Disease relevance of Oviparity

• The aim of this study was to develop an oviparous model suitable for studying the differential effects and mechanisms by which a high concentration of extracellular glucose and other sugars produce diabetes complications, particularly body growth retardation during development [1].

High impact information on Oviparity

• In oviparous vertebrates vitellogenin, the precursor of the major yolk proteins, is synthesized in the liver of mature females under the control of estrogen [2].
• Vitellogenin is a female-specific glucolipoprotein yolk precursor produced by all oviparous animals [3].
• Vitellogenin genes are expressed specifically in the liver of female oviparous vertebrates under the strict control of estrogen [4].
• The ligand specificity of the avian oocyte lipoprotein receptor supports the hypothesis that vitellogenin, which has evolved in oviparous species, represents a counterpart to mammalian apolipoprotein E [5].
• Therefore, the existence of two functionally different protein isoforms produced from the ER-alpha gene is probably a common and specific feature in oviparous species [6].

Biological context of Oviparity

• During vitellogenesis in oviparous animals, estrogens induce the synthesis of the yolk precursor vitellogenin, a lipophosphoprotein rich in cholesterol [7].
• Maternal transfer of nutrients, including steroid hormones, to embryos during gestation in viviparous amniotes is well known, but the concordant process in oviparous amniotes is poorly understood [8].
• However, little is known about the relationship between plasma steroid levels (which can influence reproductive function) and yolk steroid levels (which can influence embryonic development) in oviparous species [9].
• L-Selenomethionine, the predominant form of selenium in the eggs of oviparous vertebrates, does not generate oxidative radicals in this system, but lesions consistent with oxidative stress have been identified in fish and birds with high concentrations of Se [10].
• These results are consistent with the idea that elevated corticosterone levels inhibit reproduction, but contrast with studies of other oviparous vertebrates (e.g., lizards) in relation to the role of corticosterone in regulating egg and clutch size [11].

Anatomical context of Oviparity

• The uterus of an oviparous gecko, Hemidactylus turcicus, was analysed after ovariectomized females underwent a period of treatment (up to 14 days) with exogenous estradiol [12].
• Steroid hormones in egg yolks are increasingly recognized as an important component of maternal and offspring fitness in oviparous vertebrates [13].
• We investigated the regulation of Re by progesterone in a mammalian model (proestrous hamster uterus) and an avian model (DES-primed chick oviduct), under the same assay conditions, in an effort to compare progesterone action in viviparous and oviparous species [14].
• Progesterone (P), 17-OH-progesterone (17-OH-P), androstenedione (A), dehydroepiandrosterone (DHEA), testosterone (T), 5 alpha-dihydrotestosterone (5 alpha-DHT), and 17 beta-estradiol (E2) were measured by RIA in plasma and testes of 114 males of the oviparous lizard Podarcis s. sicula raf, a species that displays annual hibernating cycles [15].

Associations of Oviparity with chemical compounds

• Comparison of the N-terminal coding regions of different vertebrate ER-alpha reveal a conservation of the translation start methionine of the protein ER-alpha form II in other oviparous species but not in mammals [6].
• Adequate evidence exists to suggest the importance of temporal changes in steroid hormone ratios in the normal reproductive/vitellogenin cycle in oviparous and viviparous elasmobranchs and reptiles [16].
• In oviparous species, where the cycle is relatively short, secretion of gonadal hormones is synchronous; thus inhibitory actions of progesterone (P) on hepatic or reproductive tract functions would be offset by stimulatory actions of estradiol (E), resulting in appropriate vitellogenin secretion and reproductive tract development [16].
• Seasonal-dependent effect of temperature on the response of adenylate cyclase to FSH stimulation in the oviparous lizard, Podarcis sicula [17].
• Prostaglandins and corticosterone in the oviparous female lizard, Podarcis sicula sicula, during reproduction [18].

Gene context of Oviparity

• The eggs of most oviparous animals are provisioned with a class of protein called vitellogenin (Vg) which is stored as the major component of yolk [19].
• Expression and function of growth differentiation factor-9 in an oviparous species, Gallus domesticus [20].
• These results suggest that a M-CSFR-like receptor may be involved in female reproductive tracts even in an oviparous animal like fish [21].
• In summary, catalase expression in the two oviparous vertebrates appears to be completely under genetic control as the activity of this enzyme does not change in response to changes in oxygen tension [22].
• In females, this inhibition was accompanied by a concentration-dependent decrease in plasma E2 and vitellogenin concentrations; the latter observation is consistent with the fact that activation of the estrogen receptor by E2 initiates hepatic vitellogenin production in oviparous vertebrates [23].

References