AbstractEmbryo in vitro Production (IVP) and associatedAssisted Reproductive Technologies (ARTs) in goat, e.g., estrus synchronizationand superovulation, Laparoscopic Ovum Pick-up (LOPU), in vitroMaturation (IVM), in vitro Fertilization (IVF), IntracytoplasmicSperm Injection (ICSI) and in vitro Culture (IVC) attained significantattention in the recent years. However, for the success in any IVP protocolsin goat sound knowledge of physiology of gametogenesis, fertilizationand early embryogenesis in vivo is crucial because in vivoinformation form the basis and guide for any in vitro experiment.Unlike human, laboratory animals, cattle and sheep, fewer studies havebeen conducted in gametogenesis, fertilization and early embryo developmentin goat. Data for sheep and cattle are mostly used as a basis for goatIVP studies. Therefore, the current study is intended to review gametogenesis,sperm oocyte interaction, fertilization and early embryogenetic processin mammals with special reference to goat.
INTRODUCTIONIn vitro Embryo Production (IVEP) or Production(IVP) technique is currently in the central focus among all the AssistedReproductive Technologies (ARTs) in human as well as in animals. Therefore,the physiology of normal fertilization should be considered as a mustfor the development of any IVEP or IVP protocols especially for invitro Fertilization (IVF) or Intracytoplasmic Sperm Injection (ICSI)techniques. Gametogenesis, fertilization and early embryogenesis or pre-implantationembryo development are crucial periods for normal development of an embryoafterwards. Until now researches in mammalian gametogenesis, fertilizationand early embryogenesis mainly based on the laboratory animals and human(Tulsiani et al., 1997; Kupker et al., 1998; Elder and Dale,2000).
Compared with laboratory and farm animals like cattle, sheep andpig, studies in goat are scarce (Hafez and Hafez, 2000a; Miyano and Hirao,2003). Therefore, the current paper will briefly review some aspects ofgametogenesis, fertilization and early embryogenesis in mammals with specialreference to goat.GAMETOGENESISGenetically and functionally competent gametes are a prerequisite fornormal fertilization and early embryo development.
The first phase inthe sexual reproduction of an organism is gametogenesis, a process offormation of gametes from the germ cells in the testes and ovaries. Thisprocess is termed as spermatogenesis in the male and oogenesis in thefemale. It is the fundamental biological process in both the sexes andthe key event of gametogenesis is the halving of the number of chromosomesto produce haploid germ cells (sperm and oocyte) through meiosis. Thus,in goat, where the chromosome number of somatic cells is 60, each spermand each oocyte has only 30 chromosomes. However, until this point spermatogenesisand oogenesis resume their similarity. After this, in the male, each primaryspermatocyte divides meiotically and produces four spermatids, each destinedto become a functional sperm.
In the female, on the other hand, of thefour cells produced from each primary oocyte only one finally becomesa functional oocyte. A schematic diagram of gametogenesis in mammals hasbeen illustrated in.Fig. 1:Schematic diagram of gametogenesis in mammals. Modifiedfrom Hickman et al. (1986)In mammals, the male and female gametes originate from the embryonicyolk sac.
The gametes initially colonize in the primitive gonadal ridgeat the early stage of pregnancy by migration through the developing mesenteryof the embryo, where germ cells associate with somatic cells; it continueswith their multiplication, growth and maturation. Finally, migrate tothe pelvic and inguinal regions to form the ovary or testis, respectivelyand ends at fertilization.
Mammalian spermatogenesis and oogenesis arebriefly described below:Spermatogenesis: Competent sperm are required for the successfulcontribution of the paternal genotype to embryo development. The processof spermatogenesis results in the formation of the haploid male gameterequired for fertilization of an oocyte. Spermatogenesis is a continualand complex process that involves three major steps: (a) proliferation-multiplication of spermatogonia by the process of mitosis (spermatocytogenesis);(b) meiosis (spermiogenesis)- meiotic divisions whereby the chromosomenumber is reduced from diploid to haploid and (c) differentiation- transformationof the round spermatid into the complex structure of the spermatozoon(reviewed in Barth and Oko, 1989; De Kretser et al., 1998; Elderand Dale, 2000). Spermatogenesis in buck and other male mammals beginsat puberty through the proliferation of interphase germ cells, continuesthroughout adult life and takes place inside the seminiferous tubulesof the testes. The age of puberty for male goat or buck ranged between4 and 6 months (Jainudeen et al., 2000). The walls of the seminiferoustubules contain the differentiating sex cells arranged in a stratifiedlayer, 5 to 8 cells deep. The outermost layers contain spermatogonia,which have increased in number by spemtocytogenesis.
The spemtocytogenesisbegins with mitosis of the diploid A spematogonia in the basal compartmentof the Sertoli cells. The A spematogonia differentiate into B spermatogoniawhich enter their final mitotic division prior to their entrance intothe pre-leptotene phase of first meiosis (meiosis 1).
Difference B/w Gametogenesis And Embryogenesis
Meiosis occurs inthe adluminal compartment of the Sertoli cell and results in the formationof primary spermatocytes. Condensation of chromosomes occurs during theleptotene phase followed by the zygotene phase.
The long pachytene phaseinvolves the crossing over of chromosomal material and is most susceptibleto damage. Meiosis progresses through the diplotene phase, diakinesis,Metaphase I (MI) and anaphase, finally resulting in secondary spermatocytes(2c, 1n). Each secondary spermatocyte then enters the second meiotic division(meiosis 2), without the intervention of a resting period, resulting inspermatids with a haploid number of chromosomes and DNA content (1c, 1n),required for fertilization. The round-shaped spermatids proceed throughspermiogenesis and metamorphically changed into highly specialized motilecells. Spermiogenesis consists of the Golgi phase, the acrosomal cap phase,the acrosomal phase and the complex maturation stage involves developmentof the sperm tail (reviewed by Barth and Oko, 1989).
Deviations from theprocess of normal spermatogenesis result in abnormal morphology or dysfunctionof the sperm cell. The progression from spermatogonia to mature spermatozoain mammals require approximately 60 to 70 days, with at least three mitoticand two meiotic divisions during spermatogenesis (Kupker et al.,1998). Finally, the newly formed sperm are released into the lumen ofthe seminiferous tubules.
These sperm are immotile and still immaturein terms of fertilizing capability. Therefore, to acquire motility aswell as maturation they need to pass down the epididymis to the ejaculatoryduct, which is known as epididymal maturation (Elder and Dale, 2000).During epididymal maturation, the sperm shed the cytoplasmic droplet,undergo modifications in the protein, carbohydrate and glycoprotein compositionof the plasma membrane and acquire a net negative charge (Yanagimachi,1994; Harrison, 1996).
Sperm motility and capacitation are suppressedduring storage in the cauda epididymis, which is characterized by lowpH, low Ca 2+, low Na + and increased K +(Dalvit et al., 1995; Jones and Murdoch, 1996).
What are Difference between Gametogenesis and EmbryogenesisDistinguish, differentiate, compare and explain what is the main difference between Gametogenesis from Embryogenesis. Comparison and Differences. Difference between Gametogenesis from Embryogenesis1. Gametogenesis is the formation of male and female gametes. Embryogenesis is the formation of an embryo from the zygote.2. In Gametogenesis, gametes are the haploid cells.
Differentiate Between Syngamy And Fertilization
In Embryogenesis, an embryo is a diploid cell.3. Both mitotic & meiotic cell division take place in Gametogenesis. Only mitotic division occur in Embryogenesis.Tags:Difference between Embryogenesis vs GametogenesisGametogenesis vs EmbryogenesisDifferences between Embryogenesis vs Gametogenesis.