seminiferous epithelial cycle

Spermatogenic Epithelial Cycle(SEC)

By Falana Benedict Abiola

B.Sc (Hons) Unilorin; M.Sc. (Anatomy) Ile-Ife

Practice Seminar 1

Department of Anatomy, College of Medicine of the University of Lagos,

Nigeria

Matriculation Number 109091016

Outline• Introduction to SEC

• The cycle and wave

• Selected Stages

• Structure of the testes and spermatogenesis

• Evolution of the study

• Seminiferous epithelium

• Conclusion

• References

Introduction

• Spermatogenic lineage development is a complex process but occurs in an orderly manner referred to as the spermatogenic cycle ((Clermont 1972)

• Proteins and mRNAs are exchanged via cytoplasmic bridges and may help in coordinating the synchronized development of germ cell clones.( Braun et al.,1989)

Introduction

• Each stage is characterized by a combination of different types of spermtogoonia, spermatocytes and spermatids that synchronously proceed through the spematogenic process.

• The complete spermatogenic cycle in mouse was

SEC

• Layers of germ cells all develop in a coordinated, repeating programme known as seminiferous epithelial cycle.

• In rodents, successive stages are arranged in cylindrical segments along the STs.

• Its existence been demonstrated in many vertebrate species. (Kerr, 1995; Sharpe, 1994)

• They are features of vertebrate spermatogenic organization that reflect the need for a rigorous sperm production. (Timmons et al.,2002)

Cycle and Wave

Cycle and Wave

• Cycle of the seminiferous epithelium :– synchronous mitotic meiotic divisions

– 6 stages in man– 4.6 cycle from sperm release (16 days per cycle)

• Waves of the seminiferous epithelium :– in rodents and other mammals

– no waves in human seminferous tubule

Stages

• These are designated stages I-XIV of the seminiferous epithelial cycle in rat (Leblond and

Clermont,1952).

• Twelve such stages (I-XII) have been described in the mouse (Oakberg, 1965a)

Stages

• Stage duration is precisely timed.• The complete spermatogenic cycle was

determined to be 8.6 days in the mouse (Okberg

1956b) and 12.6 days in rats (Hilscher et al.,1969)

Stages in the indian gerbil field rat (Terata indica)

• Four generations of A type, a single generation of intermediate(In) and two generations of B type spermatogoonia are identified by Bilaspuri and Kaur

(1994).

Stages in T.indica

• Spermatocytes have been observed in prophase, metaphase, anaphase and telophase; in terms of size and morphology, the phases of prophase could further be subdivided. (Bilaspuri and Kaur 1994).

Stages in the Buffalo (Bos Bubalos)

• Using H&E preparations the SEC in the buffalo has been divided into 8 stages;1,2,3,4 and 8 have been subdivided. Guraya and Bilaspuri (1976)

Stages in the Buffalo

• The buffalo spermatogenesis is constituted by 4.57 cycle of seminiferous epithelium which resembles that of the bull. (Guraya and Bilaspuri 1976)

Stages 1–8 of the seminiferous epithelium cycle based on the tubular morphology system.

França L R , Godinho C L Biol Reprod 2003;68:1554-1561

©2003 by Society for the Study of Reproduction

Structure of the testes

• Tunica albuginea : fibrous connective tissue

– mediastinum :

– septa :

• Tunica vasculosa : loose connective tissue

• Lobule : 250

– seminiferous tubules : 1-4

– interstitial (Leydig) cells :

• Rete restis :

Testes

Seminiferous Tubules

• Seminiferous epithelium : stratified epithelium

– spermatogenic cells :• spermatogonia :

• spermatids :

– Sertoli cells : supporting or sustentacular cells

• Tunica propria : lamina propria

– myoid cells (peritubular contractile cells) :• rhythmic contraction

Spermatogenesis (I)

• Spermatogonial phase :– type A dark (Ad) spermatogonia :

• the stem cells of the seminiferous epithelium

– type A pale (Ap) spermatogonia :• committed to differentiation

– type B spermatogonia :• differentiated from type A spermatogonia

• the last event in the spermatogonial phase

Spermatogenesis (II)

• Spermatocyte phase : meiosis

– primary spermatocyte : 4n• produced by type B spermatogonia

• first meiotic division

• homologous chromosomes crossing-over

• give rise to secondary spermatocyte

– secondary spermatocyte : 2n• second meiotic division

• give rise to spermatid

Spermatid Phase (Spermiogenesis)

• Golgi phase :– proacrosomal granules-acrosomal vesicle

– axonemal complex : sperm tail

• cap phase : acrosomal cap

• acrosome phase :– manchette (flagellum development), nucleus condense

• maturation phase :– residual body is pinched off and phagocytized by Sertoli

cells

Spermiation

Spermatogenesis

Sperm Passway

• Seminiferous tubules :

• Straight tubules :

• Rete testis (mediastinum) :

• Efferent ductules :• Ductus epididymis : acquire motility

• Female tract : acquire fertilization ability

– capacitation : removal and replacement glycocalyx components on the sperm membrane

Structure of Mature Sperm

• Head :– acrosomal cap :

• acrosin : acrosome reaction

– nucleus :

• Tail :– neck : centrioles

– middle piece : mitochondria

– principal piece : fibrous sheath and axonemal complex

– end piece : only axonemal complex

Spermatozoa

Variation in Sperm Production

• Testis Size

• Efficiency of spermatogenesis– mitotic division

– degeneration of germ cells

• Length of spermatogenesis

Human Spermatozoon:• 60 um long, consist of a head & a tail.• Head: pear-shaped & flattened w/ a nuclear & a

acrosome (contains hydrolytic enzyme important for fertilization).

• Tail: 55um in length w/ a microtubular axoneme in the core.

Subdivided into 4 segments: (a)The neck, containing a centriole (connect) (b)The middle segment (5-7um), containing a sheath of mitochondria (provide energy). (c)The principal segment (45um), containing a fibrous sheath (support the tail). (d)The end piece (5-7um), containing a microtubular axoneme.

Evolution of the study

• The definition of stages of the cycle of seminiferous epithelium in rats was made possible by the work of (Leblond and Clermont (1952)

• The existence of a wavy nature of spermatogenic epithelium was discovered by Perey et al .,(1961)

Evolution of the study

• Further more Huckins and Clermont(1968) reported the evolution of gonocytes in the rat testes during late embryonic and early post natal life.

• Sertoli-germ cell communications network was reported to play a key role in regulating SEC Jegou (1993)

Evolution of the study

• The macro, micro and molecular research on spermatogenesis was undertaken by Kerr (1995) in a quest to understand its control.

Evidence of Expressed Proteins

• Galectin family currently includes 10 mammalian members (Cooper and Barondes, 1999), which are expressed in many different embryonic tissues and adult tissues where they may be found either in the intracellular or extracellular compartments, or both (Harrison and Wilson 1992; Hughes, 1999)

Expressed Proteins

• These proteins have been implicated in many different biological processes, including cell recognition (Puche et al.,1996), cell adhesion (Cooper et al.1991;Hadari

et al. 2001; Kuwabara and Liu 1996), organization of extracellular matrix (Hikita et al., 2000) and programmed cell death (Akahani et al., 2001; Perillo et al., 1995)

Distribution of Galectin 1

Galectin 1 expression in the developing testis.

Timmons P M et al. Development 2002;129:635-647

Seminiferous epithelium(SE)

• A complex and highly dynamic tissue.

• Male reproductive success ultimately depends on the ability of this tissue to produce prodigious numbers of sperm consistency.

Seminiferous epithelium(SE)

• Its organization into tubules serves provide maximum area for sperm production.

• The structure of the epithelium and the precise orchestration of spermatogenesis makes sperm release regular.

Seminiferous epithelium

• Developing cells gradually traverse the epithelium from the basement membrane to the apical surface .

• They are then released into the tubule lumen as spermatozoa.

• Spermatogenesis progresses.

Seminiferous epithelium

• The adult Seminiferous epithelium always contains several layers of germ cells at different stages of development.

Seminiferous epithelium

• Stages of the seminiferous epithelial cycle in sections of adult testes has been determined by light microscopy ( leblond and Clermont, 1952; Parvinen, 1982; Russell et al.,1990)

Seminiferous epithelium

Germinal epithelium

Review of the germinal epithelium

Sertoli cell Germinal epithelium

• 1. Basal lamina

• 2.Spermatogonia

• 3. spermatocyte first order

• 4.Spermatocyte second order

• 5. spermatatid

• 6.mature spermatid

• 7.sertoli cell

• 8.tight junction

Seminiferous Seminiferous TubulesTubules

Seminiferous TubulesSeminiferous Tubules

D = 150 - 250um, 30 - 70cm long,

Spermatogenic Spermatogenic cells

epithelium Sertoli cells

Basement membrane

Collagenous fibers

Limiting membrane

Myoid cells

Mis. Egg , I miss you very much!

Mr. sperm,

Mr. Sperm , I miss you very much too !

Sertoli cells: Columnar cell rest on B.M., the free surface reaches to lumen. spermatogenic cells locate b/w adjacent cells Features & function:

LM: no clear outline, basally-located, ovoid nucleus w/ a distinct nucleolus.

EM: (l) abundant sER., Gl., Ly.,

Mf., & Mt. (2) Tight junctions present

b/w adjacent Sertoli cells (isolate spermatogonia from other spermatogenic cells).

Function: (l) Support & nourish spermatogenic cells;(2) Secrete fluid to help the sperm moving; (3) Phagocytize & digest the residual bodies (4) Synthesize & secrete ABP (androgen binding

protein) which combines androgen in seminiferous tubule to stimulate spermatogenesis;

(5) Form the blood-testis barrier: Tight junction constitute the main part (rest: B.M. & limiting membrane). Function: separates germ cells from immune system & prevents auto-immune reaction.

(6) Prevent some physical & chemical factors from damaging germ cells, e.g. radiation, body temperature, infection

Conclusion

• The SEC is a conserved feature necessary for the sustenance of fertility in Man.

• Further studies on SEC in other Mammals would shed more light on these complex phenomena.

Thank You!

References

• Timmons, P.M., Rigby, P.W.J.,Poirier F.,(2002).The murine sminifeous epithelial cycle is pre-figured in the sertoli cells of the embryonic testis

• Bilaspuri, G.S and Kaur, I (1994). Spermatogenic cells and stages of the seiniferous epithelial cycle in the indian gerbil rat, Terata indica

References

• Prince C.G and Loveland K.L (2000).Germ cell suicide: New insights into apoptosis during spermatogenesis. Bioessays 22, 423-430

• Perey, B.,Clermont,Y., and leblond, C.(1961)The wave of the spermatogenic epithelium in the rat. Am .J.of Anat.108, 47-48

• Leblond, C.P andClermont,Y.(1952).Definition of the stages of the cycle of seminiferous epithelium in the rat.AnnNew yorkacad.sci.55, 548-573

References

• Kiers zemembaum, A.L. (2001). Apoptosis during spermatogenesis: The trills of being alive. Mol. Reprod. Dev. 58, 1-3

• Kerr, J.B.(1995)Macro, microand molecular research on spermatogenesis: quest to understandits control. Microsc.Res.Tech.32, 364-384

References• Jegou, B .(1993).The sertoli-germ cell

communications network in mammals. Intrev.Cytol.14725-96

• Hughes, R.C.(1999). Secretion of galectin family of mammalian carbohydrate –binding proteins. Biochim biophys.Acta.1473, 172-185

• Huckins, C and Clermont, Y.(1968).Evolution of gonocytes in the rat testes during late embryonic and early post-natal life . Arch.Anat.Histol.Embryol.51-341-354

References

• Hikita C.., Vijayakumar.,S.,Takito.,J.,Erdjument-Bromage, H.,Tempest, P.,and Al-awquati, Q.(2000).Induction of terminal differentiation on in epithelialcells requires polymerization of hensin by galectin 3..J.Cell Biol.151, 1235-1246

• Eddy, E.M., and O’Brien, D.A.,(1998).Gene expression durin mammalian meiosis. Curr.top.Dev.Biol37,141-200

References

• Enders, G.C.(1993).Sertoli-sertoli and sertoli-germ cell communication. In the sertoli cell.(ed L.D. Russel and M.D.Griswold), pp.447-460. Clearwater, FL. Cache RiverPress

• Clermont, Y and Perey, B.(1957).Quantitative study of the cell populationof the seminiferous tubules in immature rats.Am. J. Anat100, 241-268