ESTERASES IN QUAIL (COTURNIX-COTURNIX) - PHYSICOCHEMICAL AND DEVELOPMENTAL ASPECTS

1. Soluble esterases of digestive system organs of various developmental stages in the quail (Coturnix coturnix) were resolved by polyacrylamide gel electrophoresis into several molecular forms which were characterized as carboxylesterases, acetylesterases, cholinesterases and esterases sensitive to eserine. 2. The pl of the majority of esterasic activity in several quail and chicken tissues was observed in the range of 5.1-5.6, while the apparent molecular weight in liver extracts was 60,000. 3. The expression of the esterase multiple molecular forms was found to be both tissue- and developmental stage-specific, with electrophoretic patterns becoming more complex in number and/or staining intensity upon hatching and thereafter, especially in liver and intestine

CARDIAC LOOPING IN THE CHICK-EMBRYO - THE ROLE OF THE POSTERIOR PRECARDIAC MESODERM

Grafts of mesoderm taken from the precardiac region of quail embryos of stages 5-7 were inserted into the precardiac mesoderm of chick embryos of stages 5-7. The experiments were of four types and were codenamed to indicate the origin and the destination of the graft. QACP: tissue from the anterior end of the quail precardiac area was inserted into the posterior end of the chick precardiac mesoderm; QPCA: tissue from the posterior end of the quail precardiac area was inserted into the anterior end of the chick precardiac mesoderm; QACA: tissue from the anterior end of the quail precardiac area was inserted into the anterior end of the chick precardiac mesoderm; QPCP: tissue from the posterior end of the quail precardiac area was inserted into the posterior end of the chick precardiac mesoderm. In no case was precardiac tissue removed from the host. Three main types of anomaly were obtained: inverted hearts, in which looping took place to the left rather than to the right; compact hearts, in which no looping occurred, and hearts in which extra tissues or regions were apparent. The incidence of compact hearts was significantly greater with QPCA than with any other category of experiment. When older donors were used (stages 8-9), the incidence of compact hearts fell. No variations in the origin of the graft, nor in its ultimate destination in the host, were found to affect the frequency of any of the anomalies. Sections showed that quail hearts tended to have thicker walls than chick hearts; although quail tissues were often incorporated into the host chick hearts, they retained the histological characteristics of the donors. The fact that no compact hearts resulted from the experiment QACA, or from the mock operations, leads us to conclude that failure to loop in the compact hearts was not due to mechanical trauma caused by the operation, but to some specific difference between grafts taken from the anterior and posterior precardiac mesoderm. The fact that compact hearts were obtained when chick donors were used instead of quails, shows that the effect is not species-specific. We propose that a morphogen is secreted by the posterior end of the precardiac mesoderm and this plays a role in controlling the cessation of looping

Türkiye Vizyonu: Multidisipliner Çalışmalar 2019(Turkey Vision: Multidisciplinary Studies 2019)

The basic body plan of a number of vertebrates results from two processes that occur early in the development of the blastoderm: large scale rearrangements of tissue via a process called gastrulation, and axial subdivision of tissue in a process called somitogenesis. The first step of gastrulation in avians is formation of the primitive streak, which marks the first clear manifestation of the anterior-posterior axis. Cell movements that occur through the streak ultimately convert the singled layed-blastoderm into a trilaminar blastoderm comprising prospective endodermal, mesodermal and ectodermal tissue. During streak formation a group of cells moves anteriorly as a coherent column from the posterior end of the blastoderm, and as it proceeds other cells stream over the lateral edges of the furrow left behind. The anterior end of the streak is a specialized structure called Hensen's node, which serves as an organizing center for later axis formation and determination of the left-right asymmetry of the body. Soon after the primitive streak forms, Hensen's node regresses towards the tail, leaving the notochord and a pair of segmental plates parallel to the primitive streak in its wake. The posterior end of the segmental plate moves down the cranio-caudal axis with the node, as more cells are added to it by cell division within the plate and by cells entering from the primitive streak. A pair of somites forms from the anterior ends of the two plates at regular intervals. Despite the fact that much is known about the basic biological processes, the mechanisms that underlie the formation of the primitive streak and somitogensis are still unknown, and elucidating them is one of the major unsolved problems in developmental biology. Mathematical modelling has been a useful tool in this process, as it provides a framework in which to study the outcome of proposed interactions and can make experimentally testable predictions. In this paper, we outline the biological background of these processes and review existing models of them