Cardio-respiratory development in bird embryos: new insights from a venerable animal model

Abstract

-The avian embryo is a time-honored animal model for understanding vertebrate development. A key area of extensive study using bird embryos centers on developmental phenotypic plasticity of the cardio-respiratory system and how its normal development can be affected by abiotic factors such as temperature and oxygen availability. Through the investigation of the plasticity of development, we gain a better understanding of both the regulation of the developmental process and the embryo's capacity for self-repair. Additionally, experiments with abiotic and biotic stressors during development have helped delineate not just critical windows for avian cardio-respiratory development, but the general characteristics (e.g., timing and dose-dependence) of critical windows in all developing vertebrates. Avian embryos are useful in exploring fetal programming, in which early developmental experiences have implications (usually negative) later in life. The ability to experimentally manipulate the avian embryo without the interference of maternal behavior or physiology makes it particularly useful in future studies of fetal programming. The bird embryo is also a key participant in studies of transgenerational epigenetics, whether by egg provisioning or effects on the germline that are transmitted to the F1 generation (or beyond). Finally, the avian embryo is heavily exploited in toxicology, in which both toxicological testing of potential consumer products as well as the consequences of exposure to anthropogenic pollutants are routinely carried out in the avian embryo. The avian embryo thus proves useful on numerous experimental fronts as an animal model that is concurrently both of adequate complexity and sufficient simplicity for probing vertebrate cardio-respiratory development.

Critical developmental windows for morphology and hematology revealed by intermittent and continuous hypoxic incubation in embryos of quail (Coturnix coturnix)

“…The domestic chicken ( Gallus gallus ) is indisputably the main avian model for developmental studies–for recent reviews see [ 1 , 89 ]. The quail is a lesser utilized avian model, though it has figured prominently in studies of skeletal myogenesis [ 90 ], early heart development [ 91 – 93 ] and sex differentiation [ 94 ], to name just a few foci of developmental studies using quail.…”

Cardiovascular shunting in vertebrates: a practical integration of competing hypotheses

“…Another intensively studied group in the context of the development of the cardiovascular system and shunts is the developing bird, especially the chicken (for an entry into this literature see Dzialowski, , Dzialowski et al ., and Mueller, Burggren, & Tazawa, ). The use of the chicken embryo as a model for cardiovascular development began with reports by Aristotle of the beating heart of a chicken embryo exposed through an opening in the egg shell (Burggren, Flores Santin, & Rojas, ). Several studies have quantified cardiovascular shunting in chicken embryos, estimated to account for about 10–15% of total chorioallantoic blood flow (Piiper et al ., ; Tazawa & Takenaka, ; Tazawa & Johansen, ; Wakayama & Tazawa, ).…”

Follow Me! A Tale of Avian Heart Development with Comparisons to Mammal Heart Development

“…Specifically, the development of the avian heart is similar to that of the human heart [23]. The mature avian heart consists of four chambers with valves as well as inflow and outflow connections (veins and arteries, respectively), and despite some differences, it resembles the human heart [24][25][26][27]. Importantly, cardiac defects found in humans can be recapitulated in avian embryos [26][27][28][29].…”

“…The mature avian heart consists of four chambers with valves as well as inflow and outflow connections (veins and arteries, respectively), and despite some differences, it resembles the human heart [24][25][26][27]. Importantly, cardiac defects found in humans can be recapitulated in avian embryos [26][27][28][29]. Second, like humans, avian embryos remain relatively flat from early to late gastrulation stages [30], enabling time-lapse observation of both dorsal and ventral tissues by means of whole-mount ex ovo culture techniques [31,32].…”

“…Third, because avian embryos develop inside the egg, they provide easy access for cell and tissue manipulation, the longitudinal follow up of manipulations, and in vivo imaging [49][50][51][52]. The topical application of pharmacological agents directly onto the heart or by injection into the circulation is common practice [26], as is hemodynamic manipulation through surgical procedures [29]. In fact, avian embryos are the best models for altering flow patterns at will (without introducing genetic modifications or drugs), while allowing follow up studies to study hemodynamic effects.…”