Gametogenesis overview Flashcards
What are the 5 phases in prophase 1 of meiosis?
Leptotene Zygotene Pachytene Diplotene Diakinesis
What happens in the leptotene phase of meiosis 1?
Chromosomes condense, DNA replication is finished
What happens in the zygotene phase of meiosis 1?
Synapsis
What happens in the pachytene phase of meiosis 1?
Crossing over
What happens in the diplotene phase of meiosis 1?
Homologous chromosomes separate
What happens in the diakinesis phase of meiosis 1?
Transition into metaphase
What are germ cells?
Cells destined to become gametes, will reside in the gonad tissue but don’t form the gonad tissue
What happens to the germ cells once they are specified?
They stop dividing and are segregated away from the somatic cells until they are ready to move into the gonads
What are the 5 things that regulate cell identity?
Gene expression, membrane components, proteins, mRNA localization, transcription factors
What was Louis Bounoure’s experiment? What did he find and conclude?
Let an amphibian zygote grow into the 2, 4 and 8 cell stages, then split the cells apart. The cells lived and grew into two new individuals in the 2 cell stage, but none of the cells lived after being split from the 8 cell stage. Concluded there were things in the cytoplasm required for a new individual to be produced, and not every cell in the 8 cell stage had all that info
What is the germ plasm?
A particular area of the egg cytoplasm that has the mRNA and proteins localized to set the fate of the germ cells
Why are germ cells set aside so early in development?
Keep all information intact, since every cell division can produce errors. The germ cells become a library for the genetic information
What are the 2 important genes associated with germ cell specification?
Vasa and nanos
Where do the Vasa and Nanos transcripts come from?
Maternal genes that already exist in the egg as mRNA, localized in the germ plasm
What do Vasa and Nanos do?
Block transcription and translation to stop cell division
What are the 3 stages of gametogenesis?
Gonial, gonocyte, gonotid
What is a gonial cell?
The diploid product of a germ stem cell
What are 2 things that could happen to a gonial cell?
Either keeps dividing through mitosis or enters meiosis
What is the gonial stage of spermatogenesis called?
Spermatogonia
What is the gonial stage of oogenesis called?
Oogonia
What is happening in the morphogenesis example in C. elegans gametogenesis?
Gonad cells produce a signalling protein called Delta that inhibits meiosis and encourages mitosis in germ cells by interacting with the Notch receptor. The germ cells keep undergoing mitosis and eventually start to crowd each other out. Some cells get pushed away from the cells producing Delta, and will start meiosis once they are out of range.
What is a gonocyte?
A gonial cell that has entered meiosis
What is the gonocyte stage of spermatogenesis called?
Spermatocyte
What is the gonocyte stage of oogenesis called?
Oocyte
What is a gonotid?
Specialized haploid gonocyte, only applies to sperm
What is spermiogenesis?
The specialization of a spermatocyte into a spermatid, which includes development of the flagella, reduction of the cytoplasm, condensation of the chromosomes into toroids
What do the germ stem cells in Drosophila oogenesis divide into with every round of mitosis?
One GSC and one oogonium
What does the Drosophila oogonia become once it starts dividing?
Cystoblast
What sort of development does a Drosophila cystoblast undergo?
Syncytial. The cells stay connected through the cytoplasm
Does every cell in a Drosophila cystoblast become an oocyte?
No. Only one enters meiosis and the rest become nurse cells
What do follicle cells do in Drosophila oogenesis? Where do they come from?
They surround the egg and help determine body axises. They come from the gonad and not the cyst
What is Drosophila germ stem cell renewal an example of?
Morphogenesis
How do Drosophila germ stem cells renew themselves?
The GSC are anchored to the Cap cells and are receiving BMP secreted by the Cap cells, which turns off the Bam gene. When the GSC divides, mitosis is oriented so that one cell is further away and moves out of the range of BMP. Without the signal, Bam turns out and the cell becomes an oogonium and starts forming a cystoblast
Does formation of a cystoblast occur in mammalian oogenesis?
No, all mitotic divisions are completed before birth in the fetus
What happens to the oogonia after mitotic divisions are finished?
Held in stasis in follicles until sexual maturity
What is a primary oocyte?
Product of meiosis 1
What is a secondary oocyte?
A more mature oocyte that is undergoing meiosis 2 and getting ready to be ovulated
What are the two types of cells that make up the follicle?
Granulosa and thecal cells
Where are granulosa cells found?
Tightly packed around the oocyte in a follicle
Where are thecal cells found?
Loosely packed around the oocyte in a follicle
What is the purpose of the follicle structure?
Support, nutrients, secretes hormones
What is the Zona pellucida?
A thick extracellular matrix made of proteins and carbs that surrounds the oocyte
What is the corona radiata?
The granulosa cells that maintain very tight association with the oocyte
What is the antrum?
A space in the follicle structure between the corona radiata and the granulosa cells
Which parts of the follicle are ovulated with the egg?
Zona pellucida and corona radiata
What is the spermatogenesis equivalent of the cap cells in Drosophila oogenesis?
Hub cells
What is the function of the hub cells?
Tell GSC when to divide
Are cysts formed in insect spermatogenesis?
Yes
What is the signal secreted by the hub cells?
Unpaired
What does unpaired do to spermatogonia?
Causes movement of the centrosome so cytokinesis happens in a particular location
Where are sperm produced in mammals?
Seminiferous tubules
Which stage in spermatogenesis is located around the periphery of the seminiferous tubules?
Spermatogonia
Are cells closer to the central channel of the seminiferous tubules more or less mature?
More. They go through meiosis as they approach the centre
What are Sertoli cells?
Cells that maintain the endocrine environment in the testes
