Gamete Biology PDF

**[Gamete biology:]** Ectoderm external (e.g. neuron of brain) Mesoderm middle (e.g. cardiac muscle) Endoderm internal (e.g. thyroid cell) Pigs and humans share a similar PGC developmental program. **[Mouse primordial germ cells (PGCs):]** - Proximal epiblast cells induced to become PGCs by...

**[Gamete biology:]** Ectoderm external (e.g. neuron of brain) Mesoderm middle (e.g. cardiac muscle) Endoderm internal (e.g. thyroid cell) Pigs and humans share a similar PGC developmental program. **[Mouse primordial germ cells (PGCs):]** - Proximal epiblast cells induced to become PGCs by extraembryonic signals - PGCs are of mesodermal origin and colonise the gonad at around day 10.5 in mice Human and mouse PGCs are induced form different progenitors The **"indifferent gonad**". Sex determination occurs by day 11.5 through activation of **SRY** gene in males. SRY represses Dax1, and X-linked gene. **[Spermatogenesis:]** - Spermatocytogenesis = sperm formation multiplication of sperm stem cells by mitosis amplification and differentiation of primordial germ cells into spermatocytes - Meiosis initiation of meiosis allowing homologous recombination produces 4 spermatids - Molecular characteristics of sperm - Spermiogenesis differentiation into mature sperm Formation of mature sperm **[Post-meiotic sperm:]** - Transcriptionally inactive - Acquire motility during passage through epididymus - Structural changes acrosomal cap derived from golgi apparatus, accumulation of mitochondria in mid-piece - Protamines replace histones to pack DNA **[Oogenesis:]** - transcription - translation - accumulation of proteins & mRNAs **[Roles of mRNAs and proteins:]** - Sustain development - Oocyte maturation - Early development - Stability of mRNA for storage required - Temporal/spatial expression required **[Storage and regulation of oocyte mRNA and proteins:]** - RNA polyadenylation - RNA masking - RNA localisation - Antisense RNA - Protein phosphorylation [ ] - - **[RNA localisation:]** - Oocyte polarity spatial restriction in protein production essential for establishment of germ line - Germplasm is a store of RNAs and present in lower vertebrates - Mammals do not have germplasm **[Protein phosphorylation ]** - Major role in oocyte maturation, activation, signalling pathways - MOS, MPF, PKC, MAP **[Maternal to zygotic transition:]** - Mouse = 1-2 cell stage - Pig = 4-8 - Sheep = 8-16 - Cow = 8-16 - Xenopus = 4,000 **Oogenesis =** total number of eggs available in a female is established at birth **Meiotic process =** gives rise to a single egg Oocytes store mRNAs and proteins for long term Transcriptional activation varies between species **[IVF:]** - Oocyte maturation (24hrs \@39 degrees in 5% CO2) (48hrs in pigs) cannot be preserved exogenous gonadotropins added to culture medium - Sperm capacitation can be cryopreserved (except in pigs) - Fertilisation (24hrs \@39 degrees in 5% CO2) - In vitro culture (7 days 39c in 5% CO2, 5% O2, 90% N2) until blastocyst stage - Done routinely in cattle, with donors of high genetic value. Oocytes are recovered in vivo through a procedure called OPU (ovum pick up). - In other species such a sheep and pigs is more experimental. **[Nuclear transfer in mammals:]** - Generation of a genetic copy of an induvial after transfer of cell nucleus into enucleated oocyte - Performed with embryonic and somatic cells - Reconstruction of an embryo by transfer of genetic material from a donor cell to a recipient egg from which genetic material has been removed - Originally restricted to embryonic blastomeres. - Development related to stage of development of embryo and species. - Developmental stage related to MZT. - Embryo Multiplication limited by cell number. *Biological significance*: - Prove that differentiated cells have all the genetic information of an individual *Biotechnological importance*: - unlimited source of donor cells. - Cloning from adult animals. - Genetic modification **[Somatic cell types used for NT:]** - Isolated from the embryonic disc of a single Day 9 sheep embryo (1995). - Day 26 embryo derived cell line, or fetal fibroblast (1996). - Adult mammary epithelial cells (1997). - T-lymphocytes used for NT (2002) (more differentiated) **[Fetal abnormalities:]** - Hydroallantois result of placental defects - Extended gestation - Kidney - Brain - Cardiovascular - Muscle - Skeletal - No pattern **[ICSI: intracytoplasmic sperm injection:]** - Success in mouse and human (40% of current ART procedures) - In cattle, sheep, and pigs is not efficient. **[Uses of NT:]** HUMAN MEDICINE: - TRANSGENIC ANIMALS: - - - - - DEDIFFERENTIATION: - - AGRICULTURE: - TRANSGENIC ANIMALS: - - - - GENETIC PRESERVATION: - -