Skip Navigation

Integrative and Comparative Biology 2005 45(1):28-32; doi:10.1093/icb/45.1.28
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (3)
Right arrow Request Permissions
Google Scholar
Right arrow Articles by Oberdörster, E.
Right arrow Articles by McClellan-Green, P.
Right arrow Search for Related Content
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

The Society for Integrative and Comparative Biology

The Neuropeptide APGWamide as a Penis Morphogenic Factor (PMF) in Gastropod Mollusks1

Eva Oberdörster2,1, Jocelyn Romano1 and Patricia McClellan-Green1,2
1 Duke University Marine Laboratory, Beaufort, North Carolina
2 North Carolina State University, Center for Marine Science and Technologies and Department of Environmental and Molecular Toxicology, Morehead City, North Carolina


   SYNOPSIS
TOP
SYNOPSIS
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The goal of this study was to further investigate the role of endogenous APGWamide levels in imposex induction in snails. APGWamide is a common neurotransmittor/neuromodulator peptide found in many species of molluscs, and is often related to sex organ growth or reproductive behavior. Mud snails (Ilyanassa obsoleta) were collected from the Rachel Carson Estuarine Reserve near Beaufort, NC, and were dosed with the environmental contaminant tributyltin (TBT), testosterone (T), or solvent vehicle (EtOH/ saline) controls. Both TBT and T have been shown previously to induce female snails to grow penises (a condition termed imposex), and to increase male penis size. Male normalized penis length was correlated to endogenous APGWamide levels (as measured by Western blotting of whole animal homogenates, r2 = 0.475), and control males had significantly higher APGWamide levels than control females. All TBT-treated animals, (male, female, and imposex) had levels of APGWamide similar to control males and significantly higher than control females. In testosterone treated animals, APGWamide levels were the same as controls and it is likely that testosterone interferes with a downstream signaling event to induce imposex. In addition, immunohistochemistry for APGWamide expression in abdominal areas was done on female, male and imposex snails collected from the wild. The pattern of APGWamide in imposex snails was similar to male snails, showing large patches of immuno-reactive areas in the top portion of the visceral mass. In female snails, no areas of cross-reactivity were found.


   INTRODUCTION
TOP
SYNOPSIS
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The mechanism of tributyltin (TBT)-induced imposex induction, the abnormal growth of male Accessory Sex Organs (ASO,) has proven to be elusive. Although inhibition of aromatase by TBT has been implicated (Bettin et al., 1996Go), there are several lines of evidence that suggest that the mechanism is much more complex. Including: i) elevated testosterone levels are found only in late-stage imposex (Bettin et al., 1996Go); ii) the levels needed for testosterone-induced imposex in a 200 mg snail are approximately the same level as found circulating in a 70 kg man (Norman and Litwack, 1997Go); iii) other chemicals that inhibit aromatase in mud snails (Ilyanassa obsoleta) do not induce imposex (McClellan-Green, 2003Go); iv) testosterone is conjugated to fatty acids (Gooding and LeBlanc, 2001Go), and free testosterone levels are maintained at a constant level, even with addition of free testosterone (LeBlanc, 2003Go).

Peptide neurotransmitter/modulators have been implicated in imposex induction by exogenous administration or bioassays (Feral and LeGall, 1983Go; Oberdörster and McClellan-Green, 2000Go). One group of neurotransmitters/modulators that is involved in molluskan reproductive behavior is APGWamide and related peptides. These peptides are found in central neurons and in male reproductive organs in a variety of mollusk species such as gastropods (Helix aspersa, Lymnean stagnalis, Aplysia, and Ocenebra erinacea), bivalves (Mytilus edulis and Placopecten magellanicus) and cephalopods (Sepia officinialis), and are involved in such diverse processes as inhibiting the motility of the oviduct, penile eversion, and male copulation behavior, (Kuroki et al., 1990Go; Minakata et al., 1991Go; Chen and Walker, 1992Go; Croll and VanMinnen, 1992Go; Griffond et al., 1992Go; Li et al., 1992Go; vanGolen et al., 1995Go; Favrel and Mathieu, 1996Go; de Lange et al., 1997Go; Fan et al., 1997Go; Henry et al., 1997Go; McCrohan and Croll, 1997Go; Smith et al., 1997Go; de Lange et al., 1998Go; de Lange and VanMinnen, 1998Go; Henry et al., 2000Go; Koene et al., 2000Go; Ohtani et al., 2001Go; Henry and Zatylny, 2002Go; Morgan et al., 2002Go). APGWamide is a tetrapeptide with the sequence Ala-Pro-Gly-Trp, and is cleaved from a longer pre-cursor peptide (Favrel and Mathieu, 1996Go).

In the mud snail, APGWamide is able to induce penis bud formation rapidly (7 days) and at extremely low doses (10–16 moles) (Oberdörster and McClellan-Green, 2000Go). APGWamide also induces vas deferens growth in the rock shell, Thais clavigera (Horiguchi et al., 2003Go). It is thought that APGWamide can act as a Penis Morphogenic Factor (PMF), as described by Féral and LeGall (1983)Go. In the mud snail, males undergo a seasonal resorption and growth of the penis corresponding to the breeding cycle, which is under the control of a PMF (Fig. 1). Similarly, females resorb and grow an egg capsule gland following the same breeding cycle. Interestingly, females cannot be induced to become imposex during the active breeding season, from January until May for I. obsoleta. This lack of imposex inducibility is possibly due to many factors including i) ovodeposition of the TBT; ii) signaling by Egg Laying Hormone (ELH), a polypeptide hormone, which could over-ride any TBT-induced peptide signals; or iii) competition for second-messenger signaling factors. The exact mechanism of why TBT is unable to induce imposex in female I. obsoleta during the breeding season is still unclear.



View larger version (18K):
[in this window]
[in a new window]
  		FIG. 1. Male penis length changes with the annual reproductive cycle. Bars are standard deviation, and n = between 30 and 35 animals. This seasonal cycle is thought to be controlled by peptidal hormones including a Penis Morphogenic Factor, such as APGWamide

 

   MATERIALS AND METHODS
TOP
SYNOPSIS
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
The goal of this research was to determine endogenous levels of the neuropeptide APGWamide and correlate these with imposex status. I. obsoleta were collected from the Rachel Carson Estuarine Reserve near Beaufort, NC in June of 2002 and were dosed by i.p. injection with 5 µl of either vehicle (50% EtOH in saline), TBT (20 ng/animal), or testosterone (500 ng/ animal). After two weeks of dosing every other day, animals were sacrificed, imposex status determined, and endogenous levels of APGWamide measured in whole-body homogenates via Western blotting using an internal APGWamide standard. For Western blotting, snails were homogenized in 200 µl ice cold homogenizing buffer (PBS, 50 mM sodium phosphate, pH 7.4, 140 mM NaCl, 1 mM DDT, 1 mM EDTA, 5 µg/ml pepstatin A, 10 µg/ml aprotinin), and centrifuged for 10 minutes at 14,000 g at 4°C in a microcentrifuge. The supernatant was used for Westerns and to measure total protein via the Bradford assay (Bradford, 1976Go). Samples were diluted with buffer, heated to 95°C for 5 minutes, and 5 µg protein per lane was loaded into a 7.5% SDS-PAGE gel. The gel was run and transferred to PVDF membrane (Bio-Rad, cat# 162-0177), blocked overnight in 3% Carnation Instant Milk in PBS (50 mM Phosphate buffer, pH 7.4; 140 mM NaCl) at 4°C. The membranes were washed four times in PBSTx (PBS + 0.2% v/v Triton X-100), then incubated 2 hours at RT with primary antibody in PBSTx (1:100 polyclonal {alpha}-APGWamide). After four more rinses, the membranes were incubated in secondary antibody in PBSTx (1:20,000 donkey {alpha}-rabbit) for one hour at RT, then again washed four additional times in PBSTx, the bands were visualized using the Amersham Enhanced Chemiluminescent (ECL) kit and exposed to Kodak X-OMAT film. Density of bands was measured on an AlphaImager 2200 (Alpha Innotech, Inc.) densitometer, and normalized to the APGWamide standard. Controls for the specificity of the antibody were carried out prior to the assay. Pure APGWamide (Sigma-Aldrich) was blotted as described above, and both pre-immune serum and post-immune serum from the same rabbit was used for the primary antibody incubation to verify the specificity of the antibody in the post-immune serum (i.e., that cross-reactivity was not present in the pre-immune serum, data not shown).

One methodological note: APGWamide is such a small peptide that it is difficult to coat the peptide with sufficient negative charge for gel electrophoresis using SDS. The pure APGWamide peptide (Sigma-Aldrich) migrated to approximately 40 kDa due to the inability to get enough charge on the peptide. Therefore, our analyses on the Western blot used the purified APGWamide migration distance (run on every gel) to establish and confirm the location of the snail endogenous APGWamide bands. It is possible that the endogenous bands contained not only APGWamide, but polymers or precursors of APGWamide that migrated the same distance on the gel. (APGWamide is known to be cleaved from a polypeptide containing twelve repetitions of the peptide to the active APGWamide in other snail species, Favrel and Mathieu, 1996Go). However, on the gels, there was always only one discrete band of APGWamide for each snail that corresponded to the migration distance of purified APGWamide. In addition to creating difficulties in migration on gels, the small size of APGWamide made it difficult to develop ELISA techniques. After six months of trying various coating techniques, buffers, and incubation periods and temperatures, ELISAs proved inconsistent and only detected extremely high levels of APGWamide (mg range). Therefore the effort to create ELISAs was abandoned, and Western blotting was used for assaying endogenous APGWamide levels.

Immuno-histochemistry was done by embedding formalin fixed abdominal sections of snails in paraffin using standard dehydration steps. Snails were then sectioned at 7 µm intervals on a microtome, floated in 50% EtOH, and transferred to a 43°C water bath. Then sections were mounted onto Vectabond-treated slides and dried overnight. The slides were the subjected to immunohistochemical (IHC) staining using rabbit anti-APGWamide. The slides were incubated in xylene substitute (CitriSolvTM) 2x for 10 minutes, then 100% EtOH 2x for 2 minutes, followed by 3% hydrogen peroxide for 10 minutes. The slides were then blocked with 5% rabbit serum for 5 hours and rinsed 3x in 1 x PBS. Next, the slides were incubated in the primary antibody (polyclonal rabbit anti-APGWamide, 1:100 dilution) for 6 hours and rinsed 4x in 1 x PBS, and1 x PBS. The slides were then incubated overnight in the secondary antibody (HRP-linked donkey anti-rabbit 1:1,000 dilution) followed by rinsing 4x in 1 x PBS. The color was developed using the substrate diaminobenzidin tetrahydrochloride (DAB).

In a separate dosing experiment, snails were dosed with APGWamide at either 10–16, 10–14, 10–12, or 10–10 moles per snail per injection, every other day for two weeks. After two weeks, snails were sacrificed and male penis length was measured. APGWamide was also able to significantly induce imposex, and these data have been published elsewhere (Oberdörster and McClellan-Green, 2000Go). This experiment was performed during the summer of 2000 during a time when males normally have regressed or absent penises, and during a time when females are susceptible to TBT-induced imposex.


   RESULTS
TOP
SYNOPSIS
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Imposex was induced by both TBT (33%) and testosterone (18%) after two weeks of treatment, as would have been expected from earlier studies. TBT-dosed males also had significantly longer penis lengths than control or T-dosed males, and normalized male penis length (mm/cm shell width) was highly correlated (r2 = 0.475) to endogenous APGWamide levels (Fig. 2). This would indicate that TBT enhances male penis length more so than T. One possible mechanism would be via a neuromodulator, such as APGWamide, and this hypothesis was tested by administering APGWamide to the snails. Exogenously administered APGWamide significantly induced male penis growth (Fig. 3), confirming that this neuropeptide can function as a Penis Morphogenic Factor (PMF).



View larger version (14K):
[in this window]
[in a new window]
  		FIG. 2. Male penis length is positively correlated to endogenous APGWamide levels. Regression line has an r2 = 0.475

 


View larger version (24K):
[in this window]
[in a new window]
  		FIG. 3. Exogenously administered APGWamide induces penis elongation in normal males. A-16 denotes a dose of 1 x 10–16 moles of APGWamide injected every other day for two weeks, A-14 is a dose of 1 x 10–14 moles of APGWamide, and so forth. Significance was tested by ANOVA followed by post-hoc Tukey test, with an n between 5 and 15 animals per group. * P < 0.5; ** P < 0.01

 
In control animals, endogenous APGWamide levels were higher in males as compared to females (Fig. 4), as would be expected from a (PMF). TBT-induced imposex snails had APGWamide levels comparable to control males, and TBT-dosed females had APGWamide levels intermediary between control males and control females (Fig. 4). Testosterone did not alter endogenous APGWamide levels as compared to controls (Fig. 4), indicating that imposex induction by T is different from imposex induction by TBT. Immunohistochemistry (Fig. 5) showed that both male and imposex snails had clusters of APGWamide immunoreactivity, while female snails did not show any APGWamide clusters, confirming the findings of the Western blotting.



View larger version (31K):
[in this window]
[in a new window]
  		FIG. 4. Endogenous APGWamide levels in snail homogenates. TBT = 20 ng tributyltin; testosterone = 500 ng. Significance by ANOVA followed by post-hoc Tukey test. Where there are no error bars, n = 1. Otherwise, n = from 5–20. Different letters indicate significant differences of P < .05 (e.g., a is significantly different from b and c)

 


View larger version (37K):
[in this window]
[in a new window]
  		FIG. 5. Detection of APGWamide in snail sections. Female snails have no distinct APGWamide cross-reactivity, while male and imposex snails have large clusters of APGWamide reactive areas

 

   DISCUSSION
TOP
SYNOPSIS
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
In many mollusk species, APGWamide is tied to reproductive behavior and penile eversion. For example, in male Lymnaea stagnalis, several peptides and their genes have been identified in neurons that are involved in copulation behavior, and APGWamide and conopressin are thought to play central roles in regulating this behavior (de Lange et al., 1997Go, 1998Go). In earlier studies from our laboratory, conopressin was not able to induce imposex in Ilyanassa obsoleta (Oberdörster and McClellan-Green, 2000Go), suggesting that APGWamide may enhance reproduction while conopressin may not play a role in this developmental process or may repress it. In the sea hare, Aplysia, and gastropod, Helix aspersa, APGWamide was also localized to the male reproductive organs (Griffond et al., 1992Go; Fan et al., 1997Go). In H. aspersa, the APGWamide was localized to the penis, gonads, and even the heads of the spermatozoa (Griffond et al., 1992Go). Having APGWamide delivered with spermatozoa may be important in regulating the receptive female's reproductive behavior. This hypothesis is strengthened by the observation that APGWamide-related peptides decreases the tonus, frequency and amplitude of oviductal contractions in cuttlefish (Henry et al., 1997Go), and that penile eversion related to APGWamide injections increased copulatory behavior in H. aspersa pairs.

In Ilyanassa obsoleta, male snails undergo a seasonal cycle of penis growth and regression. This process is thought to be controlled by a Penis Morphogenic Factor (PMF), which could possibly be the neuropeptide APGWamide. Several lines of evidence point towards APGWamide being responsible for penile growth. First, exogenous administration induces male snails to grow longer penises in a dose-dependent manner. Second, endogenous levels of APGWamide are higher in male snails with longer penises. Finally, we have previously shown that APGWamide induces imposex as is evidenced by female snails growing a penis bud. These lines of evidence strongly suggest a role of APGWamide or an APGWamide analogue in penis morphogenesis in this species.

The data presented here shows that endogenous levels of APGWamide are elevated after TBT-dependent imposex induction, but not after testosterone-induced imposex. This means that TBT may be acting as a neurotoxicant and abnormally causing the release of APGWamide. Testosterone on the other hand does not elevate APGWamide, suggesting that the mechanism for imposex induction by the steroid hormone is down-stream or via a separate pathway from the APGWamide signaling event. In a more recent study, it was shown that TBT interacts with the RXR (retinoid X receptor) in rock shell (Nishikawa et al., 2004Go). It is possible that TBT could bind to receptors in the steroid-hormone superfamily (such as RXR), and thereby cause gene transcription that could signal development of the sex organs. These gene products could include neuromodulators such as APGWamide, or could act by an entirely different, as yet undetermined, pathway. It should be noted that even with intensive effort, estrogen receptor (ER) and androgen receptor (AR) have not been identified to date in mollusks.

APGWamide is a neurotransmitter/modulator, which is thought to act via a second messenger system. We will further investigate to which second messenger system this neuropeptide is coupled. A recent study showed that aromatase activity could be regulated by phosphorylation in a human ovarian granulosa tumor cell line (Mukasa et al., 2003Go). It is possible that in snails, APGWamide may turn on cell signaling pathways that regulate steroidogenesis or release of free testosterone from fatty acid conjugates. Although multiple hypothesis still exist for the exact mechanism of imposex induction, it appears that endogenous changes in APGWamide play a role in this process.


   ACKNOWLEDGMENTS
 
This research was funded by an EPA STAR grant #R827401-01 to EO and PMG.


   FOOTNOTES
 
1 From the Symposium on EcoPhysiology and Conservation: The Contribution of Endocrinology and Immunology presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 5–9 January 2004, at New Orleans, Louisiana. Back

2 Present address of E. Oberdörster is: Biological Sciences, Southern Methodist University, Dallas, Texas 75275-0376; E-mail: eoberdor{at}mail.smu.edu Back


   References
TOP
SYNOPSIS
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Bettin, C., J. Oehlmann, and E. Stroben. 1996. TBT-induced imposex in marine neogastropods is mediated by an increasing androgen level. Helgolander Meeresuntersuchungen, 50:299-317.

Bradford, M. 1976. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem, 77:248-254.[CrossRef]

Chen, M., and R. Walker. 1992. Actions of APGW-amide and GWamide on identified central neurons of the snail, Helix aspersa. Comp. Biochem. Physiol, 102C:509-516.[CrossRef]

Croll, R., and J. VanMinnen. 1992. Distribution of the neuropeptide Ala-Pro-GLy-Trp-NH2 (APGWamide) in the nervous system and periphery of the snail Lymnaea stagnalis as revealed by immunocytochemistry and in situ hybridization. J. Comp. Neurol, 323:1-8.[CrossRef][ISI][Medline]

de Lange, R., P. de Boer, A. ter Maat, C. Tensen, and J. van Minnen. 1998. Transmitter identification in neurons involved in male copulation behavior in Lymnaea stagnalis. J. Comp. Neurol, 395:440-449.[Medline]

de Lange, R., F. van Golen, and J. van Minnen. 1997. Diversity in cell specific co-expression of four neuropeptide genes involved in control of male copulation behaviour in Lymnaea stagnalis. Neuroscience, 78:289-299.[CrossRef][ISI][Medline]

de Lange, R., and J. VanMinnen. 1998. Localization of the neuropeptide APGWamide in gastropod molluscs by in situ hybridization and immunocytochemistry. Gen Comp Endocrinol, 109:166-174.[CrossRef][Medline]

Fan, X., R. Croll, B. Wu, L. Fang, Q. Shen, S. Painter, and G. Nagle. 1997. Molecular cloning of a cDNA encoding the neuropeptides APGWamide and Cerebral Peptide 1: Localization of APGWamide-like immunoreactivity in the central nervous system and male reproductive organs of Aplysia. J. Comp. Neurol, 387:23-62.

Favrel, P., and M. Mathieu. 1996. Molecular cloning of cDNA encoding the precursor of ALa-Pro-Gly-Trp amide-related neuropeptides from the bivalve mollusc Mytilus edulis. Neurosci. Lett, 205:210-214.[Medline]

Feral, C., and S. LeGall. 1983. The influence of a pollutant factor (tributyltin) on the neuroendocrine mechanism responsible for the occurence of a penis in the females of Ocenebra erinacea. In H. Boer (ed.), Molluscan neuro-endocrinology, pp. 173–175. North Holland Publ Co, Amsterdam.

Gooding, M., and G. LeBlanc. 2001. Biotransformation and disposition of testosterone in the eastern mud snail Ilyanassa obsoleta. Gen. Comp. Endocrinol, 122:172-180.[Medline]

Griffond, B., J. VanMinnen, and C. Colard. 1992. Distribution of APGWamide-immunoreactive substances in the central nervous system and reproductive apparatus of Helix aspersa. Zool. Sci, 9:533-539.[Medline]

Henry, J., P. Favrel, and E. Boucaud-Camou. 1997. Isolation and identification of a novel Ala-Pro-Gly-Trp-amide-related peptide inhibiting the motility of the mature oviduct in the cuttlefish, Sepia officinalis. Peptides, 18:1469-1474.[CrossRef][Medline]

Henry, J., and C. Zatylny. 2002. Identification and tissue mapping of APGWamide-related peptides in Sepia officinalis using LC-ESI-MS/MS. Peptides, 23:1031-1037.[Medline]

Henry, J., C. Zatylny, and P. Favrel. 2000. HPLC and electrospray ionization mass spectrometry as tools for the identification of APGWamide-related peptides in gastropod and bivalve mollusks: Comparative activities on Mytilus muscles. Brain. Res, 862:162-170.[Medline]

Horiguchi, T., Y. Katsu, Y. Ohta, H. Watanabe, T. Iguchi, F. Morishita, O. Matsusushima, H. Shiraishi, and M. Morita. 2003. Is inhibition of aromatase activity due to TBT exposure the primary factor of Gastropod Imposex? 12th PRIMO Symposium, May 9–14:Abstract #186.

Koene, J., R. Jansen, A. Ter Maat, and R. Chase. 2000. A conserved location for the central nervous system control of mating behaviour in gastropod molluscs: Evidence from a terrestrial snail. J Exp Biol, 203:1071-1080.[Abstract]

Kuroki, Y., T. Kanda, I. Kubota, Y. Fjuisawa, T. Ikeda, A. Miura, Y. Minamitake, and Y. Moneoka. 1990. A molluscan neuropeptide related to the crustacean hormone, RPCH. Biochem. Biophys. Res. Comm, 167:273-279.[Medline]

LeBlanc, G. A. 2003. PRIMO 12 meeting. Safety Harbor, Florida.

Li, K., A. Smit, and W. Geraerts. 1992. Structural and functional characterization of neuropeptides involved in the control of male mating behavior of Lymnaea stagnalis. Peptides, 13:633-638.[CrossRef][Medline]

McClellan-Green, P. 2003. Aromatase inhibition by TBT and 3-methylcholanthrene. General & Comparative Endocrinology. (In review).

McCrohan, C., and R. Croll. 1997. Characterization of an identified cerebrobuccal neuron containing the neuropeptide APGWamide (Ala-Pro-Gly-Trp-NH2) in the snail Lymnaea stagnalis. Invert. Neurosci, 2:273-282.[CrossRef][Medline]

Minakata, H., Y. Kuroki, T. Ikeda, Y. Fujisawa, K. Nomoto, I. Kubota, and Y. Moneoka. 1991. Effects of the neuropeptide APGW-amide and related compounds on molluscan muscles-GWamide shows potent modulatory effects. Comp. Biochem. Physiol, 100C:565-571.[Medline]

Morgan, P. T., J. Jing, F. S. Vilim, and K. R. Weiss. 2002. Interneuronal and peptidergic control of motor pattern switching in Aplysia. Journal of Neurophysiology, 87:49-61.[Abstract/Free Full Text]

Mukasa, C., M. Nomura, T. Tanaka, K. Tanaka, Y. Nishi, T. Okabe, K. Goto, T. Yanase, and H. Nawata. 2003. Activin signaling through type IB activin receptor stimulates aromatase activity in the ovarian granulosa cell-like human granulosa (KGN) cells. Endocrinology, 144:1603-1611.[Abstract/Free Full Text]

Nishikawa, J. T., S. Mamiya, T. Kanayama, T. Nishikawa, F. Shiraishi, and T. Horiguchi. 2004. Involvement of the retinoid x receptor in the development of imposex caused by organotins in gastropods. Environ. Sci. Tech. (In press).

Norman, A., and G. Litwack. 1997. Hormones, 2nd ed. Academic Press, New York.

Oberdörster, E., and P. McClellan-Green. 2000. The neuropeptide APGWamide induces imposex in the mud snail, Ilyanassa obsoleta. Peptides, 21:1323-1330.[CrossRef][ISI][Medline]

Ohtani, M., H. Minakata, and S. Aimoto. 2001. Potent antagonistic action of synthetic analogues of APGWNamide, an antagonist of molluscan neuropeptide APGWamide. Peptides. (In press).

Smith, S., J. Nason, and R. Croll. 1997. Detection of APGWamide-like immunoreactivity in the sea scallop, Placopecten magellanicus. Neuropeptides, 31:155-165.[Medline]

vanGolen, F., K. Li, and W. Geraerts. 1995. Co-localized neuropeptides conopressin and Ala-Pro-Gly-Trp-NH2 have antagonistic effects on the vas deferens of Lymnaea. Neuroscience, 69:1275.[CrossRef][ISI][Medline]


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (3)
Right arrow Request Permissions
Google Scholar
Right arrow Articles by Oberdörster, E.
Right arrow Articles by McClellan-Green, P.
Right arrow Search for Related Content
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?