Development of chick

chick development

1. P G DEPARTMENT OF ZOOLOGY MINOR 2 SEM4 TOPIC: EARLY DEVELPOMENT IN CHICK SUBMITTED TO:R K PANDITA SUBMITTED BY: VAISHALI SHARMA R.NO:01

2. Steps Involved in the Development of Chick I. Fertilization: Ova leave the ovary (ovulation) as primary oocytes. They are released in coelom and caught by the expanded funnel-like opening of oviduct. They are fertilized in the upper part of oviduct which also receives sperms from the male bird during copulation. Fertilization is thus internal in birds II. Cleavage: Cleavage begins about 3 hours after fertilization. Cleavage and early gastrulation is completed by the time the egg is laid.

3. III. Blastulation : The free margin of blastoderm grows rapidly over the surface of yolk. A small fluid-filled space appears just beneath the central mass of cells, this is the sub-germinal cavity, often called blastocoel, though not real. IV. Gastrulation: Gastrulation begins even before laying of eggs. It involves the formation of endoderm so that the monoblastic embryo or blastula is converted into diploblastic or two-layered gastrula. There is no invagination of prospective endoderm through a blastopore as found in frog.

4. V. Incubation: Egg is warmed during incubation by the bird’s breast. In artificial incubation, the required temperature (37°C to 40°C) is maintained in an incubator. With the resumption of development under heat of incubation, there occurs mesoderm formation, notogenesis (formation of notochord), neurogenesis (formation of neural tube), formation of mesoblastic somites and organogeny .

5. BLASTULATION: Between the blastoderm and the yolk of avian eggs is a space called the subgerminal cavity, which is created when the blastoderm cells absorb water from the albumin and secrete the fluid between themselves and the yolk (New 1956). At this stage, the deep cells in the center of the blastoderm appear to be shed and die, leaving behind a 1-cell-thick area pellucida ; this part of the blastoderm forms most of the actual embryo. The peripheral ring of blastoderm cells that have not shed their deep cells constitutes the area opaca . Between the area pellucida and the area opaca is a thin layer of cells called the marginal zone ( Eyal-Giladi 1997; Arendt and Nübler -Jung 1999). Some marginal zone cells become very important in determining cell fate during early chick development

6. The blastoderm will form an upper layer called the epiblast and a lower layer called the hypoblast The avian embryo comes entirely from the epiblast; the hypoblast does not contribute any cells to the developing embryo (Rosenquist 1966, 1972). Rather, the hypoblast cells form portions of the extraembryonic membranes especially the yolk sac and the stalk linking the yolk mass to the endodermal digestive tube. Hypoblast cells also provide chemical signals that specify the migration of epiblast cells. However, the three germ layers of the embryo proper (plus the amnion, chorion, and allantois extraembryonic membranes) are formed solely from the epiblast ( Schoenwolf 1991)

7. THE HYPOBLAST Shortly after the egg is laid, a local thickening of the epiblast, called Koller’s sickle, is formed at the posterior edge of the area pellucida. In between the area opaca and Koller’s sickle is a belt-like region called the posterior marginal zone (PMZ). A sheet of cells at the posterior boundary between the area pellucida and marginal zone migrates anteriorly beneath the surface. Meanwhile, cells in more anterior regions of the epiblast have delaminated and stay attached to the epiblast to form hypoblast “islands,” an archipelago of disconnected clusters of 5–20 cells each that migrate and become the primary hypoblast \ The sheet of cells that grows anteriorly from Koller’s sickle combines with the primary hypoblast to form the complete hypoblast layer, also called the secondary hypoblast or endoblast Eyal-Giladi et al. 1992; Bertocchini and Stern 2002; Khaner 2007a,b). The resulting two-layered blastoderm (epiblast and hypoblast) is joined together at the marginal zone, and the space between the layers forms a blastocoel-like cavity.

8. FORMATION OF PRIMITIVE STREAK: Avian and mammalian gastrulation takes place through the primitive streak. This can be considered the equivalent of an elongated blastopore lip of amphibian embryos ( Alev et al. 2013; Bertocchini et al. 2013; Stower et al. 2015). the primitive streak first arises from Koller’s sickle and the epiblast above it ( Bachvarova et al. 1998; Lawson and Schoenwolf 2001a,b; Voiculescu et al. 2007). As cells converge to form the primitive streak, a depression called the primitive groove forms within the streak. Most migrating cells pass through the primitive groove, which serves as a gateway into the deep layers of the embryo (FIGURE 12.4; Voiculescu et al. 2014). Thus, the primitive groove is homologous to the amphibian blastopore, and the primitive streak is homologous to the blastopore lip

9. ELONGATION OF THE PRIMITIVE STREAK The streak elongates toward the future head region as more anterior cells migrate toward the center of the embryo. Convergent extension is responsible for the progression of the streak Cell division adds to the length produced by convergent extension, and some of the cells from the anterior portion of the epiblast contribute to the formation of Hensen’s node ( Streit et al. 2000; Lawson and Schoenwolf 2001b). At the same time, the secondary hypoblast (endoblast) cells continue to migrate anteriorly from the posterior marginal zone of the blastoderm The elongation of the primitive streak appears to be coextensive with the anterior migration of these secondary hypoblast cells, and the hypoblast directs the movement of the primitive streak (Waddington 1933; Foley et al. 2000; Voiculescu et al. 2007, 2014). The streak eventually extends to 60%–75% of the length of the area pellucid

10. FORMATION OF ENDODERM AND MESODERM As soon as the primitive streak has formed, epiblast cells begin to migrate through it and into the space between epiblast and hypoblast (reminiscent of the amphibian blastocoel). Cells migrating through the anterior end pass down into the embryonic space and migrate anteriorly, forming the endoderm, head mesoderm, and notochord; Cells passing through the more posterior portions of the primitive streak give rise to the majority of mesodermal tissues ; Rosenquist 1966; Schoenwolf et al. 1992). The first cells to migrate through Hensen’s node are those destined to become the pharyngeal endoderm of the foregut. Once deep within the embryo, these endodermal cells migrate anteriorly and eventually displace the hypoblast cells, causing the hypoblast cells to be confined to a region in the anterior portion of the area pellucida. This anterior region, the germinal crescent, does not form any embryonic structures, but it does contain the precursors of the germ cells, which later migrate through the blood vessels to the gonads

11. REGRESSION OF THE PRIMITIVE STREAK AND EPIBOLY OF THE ECTODERM As mesodermal ingression continues, the primitive streak starts to regress, moving Hensen’s node from near the center of the area pellucida to a more posterior position The regressing streak leaves in its wake the dorsal axis of the embryo, including the notochord. The notochord is laid down in a head-to-tail direction, starting at the level where the ears and hindbrain form and extending caudally to the tailbud. the pharyngeal endoderm and head mesendoderm will largely induce the anterior parts of the brain, while the notochord will induce the hindbrain and spinal cord. By this time, all the presumptive endodermal and mesodermal cells have entered the embryo and the epiblast is composed entirely of presumptive ectodermal cells.

12. Axis specification and the avian “organizer” Gastrulating avian (and mammalian) embryos exhibit a distinct anterior-to-posterior gradient. While cells of the posterior portions of the embryo are still part of a primitive streak and entering the inside of the embryo, cells at the anterior end are already starting to form organs (see Darnell et al. 1999). For the next several days, the anterior end of the embryo is more advanced in its development (having had a “head start,” if you will) than the posterior end.

13. The role of gravity and the PMZ The conversion of the radially symmetrical blastoderm into a bilaterally symmetrical structure appears to be determined by gravity. As the ovum passes through the hen’s reproductive tract, it is rotated for about 20 hours in the shell gland. This spinning, at a rate of 15 revolutions per hour, shifts the yolk such that its lighter components (probably containing stored maternal determinants for development) lie beneath one side of the blastoderm. This imbalance tips up one end of the blastoderm, and that end becomes the posterior marginal zone, where primitive streak formation begins (Figure 12.9; Kochav and Eyal-Giladi 1971; Callebaut et al. 2004).

14. Left-right axis formation The vertebrate body has distinct right and left sides. The heart and spleen, for instance, are generally on the left side of the body, whereas the liver is usually on the right. The distinction between the sides is primarily regulated by the left-sided expression of two proteins: the paracrine factor Nodal and the transcription factor Pitx2.

15. Early chick embryo development ( somitogenesis ) - YouTube

16. REFRENCES: Chicken Embryo Development – YouTube Chicken Cleavage Blastulation and Gastrulation – YouTube day by day chicken embryonic development – YouTube DEVELOPMENTAL BIOLOGY – GILBERT 11 TH EDITION