Early Stages of Frog Development BIO 130 LAB PDF

EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 called micromeres TABLE OF CONTENTS...

EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 called micromeres TABLE OF CONTENTS Rate of cleavage is slower in the vegetal pole and creates I. Cleavage larger-sized blastomeres called II. Blastulation macromeres III. Gastrulation Ex. Frog A. Types of Gastrulation Movement B. Process of Gastrulation Meroblastic Zygote is only partially divided IV. Neurulation in the top portion due to the A. Process of Neurulation presence of large amounts of yolk Occurs in birds, reptiles, and fishes I. CLEAVAGE Cleavage ➔ Process of transforming single-celled zygote (fertilized egg) into a multicellular entity through a series of mitotic divisions ➔ Transforms zygote into several cleavage cells or blastomeres ➔ Two types: Holoblastic and Meroblastic ➔ Two stages: Early Cleavage and Late Cleavage Cleavage Furrow Figure 1: Two Types of Cleavage ➔ Indentation or groove that appears on the surface of cells during the final stage of cell division ➔ Separates blastomeres from each other TABLE 2. STAGES OF CLEAVAGE ➔ Occurs simultaneously with the formation of the animal and vegetal poles but finishes later than Stage of Description both Cleavage Early Cleavage First 3 mitotic divisions TABLE 1. TWO TYPES OF CLEAVAGE (2-cell stage to 8-cell stage) Each cell is referred to as a Type of Description blastomere Cleavage First Mitotic Zygote divides into two cells Holoblastic Zygote is completely divided Division (2-cell stage) from pole-to-pole/end-to-end Meridional: passes from the Occurs in mammals and animal to the vegetal pole amphibians and bisects the gray Two types: Equal and Unequal crescent. Equal Cleavage results in equal-sized Second Mitotic Zygote divides into four cells Holoblastic blastomeres Division (4-cell stage) Meridional: passes at a right Unequal Cleavage results in unequal - angle with the first mitotic Holoblastic sized blastomeres due to division presence of yolk Rate of cleavage is faster in the Third Mitotic Zygote divides into eight animal pole and creates Division cells (8-cell stage) smaller-sized blastomeres BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 1 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 Horizontal: displaced towards the animal pole producing four micromeres, and four macromeres in the vegetal pole Late Cleavage Succeeding mitotic divisions in the 16-32 cell stages Zygote is now referred to as the morula Figure 5: Photomicrograph of Early Cleavage (Lateral Cut) Figure 2: Stages of Cleavage Figure 6: Photomicrograph of Late Cleavage (Lateral Cut) Figure 3: Early (left) and Late (right) Cleavage Figure 4: Early (left) and Late (right) Cleavage Figure 7: Photomicrograph of Late Cleavage (Transverse Cut) II. BLASTULATION Blastulation ➔ Internal secretion of fluid by the blastomeres of the morula to produce a fluid-filled cavity called BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 2 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 the blastocoel or segmentation cavity cleavage Blastocoel Yolk: Packed ➔ Fluid-filled cavity that is displaced towards the animal pole of the blastula ➔ “The First Coelom” Gray Crescent ➔ Region in the zygote that appears opposite the location of the sperm cell’s entry point ➔ Determines the dorsal-ventral axis of the zygote ➔ Broadest portion becomes the dorsal/back surface of the zygote (location of the spinal cord) ➔ Region of the zygote opposite the gray crescent becomes the ventral/front surface of the zygote Figure 8: Early (left) and Late (right) Blastula Blastula ➔ Stage in embryonic development characterized by the formation of the blastocoel and more distinct animal and vegetal hemispheres ➔ Zygote reaches the blastula stage near the end of cleavage (late cleavage) Vitelline Membrane ➔ Thin, non-cellular, transparent membrane immediately surrounding the oocyte and inner to the follicle cells ➔ allows for diffusion of water and selective nutrients Fertilization Envelope ➔ Elevated vitelline membrane Figure 9: Early (left) and Late (right) Blastula ➔ Prevents further penetration of sperm and protects embryo during development TABLE 3. TWO HEMISPHERES OF BLASTULA Blastula Description Hemisphere Animal Pigmentation: Heavily Hemisphere pigmented cortex, most intense in animal pole and decreases in intensity as it moves towards vegetal pole Cell Layers: 4 or 5 cells thick, smaller cells and fewer layers in the animal pole and increases in size and layers as it moves towards vegetal pole Yolk: Very little amount Vegetal Pigmentation: Pigmented Hemisphere cortex is less evident Cell Layers: Blastomeres are Figure 10: Photomicrograph of Early Blastula (Transverse very large and few in number, Cut) indicative of less frequent BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 3 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 ◆ Jaws and teeth ➔ Mesoderm ◆ Gives rise to muscles and the skeleton ◆ Circulatory and lymphatic system ◆ Excretory and reproductive system ◆ Dermis of skin ◆ Adrenal cortex ➔ Endoderm ◆ Epithelial lining of the digestive tract ◆ Epithelial lining of respiratory, excretory, and reproductive tracts and ducts ◆ Thymus, thyroid, and parathyroid glands TYPES OF GASTRULATION MOVEMENTS 1. Invagination Figure 11: Photomicrograph of Late Blastula (Transverse Infolding of a sheet (epithelium) of cells Cut) Much like the indentation of a balloon when poked Figure 13: Invagination 2. Involution Inward movement of an expanding outer layer forming the new inner surface Figure 12: Photomicrograph of Late Blastula (Transverse Cut) III. GASTRULATION Figure 14: Involution It is the reorganization of the hollow blastula into a 3. Epiboly two-layered or three-layered embryo called gastrula Movement of epithelial cells, spreading as a unit, During gastrulation, a set of cells near the surface of to enclose the deeper layers of the embryo the blastula invaginates forming a primitive digestive tube. Begins in the area called the gray crescent Three Germ Layers ➔ Ectoderm ◆ Forms the nervous system and the outer body layer ◆ Epidermis of skin and its derivatives ◆ Pituitary gland, adrenal medulla Figure 15: Epiboly BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 4 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 ➔ Future dorsal side of the embryo PROCESS OF GASTRULATION Figure 18 Dorsal Lip ➔ The lip closest to the archenteron ➔ Refer to Figure X and X Blastopore ➔ A mouth-like opening of the archenteron on the surface of the embryo during the invagination of the archenteron ➔ Becomes the anus in the adult frog ➔ Refer to Figure X and X 2. Cells of the animal pole spread out, pushing surface cells below them toward and across the dorsal lip Figure 16: Gastrulation in a frog embryo 1. Cells in the region of the gray crescent move inward, forming the dorsal lip of the future blastopore Figure 19 Figure 17: Dorsal lip formation Gray Crescent ➔ Gray region just below the equator and opposite the point of sperm entry BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 5 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 IV. NEURULATION Establishment of the central nervous system (CNS) Begins as cells from the dorsal mesoderm form the notochord Figure 20: Photomicrographs of Early Gastrula Stage 3. The archenteron expands destroying the blastocoel The yolk plug is visible through the blastopore At the end of gastrulation, the three germ layers are formed: Ectoderm, Mesoderm, Endoderm Figure 21: Movement of archenteron to form the three germ layers Archenteron ➔ Forms the blastopore and displaces the Figure 22: Process of neurulation blastocoel ➔ Becomes the gut (digestive system) in the Notochord adult frog ➔ Derived from the mesoderm Yolk Plug ➔ Induces the ectoderm to differentiate into the ➔ Exposed endoderm cells encircled by the neural plate blastopore ➔ Induces the endoderm to differentiate into the neural fold PROCESS OF NEURULATION 1. Induction of the Neural Plate The thickening of the ectoderm in the dorsal side The thickened portion of the ectoderm will become the neural plate ○ Precursor of all cell types in the CNS Figure 21: Photomicrographs of Late Gastrula Stage BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 6 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC EARLY STAGES OF FROG DEVELOPMENT BIO 130 LAB INTARMED 2030 | Dr. Vitor | LU2 SEM 1 | SY. 2024-2025 Figure 23: Formation of neural plate Figure 26: Photomicrograph of Neural Fold Stage 3. Convergence of Neural Folds The neural folds move towards the midline and converge The fusion results in the enclosing of the neural groove and the formation of the neural tube Figure 24: Photomicrograph of Neural Plate Stage 2. Folding of Neural Plate Neural plate invaginates and forms the U-shaped neural groove Two ridges called neural folds form the lateral edges of the neural plate Figure 27: Formation of neural tube Figure 25: Formation of neural fold Figure 28: Photomicrograph of Neural Tube Stage BIO 130 LAB LU 2 SEM 1 | IMED 2030 Page 7 of 7 DE LUNA, MD; CANTO, ARBC.; HE, FJP; REYES, JCDC