WEEK 3: Gametogenesis Notes

Gametogenesis

Generation and maturation of sex cells.

Oogenesis

Formation of female gametes in ovaries.

Spermatogenesis

Generation of spermatozoa in seminiferous tubules.

Primordial Germ Cells

Generative sex cells identified in early development.

Germplasm

Material contributing to germ cell formation.

Primary Spermatocyte

First stage of sperm cell development.

Secondary Spermatocyte

Formed after meiosis I in spermatogenesis.

Spermatids

Result from meiosis II in spermatogenesis.

Germ Cell Migration

Movement of germ cells to gonads.

Multiplication of Germ Cells

Mitosis occurring in gonads.

Meiosis

Reduction of chromosome number by half.

Leptotene Stage

Thin chromatin stage in meiosis I.

Zygotene Stage

Homologous chromosomes pair during meiosis.

Pachytene Stage

Thickened chromosomes complete pairing.

Diplotene Stage

Chiasmata formation during meiosis.

Metaphase I

Homologous chromosomes align at equatorial plane.

Anaphase I

Homologous chromosomes separate to poles.

Meiosis II

Equational division separating sister chromatids.

Oogenesis Features

Arrested stages and unequal cytoplasmic division.

Functional Oocyte

Mature oocyte capable of fertilization.

Follicle Stimulating Hormone

Stimulates granulosa cell proliferation.

Luteinizing Hormone

Targets theca cells for steroid production.

Ovulation

Release of the ovum from the ovary.

Oogenesis in Amphibians

Continuous mitosis; yolk accumulation phases.

Spermiogenesis

Transformation of spermatids into spermatozoa.

Cytoplasmic Bridges

Connect sperm cells during development.

Type A Spermatogonia

Can divide or differentiate into primary spermatocytes.

Type B Spermatogonia

Last to divide, become primary spermatocytes.

Oogenesis and Folliculogenesis

Occurs in the ovaries.

Spermatogenesis

Generation of spermatozoa and occurs in the seminiferous tubules.

Gametogenesis Defined

Generation and maturation of sex cells.

Primordial Germ Cells (PGCs)

Generative sex cells (germplasm).

Germplasm

No obvious germplasm in mammals.

Primary Spermatocyte and Oocyte

Formed during growth and differentiation.

Secondary Spermatocyte and Oocyte

Formed during meiosis 1.

Spermatids and Oocyte

Formed during meiosis 2.

Phases of Gametogenesis

Generation of germ cells and migration to the gonads, Multiplication of germ cells in the gonads (mitosis), Reduction in chromosome number by half (meiosis) and Maturation and differentiation.

Generation of Germ Cells and Migration to the Gonads

Arise outside the gonads.

Amniotes

The birds, reptiles, and mammals.; PGCs identified in the yolk sac endoderm.

PGCs

are large

Hannel & Eddy

stated PGCs originally reside in the epiblast of the gastrula.

Ginsburg

stated Localized the region in the extra

Inner Cell Membrane

Will split into the epiblast.

Genital Ridges

Forming gonads of the embryo.

Rodents (as a Mammalian Model)

Development of PGCs depends on signals.; Radical expression of pluripotency markers.

Bone Morphogenetic Protein

It is a signal factor.

Proposed Migration Pathway

Primary ectoderm → yolk sac endoderm → allantois → dorsal mesentery → left and right genital ridges.

Yolk sac endoderm

PGCs become extraembryonal.

Allantois

PGCs become specified at the base.

Left and Right genital ridges

In the embryo proper.

Teratoma

A type of tumor.

Proliferation of Germ Cells

Mitotic patterns in the gonads differ widely between males and females.

For males

the process of mitosis is continuous.

For females

the process of mitosis stops early around the 5th month of oogenesis.

In males

meiosis starts at puberty.

In females

meiosis starts earlier; happens every month.

Meiosis I

Reducing the chromosome number by half (reduction); long prophase.

Leptotene Stage

46 chromosomes, 23 maternal chromosomes and 23 paternal chromosomes.

Zygotene Stage

Pairing of homologous chromosomes; Referring to the synapting stage.

Pachytene Stage

Chromosomes become thicker and shorter, and pairing is done.

Diplotene

The process of chiasmata happens (exchange of genetic material).

Metaphase I

Homologous chromosomes meet at the equatorial plane.

Anaphase I

Homologous chromosomes separate and move toward their respective poles.

Meiosis II

Ordinary mitotic division (equational division).;Sister chromatids are the ones that separate.

Diplotene and Metaphase II

During oogenesis, the stage where meiosis I and II are arrested.

Mammalian Oogenesis

PGCs → oogonia → primary oocytes → meiosis (leptotene, zygotene, Pachtene) → diplotene (1st arrest cellular molecular changes) → Diakinesis → Metaphase I → Anaphase I → Telophase I → secondary oocyte and first polar body.

Mature oocyte

Functional oocyte = zygote oocyte.

Follicle Stimulating Hormone (FSH)

Stimulates the increase of granulosa cells.

Luteinizing Hormone (LH)

Will target the theca externa and interna.

Ovarian Follicle

The yellow yolk.

Cytoplasm/Blastodisc

Lying on top of the yellow yolk.

Nucleus of Pander

Surrounding the blastodisc.

Blastoderm

Fertilized blastodisc.

Oogenesis in Amphibians

Mitosis is continuous.; Egg maturation requires 3 years.

Previtellogenic Phase

Before the accumulation of the yolk.

Vitellogenic Phase

Accumulation of the yolk; formation of cortical granules.

Balbiani Body

Intense RNA synthesis and formation of lampbrush chromosomes and nucleoli.

Spermatogenesis

PGCs → spermatozoa → mitotic multiplication → meiosis → spermiogenesis.

Stem Cells

Synchronized cell divisions.

Type A Spermatogonia

Can undergo cell division again, undergo apoptosis, or become primary spermatocytes.

Type B Spermatogonia

Last to undergo mitosis and become primary spermatocytes.

Secondary Spermatocytes

Are produced under meiosis; they came from being primary spermatocytes.

Spermatids

Undergo spermiogenesis and come from secondary spermatocytes.

Cytoplasmic Bridges

Interconnect the sperm with each other.

A. Reorganization of the Cytoplasm

Golgi apparatus, Centrioles, Mitochondria

B. Progressive Reduction in Nuclear Size/Compaction of the Nucleus

Nuclear elongation; Loss of water; Centrioles; Elimination of RNA; leaving only DNA; Not all histones are replaced.; In humans, 15

Head

Acrosome and Nucleus

Midpiece

Mitochondria

Tail (flagellum)

Normal Sperm

Abnormal Sperm

Giant head, Micro head, Double body, Double head, Long middle piece, and Rough middle piece.