ORIGIN + DEVELOPMENT OF GERM CELLS Flashcards
what are primordial germ cells?
Earliest germ cells
where do primordial germ cells arise from?
‘Migrate’ from yolk sac, through hind-gut to genital ridge
where do primordial germ cells enter?
Enter presumptive seminiferous tubes (hoops) with pro-Sertoli cells
where do primordial germ cells settle?
on the tubule wall first
what is spermatogonia?
is an undifferentiated male germ cell
where does spermatogonia take place?
outside the blood-testis barrier
what do spermatogonia undergo?
spermatogenesis to form mature spermatozoa in the seminiferous tubules of the testis
how to primordial germ cells proliferate?
by mitosis
what do primordial germ cells develop into?
into gonocytes
how do gonocytes proliferate?
by mitosis
what do gonocytes develop into?
Pro-spermatogonia
what do Pro-spermatogonia develop into?
Spermatogonia by the end of the foetal stage
what is the prepubertal phase?
Earliest spermatogonia become stem cells and acquire self-renewal capacity
what is the process of spermatogonia in rodents?
A0 considered to be stem cells
Give rise to a succession of generations of A s’gonia
what does spermatogonia in rodents allow?
allows dramatic expansion of a small stem cell pool
what is the process of spermatogonia in humans?
Adark considered to be stem cells. Apale are proliferative.
form intermediate which form new cells.
what is a difference in process between spermatogonia in humans compared to rodents?
in humans
Large reserve of stem cells & relatively few proliferative divisions
what happens to spermatogonia in the prepubertal phase?
become stem cells and acquire self-renewal capacity
what does the peri-natal spermatogonial division produce?
spermatocytes
what is all post-stem cell development?
syncitia until just before sperm release
when does spermatocytes arrest occur?
in prophase of 1st meiotic division
what do B spermatogonia give rise to?
Preleptotene spermatocytes
what do Preleptotene spermatocytes give rise to?
Leptotene s’cytes
what do Leptotene s’cytes give rise to?
Zygotene s’cytes
what do Zygotene s’cytes give rise to?
Pachytene s’cytes
what do Pachytene s’cytes give rise to?
Diplotene s’cytes
what does Diplotene s’cytes lead to?
1st meiotic division
what happens after 1st meiotic division?
Secondary s’cytes produced
cells now haploid
what does Secondary s’cytes lead to?
2nd meiotic division
what is the role of Preleptotene spermatocytes?
S-phase
what is the role of Leptotene s’cytes?
chromatin remodelling
what is the role of Zygotene s’cytes?
chromatin remodelling
what is the role of Pachytene s’cytes?
transcription, translation increase in size
what do Diplotene s’cytes do?
enter meiosis
what is spermatogenesis?
Development of spermatids
what are the 3 types of spermatids?
round, elongating, maturation phase
what are the round spermatids a product of?
the 2nd meiotic division
what happens in round spermatids?
Nucleus still capable of transcription, DNA repair etc but activity diminishes. Nuclear histones are replaced by transition proteins
what happens at the opposite pole?
Onset of flagellum development and acrosome dev.
what are elongating spermatids?
transcriptionally inactive
what are transition proteins replaced by in elongated spermatids?
protamines, much higher order of packing, dramatic reduction in nuclear size - essential for motility
what happens to elongating spermatids?
Flagellum develops fully. Cytoplasm shrinks away to form droplet
what are Maturation phase spermatids?
have morphology of mature spermatozoa
what happens to Maturation phase spermatids?
Shed into lumen of tubule at spermiation. Cytoplasmic droplet phagocytosed by Sertoli cell
what is a oogonium?
Primordial germ cell
what does oogonium develop into?
primary oocyte arrested in prophase of meiosis I (diplotene)
what happens at ovulation?
expulsion of 1st polar body (metaphase II)
what happens after ovulation?
2nd period of arrest
what happens at fertilisation?
expulsion of 2nd polar body
in females where do all germ cell, mitotic activity occur?
during foetal life
what is the final number of cells in the egg fixed?
in utero
what happens at completion of mitoses?
cells enter meiosis but are arrested at diplotene
what happens once the cells enter mitosis?
form germinal vesicle
what happens at the dictyate stage?
Large numbers of dictyate germ cells die (by apoptosis) in last trimester
what is an oogonium bounded by?
by basement membrane & surrounded by spindle-shaped cells
forms germinal vesicle
what happens following arrest in gametogenesis?
1º oocyte surrounded by granulosa cells: primordial follicle
what happens at puberty?
a few primordial follicle’s recruited to re-commence development
what is Folliculogenesis?
-> 1º, 2º pre-ovulatory follicles
what is the Pre-Antral follicle?
Secretion of glycoproteins forms zona pellucida
what happens with Pre-Antral follicle?
Division of granular cells: cytoplasmic processes to oocyte; gap junctions; avascular
what do Ovarian stromal cells form?
theca around follicle (interna +externa)
what happens with the Antral (Graafian) follicle?
Granular cell proliferation increase in follicle size
what does the secretion of follicular fluid do?
mucopolysaccharides + serum forms antrum
what is the oocyte connected to?
to thick gran. cell layer (cumulus oophorous) by stalk
what does the oocyte continue to store?
mRNA
what is gonadotrophin?
hormone stimulates activity of the gonads
Synthesis of steroids
what is the Pre-ovulatory follicle?
Transient peak of LH stim’s ovulation.
Breakdown of nuclear memb, separation of chrom’s + unequal division of cytoplasm, extrusion of 1st polar body
what develops after the separation of chromatids?
metaphase plate 2nd meiotic arrest
