|A personal message from Dr Mark Hill (May 2020)
| I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!
These notes are intended to introduce the concept of time as a developmental mechanism. See also Timeline human development.
The concept can historically be seen in the staging of different species development and gestation by hours, days, and months.
More recently with molecular development and cellular dynamics we are looking at changes in the range from minutes down.
Some Recent Findings
- Scaling of pattern formations and morphogen gradients "The concentration gradient of morphogens provides positional information for an embryo and plays a pivotal role in pattern formation of tissues during the developmental processes. Morphogen-dependent pattern formations show robustness despite various perturbations. Although tissues usually grow and dynamically change their size during histogenesis, proper patterns are formed without the influence of size variations. Furthermore, even when the blastula embryo of Xenopus laevis is bisected into dorsal and ventral halves, the dorsal half of the embryo leads to proportionally patterned half-sized embryos. This robustness of pattern formation despite size variations is termed as scaling. In this review, I focused on the morphogen-dependent dorsal-ventral axis formation in Xenopus and described how morphogens form a proper gradient shape according to the embryo size."
- Heterochrony and Morphological Variation of Epithalamic Asymmetry "Heterochrony is one proposed mechanism to explain how morphological variation and novelty arise during evolution. To experimentally approach heterochrony in a comprehensive manner, we must consider all three aspects of developmental time (sequence, timing, duration). This task is only possible in developmental models that allow the acquisition of high-quality temporal data in the context of normalized developmental time. Here we propose that epithalamic asymmetry of teleosts is one such model. Comparative studies among related teleost species have revealed heterochronic shifts in the timing of ontogenic events leading to the development of epithalamic asymmetry. Such temporal changes involve neural structures critical for tissue-tissue interactions underlying the generation of asymmetry and are concurrent with the appearance of morphological differences in the pattern of asymmetry between species. Based on these findings, we hypothesize that interspecies variation of epithalamic asymmetry results from changes in the timing of tissue-tissue interactions critical for the establishment of asymmetry during ontogeny. Importantly, this hypothesis can be tested by systematic comparative approaches among teleosts species based on normalized developmental time, combined with experimental manipulation of epithalamic asymmetry development."
|More recent papers
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Search term: Developmental Mechanisms
<pubmed limit=5>Developmental Mechanisms</pubmed>
Species Embryonic Comparison Timeline
|Note these Carnegie stages are only approximate day timings for average of embryos. Links: Carnegie Stage Comparison
O'Rahilly R. (1979). Early human development and the chief sources of information on staged human embryos. Eur. J. Obstet. Gynecol. Reprod. Biol. , 9, 273-80. PMID: 400868
Otis EM and Brent R. Equivalent ages in mouse and human embryos. (1954) Anat Rec. 120(1):33-63. PMID 13207763
Theiler K. The House Mouse: Atlas of Mouse Development (1972, 1989) Springer-Verlag, NY. Online
OTIS EM & BRENT R. (1954). Equivalent ages in mouse and human embryos. Anat. Rec. , 120, 33-63. PMID: 13207763
Witschi E. Rat Development. In: Growth Including Reproduction and Morphological Development. (1962) Altman PL. and Dittmer DS. ed. Fed. Am. Soc. Exp. Biol., Washington DC, pp. 304-314.
Pérez-Cano FJ, Franch À, Castellote C & Castell M. (2012). The suckling rat as a model for immunonutrition studies in early life. Clin. Dev. Immunol. , 2012, 537310. PMID: 22899949 DOI.
- ↑ Inomata H. (2017). Scaling of pattern formations and morphogen gradients. Dev. Growth Differ. , 59, 41-51. PMID: 28097650 DOI.
- ↑ Signore IA & Concha ML. (2017). Heterochrony and Morphological Variation of Epithalamic Asymmetry. J. Exp. Zool. B Mol. Dev. Evol. , 328, 157-164. PMID: 27659033 DOI.
Search PubMed: Developmental Mechanisms
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Cite this page: Hill, M.A. (2020, June 3) Embryology Developmental Mechanism - Time. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Developmental_Mechanism_-_Time
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- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G