Studies of the structure, function, and differentiation of the trophotaeniae and gut in embryonic goodeid fishes
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- Tez No: 400422
- Danışmanlar: DR. JOHN P. WOURMS
- Tez Türü: Doktora
- Konular: Zooloji, Zoology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1999
- Dil: İngilizce
- Üniversite: Clemson Unıversıty
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Zooloji Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
A tracer (CF) study was performed on Ameca splendens to test the hypothesis that large molecules present within the maternal blood vascular system leave it and pass through the ovarian epithelium and into the ovarian fluid. To visualize the transfer of high molecular weight, protein molecules from mother to embryo, cationized ferritin (CF, MW 480,000) and horseradish peroxidase (HRP, 40,000) were used. Tracers were injected into gravid females at several different (early, mid, late) developmental stages of Ameca splendens to investigate the uptake of proteins that have a range in size from 40,000-480,000 MW.Transfer of nutrients from the maternal bloodstream to that of the embryo involves the passage of materials across six layers of maternal and embryonic tissue. In early stage embryos, there was evidence of transfer of CF from the peritoneal cavity to the ovarian lumen and subsequent uptake of CF by trophotaenial cells. CF can be detected in the lumen of ovary. No evidence was found of transfer to the ovarian lumen or uptake of CF by the trophotaeniae of late-stage embryos. The mechanism(s) of maternal transport of macromolecules from the blood vascular system to ovarian fluid is functional during the early and mid phases of gestation, but becomes non-operative during the late phases of gestation. During late gestation, the paracelMar passage of large molecules was occluded by the development of arrays of tight junctions. Small molecules, however, can still pass into the ovarian fluid. Taken together, these experiments demonstrate that there is transfer of macromolecules (40,000-480,OOOMW) from mother to embryos.Trophotaeniae, the chief site of nutrient absorption, are perianal extensions of the embryonic intestinal epithelium that develop and persist during gestation.Trophotaeniae are advantageous during gestation but they present a potential hazard as gestation ends. When the embryos are born in aquarium water, which has almost zero osmolality, they undergo ecdysis of their trophotaeniae usually within 24 hours. At parturition, the newborn embryo leaves an isosmotic environment and enters a hypo-osmotic environment. Trophotaeniae, which are the exchange site of the embryo when they were in the ovary, are“autotomized”at a site adjacent to the terminal end of the embryonic gut. After birth, embryos replace the endodermal lining of the vent with ectoderm to form a typical anus (=proctodaeum). The process of trophotaenial loss was studied to ascertain the mechanism of shedding after the embryos are bom. The hypothesis was that a zone of cells around the terminal end of the embryonic gut undergoes apoptosis and that this zone is the site at which“autotomy”occurs. The experimental results did not support the hypothesis that there was a discrete apoptotic zone at which autotomy occurs. There were relatively few apoptotic cells in the trophotaeniae and they were not localized at the base of trophotaeniae. There was no evidence of an apoptotic zone of autotomy. Another hypothesis was tested to determine whether the reduced osmolarity of the environment into which the embryos are bom might be the signal that initiates the shedding of trophotaeniae. Experiments reveal that an isosmotic environment maintains trophotaeniae and that the sudden change in osmolarity at parturition is associated with ecdysis of trophotaeniae. The osmolarity of the environment into which the embryos are bom may cause the shedding of trophotaeniae. Osmolarity experiments indicate that it would appear that shutting off the blood circulation in trophotaeniae is associated with process of ecdysis. It is not knownwhether shutting off blood circulation per se causes ecdysis or whether it is merely associated with process of trophotaenial ecdysis.
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