Fish development
The
Cleavage
Most bony fish eggs are referred to as telolecithal which means that most of the egg cell cytoplasm is yolk.
The fate of the first cells, called blastomeres, is determined by its location. This contrasts with the situation in some other animals, such as mammals, in which each blastomere can develop into any part of the organism.[2] Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable.[4] During this time three cell populations become distinguished. The first population is the yolk syncytial layer. This layer forms when the cells at the vegetal pole of the blastoderm combine with the yolk cell underneath it. Later in development the yolk syncytial layer will be important in directing cell movements of gastrulation. The second cell population is the enveloping layer which is made of superficial cells from the blastoderm that eventually form a single epithelial cell layer.[1] This layer functions in protection by allowing the embryo to develop in a hypotonic solution so the cell will not burst.[5] Finally, the third set of blastomeres are the deep cells. These deep cells are located between the enveloping layer and the yolk syncytial layer and eventually give rise to the embryo proper.[1]
Germ layer formation
Once blastoderm cells have covered almost half of the yolk cell, thickening throughout the margin of deep cells occurs. The thickening is referred to as the germ ring and is made up of a superficial layer, the epiblast which will become ectoderm, and an inner layer called the hypoblast which will become endoderm and mesoderm.[6] As the blastoderm cells undergo epiboly around the yolk the internalization of cells at the blastoderm margin start to form hypoblast. Presumptive ectoderm or epiblast cells do not internalize but the deep cells (inner layer of cells) do and they become the mesoderm and endoderm. As the hypoblast cells move inward future mesoderm (hypoblast cells) start to move vegetally and proliferate but later in development these cells alter their direction and start moving towards the animal pole. However, endodermal precursors seem to lack a pattern and move randomly over the yolk.[7]
Axis formation
Once the egg has become multicellular and positioned its germ layers with ectoderm on the outside, mesoderm in the middle, and endoderm on the inside body axes have to be determined for proper development.
Neurulation
Neurulation, the formation of the central nervous system, is different in fishes than in most other chordates. Convergence and extension in the epiblast recruits presumptive neural cells from the epiblast towards the midline where they form a neural keel. A neural keel is a band of neural precursors that develops a slit like lumen to eventually become the neural tube.[1] The neural tube begins as a solid cord formed from the ectoderm. This cord then sinks into the embryo and becomes hollow, forming the neural tube. This process contrasts with the process in other chordates, which occurs by an infolding of the ectoderm to form a hollow tube.[10]
Throughout the years advances in research have shown that neural formation relies on interactions between extrinsic signaling factors and intrinsic transcription factors. Extrinsic signals involved are BMP, Wnt, and FGF and intrinsic transcription factors like SoxB1 related genes. Secreted proteins such as BMP and its antagonist Noggin and chordin act permissively to establish the fate of neural tissue in the dorsal ectoderm and enables the formation of the neural plate.[11]
Sex determination
Sex determination is variable in fish from environmental factors like temperature to genetic mechanisms. Some fish have XX/XY chromosomes and others have ZZ/ZW. So far one gene in specific,
Notes
- ^ a b c d e Gilbert 2014, pp. 273–6.
- ^ a b Gilbert 1994, pp. 185–7.
- ^ Lee, Webb & Miller 2003.
- ^ Kane & Kimmel 1993.
- ^ Fukazawa et al. 2010.
- ^ Keller et al. 2008.
- ^ Pézeron et al. 2008.
- ^ a b Gilbert 2014, pp. 277–81.
- ^ Schier 2001.
- ^ Gilbert 1994, p. 247.
- ^ Schmidt, Strähle & Scholpp 2013.
- ^ Zhang et al. 2009.
- ^ Gilbert 1994, pp. 781.
References
- Fukazawa, Cindy; Santiago, Celine; Park, Keon Min; Deery, William J.; Gomez de la Torre Canny, Sol; Holterhoff, Christopher K.; Wagner, Daniel S. (2010). "poky/chuk/ikk1 is required for differentiation of the zebrafish embryonic epidermis". Developmental Biology. 346 (2): 272–83. PMID 20692251.
- Gilbert, Scott F. (1994). Developmental Biology (4th ed.). Sinauer. ISBN 978-0-87893-249-8.
- Gilbert, Scott F. (2014). Developmental Biology (10th ed.). Sinauer. ISBN 978-1-60535-173-5.
- Kane, D. A.; Kimmel, C. B. (1993). "The zebrafish midblastula transition". Development. 119 (2): 447–56. PMID 8287796.
- Keller, P. J.; Schmidt, A. D.; Wittbrodt, J.; Stelzer, E. H.K. (2008). "Reconstruction of Zebrafish Early Embryonic Development by Scanned Light Sheet Microscopy". Science. 322 (5904): 1065–9. S2CID 7594561.
- Lee, Karen W; Webb, Sarah E; Miller, Andrew L (2003). "Ca2+ released via IP3 receptors is required for furrow deepening during cytokinesis in zebrafish embryos". The International Journal of Developmental Biology. 47 (6): 411–21. PMID 14584779.
- Pézeron, Guillaume; Mourrain, Philippe; Courty, Sébastien; Ghislain, Julien; Becker, Thomas S.; Rosa, Frédéric M.; David, Nicolas B. (2008). "Live Analysis of Endodermal Layer Formation Identifies Random Walk as a Novel Gastrulation Movement" (PDF). Current Biology. 18 (4): 276–81. S2CID 11428272.
- Schier, Alexander F (2001). "Axis formation and patterning in zebrafish". Current Opinion in Genetics & Development. 11 (4): 393–404. PMID 11448625.
- Schmidt, Rebecca; Strähle, Uwe; Scholpp, Steffen (2013). "Neurogenesis in zebrafish – from embryo to adult". Neural Development. 8: 3. PMID 23433260.
- Zhang, Quanqi; Sun, Xiaohua; Qi, Jie; Wang, Zhigang; Wang, Xinglian; Wang, Xubo; Zhai, Teng (2009). "Sex determination mechanisms in fish". Journal of Ocean University of China. 8 (2): 155–60. S2CID 84734850.