3. Phillips, O. L. et al. Changes in the carbon balance of tropical forest: evidence from long-term plots.

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(Cambridge Univ. Press, Cambridge, UK, 1991).

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increased atmospheric CO2. Funct. Ecol. 6, 680–685 (1992).

15. Granados, J. & Korner, C. In deep shade, elevated CO2 increases the vigour of tropical climbing plants.

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16. Perez-Salicrup, D. R., Sork, V. L. & Putz, F. E. Lianas and trees in Amazonian Bolivia. Biotropica 33,

34–37 (2001).

17. Laurance, W. F. et al. Rain forest fragmentation and the structure of Amazonian liana communities.

Ecology 82, 105–116 (2001).

18. Phillips, O. L. & Gentry, A. H. Increasing turnover through time in tropical forests. Science 263,

954–958 (1994).

19. Phillips, O. L. The changing ecology of tropical forests. Biodivers. Cons. 6, 291–311 (1997).

20. Putz, F. E. Liana biomass and leaf-area of a tierra firme forest in the Rio Negro basin, Venezuela.

Biotropica 15, 185–189 (1983).

21. Retallack, G. J. A 300 million year record of atmospheric carbon dioxide from fossil plant cuticles.

Nature 411, 287–290 (2001).

22. Gentry, A. H. in The Biology of Vines (eds Putz, F. E. & Mooney, H. A.) 3–49 (Cambridge Univ. Press,

Cambridge, UK, 1991).

23. Gentry, A. H. in The Biology of Vines (eds Putz, F. E. & Mooney, H. A.) 393–423 (Cambridge Univ.

Press, Cambridge, UK, 1991).

24. Phillips, O. L. & Gentry, A. H. The useful plants of Tambopata, Peru. II: Additional hypothesis testing

in quantitative ethnobotany. Econ. Bot. 47, 33–43 (1993).

25. Malhi, Y. et al. An international network to monitor the structure, composition and dynamics of

Amazonian forests (RAINFOR). J. Vegn. Sci. (in the press).

26. Gerwing, J. J. & Lopes Farias, D. Integrating liana abundance and forest stature into an estimate of

total aboveground biomass for an eastern Amazonian forest. J. Trop. Ecol. 16, 327–335 (2000).

27. Brown, S. Estimating Biomass and Biomass Change of Tropical Forests: a Primer (Food and Agriculture

Organisation Forestry Paper 134, Rome, 1997).

28. Sombroek, W. G. Spatial and temporal patterns of Amazon rainfall: consequences for the planning of

agricultural occupation and the protection of primary forests. Ambio 30, 388–396 (2001).

29. van Reeuwijk, L. P. (ed.) Procedures for Soil Analysis, Tech. Pap. 9, 5th edn (International Soil Reference

and Information Centre, FAO, Rome, 1995).

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(Missouri Botanical Garden, St Louis, in the press).

Supplementary Information accompanies the paper on Nature’s website

(http://www.nature.com/nature).

AcknowledgementsWe acknowledge the contributions of more than 50 field assistants in Peru, Ecuador andBolivia, the residents of Constancia, Infierno, La Torre, Mishana and Florida, as well aslogistical support from Instituto Nacional de Recursos Naturales (INRENA), AmazonCenter for Environmental Education and Research (ACEER), Cuzco Amazonico Lodge,Explorama Tours SA, Instituto de Investigaciones de la Amazonıa Peruana (IIAP), ParqueNacional Noel Kempff, Peruvian Safaris SA, Universidad Nacional de la AmazonıaPeruana, and Universidad Nacional de San Antonio Abad del Cusco. Field research wassupported by the EU Fifth Framework Programme (RAINFOR), the UK NaturalEnvironment Research Council, the National Geographic Society, the AmericanPhilosophical Society, the National Science Foundation, the WWF-U.S./ Garden Club ofAmerica, Conservation International, the MacArthur and Mellon Foundations, US-AID,the Max-Planck Institute for Biogeochemistry and the Royal Society (Y.M.). Themanuscript benefited from comments by C. Korner and N. Pitman. We are indebted to thelate A.H. Gentry for helping to make this work possible.

Competing interests statement

The authors declare that they have no competing financial interests.

Correspondence and requests for materials should be addressed to O.P.

(e-mail: o.phillips@geog.leeds.ac.uk).

..............................................................

Involvement of DARPP-32phosphorylation in thestimulant action of caffeineMaria Lindskog*, Per Svenningsson†, Laura Pozzi*‡, Yong Kim†,Allen A. Fienberg†, James A. Bibb†‡, Bertil B. Fredholm§,Angus C. Nairn†, Paul Greengard† & Gilberto Fisone*

* Department of Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden† Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University,New York, New York 10021, USA§ Department of Physiology and Pharmacology, Karolinska Institutet, 17177Stockholm, Sweden‡ Present addresses: Department of Neuroscience, “Mario Negri” Institute forPharmacological Research, Milan, Italy (L.P.); Department of Psychiatry,UT Southwestern Medical Center, Dallas, Texas, USA (J.A.B).............................................................................................................................................................................

Caffeine has been imbibed since ancient times in tea and coffee,and more recently in colas. Caffeine owes its psychostimulantaction to a blockade of adenosine A2A receptors1, but little isknown about its intracellular mechanism of action. Here we showthat the stimulatory effect of caffeine on motor activity in micewas greatly reduced following genetic deletion of DARPP-32(dopamine- and cyclic AMP-regulated phosphoprotein of relativemolecular mass 32,000)2. Results virtually identical to those seenwith caffeine were obtained with the selective A2A antagonistSCH 58261. The depressant effect of the A2A receptor agonist,CGS 21680, on motor activity was also greatly attenuated inDARPP-32 knockout mice. In support of a role for DARPP-32 inthe action of caffeine, we found that, in striata of intact mice,caffeine increased the state of phosphorylation of DARPP-32 atThr 75. Caffeine increased Thr 75 phosphorylation throughinhibition of PP-2A-catalysed dephosphorylation, rather thanthrough stimulation of cyclin-dependent kinase 5 (Cdk5)-cata-lysed phosphorylation, of this residue. Together, these studiesdemonstrate the involvement of DARPP-32 and its phosphory-lation/dephosphorylation in the stimulant action of caffeine.

Striatal medium spiny neurons have an important role in thecontrol of voluntary movements. A large subpopulation of theseneurons project to the substantia nigra pars reticulata, the major

Figure 1 Emulsion autoradiogram illustrating co-expression of adenosine A2A receptor

mRNA (silver grains) and DARPP-32 mRNA (dark cells). Shown are subpopulations of

medium spiny neurons in mouse (a) and rat (b) striatum. Single arrows indicate neurons

that only express DARPP-32 mRNA. Double arrows indicate neurons that express both

DARPP-32 mRNA and adenosine A2A receptor mRNA.

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output area of the basal ganglia, via the globus pallidus andsubthalamic nucleus3. It is generally believed that activation ofthis ‘indirect’ striato-pallidal pathway reduces motor activity byinhibiting glutamatergic thalamo-cortical neurons3. Striato-pallidalneurons express high levels of the A2A receptor subtype for theneuromodulator adenosine4,5. Adenosine A2A receptors are posi-tively coupled to adenylyl cyclase via the olfactory-neuron-specificG protein, Golf

6, and their activation stimulates the cAMP path-way6,7. The psychostimulant caffeine is an adenosine receptorantagonist, able to produce a long-lasting increase in motoractivity1. Recent evidence obtained in A2A receptor knockout miceconfirms that the ability of caffeine to block adenosine A2A receptorsis responsible for the motor stimulant properties of this drug8,9.However, almost nothing is known about the intracellular mecha-nisms underlying the behavioural effects of caffeine.

Striatal projection neurons express high levels of DARPP-32(refs 2, 10). By double in situ hybridization, we found thatmessenger RNA for adenosine A2A receptors was expressed in asubset of striatal neurons containing DARPP-32 (Fig. 1). The cells

expressing A2A receptors represented about 50% of all DARPP-32-containing neurons. To determine whether DARPP-32 might beinvolved in mediating the behavioural effects of caffeine andselective adenosine A2A receptor antagonists and agonists, weexamined the effects of these drugs on motor activity in DARPP-32 knockout mice. Administration of 7.5 mg kg21 of caffeine towild-type mice produced, as expected, a large increase in motoractivity, measured both as long-range movements (locomotion)(Fig. 2a, b) and as short-range movements (motility) (Fig. 2c),which were still present 100 min after drug administration (Fig. 2a).When the same dose of caffeine was injected into DARPP-32knockout mice, a significant attenuation of the stimulant effectwas observed on both locomotion (Fig. 2a, b) and motility (Fig. 2c).The DARPP-32-dependence of the stimulatory effect of caffeine onmotor activity could be overcome by increasing the dose to15 mg kg21 (Fig. 2g).

To further evaluate the possible involvement of DARPP-32 in thebehavioural response to blockade of adenosine A2A receptors, weexamined the motor stimulant effects produced by the selective A2A

Figure 2 DARPP-32 is required for the stimulatory effects of caffeine and the selective

adenosine A2A receptor antagonist, SCH 58261, on motor activity. After a two-hour

habituation period, wild-type (WT) mice (filled symbols) and DARPP-32 knockout (KO)

mice (open symbols) received an injection of caffeine (7.5 or 15 mg kg21, i.p.) (a–c, g),

SCH 58261 (10 mg kg21, i.p.) (d–f) or vehicle (h) and were immediately returned to their

individual cages. a, d, g, h, Time course of the effects of caffeine, SCH 58261 or vehicle

on locomotion measured over 20-min intervals. b, e, Total locomotion counts determined

during the 100-min period following administration of caffeine (b) or SCH 58261 (e).

c, f, Total motility counts determined during 100 min following administration of caffeine

(c) or SCH 58261 (f). Data represent means ^ s.e.m. (n ¼ 15–20). Asterisk, P , 0.05

versus wild-type, Student’s t-test.

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receptor antagonist, SCH 58261, in wild-type and DARPP-32knockout mice. As with caffeine we found that the increases inlocomotion (Fig. 2d, e) and motility (Fig. 2f) induced by admin-istration of SCH 58261 were reduced in DARPP-32 knockout mice.

Stimulation of adenosine A2A receptors depresses motor activityand produces catalepsy11. We found that, in wild-type mice, the A2A

receptor agonist CGS 21680 (0.1 mg kg21, administered intraperi-toneally, i.p.) reduced motor activity by about 50% (Fig. 3, filledsymbols). When the same dose of CGS 21680 was administered toDARPP-32 knockout mice, we observed a significant attenuation inthe motor depressant effect of the A2A receptor agonist (Fig. 3, opensymbols).

The results shown in Figs 2 and 3 indicated that DARPP-32 isimportant in mediating the behavioural effects of caffeine and otheradenosine A2A receptor ligands. There is now compelling evidenceindicating that DARPP-32 function is regulated by phosphorylationat multiple sites. Notably, our recent studies have indicated thatCdk5 phosphorylates DARPP-32 at Thr 75 and converts the proteininto an inhibitor of PKA12. Moreover, phospho-Thr 75 of DARPP-32 is dephosphorylated by protein phosphatase 2A (PP-2A), aprocess that contributes to signal amplification involving DARPP-32 (refs 13, 14). We therefore examined the effects of adenosine A2A

receptor antagonists on phosphorylation of DARPP-32 at Thr 75.Administration of caffeine (7.5 mg kg21) increased Thr 75 phos-phorylation (Fig. 4a). SCH 58261 (10 mg kg21) mimicked the effectof caffeine on Thr 75 phosphorylation (Fig. 4b). Caffeine produced

an increase in Thr 75 phosphorylation, which was still significant 2 hafter injection, whereas SCH 58261 was less effective at late timepoints (Fig. 4), probably owing to its shorter half-life15. Thecaffeine-induced increase in Thr 75 phosphorylation was abolishedby the previous administration of roscovitine, an inhibitor of Cdk5(data not shown), confirming that we were examining the Cdk5/PP-2A site of DARPP-32.

An increased phosphorylation at Thr 75 of DARPP-32 could beachieved by activation of Cdk5, by inhibition of PP-2A, or by bothmechanisms. Cdk5 activity was measured in striatal extracts frommice which had been administered either 7.5 mg kg21 of caffeine orvehicle. No difference was observed in the rate of Cdk5-catalysedsubstrate phosphorylation between caffeine- and vehicle-treatedanimals (Fig. 5a). To examine the role of PP-2A in mediating theeffects of A2A receptor regulation on Thr 75 phosphorylation, weused a slice preparation from mouse dorsal striatum. A decrease inphospho-Thr 75 was produced by the A2A receptor agonist, CGS21680. Moreover, this decrease was abolished by pre-incubationwith okadaic acid, an inhibitor of PP-2A (Fig. 5b). Together, thesestudies suggest that adenosine A2A receptors alter Thr 75 phos-phorylation levels by regulating PP-2A activity.

These results clearly implicate DARPP-32 in the behaviouraleffects produced by caffeine and other adenosine A2A receptorligands. Furthermore, the data implicate phosphorylation at Thr75 of DARPP-32 in the psychostimulant action of caffeine. Itwas recently demonstrated that phospho-Thr 75-DARPP-32 is an

Figure 3 DARPP-32 is required for the depressant effect of the selective adenosine A2A

receptor agonist, CGS 21680, on motor activity. Wild-type mice (filled symbols) or DARPP-

32 knockout mice (open symbols) were treated with vehicle or CGS 21680 (0.1 mg kg21)

and placed in individual cages 10 min after the injection. The dose of CGS 21680 was

chosen on the basis of previous studies indicating that it caused a substantial reduction in

motor activity23, without inducing catalepsy24. a, Time course of the effect of CGS 21680

measured over 20-min intervals. b, c, Total locomotion counts (b) and total motility counts

(c) determined during the 100-min period following administration of CGS 21680. Data

represent means ^ s.e.m. (n ¼ 20–25). Asterisk, P , 0.001 versus wild-type mice

treated with vehicle; double asterisk, P , 0.05 versus wild-type mice treated with CGS

21680, Student’s t-test. The effect of CGS 21680 was significantly reduced in DARPP-32

knockout mice (P , 0.05, two-way ANOVA).

Figure 4 Effect of caffeine and SCH 58261 on DARPP-32 phosphorylation at Thr 75. Mice

were treated i.p. with caffeine (7.5 mg kg21) (a) or SCH 58261 (10 mg kg21) (b) and

decapitated at the indicated times after injection. The dose of caffeine was chosen based

on studies indicating that 7.5 mg kg21 of caffeine was able to produce a maximal increase

in Thr 75 DARPP-32 phosphorylation (data not shown). The dose of SCH 58261 was

chosen on the basis of previous studies indicating that 10 mg kg21 of SCH 58261 was

able to abolish the increase in DARPP-32 phosphorylation at Thr 34 induced by

eticlopride, a dopamine D2 receptor antagonist25. The striatal levels of phospho-Thr

75-DARPP-32 were determined as described in Methods. Upper panels show

representative autoradiograms; lower panels show summary of data expressed as

means ^ s.e.m. (n ¼ 10). The amount of phosphorylated DARPP-32 is expressed as a

percentage of that determined after vehicle administration. Asterisk, P , 0.05 versus

vehicle injected mice, Student’s t-test.

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effective inhibitor of PKA12. In addition, evidence was obtainedsuggesting that a cascade involving increased cAMP, activation ofPKA and activation of PP-2A leads to the dephosphorylation of Thr75 (ref. 14). The removal of the inhibitory constraint on PKA bydephosphorylation of Thr 75 provides a mechanism for amplifica-tion of the PKA signal transduction pathway14. Conversely, wehypothesize that the inhibition of the cAMP pathway producedby low caffeine levels would be amplified by the concomitantincrease in phosphorylation at Thr 75 of DARPP-32 leading tofurther reduction of PKA activity. The present results indicate that ahigh (15 mg kg21) dose of caffeine is sufficient to shut down thePKA pathway without the need for this amplification. By the samelogic, the similarity of the initial responses of wild-type and DARPP-

32 knockout mice to the motor stimulant effects of a lower caffeineconcentration (7.5 mg kg21), in spite of the rapid increases in Thr75 phosphorylation, can be explained by considering that, at thisearly stage, the level of caffeine is sufficiently high to produce near-maximal suppression of PKA activity. Nevertheless, as the levels ofcaffeine decrease, DARPP-32 and its phosphorylation at Thr 75 isused to maintain heightened locomotor responses.

In conclusion, we propose a model in which caffeine achieves itsbehavioural action in striato-pallidal neurons through a signallingcascade involving adenosine A2A receptor blockade, decreasedcAMP formation, decreased PKA activation, decreased PP-2Aactivation and increased phosphorylation of Thr 75 of DARPP-32.The caffeine-induced increase in the state of phosphorylation of Thr75 would further lower PKA activity, thereby providing a positive-feedback amplification mechanism for shutting down adenosineA2A receptor-stimulated PKA signalling pathways. A

MethodsIn situ hybridizationDigoxigenin or 35S-labelled riboprobes were prepared by in vitro transcription fromcomplementary DNA clones corresponding to fragments of DARPP-32 (ref. 16) andadenosine A2A receptor mRNA5, respectively. Coronal cryostat sections at different levelsthrough striatum were hybridized as previously described17. Neurons containing a numberof silver grains at least twofold higher than background were considered to be labelled foradenosine A2A receptor mRNA.

Determination of adenosine A1 receptor bindingThe densities of adenosine A1 receptors in wild-type and DARPP-32 knockout mice weredetermined by receptor autoradiography as previously described18, using [3H]1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX; from DuPont-NEN) as the ligand.

Measurement of motor activityWe measured horizontal motor activity by means of an infrared-sensitive motion detector(Motron Products) consisting of 48 photosensors mounted in 4 £ 4 cm squares andplaced in the floor of the cage in two identical boxes. A motility count was defined as anymovement covering two adjacent rows of photosensors and a locomotion count wasdefined as passing from one box to the other and crossing at least eight photosensors in thenew box19. Wild type and DARPP-32 knockout mice20 were generated from the offspringof DARPP-32þ/þ £ DARPP-32þ/þ and DARPP-32 2/2 £ DARPP-322/2 mating pairs. Allmice were age-matched and only male offspring were used. No differences were observedbetween wild-type and DARPP-32 knockout mice in the densities of adenosine A2A

receptors18 or A1 receptors ([3H]DPCPX binding in striatum and cortex of DARPP-32knockout mice was 96.6 and 96.4% of wild type, respectively). The animals wereaccustomed to the experimental room for 40 min before the start of the experiments. Toexamine the motor stimulant effects of caffeine and SCH 58261, mice were first placed inindividual cages for 2 h (habituation period). At the end of the habituation period theanimals received an injection of caffeine (7.5 or 15 mg kg21, i.p.) or SCH 58261(10 mg kg21, i.p.) and were immediately returned to their individual cages. To examine themotor depressant effect of CGS 21680, mice were treated with vehicle or 0.1 mg kg21 ofCGS 21680 and placed in individual cages 10 min after the injection. To avoid the effects ofdecreased blood pressure caused by activation of peripheral A2A receptors, mice weretreated with the A2A receptor antagonist 8-para-sulpho-theophylline (10 mg kg21, i.p.)10 min before the administration of CGS 21680. 8-para-sulpho-theophylline does notcross the blood–brain barrier and, when administered alone, did not produce anysignificant biochemical or behavioural changes (data not shown).

Determination of phosphoThr75-DARPP-32Male C57BL/6 mice (20–30 g; M&B) were injected intraperitoneally with vehicle or drugsand killed by decapitation. When combinations of two drugs were used, the mice werekilled 15 min after the second injection. The heads of the animals were immediatelyimmersed in liquid nitrogen for six seconds. The brains were then removed and the dorsalparts of the striata rapidly (20 s) dissected out on an ice-cold surface, sonicated in 750 ml of1% sodium dodecylsulphate and boiled for 10 min. For slice experiments, we preparedbrain coronal slices (200 mm) using a vibroslice (Campden Instruments). Dorsal striatawere then dissected out from each slice under a microscope. Two striatal slices were placedin individual 5-ml polypropylene tubes containing 2 ml of Krebs–Ringer bicarbonatebuffer (KRB): 118 mM NaCl, 4.7 mM KCl, 1.3 mM CaCl2, 1.5 mM MgSO4, 1.2 mMKH2PO4, 25 mM NaHCO3, 11.7 mM glucose, equilibrated with 95% O2/5% CO2 (v/v),pH 7.3. The samples were equilibrated at 30 8C for two 30-min periods, each followed byreplacement of the medium with 2 ml of fresh KRB. Test substances were then added. Afterincubation, the solutions were rapidly removed, the slices were sonicated in 200 ml of 1%sodium dodecylsulphate and boiled for 10 min. Phospho-Thr 75-DARPP-32 was detectedas described using a polyclonal antibody12. In some experiments, a monoclonal antibody(C24-5a) (diluted 1:10,000)21 generated against DARPP-32, which is notphosphorylation-state-specific, was used to measure the total amount of DARPP-32.Antibody binding was revealed using goat anti-mouse horseradish peroxidase (HRP)-linked IgG (diluted 1:10,000), and the enhanced chemiluminescence (ECL)

Figure 5 Adenosine A2A receptor regulation of DARPP-32 phosphorylation at Thr 75 by

modulation of PP-2A. a, Mice were treated with vehicle or 7.5 mg kg21 of caffeine and

decapitated 15 min later. Dorsal striata were dissected out, homogenized in lysis buffer

and subjected to immunoprecipitation (IP) with either a Cdk5 antibody (C8) or normal

rabbit IgG. Cdk5 in the immunoprecipitates was assayed using histone H-1 as substrate in

the absence or presence of 10 mM butyrolactone, a specific Cdk5 inhibitor22. Upper panel,

autoradiogram showing histone H-1 phosphorylation. Lower panel, data are

means ^ s.e.m. (n ¼ 8). b, Slices from dorsal striatum were preincubated with

adenosine deaminase for 30 min, to prevent the build up of endogenous adenosine and

then incubated for 20 min in the presence of 1 mM okadaic acid13 and for an additional

10 min in the presence of okadaic acid plus the A2A receptor agonist CGS 21680 (1 mM).

Upper panel, autoradiogram showing phosphorylation at Thr 75 of DARPP-32. Lower

panel, data are means ^ s.e.m. (n ¼ 7). The amount of phosphorylated DARPP-32 is

expressed as a percentage of that determined after vehicle administration. Asterisk,

P , 0.01 versus vehicle-treated group, Student’s t-test.

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immunoblotting detection system. Chemiluminescence was detected by autoradiography.Quantification of the phospho-DARPP-32 bands was done by densitometry, using NIHImage (version 1.52) software.

Determination of Cdk5 activityMice were treated intraperitoneally with vehicle or 7.5 mg kg21 of caffeine and decapitated15 min later. The brains were rapidly removed, and the dorsal striata were dissected outand homogenized in lysis buffer. Cdk5 was immunoprecipitated with anti-Cdk5 (C8)antibody and its activity was assayed in the absence or presence of butyrolactone (10 mM)by using histone H-1 as the substrate as described22.

Received 21 February; accepted 3 April 2002; doi:10.1038/nature00817.

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AcknowledgementsWe thank R. Rimondini and S.-O. Ogren for help in performing behavioural experimentsand A. Nishi for discussions. This work was supported by the Swedish Research Council(G.F. and B.B.F.), the Swedish Society for Medical Research (M.L.), the FoundationBlanceflor Boncompagni-Ludovisi, nee Bildt (L.P.) and by funding from the NationalInstitute of Mental Health and the National Institute of Drug Abuse (A.C.N. and P.G.).

Competing interests statement

The authors declare that they have no competing financial interests.

Correspondence and requests for materials should be addressed to G.F.

(e-mail: gilberto.fisone@neuro.ki.se).

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Sperm from neonatal mammaliantestes grafted in miceAli Honaramooz*, Amy Snedaker*, Michele Boiani†, Hans Scholer†,Ina Dobrinski* & Stefan Schlatt†‡

* Male Germ Cell Biology Group, and † Germline Development Group,Center for Animal Transgenesis and Germ Cell Research, New Bolton Center,School of Veterinary Medicine, University of Pennsylvania, Kennett Square,Pennsylvania 19348, USA‡ Institute of Reproductive Medicine, University Munster, Domagkstrasse 11,D-48149 Munster, Germany.............................................................................................................................................................................

Spermatogenesis is a productive and highly organized processthat generates virtually unlimited numbers of sperm duringadulthood. Continuous proliferation and differentiation ofgerm cells occur in a delicate balance with other testicularcompartments, especially the supporting Sertoli cells1. Manycomplex aspects of testis function in humans and large animalshave remained elusive because of a lack of suitable in vitro or invivo models. Germ cell transplantation has produced completedonor-derived spermatogenesis in rodents2–6 but not in othermammalian species7–9. Production of sperm in grafted tissuefrom immature mammalian testes and across species has not yetbeen accomplished. Here we report the establishment of com-plete spermatogenesis by grafting testis tissue from newbornmice, pigs or goats into mouse hosts. This approach maintainsstructural integrity and provides the accessibility that is essentialfor studying and manipulating the function of testes and forpreserving the male germ line. Our results indicate that thisapproach is applicable to diverse mammalian species.

Transplantation of spermatogonial stem cells from fertile donormice to the testes of infertile recipient mice results in completespermatogenesis2–3,10 and autologous transplantation is successfulin the monkey11, which open up the field for medical applications12.Cross-species transplantation of spermatogonial stem cells fromdonor rats or hamsters to recipient mice results in the establishmentof rat or hamster spermatogenesis in the mouse testis5,6; however,the transplantation of germ cells from phylogenetically more distantspecies including rabbits, dogs, pigs, bulls, horses and primates into

Figure 1 Grafting of testis tissue from newborn piglets under the skin of nude mice.

a, b, The size of the pig testis grafts at the time of transplantation was about 0.5–1 mm in

diameter (a) and expanded to 4–8 mm at 10 weeks after grafting (b). Scale bars, 5 mm.

Most grafts from later time points contained sperm. c, A sperm extracted from a week 27

graft. Scale bar, 20 mm.

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