Honours / Core Course (CC)
Unit 1: Early Embryonic Development
Gametogenesis: Spermatogenesis, Oogenesis (sea urchin & mammal); Types of eggs, Egg membranes; Fertilization in sea urchin and mammal; Planes and patterns of cleavage; Types of Blastula [frog and chick]; Fate map in chick embryo, fate mapping using vital dye and radioactive technique; Gastrulation in frog and chick; Embryonic induction and organizers in Xenopus (Spemann & Mangold’s experiment)
Q.What is DAZL protein?
i)The DAZ (deleted in azoospermia) gene family encodes potential RNA binding proteins that are expressed in prenatal and postnatal germ cells of males and females.
ii)The protein encoded by this gene is localized to the nucleus and cytoplasm of fetal germ cells and to the cytoplasm of developing oocytes.
iii)In the testis, this protein is localized to the nucleus of spermatogonia but relocates to the cytoplasm during meiosis where it persists in spermatids and spermatozoa.
iv)Transposition and amplification of this autosomal gene during primate evolution gave rise to the DAZ gene cluster on the Y chromosome. Mutations in this gene have been linked to severe spermatogenic failure and infertility in males.
In mice and pigs deficient in DAZL, PGCs migrate to the gonad but do not undertake germ cell determination, and may instead produce germ cell tumors.
Q.What is the role of Wnt4?
Female germ cells are essential for organogenesis of the ovary; without them, ovarian follicles do not form and functional and structural characteristics of the ovary are lost. Wnt4 or β-catenin was inactivated in the fetal ovary, female germ cells underwent degeneration.
Activation of β-catenin in somatic cells in the Wnt4 knockout ovary restored germ cell numbers, placing β-catenin downstream of WNT4.
In the absence of Wnt4 or β-catenin, female germ cells entered meiosis properly; however, they underwent apoptosis afterwards.
WNT4 maintains female germ cell survival by inhibiting Inhbb (inhibin subunit beta B) expression via β-catenin in the somatic cells. Maintenance of female germ cells hinge upon a delicate balance between positive (WNT4 and β-catenin) and negative (activin βB) regulators derived from the somatic cells in the fetal ovary.
(One of the most fundamental sets of signals regulates the timing of meiosis, and these signals include Wnt4 and retinoic acid.)
Q.What do you mean by morphogenetic movement?
The special type of irreversible gastrulation movement, involving different groups of cells which may have been far removed from one another and brought close enough together to undergo the inductive interactions and also enable cells to remain in the position into which it was brought by the proceeding movement and result in the rearrangement of the embryo from the blastula to a stage characterized by the presence of 3 germ layers and appears to be movements of large parts of the whole embryo, which stretch, fold, contract or expand, is known as morphogenetic movement.
Q.What is the role of retinoic acid in early embryogenesis?
Retinoic acid (RA) is a morphogen derived from retinol (vitamin A) that plays important roles in cell growth, differentiation, and organogenesis. The production of RA from retinol requires two consecutive enzymatic reactions catalyzed by different sets of dehydrogenases. The retinol is first oxidized into retinal, which is then oxidized into RA. The RA interacts with retinoic acid receptor (RAR) and retinoic acid X receptor (RXR) which then regulate the target gene expression during early embryonic development.
Developmental Biology - A Complete Journey:
Types of morphogenetic movements:
Unit 2: Late Embryonic Development
Extra-embryonic membranes in Chick; Implantation of embryo in humans, Placenta (Structure, types and functions of placenta)
Q. Make a comparative analysis between epitheliochorial placenta and endotheliochorial placenta.
Epitheliochorial Placenta : This type of placenta involves the contact of the chorionic epithelium with that of uterine epithelium and thus the term epitheliochorial. The epitheliochorial placenta involves 6 tissue barriers between the foetal and maternal circulation. It is the primitive type from which others have been derived and is seen in pig, horse, cattle etc.
1-Endothelium of foetal blood vessel, 2-Chorionic connective tissue, 3-Chorionic epithelium, 4-Uterine epithelium, 5-Endometrial connective tissue (mucosa), 6.Endothelium of maternal blood vessel
In endotheliochorial placenta the uterine mucosa is reduced and the chorionic epithelium comes in contact with the endothelial wall of maternal blood vessels. This type of placenta is characteristic of carnivores like dog, cat, bear etc. Here only 4 barriers remain between the two blood streams.
Unit 3: Post Embryonic Development
Development of brain and Eye in Chick. Molecular Induction in Brain and Eye development.
Q.Briefly describe the process of optic cup formation in chick embryo and comment on induction for lens formation.
At ~55 hours of development the external surface of the optic vesicles flattened out and invaginate inward. So the single walled vesicle transform into double walled, cup like structure, called optic cup. The invaginated walls of the cup is much more thicker than the external. The first develop into sensory retina and later into the pigment coat and retina (taptum nigram) (For further information follow our contact section).
Figure: Progressive steps involved in eye formation in Chick (T.S. Through eye region)
Unit 4: Implications of Developmental Biology
In vitro fertilization (IVF), Stem cell: Concept of potency, types, markers and applications of stem
cell therapy in bone marrow transplantation and cartilage regeneration
Q. State the important properties of stem cells.
Can be defined as a relatively undifferentiated cell that when divides produces at least one of two daughter cells that retains its undifferentiated characters (self-renewal) and a daughter cell that can undergo further differentiation. All stem cells- regardless of their source have 3 general properties. They are capable of dividing and renewing themselves for long periods, they are unspecialized and they can give rise to specialized cell types. Stem cell concept explains the possible strategy, origin and types of cell population produced from stem cells and can be expressed under 3 headings, follows- single cell asymmetry, population asymmetry, adult stem cell lineage.
Q. What do you mean by in vitro fertilization?
In vitro fertilization (IVF) is a treatment for infertility or genetic problems. Some reasons for opting IVF are as follows—
a)Fallopian tube damage or blockage:
Fallopian tube damage or blockage makes it difficult for an egg to be fertilized or for an embryo to travel to the uterus.
If ovulation is infrequent or absent, fewer eggs are available for fertilization.
c)Premature ovarian failure:
Premature ovarian failure is the loss of normal ovarian function before age 40. If your ovaries fail, they don't produce normal amounts of the hormone estrogen or have eggs to release regularly.
Endometriosis occurs when the uterine tissue implants and grows outside of the uterus — often affecting the function of the ovaries, uterus and fallopian tubes.
Fibroids are benign tumors in the wall of the uterus and are common in women in their 30s and 40s. Fibroids can interfere with implantation of the fertilized egg.
f)Previous tubal sterilization or removal:
(If you've had tubal ligation — a type of sterilization in which your fallopian tubes are cut or blocked to permanently prevent pregnancy — and want to conceive) IVF may be an alternative to tubal ligation reversal.
g)Impaired sperm production or function:
Below-average sperm concentration, weak movement of sperm (poor mobility), or abnormalities in sperm size and shape can make it difficult for sperm to fertilize an egg. If semen abnormalities are found, your partner might need to see a specialist to determine if there are correctable problems or underlying health concerns.
Unexplained infertility means no cause of infertility has been found despite evaluation for common causes.
i)A genetic disorder:
If any one partner is at risk of passing on a genetic disorder to your child, you may be candidates for preimplantation genetic diagnosis — a procedure that involves IVF. After the eggs are harvested and fertilized, they're screened for certain genetic problems, although not all genetic problems can be found. Embryos that don't contain identified problems can be transferred to the uterus.
j)Fertility preservation for cancer or other health conditions:
If anyone is about to start cancer treatment — such as radiation or chemotherapy — that could harm your fertility, IVF for fertility preservation may be an option. Women can have eggs harvested from their ovaries and frozen in an unfertilized state for later use. Or the eggs can be fertilized and frozen as embryos for future use.
Women who don't have a functional uterus or for whom pregnancy poses a serious health risk might choose IVF using another person to carry the pregnancy (gestational carrier). In this case, the woman's eggs are fertilized with sperm, but the resulting embryos are placed in the gestational carrier's uterus.
Q.What is intra-cytoplasmic-sperm injection?
Intracytoplasmic sperm injection (ICSI) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of embryos that may be transferred to a maternal uterus. The male partner produces too few sperm to do artificial insemination (intrauterine insemination [IUI]) or IVF. With this method, the acrosome reaction is skipped.
ICSI is generally performed following a transvaginal oocyte retrieval procedure to extract one or several oocytes from a woman. In ICSI the male partner or a donor provides a sperm sample on the same day when the eggs are collected. The sample is checked in the lab, and if no sperm is present, doctors will extract sperm from the epididymis or testicle. The extraction of sperm from epididymis is also known as percutaneous epididymal sperm aspiration (PESA) and extraction of sperm from testicle is also known as testicular sperm aspiration (TESA). Depending on the total amount of spermatozoa in the semen sample, either low or high, it can be just washed or capacitated via swim-up or gradients, respectively.
The sperm may not move in a normal fashion. The sperm may have trouble attaching to the egg. A blockage in the male reproductive tract may keep sperm from getting out. Eggs have not fertilized by traditional IVF, regardless of the condition of the sperm. In vitro matured eggs are being used. Previously frozen eggs are being used.
Stem Cell I Stem Cell Therapy
Stem Cell I Audio Note Book: