DEVELOPMENTAL

BIOLOGY Lecture II: SPERMATOGENESIS

SPERMATOGENESIS According to Hess

et al., 2008

Spermatogenesis is the transformation of spermatogonial cells into spermatozoa over an extended period of time within the seminiferous tubule boundaries of the testis.

SPERM: DISCOVERY Anton van Leeuwenhoek and

Nicolas Hartsoeker

First to discover the sperm, and believe that these are “parasitic animals”

Leeuwenhoek also wrote that sperm were seeds, and that the female merely provide the nutrient soil in which seeds are planted

Hartsoeker drew the homunculus, sperm contained the entire embryonic organism

SPERM: DISCOVERY J.L Prevost and J.B. Dumas

claimed that sperm were not parasites, but rather the active agents of fertilization.

They proposed that the sperm entered the egg and contributed materially to the next generation.

SPERM: DISCOVERY Oscar Hertwig and Herman

Fol

In 1876, independently demonstrated sperm entry into the egg and the union of two cells’ nuclei

Hertwig repeatedly observed sperm entering the eggs and noted that only one sperm can enter each egg

SPERM: DISCOVERY A. Von Kolliker

Described the formation of sperm formation from cells in the adult testes

Believed that sperm excited the egg to develop

SPERM: STRUCTURE Each sperm cell consists of a haploid nucleus,

a propulsion system to move the nucleus, and a sac of enzymes that enable the nucleus to enter the egg.

Acrosome

Derived from the cell’s Golgi apparatus and contains enzymes that digest proteins and complex sugars

SPERM: STRUCTURE The core of the

axoneme consist of 2 central microtubules surrounded by a row of 9 doublet microtubules

SPERM: STRUCTURE Only one microtubule of

each doublet is complete, having 13 protofilaments; the other is C-shaped and has only 11 protofilaments

Profilaments ar made of dimeric protein tubulin

SPERM: STRUCTURE

Although tubulin is the basis for the structure of the flagellum, other proteins are also critical for flagellar function. The force for sperm propulsion is provided by dynein, a protein attached to the microtubules

SPERM: STRUCTURE Dynein is an ATPase, an enzyme that hydrolyzes ATP,

converting the released chemical energy into mechanical energy to propel the sperm.

This energy allows the active sliding of the outer doublet microtubules, causing the flagellum to bend (Ogawa et al. 1977; Shinyoji et al.1998).

The "9 + 2" microtubule arrangement with dynein arms has been conserved in axonemes throughout the eukaryotic kingdoms, suggesting that this arrangement is extremely well suited for transmitting energy for movement.

The ATP needed to whip the flagellum and propel the sperm comes from rings of mitochondria located in the midpiece of the sperm.

SPERMATOGENESIS

SPERMIOGENESIS The centriole produces a long

flagella at what will be the posterior end of the sperm, and the golgi apparatus forms the acrosomal vesicle at the future anterior end.

The mitocondria collect around the flagellum near the base of the haploid nucleus and become incorporated into the midiece of the sperm.

HORMONAL FUNCTION AND CELLS INVOLVED IN TESTICULAR FUNCTION

SERTOLI OR SUSTENTACULAR CELL Sertoli cells are supporting

cells that stretch from the lumen to the edge of the tubule

nourish the developing sperm

form a blood-testis barrier to control spermatogenesis (similar to the blood-brain barrier)

These cells also inhibit spermatogenesis before puberty and stimulate the process after puberty.

It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.

Sertoli-Sertoli junctions divide seminiferous tubules into basal and adluminal compartments

the Sertoli cell has also been called the "mother" or "nurse" cell.

Sertoli cells also act as phagocytes, consuming the residual cytoplasm during spermatogenesis.

LEYDIG OR INTERSTITAL CELLS

Leydig cells, also known as interstitial cells of Leydig

found adjacent to the seminiferous tubules in the testicle

They produce testosterone in the presence of luteinizing hormone (LH).

Leydig cells release a class of hormones called androgens

stimulates Leydig cells to produce testosterone in the testes

Luteinizing Hormone

stimulates Sertoli cells to produce androgen-binding protein (ABP), thereby stimulating spermatogenesis

SH also stimulates Sertoli cells to produce inhibin, which provides negative feedback to the anterior pituitary to decrease FSH secretion

Follicle-Stimulating

Hormone

HORMONES

gonadotropin-releasing hormoneSecreted by hypothalamusStimulates secretion of anterior pituitary secretion hormones (FSH/LH

Secreted by cells of Leydig (Interstitial cells of seminiferous tubules)

Exert negative feedback on hypothalamic and ant. pituitary hormones

Stimulates spermatogenesis by binding to ABP and development of secondary sex characteristics

GnRH

Testosterone

is a hormone found in humans and other animals.

It is synthesized and secreted by gonadotrophs of the anterior pituitary gland.

FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body.

FSH and luteinizing hormone (LH) act synergistically in reproduction.

FOLLICLE STIMULATING HORMONE

also known as lutropin and sometimes lutrophin

is a hormone produced by gonadotroph cells in the anterior pituitary gland.

In females, an acute rise of LH ("LH surge") triggers ovulation and development of the corpus luteum.

In males, where LH had also been called interstitial cell-stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone.

It acts synergistically with FSH.

LUTEINIZING HORMONE

Temperature

The optimal temperature for spermatogenesis is 34-35 ⁰ C.

Diet

Diet must contain vitamin A, B12, folic acid and vitamin C and E which is essential for spermatogenesis.

NON-HORMONAL FACTORS