Talk:Echidna Development
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Cite this page: Hill, M.A. (2026, Mayıs 12) Embryology Echidna Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Talk:Echidna_Development |
2011
Monotreme ossification sequences and the riddle of mammalian skeletal development
Evolution. 2011 May;65(5):1323-35. doi: 10.1111/j.1558-5646.2011.01234.x. Epub 2011 Feb 18.
Weisbecker V. Source Earth Sciences, University of Cambridge, Downing St. CB2 3EQ, Cambridge, United Kingdom. vw248@cam.ac.uk
Abstract
The developmental differences between marsupials, placentals, and monotremes are thought to be reflected in differing patterns of postcranial development and diversity. However, developmental polarities remain obscured by the rarity of monotreme data. Here, I present the first postcranial ossification sequences of the monotreme echidna and platypus, and compare these with published data from other mammals and amniotes. Strikingly, monotreme stylopodia (humerus, femur) ossify after the more distal zeugopodia (radius/ulna, tibia/fibula), resembling only the European mole among all amniotes assessed. European moles also share extreme humeral adaptations to rotation digging and/or swimming with monotremes, suggesting a causal relationship between adaptation and ossification heterochrony. Late femoral ossification with respect to tibia/fibula in monotremes and moles points toward developmental integration of the serially homologous fore- and hindlimb bones. Monotreme cervical ribs and coracoids ossify later than in most amniotes but are similarly timed as homologous ossifications in therians, where they are lost as independent bones. This loss may have been facilitated by a developmental delay of coracoids and cervical ribs at the base of mammals. The monotreme sequence, although highly derived, resembles placentals more than marsupials. Thus, marsupial postcranial development, and potentially related diversity constraints, may not represent the ancestral mammalian condition.
© 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.
PMID: 21521190 http://www.ncbi.nlm.nih.gov/pubmed/21521190
DDX4 (VASA) Is Conserved in Germ Cell Development in Marsupials and Monotremes
Biol Reprod. 2011 Jun 8. [Epub ahead of print]
Hickford DE, Frankenberg S, Pask AJ, Shaw G, Renfree MB.
Abstract
DDX4 (VASA) is an RNA helicase expressed in the germ cells of all animals. To gain greater insight into the role of this gene in mammalian germ cell development we characterized DDX4 in both a marsupial (the tammar wallaby) and a monotreme (the platypus). DDX4 is highly conserved between eutherian, marsupial and monotreme mammals. DDX4 protein is absent from tammar fetal germ cells but is present from Day 1 postpartum in both sexes. The distribution of DDX4 protein during oogenesis and spermatogenesis in the tammar is similar to eutherians. Female tammar germ cells contain DDX4 protein throughout all stages of post-natal oogenesis. In males, DDX4 is in gonocytes and during spermatogenesis it is present in spermatocytes and round spermatids. A similar distribution of DDX4 occurrs in the platypus during spermatogenesis. There are several DDX4 isoforms in the tammar, resulting from both pre- and post-translational modifications. DDX4 in marsupials and monotremes has multiple splice variants and polyadenylation motifs. Using in silico analyses of genomic databases, we found that these previously unreported splice variants also occur in eutherians. In addition, several elements implicated in the control of Ddx4 expression in the mouse, including RGG (arginine-glycine-glycine) and dimethylation of arginine motifs and CpG islands within the Ddx4 promoter, are also highly conserved. Collectively these data suggest that DDX4 is essential for the regulation of germ cell proliferation and differentiation across all three extant mammalian groups--eutherians, marsupials and monotremes.
PMID: 21653890 http://www.ncbi.nlm.nih.gov/pubmed/21653890
The development of the olfactory organs in newly hatched monotremes and neonate marsupials
J Anat. 2011 Aug;219(2):229-42. doi: 10.1111/j.1469-7580.2011.01393.x. Epub 2011 May 17.
Schneider NY. Source Department of Zoology, The University of Melbourne, Melbourne, Victoria, Australia.
Abstract
Olfactory cues are thought to play a crucial role in the detection of the milk source at birth in mammals. It has been shown that a marsupial, the tammar wallaby, can detect olfactory cues from its mother's pouch at birth. This study investigates whether the main olfactory and accessory olfactory system are similarly well developed in other marsupials and monotremes at birth/hatching as in the tammar. Sections of the head of various marsupial and two monotreme species were investigated by light microscopy. Both olfactory systems were less well developed in the kowari and Eastern quoll. No olfactory or vomeronasal or terminal nerves could be observed; the main olfactory bulb (MOB) had only two layers while no accessory olfactory bulb or ganglion terminale were visible. All other investigated marsupials and monotremes showed further developed olfactory systems with olfactory, vomeronasal and terminal nerves, a three-layered MOB, and in the marsupials a prominent ganglion terminale. The main olfactory system was further developed than the accessory olfactory system in all species investigated. The olfactory systems were the least developed in species in which the mother's birth position removed most of the difficulty in reaching the teat, placing the neonate directly in the pouch. In monotremes they were the furthest developed as Bowman glands were found underlying the main olfactory epithelium. This may reflect the need to locate the milk field each time they drink as they cannot permanently attach to it, unlike therian mammals. While it still needs to be determined how an odour signal could be further processed in the brain, this study suggests that marsupials and monotremes possess well enough developed olfactory systems to be able to detect an odour cue from the mammary area at birth/hatching. It is therefore likely that neonate marsupials and newly hatched monotremes find their way to the milk source using olfactory cues, as has been previously suggested for the marsupial tammar wallaby, rabbits, rats and other eutherians.
© 2011 The Author. Journal of Anatomy © 2011 Anatomical Society of Great Britain and Ireland.
PMID: 21592102 http://www.ncbi.nlm.nih.gov/pubmed/21592102
2010
Those other mammals: the immunoglobulins and T cell receptors of marsupials and monotremes
Semin Immunol. 2010 Feb;22(1):3-9. Epub 2009 Dec 8.
Miller RD. Source Center for Evolutionary and Theoretical Immunology, Department of Biology, University of New Mexico, Albuquerque, NM 87110, USA. rdmiller@unm.edu
Abstract
This review summarizes analyses of marsupial and monotreme immunoglobulin and T cell receptor genetics and expression published over the past decade. Analyses of recently completed whole genome sequences from the opossum and the platypus have yielded insight into the evolution of the common antigen receptor systems, as well as discovery of novel receptors that appear to have been lost in eutherian mammals. These species are also useful for investigation of the development of the immune system in organisms notable for giving birth to highly altricial young, as well as the evolution of maternal immunity through comparison of oviparous and viviparous mammals.
(c) 2009 Elsevier Ltd. All rights reserved.
PMID: 20004116 http://www.ncbi.nlm.nih.gov/pubmed/20004116
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