Topic: MOLECULAR GENETIC MECHANISMS OF ONTOGENESIS. DISORDERS OF ONTOGENESIS AND THEIR PLACE IN HUMAN PATHOLOGY Plan 1. Ontogenesis, its periodization. 2. Embryonic development, its stages. Provisional organs. 3. Molecular and cellular mechanisms of differentiation. 4. Differentiation of embryonic leaves and tissues. Embryonic induction. 5. Critical periods of human embryonic development. Teratogenic environmental factors. 6. Congenital malformations, their modern classification: hereditary, exogenous, multifactorial; embryopathy and fetopathy; phylogenetically determined and non- phylogenetic. 7. Postembryonic human development and its periodization. Neurohumoral regulation of growth and development. 8. Aging as a stage of ontogenesis. Theories of aging. The concept of gerontology and geriatrics. 9. Clinical and biological death. Recommended literature: 1. Medical Biology : text-book / Bazhora Yu. I., Bylyk R. Ye., Chesnokova M. M. et al. 2nd ed., revised and updated. Vinnytsia : Nova Knyha, 2019. 448 p. 2. Organismic level of life organisation. Bases of human genetics. Training text-book on Medical biology (module II) for students of medical and stomatological faculties / Dubinin S.I., Ovcharenko O.V., Vatsenko A.V. et al. Poltava, 2014. 78 p. 3. Lazarev K.L. Medical Biology: Text-book. Second edition. – Simferopol: IAD CSMU, 2003. 592 p. 4. Medical biology: The study guide of the practical classes course / O.V. Romanenko, O.V. Golovchenko, M.G. Kravchuk, V.M. Grinkevych. Edited by O.V. Romanenko. – K.: Medicine, 2008. 304 p. 5. Bekish O.-Y.L. Medical biology: Textbook for students of higher educational establishments. Vitebsk: VSMU Press, 2003. 346 p. 6. Green N.P., Stout G.W., Taylor D.I. Biological Science. Cambridge, 1994. 7. Kimball, John W. Cell biology. Addison-Wesley Publishing company, Inc, 1984. Ontogenesis (the individual development of an organism) Ontogenesis (also, ontogeny from the Greek – «ontos» – «being, existence» + «genesis» – «origin») is the set of morphological, phisiological and biochemical transformations from the moment of germing up to death; the entirety of an organism's lifespan. Ontogeny is the developmental history of an organism within its own lifetime, as distinct from phylogeny (from the Greek phyla, meaning «tribe» and genesis meaning «origin»), which refers to the evolutionary history of a taxon (species): individual organisms develop (ontogeny), while species evolve (phylogeny). Recapitulation theory • «ontogeny recapitulates phylogeny» (Ernst Haeckel,1866): embryonic development (ontogeny) repeats phylogeny (the genealogy of the species). • It means, we pass through some (not all) of the embryonic stages that our ancestors passed through.

Ernst Haeckel 1834–1919 Analogous and homologous structures

• Same structure, different functions • Show common ancestor

• Different structure, similar functions • Evidence of common environmental demand Rudiments (vestigial structures) remains of structures / organs, that once had an importance in ancestor’s organism and no longer useful

Vestigial Human Parts: • Gill slits – once used to breathe oxygen in water • Yolk sac – once used to nourish developing embryo • Tailbone – once used for balance • Appendix – once used to digest plants • Wisdom teeth – once used to grind plant tissue, etc.

• Human has up to 90 Darvin’s tubercle vestigial structures • Evidence Conclusion: Indicates common ancestry Atavisms reappearence of ancestral traits after they have been lost in previous generations

Atavisms in humans: • Human tails • Supernumerary nipples in humans (and other primates) • Hypertrichosis • Color blindness in humans Types of ontogenesis in animals:

1. larval type: development of an organism by metamorphosis – the change of shape or structure of organism from one developmental stage to another. Example: mosquito: ovum – larva – pupa – imago; louses: ovum – larva – imago; pincers: ovum – larva – nymph – imago. 2. non-larval type: formation of an organism in an egg (reptiles, birds). 3. intrauterine ontogenesis: development of an organism inside a maternal organism (mammals).

Prezygotic (pre-embrionic = progenetic) period

Progenesis – is a period of maturation of specialized generative cells – gametes. This maturation process is called spermatogenesis in males and oogenesis in female. Main stages of prenatal period:

1)Pre-embrionic (weeks 1-2) 2)Embryonic (weeks 3-8) 3)Fetal (weeks 9-38) Main processes of prenatal period: • Fertilization is fusion of a female and male gamete with forming of zygote: ♀ gamete (n) + ♂ gamete (n) = zygote (2n) • Cleavage is the series of rapid cell divisions of the zygote with the formation of blastula (2-8 cells), morula (solid ball of 12- 16 cells) and blastocyst (hollow ball of many calls with inner cavity – blastocoel): zygote → blastula → morula → blastocyst • Gastrulation is the process of formation in embryo the three germ embryonic layers (ectoderm, mesoderm and endoderm): blastocyst → gastrula + extraembryonic membranes • Histogenesis • Organogenesis The stages of pre-embryonic development: fertilization → implantation (the 1st week of ontogenesis) Fertilization Kinds of cleavage corresponds to the type of egg by yolk distribution

I. Holoblastic (complete) cleavage II. Meroblastic (incomplete) cleavage A. Isolecithal (sparse, evenly distributed yolk) A. Telolecithal (dense yolk throughout most • Radial cleavage of cell) (echinoderms, hemichordates) • Bilateral cleavage (cephalopod • Spiral cleavage (annelids, molluscs) most mollusks, flatworms) • Discoidal cleavage (some fish, reptiles • Bilateral cleavage (tunicates) and birds) • Rotational cleavage (placental B. Centrolecithal (yolk in center of egg) mammals, nematodes) • Superficial cleavage (most insects) B. Mesolecithal (moderate vegetal yolk disposition) • Displaced radial cleavage (amphibians, some fish [the lampreys, gars and bowfins) The cleavage of human zygote

In a man the cleavage of zygote is holoblastic, rotational and asynchronous: • In Holoblastic cleavage the zygote and blastomeres are completely divided during the cleavage, so the number of blastomeres doubles with each cleavage. • Rotational cleavage involves a normal first division along the meridional axis, giving rise to two daughter cells. The way in which this cleavage differs is that one of the daughter cells divides meridionally, whilst the other divides equatorially. • Mammals display rotational cleavage and an isolecithal distribution of yolk (sparsely and evenly distributed). Because the cells have only a small amount of yolk, they require immediate implantation onto the uterine wall in order to receive nutrients. • Mammals have a slow rate of division that is between 12 and 24 hours. These cellular divisions are asynchronous. Cleavage is the series of rapid cell divisions of zygote without increasing in size with the formation of morula (solid ball of 12-16 cells) and blastocyst (hollow ball of many cells with inner cavity – blastocoel).

Blastomeres: • cells of blastula • genetically equal • have identical developmental potency (not differentiated) • so each of them can give rise to a new individual • their sizes decrease during cleavage as they continue to be retained within the zona pellucida of an egg Blastocyst

The stage with a cavity inside that is filled with fluid, 2 different cell populations: trophoblast + inner cell mass (embryoblast), during the day 5 Gastrulation is the reorganizing of single- layered blastula into a multilayered structure – gastrula: • the main body axis and polarity begin to become apparent (dorsal-ventral, anterior- posterior); • cell migrations to positions where they will form the three germinal cell layers: ectoderm, mesoderm and endoderm; • develops on 7 th day and lasts to the end of the 2nd week after fertilization. Types of Cell movement in Gastrulation

→ In human the gastrulation occurs by type of delamination ! The germinal layers give rice to various tissues and organs of animals (histo- and organogenesis):

Endoderm: Mesoderm: Ectoderm: digestive tract, lungs, liver, connective tissue, bones, muscles, skin (epidermis), hair, nails, the pancreas, thyroid gland, urinary dermis, heart, blood vessels, gonads, eye lens, the pituitary gland, bladder excretory organs (kidneys) and the the epithelium of the nasal notochord (the dorsally located cavity, mouth, anal canal, supportive rod of all chordates) nervous system, sense organs Provisional organs (extraembryonic membranes) • are temporary organs formed by the embryo during embryogenesis and which ensure its growth and development. • include the chorion, amnion, placenta, allantois, yolk sac, umbilical cord. Extraembryonic membranes:

• amnion – originates from epiblast, forms an amniotic membrane that produces amniotic fluid, which creates the aqueous environment for embryo development; • chorion (chorionic villi) – originates from trophoblast, surrounds embryo and all other membranes, penetrates the lining of the uterus and forms the placenta with it; • yolk sac – originates from hypoblast, site of early blood cell formation, actively involved in the nutrition and respiration of embryo, but 8 weeks later undergoes a reversal; • allantois (urinary sac) – outpocketing of embryo’s gut, incorporated into umbilical cord, is an organ of nutrition, gas exchange and excretion in the early stages of embryonic development, and in the 2nd month of embryogenesis is reduced. Placenta

• placenta is a special organ that: • provides the fetus with nutrients and oxygen, absorbs the end products of metabolism, secretes hormones, and serves as a barrier to harmful substances; • functions as a fetomaternal organ which develops on 23-rd day of embryonic development from fetal chorion and allantois, and the maternal uterine tissue; • within the placenta there is no mixing of maternal and fetal blood; • umbilical cord provides the embryo with nutrients and oxygen, prevents the penetration of harmful substances from the placenta into the embryo. The critical periods in human development – are periods when organism is particularly sensitive (less resistant) to the effect of various environmental factors.

• Implantation (7 day after fertilization) – introduction of a zygote in a wall of an uterus. • Formation of embryonic layers (the first three weeks of fetal life). • Placentation (the end of 2nd week of pregnancy) – forming of a placenta at embryo. • Perinatal period (from 28 week of pregnancy to 7 day after birth) – is transferring a fetus out of aqueous into air. • Postnatal period (congenital, ontophylogenetical and acquired, non-phylogenetic developmental disorders): • juvenile (before puberty); • maturity (an adult pubertal stage); • old age (ageing), which ends to death. Congenital malformations are persistent morphological changes of an organ which occurs before birth, revealed immediately or after birth and cause organ disfunction. Congenital defects are divided into:  By affected structure: 1) cellular (cell heterocopies, heteroplasia, immaturation of cells and their structures, persistence, ); 2) tissue (tissue heterotopia, syndactyly); 3) organ.  By the sequence of arising: 1) primary (caused by the action of the harmful factors, according to WHO, 1971 classification are divided into: • hereditary (genetic, chromosomal); • exogenous (damage of the embryo or fetus caused by teratogenic factors); • multifactorial (genetic + exogenous factors) 2) secondary – a complication of the primary defects. Groups of congenital abnormalities 1. Malformations: occurs during the organogenesis and results in partial or complete non formation or alterations in the normal structure (in the 3rd to the 8th week of gestation). Example: Cleft lip, cleft palate. 2. Disruptions: results in morphological change of the already formed structure due to exposure to destructive process. Example: vascular accidents leading to intestinal atresia, amniotic band disruption. 3. Deformations: due to mechanical forces that affect a part of the fetus over a long period. Example: talipes equinovarus deformity. 4. Syndrome: is a group of anomalies occurring together due to a common cause. Types of congenital abnormalities Atresia – Stenosis – lack of natural channels or holes. narrowing of the channel or hole. Types of congenital abnormalities Aplasia – – congenital absence of an organ. is underdevelopment or incomplete development of a tissue or organ (lack of mass or size).

Aplasia cutis congenita Types of congenital abnormalities Ectopia – – any of various types of location of an organ in unusual place. abnormal growth or development of cells (microscopic scale) and/or organs (macroscopic scale). Ectopia cordis Types of congenital abnormalities – – the increase in the an increase in the amount of volume of an organ or tissue due to the organic tissue that results from cell enlargement of its component cells proliferation. (sizes of cells increase, but not number). Types of congenital abnormalities

Anaplasia (structural differentiation loss within a cell or group of cells). (connective tissue growth). (conversion in cell type). Neoplasia (abnormal proliferation). Prosoplasia (development of new cell function). Abiotrophy (loss in vitality of organ or tissue). (reduced functionality of an organ, with decrease in the number or volume of cells). (any degenerative disorder resulting from improper or faulty nutrition). Congenital malformations: Neural tube defects (NTD) Congenital malformations: cleft lip and cleft palate

Orofacial cleft is a group of congenital condition, that includes cleft lip, cleft palate or both together. As a baby develops during pregnancy, body tissue and special cells from each side of the head grow toward the center of the face and join together to make the face. Cleft lip and palate birth occur when a baby’s lip or mouth do not form properly during pregnancy. A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. It forms between the 4th and 7th weeks of pregnancy. A cleft palate occurs when the roof of the mouth contains an opening into the nose. It forms between the 6th and 9th weeks of pregnancy. Result: feeding problems, speech problems, hearing problems, and frequent ear infections. Periodization of the human ontogenesis regarding to developmental malformations 1. Progenesis (gametopathy): mutations or recombinations at the molecular and cellular levels in gametes. Mutant (unbalanced) gametes in most cases destroyed (eliminated), but during fertilization and formation of a zygote monogenic and chromosomal disorders can occur too. 2. Kimatogenesis (kimatopathy): a) blastogenesis (blastopathy) – from fertilization to 15 days of gestation (cleavage, forming of embryoblast + trophoblast). Disorders lead to the death of the embryo; b) embryogenesis (embryopathy) – disorders occur from 15 days to 8 weeks of embryonic development (organogenesis, formation of the amnion + chorion). Form the basis of congenital malformations; c) fetogenesis (fetopathy) – after 10 weeks of embryonic development (the development of the fetus, placenta formation, childbirth). This period characterized by abnormalities in the form of lower body weight, delayed intellectual development, etc. Teratogenic environmental factors

Factors that may cause developmental disorders (anomalies and defects) are called teratogenic (from the Greek teratos – injury). Human Teratogens Sensitivity to teratogens during pregnancy

high sensitivity to teratogens less sensitivity to teratogens Teratogenic effects on fetal and maternal systems during pregnancy Teratogenic action of radiation

• Ionizing radiation kills rapidly proliferating cells, producing any type of birth defect depending upon dose and stage of development. • Exposure of the pregnant woman to a large dose of X-ray can lead to microcephaly, spina bifida or cleft palate. Teratogenic drugs Teratogenic drugs: thalidomide Thalidomide is a mild sedative which is widely used in Europe in the 1960s until there where evidences that it was the cause of significant disorders of fetal development when used during pregnancy. The sensitive period – 23 to 28 days post-conception, with the critical period no longer than 14 days. About 20% of pregnancies exposed during this period resulted in infants with anomalies, the most notable of which were limb defects. The children had normal intelligence. Experts estimate that the drug thalidomide led to the death of approximately 2,000 children and serious birth defects in more than 10,000 children, about 5,000 of them in West Germany. Teratogenic effects of alcohol Fetal alcohol syndrome (FAS ) – is a condition, caused by fetal exposure of alcohol during pregnancy. Teratogenic infections

TORCH series – Blood Tests during pregnancy for: • Toxoplasma protista • Other (hepatitis B & chickenpox) • Rubella (German measles) • CMV cytomegalovirus • HSV herpes simplex 1, 2 Post-embryonic (postnatal) period

After the organism has gone out of ovum shells (birth), there begins its postembryonic (postnatal) period of its development.

In humans, 5 periods are singled out: 1) juvenile period (before puberty) 2) puberty (sexual maturing) 3) maturity 4) aging 5) death.

After the pubertal period, there develop definitive body proportions and organ systems come to the mode of functioning inherent to a mature organism. Phases of a human postnatal development • infancy – period during 0–1 year of the age (the first two weeks of infancy are called as the newborn, or neonatal period). • childhood – from 13 month until 12 to 13 years; the primary teeth appear and are replaced by the secondary or permanent teeth. • puberty – is the period between 12–15 years in girls and 13–16 years in boys, during which secondary sexual characteristics develop. • adolescence – follows the puberty and ends 3–4 years after it; the organism reaches sexual but also physical, mental and emotional maturity. • adulthood – a period in which developmental changes occur very slowly and are mostly characterized by selective loss of highly specialized cells and tissues. Postnatal development of the human is studied and treated with various medical branches. The main mechanisms of ontogenesis:

• proliferation (cell division); • migration (cell movement); • cell sorting; • cell death; • cell differentiation; • induction and competence (contact interactions); • distant interaction of cells, tissues and organs (humoral, nervous mechanisms of integration). The types of cell elimination (cell death) Characteristics of postnatal period of ontogenesis: • Growth • Development • Regeneration • Maturation and aging • Death. Growth • Is an increase in the mass and linear dimensions of an organism (and its parts). • In the basic of the growth, there lie the processes of protein biosynthesis, increase in dimensions and number of cells and non-cellular structures. • It is a universal feature of the living matter characteristic of any level of its organization – from the molecular to the biospheric. KINDS OF GROWTH

FALSE GROWTH TRUE GROWTH Mechanisms: Mechanisms: • oedema • protein synthesis (water retention) • cell division • fat deposition • cell growth TRUE GROWTH

Definite Indefinite (limited) (unlimited) During an interval (part) During the whole of postembryonic period postembryonic period of of ontogenesis ontogenesis (mammals, humans) (fish, crocodiles) TRUE GROWTH

Allometric Isometric with no preservation of with the preservation of the proportions of body the proportions of body parts (mammals, parts humans) (fish, crocodiles)

В1

А1 В2

А2

В1 В2 = А1 А2 TRUE GROWTH

Aucsentical Proliferative At the expense of cell At the expense of cell growth divisions

Accrecional Typical for tissues, that contain stem cells. Number of cells Nn = 2n increases linearly (in the arithmetic progression). Multiplicative Each daughter cell N = 2n enters to mitosis again. n In this type of growth. So the amount of cells is increased in a geometric progression. Development • It is a totality of relatively slow progressive changes resulting in the appearance of multicellular organisms. • Usually, the organismic development begins with the fertilization and comes to an end only at the death. Regeneration is the restoration of the lost parts of the organism (cells, tissues or organs) Physiological Reparative restoration of the structures, restoration of structures which loss is a natural event which were damaged or lost of ontogenesis as a result of the injury or disease Example: renewal of erythrocytes, the epidermis Example: healing of the cuts, of the skin, intestinal the restoring of the lost tail epithelium, and etc. at a lizard, etc. Regeneration types by the final result:

Typical – Atypical, or pathological – Homomorphosis Heteromorphosis the lost structure is replaced the lost structure is replaced by exactly the same by distinctly another Ways of reparative regeneration Main: Endomorphosis Epimorphosis Morphollaksis regenerating the size, regenerating both the regenerating the shape, but not the shape of size and shape of the but not the size of the the lost organ lost organ lost organ

Example: human liver Example: the tail of a Example: insect limb after its partial removal lizard or body of Hydra Ways of reparative regeneration Auxiliary:

Epithelization Compensatory hypertrophy The healing of the wounds The hypertrophy of the organ after with a damaged epithelium. the damage other organ this system.

Example: cuts of the skin Example: increase in size and increased function of the second kidney after removal of the first one Aging

Aging is a regularity process of age-decaying changes of the organism resulting in a decrease in the organism adaptation ability and in an increase in the probability of the death.

Herontology (from Greek «herontos» – an old man + «logos» – science) – is the science about old age and aging. It studies the processes of aging from the biological point of view and investigates the essence of the old age, as well as the influence of aging on both the individual and society. Signs of aging External signs of the old age

• changes in bearing (carriage) and gait; • decrease in mobility, • changes in the voice timbre, • skin wrinkles; • decrease of memory characteristic; • changes in behavior, way of life, place and position in society. Death

Death is the termination of the organism life activity, the extinction of the organism as an isolated living system.

The science that studies kinds and mechanisms of the death is called tanatology. PHYSIOLOGICAL PREMATURE Caused by natural aging Caused by illnesses and processes. diseases, damages of organs important for life.

DEATH

CLINICAL BIOLOGICAL Reversible state. Irreversible state. Reanimation is possible in the Reanimation is not possible absence of damages of life- even in the absence of damages important organs. in life-important organs. Signs and characteristics of clinical death • Absense of heart-beating, • Absence of respiration, • Absense couscionsness, • Absense of the pupil reflex.

• Duration: 6-7 minutes. The cortex of large hemispheres, sub-cortex structure and marrow stem do not function, but retain (preserve) a life ability. Cells of all organs and tissues remain alive in a human being. Signs and characteristics of biological death • Preservation (retention) of a changed form of the pupil at constraining the pupil of an eye, • Appearance of putrid (cadaverous) spots, • Sings of tissue decomposition.

• It comes after the clinical death. The Harward criterion – death of cerebral marrow (including marrow stem) with the disappearance of all the stem reflexes. It is characterized by a certain sequence (not simultaneons of the death of all tissue cells and organs of a human being). Genetic control of development Does the genome differ in different types of cells?

The scheme of John Gurdon’s experiment (1962) with the enucleated eggs of the frog Xenopus laevis Conclusion: Different cells, having the same genome, differ in the expression of their genes, that is, in different cells the genes differently “turn on” and “turn off”. Determination – a genetically programmed direction of cell differentiation. In the early stages of animal embryogenesis the embryo of an organ, being transplanted to another area of ​​the body, differentiates into that organ that should normally form from it.

The scheme of Wilhelm Roux’ experiment (1887) Conclusion: the embryo is a mosaic of blastomeres, the fate of which is predetermined. Embryonic induction – an influence of some parts of the embryo, that directs the development of neighbor groups of cells into particular tissues and organs by means of exreted regulation substances.

Hans Spemann and Hilde Mangold Organizer experiment with embryo of newt (1924)

Conclusion: during embryogenesis, some parts of the embryo affect the development of neighboring areas. References: • https://www.britannica.com/video/192622/Human-embryonic-development- birth-fertilization • https://study.com/academy/lesson/extraembryonic-membranes-in-humans.html • https://www.khanacademy.org/test-prep/mcat/cells/embryology/v/germ-layer- derivatives • https://pt.slideshare.net/jayswan/chapter-46-animal- reproduction/14?smtNoRedir=1 • https://dev.biologists.org/content/140/12/2449 • https://www.slideshare.net/E_neutron/molecular-genetic-mechanisms-of-onto- genesis • https://en.ppt-online.org/483044 • https://slideplayer.com/slide/5956764/ • https://www.slideshare.net/msmaybelle/teratogens-37341778 • https://www.docsity.com/en/congenital-malformations-teratology-introduction- to-embryology-lecture-slides/211242/ • https://slideplayer.com/slide/4092149/