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Medically Assisted Conception: An Agenda for Research (1989)

Chapter: The Fertilizing Sperm: Structure, Maturation and Function

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Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
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Page 250
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 251
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 252
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 253
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 254
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 255
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 256
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 257
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 258
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 259
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 260
Suggested Citation:"The Fertilizing Sperm: Structure, Maturation and Function." Institute of Medicine. 1989. Medically Assisted Conception: An Agenda for Research. Washington, DC: The National Academies Press. doi: 10.17226/1433.
×
Page 261

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THE EKING Sew: 5~, ~[m ~ ~m Patrick M. ,~1 irk IN~= It is ~i~ ir~siT~ly ~z~t that highly served Solar rea~itia1 am e~ra~ll~llar sigh Fire ~i~ are 13~ ~ cells In widely divergent system. Investigation of _lian games at the cellular and near levels has An extensive cloying He last Am, Reading At the pro:= of fertilization Arises an elegant exile of cellular interactia~ are ~nunicatia~. Be cansiderable - information ~at has ~ ~ it ~=ible to begm ~aring varia~s ads of sixth sperm are Gus; :~ differs E;pecies art to atomic median of cxx~ patterns Al principles. Since sE~ interaction captives one of me old reedition systems An, go;' ns~ of conserved Aim ~ ~ An Grimy. Insight ink cat lular arx] m:~lea~ar Hartley across Lies lariat= ~= a narti~larlv important tonic with ~ to human in vitro ^, ~ ~ _ , - _ . a _ · , · _ ~ ~ s us _ _ _ _ · ~ · ~ fertilizatic~n. ~ basic moldy arid Editions 1~ for that pr~derive entirely f~parallelwork~n ani~1~1 system;, smarting ~ fetal deformity. Farther Cam clinically, both for the proration are the prevention of fertilit-v, now denand a ~~ deluded ~r~ of gag; are their interaction. Ice sad Is true, of course, in veterinary arx] other animal scierxxs. But for scare Sian species, incl~ir~ the Han, it ~ diffir~S,Qt to cony novel, foal Beam due to limi~tians of material as well as ethical =iderati~. Bus, it be; important to evaluate ache anion Gel Stems urger stay Firstly for them a~r~riater~; in ~i~ the Lear basis of lien gamete interaction Gently. Portly, a host of Criers ~ ganete strum am fur~ti~ have aE - arm. A list of saw of these ~ prairie at the ~ of this *her. Aver Han AL ~ duplicate that work, ~ will stress tat this hips homologies are An As that have men recognized an; many Italian Lies reedit sperm morphology, sperm maturation in the ~?idid~, am gal induction log to f~tilizati~. Surfing differences have Ed varicose investigators to sagest At different Bile; Splay diverse Aim for garde in~ractic~n. E~ver, sufficient dad fist, I believe, to sagest a gereral sag for the s~oellular ~ of - mate interaction that may Sly to all normals. Finally, in closing, ~ will try to point to Bee tc~ics for whim findings fed g~raliz" me pys0E; are or are not likely to be z - ~ - riate for a particular species. SKI ~ Hat He polarized tripartite form of sperm head, m~c~piece, are tail lo <x~served Al Gals has been reseized for Am;. since by fads here Is the fertilizing furK:tioa~ of Berm, I will lint further icon to the sperm bawl, this being the 'using= em" of the with Rae gage interaction. this Is not to say that other 250 -

repins of Me cell are ret utilized Doria fertilizaticn; the motile Carat of the - ;1 's principal pin an the mit~3ria of Me miApi~ are Initial in transic~-~tic~n arm energy pin, fly. ~ ~ is no eerie to ~ ~t participate In specific ir~racticms with the en are local in these lamer ice - . In Critic to I;imilarity of overall cellular stricture, many feats of s~lular ~aniza~ci=~, art of specific sepal al~ral:icrm, are Its for not it sot. bite Weir specific di~nsi~ an suntan may vary ~;iderably, Cam head; of different: ties Assist of We mare Ants relit;. For each species;, Math the plasma no—cane a secretory granule, the an, ~ fan at the ~~l's apex situated ~ a cap Aver Me anterior Portia of a rigid, highly c~ ~~ - C. Me an ~ an Orville r - Fin for fertiliza~ In and i= Hal Aleutian during interaction win the egg Carets art germinal these r~rrir~ to* the animal kid. Pop: work Hats Cat this everTt, the acreage reaction (AR), Institutes a cI^==ic example of highly regulated Ho, arx] will be did fur]. Wring the acreage reaction, the alter act Insane fuse; wit the plod Crane at various lc~uti~s, ally Are of the accusal AL to We e~cracellu:[ar ~im~rtc. One portion of the across that ext~x3s laterally to the nu`:1—~c, termed the equatorial sent, He not participate In the fusion events of the AR. Be Arid vesicles for Arid the AR ad lop Sally fad the ~1 surface, with the the inner amoral Serene An; - Me L's limiter Brad anteriorly. these sternal features of acre exits are Extant for all Sian Term spied Pus far. CX~N AWE; IN LIE Hill SI=:ENCE: OF ~ ~='1= Formation m~nir~ Me molar organization ark condition of Me Gates' surfaces Is essential for an Slid of they int~ctic~n. }ever, before the Lear - Ids for the interaction can be eel, it Is r~ssazy to establish the cellular He, particularly for the sperm cell tick ~ In to urn dramatic sternal re~organizaticn. ~mini~ Be are den the AR cxxa~rs d~irx3 gate interacticm, for 5rs~, is important Cause it definer; He n~rhrane surfed, either plow Humane or Fir aQ~l Humane, us" by the sin ~rrirx3 the steps of fertilizaticm. While ~sic3erable Bate and ·4i~icn has ~ definition of set of events desire gate ir~eractia~, ~;ive effort redly has led to fistic that sanest a Awn pattern at the cellular level. Me major c~x:lusi~s Cat have ~ freon Cat work will be Grid briefly. No ate* ~ ~ to include ir~ivi~1 raft; bare but By may be fat in We repins city at We erg of This - T. ~paci~"tian. ]~is fir~ ma~rati~ pase of ~e s~rm ~11 oamrs nasally ~ Me fetale relive Duct, but can be pro by irx~ibaticm In vitro for a large "mberof Skip. refire c~ratic~lly as the amid ability of seem to fertilize eggs But copay, this reversible process Is poorly worsts. ~:ies~t alteratic~; in · 251 -

several E~t~s, in loin holism, ionic ca~ositic~n, Isolate - :1~-~ activity, and subtleties of ~a~1 strip, have arm report—, skirt analysis of 03 ~ features of the pass Iffy. At least too ppecies-ir~t alterations ~ he ~perm's play Insane are now r~iz" as a fur~ic~n of ~citation: charges in Trot arm Spice levels, arm the Sac of surfa~asaxia~ i. I!xse alt:eratims may be risible for he rE - rid ~ ~ membrane fluidity that also hers hire ca~citaticn. In tie ~citat" state, sham are unable to urn physiologic ARs arm c~c~tatia~ can be Casio a prerequisite for this earn. II. ~eractian Iffy he Amorous ma1:r~x. At he fine of fercilizati~ he aviduc:t, the cite is often Barr by two extra~llular matrix. Ire ironer layer, the zeta pellucida (zp), al; to be a Excretory pit of the egg, arm will be Hi^~ further - 1cm. he alar layer, in which the cumulus Ills are era, is not yet well define hat firs to be a print of this peculation of differentiated grarmlosa Ills. Fir hi, ~se, arx] rabbit sperm, wee different pupations of firm ails have ban c~;erv~, caly capacitated, intact firm can paces to the cumulus matrix to the zp; bath ~citated arm abreact cells are retains at the alar margin of this layer. Specific fibs of the firm surface do not Ear resistible for this passage, sires a variety of ~11 types bearing the Mann feature of Utility readily penetru~ the hatter ~n=~.= matr=. Ether, it appears that the cordite may be true, that the real of ~tr~cir~ factors Emu the sperm surface is emissary for flus matrix penetration. In at let two species, the cow and the pig, it Is ~ 1 Whether the am ~ us Is present at the Hi of go - te interaction, a finding that also makes it difficult to invoke a specific interactive function for the cumulus matrix. The physiological role of this matr ~ may be, therefore, to regulate the are-== of capacitated, acrosoce-intact sperm to the vicinity of the egg. 111. Interaction with the zone pellucida. The first -=r--ific interaction between the gamete cars at the level of the zone pellucida caps. ZP cognition has nag been stied in several Dies, with the Cameron , ~ a ma a a ha a a a a _ a a _ ~ _ ~ ~ a _ a a _ _ fling Eat it is a relatively staple sty Lyrist principally of 3-5 glyc~roteir~c. Hailed emanation of the in~cti~ of individual Rose up glycq?rateins with homologa~s s ~ no has det ~ mi ~ that ~ e of the zp glyoo proteins, ZP3, serves as the primary ligand for sperm binding. Mbre recent work using pig zp suggests similar findings. Reports of gamete interaction studies with individual ED DrO~ein~ f Am other dies have not yet appeared. _,= = ~ In initial systematic studies using made gametes, and considered contrcversial for some ties, it Is found that fertilizing sperm initiate birding to the up win ache ploy me—cane in the acreage ir~cacL state. fitly, He same firers have- ~ for a large fir of fiord spies (Table 1) and can near be Considered a generalizes] He of ~ fan Gage ir~ractic~n. - 952 -

THEME 1: Species ~ which acrcsc~e-intact sperm initiate zp-bi ~ cow guinea pig halt h.~'oa.n ' met pig rabbit sheep Sperm that have penetrated the zp and are located in the perivitelline space are reported universally to be acrosoc e-reacted. Together with the preceding information on primary binding to the zp, it may be concluded that.the lo cation of the AR is the zp surface following primary binding. This he= now been observed for several Naperies, as has the ~ ion of ARs by isolated, solubilized zp (Iable 2~. TABLE 2: Specimc dencrEtrating zp-induced acrosome react) cow hamster human masse rabbit The mal^~,lar events sucrcunLing the AR are not Understood fully, but recent work implicates mechanisms common to other receptor~effec*or Is, sum as hand arm grad fac*o~re~;ive cells. For iret~, he n~:leo~cide~ir~i~ proteins (G~prc~eins) lee not only been identified in Sperm f~ smrera1 Italian denies (1tible 3), but a Gemlike protein of dose dam has been -Ida E~ifica~ly with Ache Physiological AR Irma by ZP3. E~rore, rat st~ies irxlicate that ZP3 trip ARs by aggregating the pperm's ZP3 recx~kors ant that he M's ~r=;ine Please activity is stim~lat~l by ZP3 birding. Mile still city and confined primarily to Ned Warm, these fifties are striking ~ their parallel with rats fed a wale varier of different call types, and shyest the use of highly coed extra~lular signal thwarting ~i~ for anal ~is. WEIR 3: Species with G~-like proteins in sperm bull . . Guinea peg mimic.= pig Once the AR has been triggered, sperm do not ~;==n~iate from the zp and binding is rainenined. In the Rouse, ZP2 is the glyc~protein ligand responsible for this secondary phase of binding with acre come-reacted sperm. Strong evidence from experiments using hear sperm indicate= that sperm employ proacrc Bin for this interaction. This sperm~specific - 253 -

zym~n arx] its enzymatic active ~t~rt, a~im, are fat In all Can Mann Ad. ~ Wide in guinea pigs, his, Moe and rats EP~orts Me m~ of preen In this role. Posher work, particularly with Mar ppenn, indict that limits p~l~is Other with sperm Utility is Bible for Term penetration through the up matrix. Fly ex~ acres, perhaps with He coordination of other a~1 enzymes, perform; the digestive rat for zp penetration. W. Sperm fusion with the Splat Phrase. Within Me per~vit~ll~ne E - oe, the acr~react~ sperm Is in dint contact with Me egg plasm nE'rbr~ne, to Side it A~ Ad fan. ~~ ~~" of ~ different ~lian species irxticat~ Cat Me region of the cell utilized for Me initiatia~ of ~rhrare fusion ~ the plum neural o~erlyir~ the equatorial sent. It scald be Reilly that, Sir He AR, this posterior section of the anal cap dues not participate in Membrane fusion, Vegas at this later point Doria Grate iT~actic~n, eq - tories so initiate He fusion event. His cxx~ed sequel of cellular events implies ~v~ organization of these lular domains at the Basilar level. Fusion Hen prams.= to incorporate He Bin sperm into the Blown of He egg, except for ache inner act Membrane whim does not fuse, hit ~ inc=rpo~ted into a p~eic vesicle. A GENES L ~ ION GAME: INrE~Ac=m these remet irnrestigatia~s at the cellular and Alar levels praise sufficient data to sagest a ~ of gate interactions that may ably generally to Canals. 5~3 aspects of this serpent AL summarized In Figure 1. It Is ~ that the Amorous matrix functions to restrict are-== of anly capacitat ~ ~ rm to the egg. As a r ~ t, under the normal conditions of fertilization, only a select population of capacitated, acrosoc c-intact sperm Fill arrive at the ~ surface. Binding to the zp is initiated by plasma membrane receptors interacting with ZP3. Primary binding results in receptor aggregation, which itself is the triggering event for acrcscral exacyto6~s. This signal is transmitted in~aceOularly via Nonproteins arm rots ~ regulate fusion between the plasma and Aster accusal Cranes. ~ a c~, proacrwin is em. Mary binding by ZP2 and proac~;~n of a~rereacti~,/react~ sperm cx~ together with pit autoactivaticn of proa~;~n to Alvin. Sperm m~iJi~r, together witch Me action of attain to Caters limited p~teol,?sis of the zp matrix, permit sperm penetration of Me pp. ~rt3act~ sperm in the periv~lline space associate rapidly with the egg plaice Crane. Fossil been sperm and egg is initiated in the region of the sperm's plasma Membrane overlying the "3qatoria' sent. The many diverse observations map in experiments using different Lies ~ ght lead one to question the g ~ ity of this scheme. I believe' however/ that many of the apparent differences between species can be e~-~-r1~t^~ in this scheme if two variable factors, the affinity of the interactions and their kinetics, a ~ considered. ok use sperm and g ~ pig sperm, for example, may Represent two eXtIesL6 of the spectrum for these two parameters. For man=- sperm, it is cc~mcnly observed that ac~ir~act sperm initiate zp binding, Areas e.~reac~ sperm are incapable of initiating binding but will rerain associated with the zp if the ARhas occurred at the zp surface. In contrast, with guinea pig - 254

,"=RE KIND Fioura 1: EN general He for Brian Gas infraction. A) Lam pe~ratia~ TV the Claus matrix is achieved by Ye Call `8 1=tili~, hem with Variate surface ~araC~isti~ Infers by mpaci~catic~n. specific r~*:o~ligar~ i~c~ia~s do no Cur, arm enzymatic ~.i~ are fly far perw~=tia~. she Plus Us to regulate sperm arc to the pp. Dim that only capacitated, Intact Worm arrive at We up surface. B) At the up ~rfa~x, priory binding ours ~ r~t~ on the pi hare of the sperm aid Me Zp gly~tein ZP3. C) The ex~acellular signal of up birdie ~ transmitted acmes We spend ~ to trigger We AR in a pro involving Me abrogation of tile ~m'8 ZP3 ~ by ZP3. Ethic a~rqatia~ signal pro; the Lions of a Mine kinase whim is invc~lved in the ~7e activation of Glottis, and I~= to Ye Be of events ratio in Ye AR. Fusic~n is initial at Triple loca~cims Ben the ply and alter a~1 z~rbranes File the Cam ~ bay to ZP3 at Ye zp surface. ~ birdie Ben the a~ctin; spew and ZP2 foulers direly after the fusion event. ~ac~;~n Ores as at least ale of the major Ban ~9 partici~?ati~ in scary bindi - . D) USA acr~1 PI during the AR 1~= to activation of proacrmin, r - ;ulting in the forrratian of acumen. the Dined motile farm of the Cam and the enzymatic Lability of rawly es acrosin EN s~ees-irx~ pyrolytic penetration thrash the up matrix. E) A r~ Patti split throb the zp is created due to the limits prot~lytic activity of acrmin. hybrid vesicles bearing sperm r~ far Zen remain at Ye up Sofas' and Satire can be seen as a odor thresh which the exam penetrate. :— Am: . ~3 ,, ~~ t~ A - __ An, ~ . _~~ of_ 1~ Do 255 - _ Primary Binding ZP3-Mediated Secondary Binding ~ ZP2-Mediated

sperm, ac~intact sperm associate weakly arrt In low hers with the Ha?, arx] ac~reacted Sperm display tenacious interaction with the Ha? surface. With Ed primary binding, the affinity between the sperm's r~rs and ZP3 may vary aver a wide range for different species. This affinity could be considered high for Ease sperm arm lo for guinea pig sperm. O~;i~ affinities may ably to the dies for Mary birding. Similarly, with rears kinetics, perhaps ZP3~ti~1at~ ARs Ear sufficiently slowly in Ease Glenn to permit e~peri~tal d~ervaticn Woo the En is bound to the up surface, Whereas in many ather Species the event Is more difficult to detect due to rapid AR induction at that location. Species variations mill be observed, but it seems unlikely that the== mill involve major differences in fundamental design or mechanism, but rather variations in the affinity or kinetics of individrm~ events. CoMMON THEMES DURING EPIDIDYM~L TRANSIT Following the differentiation of the haploid spermatozoon, the ~11 is liberated from the seminiferous epi~chelimn and passes frees the testy to the epidid~rmis. Despite the Mince of grass ~rp~ologi~a~ *lard, Sperm acquire ache ability to ~n~ceract su~cfully with arm ~ feminize h~logals Us during epididymal transit. ~xi~1 ppidic~nal Sperm are wea}cly mobile (at best), coot Ebonize the zone pellucida, and cannot Undergo p~ysiologi~a1 ARs; distal epididymal sham are vigorously ~tile, bird readily ark ~ large numbers to the zp, ark undergo ARs when challenged with zp. Although their lengths may vary, three major subdivisions have been identified cyclically for all Lies mimic: Me caput, the corpus ark the cauda epididymis. Transit throb Me organ ryes approximately 1-2 weeks; the exact duration varies Long Species, but the principle that transit r~ui~ a period of days ~ constant. Biochemical analysis rerolls Mat the fluid reverb Mu Me epididymal lumen displays major differences in polypeptide ~6ition ~i~ upon the region from which fluid Is Volleyed. Sperm are, therefore, subject to Charming environments during transit t~h tile epididymis. Not surprisingly, surface reeling at the ~leallar level Is a general feature of epididymal transit for allm~ian Species Maid (lable 4~. ME 4: Sperm surface Crane n~ificatic~ns detected desire ppididymal transit 1. Large 2. lect~n-bir~i~ 3. intr~nbran~us particle distri~ti~ 4. lipid position 5. amoral of rear Pi - Ross 6. Edification of egoistic fits The mechanisms which bring about these surface alterations have not yet been elucidated. Similarly, it ~ not known which of these modifications are related to the acquisition of fertilizing function by sperm. Identification of the molecules used by sperm for gamete interaction is reces=~ry before the relevant mechanisms can be ascertained. The approach taken toward this topic ~ ~ laboratory has involved the identification of sperm components that participate in — 256 —

fertilization Art He 1~ of anti~rm zmxx:l~al antibodies (my). He pry; have bun us" ~ Irvin Flume sties to lac~zze ye particular Arm moieties, ~ Fannie sties, bay in vine art in viva to Smirk ~ rule of ye At in gamete ir~eractia~, and in bionics Dies; to incite ye Ye involve. We Den have Be Corey to ~ a Pacific At as ~ function of lipid maturatiar~. He of ~ sperm Ants Cat we have st~ied unwire this aback is tensed M42 antigen singe it was fiat identified unwire He M42 mob. M42 antigen ~ a high Mr doublet (200/220 I)), located in a restricts region of play n~rhrane c~erlyir~ the acre. The M42 mob bay; f~ilizaticm ~ a ~tian ~t Far, bay in vitro are ~ viva; the Pacific event preen is the ZP3-ir~1 OR. Am r~ from each of the three major ppidi~ymal regic~ Cain He M42 antigen in an i~isti~le localization pattern despite He fibrin that Cut Term will not ~ z~i~sd ARs. Analysis of the M42 antigen itself Awls that it ~ steal n~dificaticn ~ shift from 220/240 kO in immature sperm to 200/220 id) ~ mature sperm) coincident with He Here's Fair ability undergo z~i~ ARs. M42 antig~'s steal Deification d~ not Char as a fur~tian of c3ura~cioa, of ~sit, singe Arm retail experimentally ~ e At ppididymis for 2 way do not display the mature form of the antigen nor do they Argo Fir ARs. these results suggest that it ~ resay to expose Sam to particular ~riz~ta1 a~itic~ns fat in the ppididy~1 llmen distal to He caput to apiece a functic~ Arm ~1. Sly ~~ work is Aid before it can be established that p ~ t-trarE;laticmal ~ ification of ~ astir surface pr ~ Bins, such as that found for MY antigen, represents a universal mechanism for sperm maturation. Nev ~ "c=, it is apparent that the identification of functional components of the sperm constitutes an essential first step for an understanding of the molecular basis Bach of gamete interaction and of Acidic maturation. PAR WHAT By; OF SIUD:l Pa A;RE ~ SWISH; APED an the preening I-ion, ~ have attempted to illustrate that the cellular and ~ 1~-~1ar patterns of gamete interaction appear to be hi ~ y conserved. This does nct imply that all bells will ~~ exactly identical malec`Oes for each event of the prcoess. It ~ well known from many physiological studies that several aspects of gamete interaction display substantial species specificity. However, the conserve, pattern of gamete interaction does imply that, for a species ~ which ~rileental malaria is limit or for me that has not been investigated pr~rialsly, considerable infon~Qtian ~xrnir~ the nature of a Illume of intent may be available to facilitate its identification,, Ablation anc] in~restigaticm. ~ anticipate that Axe miles involved ~ rendition evens, which are likely to be present in leer aunts, will be ammo those that da~trate species differences. Her, the abated ~nfonnati~ derive fray eral Martian ins rats that be HAL likely lattice for sperm Alleles involve in primary interactic~n with e 8p, for beta ~ , is the pi a ~ Drone averlyir~ the acz ~ ane. With sim;1ar reasoning, the plasma membrane overlying the equatorial segment should be examined to identify the sperm con portent(s) that initiate fusion with the egg plasma membrane. Given the polarized structure of the sperm cello specification of a componenk's location is extremely vzl~hle, - 257 -

~mi~ir~ i~i~ for; ~ a reprice area of Me cell za~r Ian on ger~ral exam~natia~ of Me entire cc~plex strep. Alternatively, it can arise }:e anticipate eat sap of the Yes Dive in Gas interacticn will be very similar AL a wide rarer of Species;' paint arly Me involved ~ c—I] fu~imo SUCH AS iCO fib are in extra~llular signal Dial. An eagle of the latter may Day be fag in He ic3entifica~ of a 41 kD G~-like protein in the sperm of at let 5 different _lian ~~ ins. OR files may be r~r~ntel by Be ~erm's shy for for ZP2, Slim at to be prOaC~Ul, at }A the ~8 digestive enzyme for zp permeation, acted. For all Dies att~i~ to identify pa or Dots utilize naturally by Gag; ~ viva, it is tip hat heralds gamete systems be mpl~ Infer p~ysiolc~ical cx~iti~s. Trials results ~d emerge, are already have Do, fin the use of heterol~s gan~:;e interaction shies or the ,'~ of rx~hysiologi~ clitic;. Two examples that hence arisen In by An lab may be i~e. Me first Is ~= sb~iee; An the ~i~ of then AR arm the so, wig the i`3entificati~ of sperm Dents involved In fusion with the egg pled Crane. ~ of Air work an the AR In ~ storm has fog ~ He M42 antigen, err! inhibition of He process with the M42 mAb, which was d;- artier. In that work, it was fairs that M42 mAb inhibited only p2~siologi~al1y-ir~d (i.e., unwire zp) Us, kilt did cat inhibit pharmacologi~lly-ir~d (i.e., unwire Cal i~re A23187 or 1Y~ti~l~line) Ads. aft Lamination of He ability of Muse sperm r~ from the fit, oc)rpus, are cauda ppididyni,; to ~ ARs regaled Cat all Cam Rations Cold be stagnated to udders phazmacologi~1 Ads, but Ply mature sperm wend stipulated to undergo physiological Be. Immature caret epididyDa1 Berm do not red to zp by Moire Ad;. Teether, these results sagest that important regulatory aspens of the AR ideation Mania are gypsy durir~ phanmoological AR sti~latic~n, and He results of experiments unwire p~cologi~1 Haitians exclusively to stay He AR should be Debt Ply. He seed example dog with He identifi=~ticm of germ Dots mat participate in fusion wig the Ad. We initiated Dies; an this Epic thresh the use of He M29 fib. His mAb Sizes a 60 kO rmpn~teinrastrictedto He equatorial ~rent, sax! inhibits fertili7~tian, both ~ vitro arx! in biro, by blanking l~l~s Berm fusion with He erg plug membrane. Ire mAb Is ineffective In the heterol~s cams of Mae Hem are zala-free Hester Do. A me result has also been fag ~ Paul Pri~ff arx! Diana styles' 1~ (livid ~ ;ity of ~ tialt, Fa Hi ~ ). They have identified a mAb ~ t guinea pig sperm that blocks fusion with the egy plasma membrane, but only in a heterologous cross (guinea pig sperm + hamster eggs). The mob is ineffective in the homologous situation (guinea pig sperm ~ guinea pig eggs), suggesting its irrelevance as a probe to define physiologically meamiDgfu1 sperm ccrlonents. Although opposite findings Merged, the results of these No studies indicate the importance of using homologous ~ 2~S

gamete £;ys~ in attempts to define Et~siologi~lly ZeleVailt ~tS in ~ pa~ia~ar Icier;. ,S~ In the foreskin di~=icm, ~ has tried to - Prize eerie to Be: ~at, demise r~tei differs, Me ~ of gamete tactic al ~ in: lik`31y to be Dare E;im;lar than it IS differs. Sties di~i~tiCBE; will be fat, hat Me ~ Sign of thy ~ for each species is likely to Am to a Cal pattern. 1 acme t:nat ~ ~l~]l~ i~l~ ~ ~ Aids ~ say be hamlets, hat witch varying s~ificityr for ~~= Lies;. OR sperm Alleles that are r~pcnsible for highly ~ cellular furx~tions, as ice tort are ir~Llular ';ignalling, are likely to be less variable Al species. As, Dies in my ~ have predict, arm are ~;rui~ to provide, an invaluable body of information Ox cellular are ~lea~lar ~ ~ which fertilization axons. Here ~ no Seine for the sty of hcnx~l~ws Gates in physiological Clitics to identify individual Axles At participate In Gate interaction, ho ex~ive sties In m~e] ~; can dirt attention imE~i~t^]y to He Be of Blue ~t ~ Any Any facili~cate investigations In any Italian species of intern. _ ~ ~ ~ ~ ~ ~ - 259

Reviews deco it for ~ail" inf~mati~ arm references Eddy, E.M. 1988. The sperma~zcc~. Pp. 27~68 ~ ~ysioic~y of ~eia,, Vol.1. E. Ail arm J. Neill, ~c. Now York: Raven As. Thornier romps, S. AL M. C—rot. 1987. zap pellucida bigwig activity. ford Retrim of P - Ire Biology 9:294-321. F~, L.R. arm K.K. Ouija. 1988. Colic ~ surface events in fertilizatian. Gate Re';. 20:491-519. Canes, R. 1989. Crane r~3elir~ rim ~ maturation in the ~idipymis. oxford Redried of P—five Biopsy, 11:285-337. la - Dais, J. and K.D. Remits ED. 1985. A Car zebras n~1 of Mann ~p~ci~cation arm me acre reaction of Sian spermatozoa. Game Pes 12. 183-224 · · — Olds~Clarke, P. 1988. Germanic analysis of seem function in foci ~ ization. Ate Pees. 20:241-264. Oliphallt, G., A.8. ~yr~lds, arm T.S. Ideas. 1985. sperm surface its involve in the cxx~1 of the acreage r~3acti~. Am. J. Ar~at. 174: 269-283 . O'Ra~, M.G. 1988. SE~g recognition arm barriers to ivies f~ilizatic~n. Gamete P—s. 19:315-328. Veteran, R.N. arx] L.D. R'l=~1l. 1985. The Clears spermatozoon: A Ides for me sib of r~i~ spe`:ifici~ in plasma Curare organization arm fanatic. Tissue arm cell 17:769-799. P0aire, B. arm L. I. 1988. Efferent Ants, epididymis, and was c3eferens: Stature, fury and few radiation. Pp. 999-1080 in Physiology of P - Rich, Vol.1. E. Kr0;l arm J. Neill, Eric. NO York: Raven P=ss. Air, P.M. 1989. Sian sperm interacticx~ why e~ccra~llular matrix= of ~ egg. Oxford Review of P - revive Biology, 11:339-388. retell, B. arxl D.E. Braces. 1988. Ar~atapy, vasalla~re, inrervation arm feeds of me male ` - revive crack. Pp. 753-836 in Physiology of Otis, Vol.1. E. Rail are J. Neill, eden. NO York: Raven Press. Topfer Per, E., A.E. Prim=, A. I~,arxI W.-B. Sc~il1. 1987. Is a fus~bir~i~ protein invo1v~ in ~ interaction in me pig? Pp. 287-296 in NO H=iza~s in sperm call E~rch. H. Sari, ed. If: Japan Scientific Society Pres;. In, P.M. 1987. The biology arxt Misery of fertilization. Science 235: 553-560. In, P.M. 1987. Sly events in Italian fertilization. Arm. Rev. cell Biol . 3 :109-142 . 260 -

In, P.M. 1988. The _Lian ovum. Pp. 69-102 ~ ysiol~y of Pubis, Vol.1. E. ~i, ark J. mill, us. New York: Raven Pz~;s. _rnan, P.M. 1988. Zeta pell~xida gly~r~eir~. Ann Rev Biopsy 57: 415~442. Yan~gi~i, R. 1988. Ion fertilization. Pp. 135~185 in sociology of Ibis, Vol.1. E. Gil ark J. Nail, fix. Not York: Even Press. - 261 -

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This book results from a study by a committee of the Institute of Medicine and the National Research Council's Board on Agriculture. The committee examined the scientific foundations of medically assisted conception and developed an agenda for basic research in reproductive and developmental biology that would contribute to advances in the clinical and agricultural practice of in vitro fertilization and embryo transfer. The volume also discusses some barriers to progress in research and ways of lowering them, and explains the scientific issues important to ethical decision making.

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