liver and midgut tissue, and cell cycle of tail fin and gill tissue in far eastern catfish, Silurus asotus were analyzed. In the infertile triploid fish, the nucleus and/or cell size of secondary proximal tubule cells of trunk kidney, hepatocyte and midgut epithelium are much larger than those of the corresponding cells in the diploid fish (P<0.05). However, triploid tissue showed fewer number of outer nuclear layer in retina and nuclei in secondary proximal tubule of trunk kidney than those for diploid tissue. The mean percentages of the Gl-, the S- and the G2+M-phase fractions were 92.5%, 3.2% and 4.3% in tail fin tissue of diploid, and 93.4%, 2.6% and 4.0% in those of triploid, respectively. There were no significant differences in the percentages of each cell cycle fraction between diploid and triploid. The mean percentages of each phase fractions were 75.1%, 11.1% and 13.8% in gill tissue of diploid and 85.2%, 8.9% and 5.9% in those of triploid, respectively. The differences of cell cycle between tail fin tissue and gill tissue were statistically significant in diploid and triploid (P<0.05). Also, the differences between diploid and triploid were statistically significant in tail fin tissue and gill tissue (P<0.05). Cyclin D1 and cyclin E expressions were not significantly difference between gill tissue and tail fin tissue, and protein expressions of induced triploid were higher than those of diploid. Results from this study suggest that some characteristics in the triploid exhibiting larger cell and nucleus size with fewer number of cell than diploid can be used as an indicator in the identification of triploidization and ploidy level in far eastern catfish.

Chronic sublethal exposure to silver nanoparticles disrupts thyroid hormone signaling during Xenopus laevis metamorphosis

Nanoparticles (NPs) are engineered in the nanoscale (<100nm) to have unique physico-chemical properties from their bulk counterparts. Nanosilver particles (AgNPs) are the most prevalent NPs in consumer products due to their strong antimicrobial action. While AgNP toxicity at high concentrations has been thoroughly investigated, the sublethal effects at or below regulatory guidelines are relatively unknown. Amphibian metamorphosis is mediated by thyroid hormone (TH), and initial studies with bullfrogs (Rana catesbeiana) indicate that low concentrations of AgNPs disrupt TH-dependent responses in premetamorphic tadpole tailfin tissue. The present study examined the effects of low, non-lethal, environmentally-relevant AgNP concentrations (0.018, 0.18 or 1.8μg/L Ag; ∼10nm particle size) on naturally metamorphosing Xenopus laevis tadpoles in two-28 day chronic exposures beginning with either pre- or prometamorphic developmental stages. Asymmetric flow field flow fractionation with online inductively coupled plasma mass spectrometry and nanoparticle tracking analysis indicated a mixture of single AgNPs with homo-agglomerates in the exposure water with a significant portion (∼30–40%) found as dissolved Ag. Tadpoles bioaccumulated AgNPs and displayed transient alterations in snout/vent and hindlimb length with AgNP exposure. Using MAGEX microarray and quantitative real time polymerase chain reaction transcript analyses, AgNP-induced disruption of five TH-responsive targets was observed. The increased mRNA abundance of two peroxidase genes by AgNP exposure suggests the presence of reactive oxygen species even at low, environmentally-relevant concentrations. Furthermore, differential responsiveness to AgNPs was observed at each developmental stage. Therefore, low concentrations of AgNPs had developmental stage-specific endocrine disrupting effects during TH-dependent metamorphosis.

Evaluation of the effects of titanium dioxide nanoparticles on cultured Rana catesbeiana tailfin tissue

Nanoparticles (NPs), materials that have one dimension less than 100 nm, are used in manufacturing, health, and food products, and consumer products including cosmetics, clothing, and household appliances. Their utility to industry is derived from their high surface-area-to-volume ratios and physico-chemical properties distinct from their bulk counterparts, but the near-certainty that NPs will be released into the environment raises the possibility that they could present health risks to humans and wildlife. The thyroid hormones (THs), thyroxine, and 3,3′,5-triiodothyronine (T3), are involved in development and metabolism in vertebrates including humans and frogs. Many of the processes of anuran metamorphosis are analogous to human post-embryonic development and disruption of TH action can have drastic effects. These shared features make the metamorphosis of anurans an excellent model for screening for endocrine disrupting chemicals (EDCs). We used the cultured tailfin (C-fin) assay to examine the exposure effects of 0.1–10 nM (~8–800 ng/L) of three types of ~20 nm TiO2 NPs (P25, M212, M262) and micron-sized TiO2 (μ TiO2) ±10 nM T3. The actual Ti levels were 40.9–64.7% of the nominal value. Real-time quantitative polymerase chain reaction (QPCR) was used to measure the relative amounts of mRNA transcripts encoding TH-responsive THs receptors (thra and thrb) and Rana larval keratin type I (rlk1), as well as the cellular stress-responsive heat shock protein 30 kDa (hsp30), superoxide dismutase (sod), and catalase (cat). The levels of the TH-responsive transcripts were largely unaffected by any form of TiO2. Some significant effects on stress-related transcripts were observed upon exposure to micron-sized TiO2, P25, and M212 while no effect was observed with M262 exposure. Therefore, the risk of adversely affecting amphibian tissue by disrupting TH-signaling or inducing cellular stress is low for these compounds relative to other previously-tested NPs.

Differential expression of heat-shock proteins in F2 offspring from F1 hybrids produced between thermally selected and normal rainbow trout strains

Rainbow trout Oncorhynchus mykiss is a cold-water aquaculture species, and a thermally selected strain has been developed by multigenerational high-temperature breeding in Japan. We examined the expression of heat-shock proteins as candidates responsible for thermotolerance in rainbow trout using F2 offspring from F1 hybrids produced between thermally selected and normal strains. From F2 offspring, two groups were selected for western blot analysis, namely, low- and high-thermotolerance groups (times to loss of equilibrium were <30 and ≥60 min, respectively). We demonstrated that the expression levels of Hsp70, Hsp60, and Hsp40 in tail fin tissues were significantly higher in the individuals with high thermotolerance than in those with low thermotolerance under non-heat-shock conditions. In particular, Hsp70 was expressed only in the individuals with high thermotolerance. These results suggest that Hsp70 is a major protein responsible for conferring thermotolerance in rainbow trout.

Influence of Nitrate and Nitrite on Thyroid Hormone Responsive and Stress-Associated Gene Expression in Cultured Rana catesbeiana Tadpole Tail Fin Tissue

Nitrate and nitrite are common aqueous pollutants that are known to disrupt the thyroid axis. In amphibians, thyroid hormone (TH)-dependent metamorphosis is affected, although whether the effect is acceleration or deceleration of this developmental process varies from study to study. One mechanism of action of these nitrogenous compounds is through alteration of TH synthesis. However, direct target tissue effects on TH signaling are hypothesized. The present study uses the recently developed cultured tail fin biopsy (C-fin) assay to study possible direct tissue effects of nitrate and nitrite. Tail biopsies obtained from premetamorphic Rana catesbeiana tadpoles were exposed to 5 and 50 mg/L nitrate (NO3–N) and 0.5 and 5 mg/L nitrite (NO2–N) in the absence and presence of 10 nM T3. Thyroid hormone receptor β (TRβ) and Rana larval keratin type I (RLKI), both of which are TH-responsive gene transcripts, were measured using quantitative real time polymerase chain reaction. To assess cellular stress which could affect TH signaling and metamorphosis, heat shock protein 30, and catalase (CAT) transcript levels were also measured. We found that nitrate and nitrite did not significantly change the level of any of the four transcripts tested. However, nitrate exposure significantly increased the heteroscedasticity in response of TRβ and RLKI transcripts to T3. Alteration in population variation in such a way could contribute to the previously observed alterations of metamorphosis in frog tadpoles, but may not represent a major mechanism of action.

A zebrafish model for nevus regeneration

A zebrafish model for nevus regeneration

Triclosan and Anuran Metamorphosis: No Effect on Thyroid-Mediated Metamorphosis in Xenopus laevis

Nieuwkoop and Faber stage 51 Xenopus laevis larvae were exposed for 21 days to four different concentrations of triclosan (TCS): <0.2 (control), 0.6, 1.5, 7.2, or 32.3 microg TCS/l. Primary endpoints were survival, hind limb length, body length (whole; snout to vent), developmental stage, wet whole body weight, and thyroid histology. Thyroid hormone (TH) concentrations were determined in whole thyroid and plasma samples from stage-matched exposure day 21 specimens. TH receptor-beta (TRbeta) expression was measured in stage-matched tail fin tissue samples collected at exposure days 0 and 21. Reduced larval growth occurred at exposure day 21 with 1.5 microg/l treatment. Larval developmental stage at exposure day 21 was not significantly different from controls based on observed parameters. Thyroid histology was not affected by TCS, and thyroxine (T4) levels in thyroid glands or plasma were not different from controls. A concentration-dependent increase in TRbeta expression in exposure day 21 larvae was not detected. However, increased expression was found in stage-matched larvae exposed to 1.5 or 7.2 microg TCS/l. Our study indicates that environmentally relevant TCS concentrations do not alter the normal course of thyroid-mediated metamorphosis in this standard anuran model.

Perturbation of DNA repair gene expression due to interspecies hybridization

The effect of interspecies hybridization on gene regulation was examined using real-time polymerase chain reaction (RT-PCR) to measure the expression of five base-excision repair genes in brain, eye, gill, liver, and tailfin tissues from Xiphophorus parental species and F 1 hybrids. Relative mRNA levels of uracil N-glycosylase ( Ung), Apurinic/apyrimidinic endonuclease ( Ape1), polymerase-β ( Polb), flap endonuclease ( Fen1), and DNA ligase ( Lig1) were measured in three parental Xiphophorus species ( X. maculatus Jp 163 B, X. helleri Sarabia, and X. andersi andC) and in two interspecies F 1 hybrids, the Sp-helleri hybrid ( X. maculatus Jp 163 B × X. helleri Sarabia) and the Sp-andersi hybrid ( X. maculatus Jp 163 B × X. andersi) to identify genes that undergo changes in expression levels upon interspecies hybridization. Significant differences in gene expression were observed between parental animals and their respective F 1 hybrids in both interspecies crosses. Generally, marked increases in DNA repair gene mRNA levels were observed across all tissues in F 1 hybrid animals from the Sp-helleri cross compared to either X. maculatus or X. helleri parents. In contrast, the Sp-andersi F 1 hybrid animals generally exhibited decreased base-excision repair gene expression, although this trend was more specific to individual tissues than observed for Sp-helleri hybrids.

Maternally controlled (beta)-catenin-mediated signaling is required for organizer formation in the zebrafish.

We have identified and characterized a zebrafish recessive maternal effect mutant, ichabod, that results in severe anterior and dorsal defects during early development. The ichabod mutation is almost completely penetrant, but exhibits variable expressivity. All mutant embryos fail to form a normal embryonic shield; most fail to form a head and notochord and have excessive development of ventral tail fin tissue and blood. Abnormal dorsal patterning can first be observed at 3.5 hpf by the lack of nuclear accumulation of (beta)-catenin in the dorsal yolk syncytial layer, which also fails to express bozozok/dharma/nieuwkoid and znr2/ndr1/squint. At the onset of gastrulation, deficiencies in expression of dorsal markers and expansion of expression of markers of ventral tissues indicate a dramatic alteration of dorsoventral identity. Injection of (beta)-catenin RNA markedly dorsalized ichabod embryos and often completely rescued the phenotype, but no measurable dorsalization was obtained with RNAs encoding upstream Wnt pathway components. In contrast, dorsalization was obtained when RNAs encoding either Bozozok/Dharma/Nieuwkoid or Znr2/Ndr1/Squint were injected. Moreover, injection of (beta)-catenin RNA into ichabod embryos resulted in activation of expression of these two genes, which could also activate each other. RNA injection experiments strongly suggest that the component affected by the ichabod mutation acts on a step affecting (beta)-catenin nuclear localization that is independent of regulation of (beta)-catenin stability. This work demonstrates that a maternal gene controlling localization of (beta)-catenin in dorsal nuclei is necessary for dorsal yolk syncytial layer gene activity and formation of the organizer in the zebrafish.

Tissue-Specific Induction of Hsp90 mRNA and Plasma Cortisol Response in Chinook Salmon following Heat Shock, Seawater Challenge, and Handling Challenge.

In studying the whole-body response of chinook salmon (Oncorhynchus tshawytscha) to various stressors, we found that 5-hour exposure to elevated temperature (mean 21.6 degrees C; + 10.6 degrees C over ambient) induced a marked increase in Hsp90 messenger RNA accumulation in heart, brain, gill, muscle, liver, kidney, and tail fin tissues. The most vital tissues (heart, brain, gill, and muscle) showed the greatest Hsp90-mRNA response, with heart tissue increasing approximately 35-fold. Heat shock induced no increase in plasma cortisol. In contrast, a standard handling challenge induced high plasma cortisol levels, but no elevation in Hsp90 mRNA in any tissue, clearly separating the physiological and cellular stress responses. We saw no increase either in tissue Hsp90 mRNA levels or in plasma cortisol concentrations after exposing the fish to seawater overnight.

Mitotic and pigment-translocating activities of cultured chromatophores of the guppy, Lebistes reticulatus

1. Using Ham's F-12 medium, an in vitro culture system permitting cellular survival for over 6 months has been developed for the chromatophores of the guppy. 2. In this culture system, the various types of chromatophores (melanophores, erythrophores and xanthophores) migrated out of the explanted tail fin tissue, retained their pigmentation, and displayed both mitotic and pigment-translocating activities. 3. The mitotic activity was evident during the first 3 or 4 weeks in culture, whereas the pigment-translocating ability persisted for 16 weeks. 4. The cultured chromatophores of male fish displayed pigment aggregation in response to adrenergic agents (epinephrine and norepinephrine) and pigment dispersion in response to α-melanocyte stimulating hormone (α-MSH), cyclic AMP and dibutyryl cyclic AMP. 5. Cyclic GMP did not elicit pigment-translocating responses in any of the chromatophores.

Changes in specific prolactin binding in Rana catesbeiana tadpole tissues during metamorphosis and following prolactin and thyroid-hormone treatment

The prolactin-binding affinity ( K D ) and number of binding sites N in Rana catesbeiana tadpole, tail fin and kidney tissues were studied during metamorphosis and following administration of oPRL and L-T 3 to premetamorphic tadpoles. With increasing developmental stage there was an increase in N; a maximum was found at stage XVIII followed by a gradual decrease in N through metamorphic climax for all 3 tissues. No change in K d was noted. lL-T 3 treatment of premetamorphic tadpoles for 7 days caused a significant decrease in tail length and height and body length and an increase in hindlimb length with a concurrent increase in N of approximately 3-fold while treatment for 1 or 3 days was without effect on tadpole morphology or oPRL binding. oPRL treatment for 7 days caused a significant increase in tail length and height and body length with no significant changes in hindlimb length and a 3–5-fold increase in N. Treatment with both L-T 3 and oPRL for 7 days resulted in an inhibition of the T 3- induced decrease in tail length and height and body length and no inhibition of the hindlimb length increase. N increased in all tissues similar to that found with either treatment alone. No change in K D was noted in any of these studies. Therefore, oPRL and L-T 3 are able to regulate the numbers of specific oPRL-binding sites in amphibian tissues. The change in N with development parallels the reported change in tadpole pituitary capacity to stimulate growth but occurs prior to the reported surge of endogenous T 3 during metamorphosis. Thus, the variation in the number of oPRL-binding sites may be due to the changes in endogenous PRL levels during development.

Formula omitted] stimulation of tadpole tail regression by cyclic AMP

Treatment of Rana catesbeiana tail fin tissue in vitro with 0.1 mM or 0.5 mM cyclic AMP or with triiodothyronine induces an increase in the specific activity of hexosaminidase, a lysosomal marker enzyme, and a decrease in tissue area. Lithium chloride (8 mM), an inhibitor of adenylate cyclase, inhibits these changes when initiated by triiodothyronine but not when initiated by cyclic AMP. The levels of cyclic AMP, determined by radioimmunoassay techniques, increased 110 ± 10% over matched discs in culture after only one day's exposure to triiodothyronine. These results indicate the effect of triiodothyronine on fin resorption may be mediated by cyclic AMP.