Stem Cells and Gametogenesis

Stem Cells

cells that have clonogenic and self-renewing capabilities and differentiate into multiple cell lineages

History Mid of 1800

the discovery that some cell could generate other cells

History early 1900

the first stem cells were discovered to generate blood cells

History in 1998

James Thomson and coworker derived the first human embryonic stem cell

History in 2005

Scientists at Kingston University in England were purported to have found another category of stem cell.

History 2004-2005

Hwang Wol-suk claimed to have created several human embryonic stem cell lines from unfertilised human oocytes by cloning

History 2006

Scientists at Newcastle University create the first ever artificial liver cells using umbilical cord

History 2007

1. Dr. Anthony Atala claimed that a new type of stem cells had been isolated in amniotic fluid

2. Mario Capecchi, Martin Evans, and Oliver Smithies won the 2007 Nobel prize for physiology or medicine

History 2009

Found a way to improve chemotherapy of mouse muscle stem cells

History 2010

Human embryonic stem cells have been cultured under chemically controlled conditions without the use of animal substances

Classification of stem cells

1. on the basis of Potency

2. on the basis of their sources

on the basis of Potency

1. totipotent

2. pluripotent

3. multipotent

4. unipotent

5. oligopotent

on the basis of their sources

1. embryonic stem cells

2. adult stem cell

3. induced pluripotent

Totipotent

the ability to differentiate into all possible cell types

Totipotent examples

Zygote formed at egg fertilization and the first few cells that result from the division

- gensis

formation

Pluripotent

differentiate into almost all cell types

Pluripotent example

embryonic stem cells and cell that are derived from the mesoderm, endoderm, and ectoderm germ layers

Multipotent

differentiate into a closely related family of cells

Multipotent example

include Hemopoietic stem cells that can become red and white blood cells

Oligopotent

ability to differentiate into few cells

Oligopotent

differentiate into few cells

Oligopotent example

include lymphoid or myeloid stem cells

Unipotent

only produce their own type

Unipotent

Include muscles stem cells

Early or Embryonic

found in the inner cell mass of a blastocyte after approximately five days of development and include totipotent or pluripotent (typically 4-5 days old and hollow microscopic ball of cell called blastocytes)

Mature or Adult

found in specific mature body tissue as well as the umbilical cord and placenta after birth and includes multipotent, oligopotent and unipotent cells

Induced pluripotent stem cells (iPS)

Lab made. they are reprogramming somatic cells back to pulripotent state

goal of stem cell therapies

to promote cell replacement in organs that are damaged and do not have the ability for self repair

PGCs

Promordial germ cells

gametogensis

the differentiation of the germ cells into gametes: eggs and sperms

Spermatogenesis

the development pathway from germ cell to mature sperm

male gametes are formed in

the testis within the seminal tubules

Testicular tissue consists of

tunica capsule surrounding a large number of long, tubular convoluted seminal tubes that form sperms

seminal tubules are linked to each other by

connective tissue rich in blood vessels known as tubular connective

Primoridial germ cells

initiate the formation of spermatogonia that move during its transformation into sperm to the inner region

Ledge cells

secrete the hormone the hormone testosterone

Stages of spermatogenesis

1. Multiplication

2. Growth phase

3. Maturation

4. Differentiation

Multiplication

primary germ cells divide several consecutive divisions by indirect mitosis method, producing a large number of Spermatogenic cells, each containing (2n)

Growth phase

The spermatogenic cells stop dividing and grow and increase in size, so the nucleus enlarges and this moves towards the center of the tubule and forms the primary spermatocytes cells

Maturation phase

primary spermatocytes divide by meiosis

Maturation phase include

1. Meiosis 1st

2. Meiosis 2nd

meiosis 1st

leads to the formation of two cells of equal size and whose nucleus contain an odd number of chromosomes (secondary spermatocytes)

meiosis 2nd

division of each two secondary spermatogenic cells divides into two spermatids each containing (n) thus 4 spermatids are formed

Differentiation

each spermatids will start to differentiate into sperms

each spermatids is a cell that contains

1. a round nucleus is relatively small in size

2. chromatin bodies

3. cytoplasm contains the Golgi apparatus near the nucleus

4. two centrioles near the periphery of the cell

5. chromatid body, along with other organelles

Golgi Phase

perforating body

acrosome

Cap phase

1. gap that contains the acrosomal loses the fluids in it and relaxes over the top of the sperm and becomes what is known as the head cover

2. nucleus shrinks gradually and the chromosomes are confined to a narrow space, which helps reduce the size and weight of the sperm

3. Centeral bodies move toward the posterior pole of the nucleus

capitis

head cover

Anterior Central Body

one of the two bodies take a position close to the nucleus

Posterior Central Body

the bodies that take a distant position and is known as the posterior central body, which rests at the base of the tail that began to elongate

Acrosomal Phase

1. the nucleus moves to the edge and elongate or flattens.

2. most of cytoplasm moves to the back end of nucleus and then surrounds the front part of tail to which the mitrichondria migrate (mid piece)

3. the chromatid body moves towards distal central body (tail)

Maturation

1. transform into a sperm is complete

2. nucleus and the apex take the final form

3. annular centering body moves away in the direction of the tail

4. mitochondria are concentrated in the middle segment

5. a large number of organelles are destroyed by the sertoli cells

what shape does a mouse nucleus take

sickle

Function of the Sertoli cells

1. protection through tight junction

2. remove the cytoplasmic bodies that excrete them sperm

3. secretion of fluid flowing from the cavities of the seminal tubules toward the genital canals

4. helping in the release of the sperms

5. provides nutrients

6. secrete ABP

ABP

Androgen-Binding protein

Sperms Head

contains the nucleus, and the enzyme acrosome

Acrosome

works to penetrate the outer membrane of the egg with the enzyme it secretes

middle piece of the sperm

contains the mitochondria and two centrioles

Sperms tail

helps the sperm move forward due to the presence of fine fibers in the form of tubules.

Oogenesis

1. multiplication

2. growth phase

3. maturation

Ovum structure

composed of plasma membrane, nucleus, and cytoplasm that contain extra structures such as yolk, colored granules, cortical granules, and glycoproteins

oocyte poles

1. animal pole

2. vegetative pole

animal pole

upper half containing the nuclues

vegetative pole

lower half containing the amount of yolk

Ovum membranes

1. primary

2. secondary

Primary membrane

formed while the egg cell is inside the ovary

Primary membrane contains

1. plasma membrane

2. radial layer

3. transport membrane

4. granular layer

vitelline membrane are

the transport membrane of amphibian and birds

chorion are

the transport membrane of fish

Secondary membrane

they are the membranes secreted by the oviducts, uterus, or some secondary glans

secondary glans are

1. albumin

2. double shell membrane

3. hard calcareous crust

classification of oocytes

1. isolecithal

2. mesolecithal

3. telolecithal

4. centrolecithal

Isolecithal

very little yolk like in placental mammals

Mesolecithal

Moderate amount of yolk like in amphibian and fish eggs

Telolecithal

Lots of yolk at vegetal pole like in reptiles and birds egg

Centrolecithal

lots of yolk centrally located like in insects

Generation of human iBlastoids

Blastocyst

Embryonic Stem Cell Colony

Mature / Adult cells

Reprogrammed Somatic cells

Induced Pluripotent stem cell

Spermatogenesis

Golgi phase

Cap phase

Acrosomal phase

Maturation phase

Mature Sperm

Sertoli cells

Oogenesis phases

Structure of an ovum

Vitelline membrane

Plasma membrane

Transport membrane

Radical layer

Granular layer

Air cell

Thick Albumen