The peri-albumen layer: a novel structure in the envelopes of an avian egg

Morfologia e histologia do oviduto de marrecas Ana boschas

Avaliaram-se o comprimento do infundíbulo, do magno, do istmo, do útero e da vagina e o número de pregas do magno e do istmo do oviduto de 20 marrecas Ana boschas na fase reprodutiva. O infundíbulo apresenta mucosa com pregas longitudinais e baixas, revestidas por epitélio pseudoestratificado cilíndrico ciliado, com células caliciformes. O magno, compartimento mais longo do oviduto, 25,38cm±3,20, encontra-se constituído por uma camada mucosa com pregas altas e espessas revestidas por células cilíndricas ciliadas e abundantes células caliciformes. O istmo é formado por uma mucosa com pregas estreitas e curtas e numerosas glândulas tubulares que se estendem para o interior da lâmina própria. O útero, região curta do oviduto, 5,25cm±1,26, apresenta parede com pregas e cristas baixas e numerosas glândulas tubulares enoveladas, dirigidas para o interior da lâmina própria. A vagina, um estreito tubo muscular, está constituído por oito anéis circulares, em média, e uma camada muscular altamente desenvolvida e espessa. A morfologia do oviduto da marreca apresenta características morfológicas e histológicas distintas dos galiniformes, observando-se que a vagina e a porção cranial do infundíbulo apresentam pregas e células caliciformes, respectivamente, sendo estas últimas estruturas ausentes nos galiniformes.

The asymmetry of avian egg-shape: an adaptation for reproduction on dry land

The present study describes the biological meaning of the asymmetrical shape in avian reproduction using quail. During the incubation of eggs, water was gradually lost and the air chamber which appeared in between the inner and outer shell membranes at the blunt end expanded, so that the angle made by the long egg-axis and the horizontal line increased, presumably because the centre of gravity of the egg contents moved toward the sharp end. The increase in angle occurred in both fertile and infertile eggs, suggesting that this phenomenon occurs irrespective of fertility and is due to the asymmetrical shape. The increase in the volume of the air chamber resulted in an increase in the area of the inner shell membrane at the chamber to satisfy the amount of gas exchange needed by the developing embryo for better hatching. We isolated a 300-kDa protein from the inner shell membrane. It was produced by cells in the luminal epithelium of the oviductal isthmus and was found in the cortex of the fibres of shell membranes and a lining surrounding the air chamber. The lining comprised a medial layer between the inner and outer shell membranes in uterine eggs. The asymmetrical ellipsoid produces the air chamber at the blunt end of the avian egg during its sojourn in the oviductal isthmus, to maintain the blunt end up after oviposition and to raise that end during incubation in a dry environment, leading to high hatchability.

Transient activation of calcineurin is essential to initiate embryonic development in Xenopus laevis

At fertilization, an increase of cytosolic calcium ions (Ca2+) triggers various activation responses in animal eggs. In vertebrates, these responses include exit from metaphase arrest in meiosis II (MII exit) and cortical remodelling initiated by cortical granule exocytosis. Although the essential requirement of Ca2+/calmodulin-dependent protein kinase II for inducing MII exit has been documented, a role of the Ca2+/calmodulin-dependent protein phosphatase calcineurin in egg activation has not been investigated. Here we show, using cell-free extracts from unfertilized eggs of Xenopus laevis, that calcineurin is transiently activated immediately after Ca2+ addition to a concentration that induces MII exit. When calcineurin activation is inhibited, cyclin-dependent kinase 1 (Cdk1) inactivation by means of cyclin B degradation is prevented and sperm chromatin incubated in the extracts remains condensed. Similarly, if calcineurin is inhibited in intact eggs, MII exit on egg activation is prevented. In addition, the activation contraction in the cortex is suppressed whereas cortical granule exocytosis occurs. We further demonstrate that, when a high level of calcineurin activity is maintained after activation, growth of sperm asters is prevented in egg extracts and, consistently, migration of male and female pronuclei towards each other is hindered in fertilized eggs. Thus, both activation and the subsequent inactivation of calcineurin in fertilized eggs are crucial for the commencement of vertebrate embryonic development.

Amino acid sequences and phosphorylation sites of emu and rhea eggshell C-type lectin-like proteins

Avian calcified eggshell layers contain in their organic matrix one or two C-type lectin-like proteins. Previously characterized eggshell proteins of this family are chicken ovocleidin-17 (OC-17), goose ansocalcin and ostrich struthiocalcins 1 and 2 (SCA-1, SCA-2). In this report we present the amino acid sequences of two emu (Dromaius novaehollandiae) (dromaiocalcin-1 and -2; DCA-1, DCA-2) and of two rhea (Rhea americana) (rheacalcin-1 and -2; RCA-1, RCA-2) C-type lectin-like eggshell proteins, thus doubling the data set for comparison of these major specific eggshell proteins. The ratite proteins can be divided into two groups. Group 1, comprising SCA-1, DCA-1 and RCA-1, shows by 70--77% identity of sequences, the lack of phosphorylation, and a variable number (7--9) of cysteines. Group 2, consisting of SCA-2, DCA-2 and RCA-2, shows 78--85% identical sequences, 2--3 phosphorylated serines located at almost identical sites, and contains only the common set of six conserved cysteins characteristic for this family of proteins. While goose ansocalcin fits perfectly into group 1 with a sequence identity of 63--70% to the other members, no phosphorylation, and seven cysteines, chicken OC-17 was assigned to group 2 in spite of only 42--47% sequence identity (and 37--39% to group 1) because of its two phosphorylated serines and its regular set of six cysteines. At present it remains unknown why ratites, but not goose or chicken, require two different types of C-type lectin-like proteins to construct their eggshells.

The Magnum-Isthmus Junction of the Fowl Oviduct Participates in the Formation of the Avian-type Shell Membrane

Avian eggs possess a shell membrane in the shape of an asymmetrical ellipsoid and with a limiting membrane that is a smooth layer of homogeneous, dense materials. We describe the role of the magnum-isthmus junction (MIJ) of the oviduct in the formation of the avian-type shell membrane in the domestic fowl Gallus domesticus. The narrow width of the lumen at the MIJ indirectly participates in the determination of the asymmetrical ellipsoid shape of eggs that are encased by the egg-white layer and subsequently by the peri-albumen layer (PL) and the shell membrane. The PL reacts with Alcian blue and exists between the egg white and the limiting membrane. It is added to the ovulating egg at the MIJ and covers the outermost surface of the egg-white layer. The function of the PL is to provide a smooth surface by covering the irregular surface of the egg-white layer. The materials of the PL consist of an Alcian blue-positive polysaccharide (or glycoprotein) of 240 kDa and five proteins of 135, 116, 72, 49, and 46 kDa. The isolated materials have an affinity to bind with the egg-white mass. An antiserum against quail PL materials stains the domestic fowl PL and secretory cells of the luminal epithelium at the MIJ, and cross-reacts with the molecules of 240, 135, and 116 kDa.

Possible Involvement of a Sperm-associated Body in the Process of Fertilization in Quail

The present paper describes a novel structure, termed the sperm-associated body, which is found both in the lumen at the oviductal infundibulum and in the vitelline membrane of the ovum in the quail Coturnix japonica. The fully developed sperm-associated body, which is about 100 microm long, consisted of two parts; a core of concentric-circular appearance and a cortex of needle-like projections. The outer surface of the body was coated with CaCO3. The body was always accompanied by spermatozoa. About 70 sperm-associated bodies were observed in a single ovum. Electron-microscopically, small numbers of holes were detected in the vitelline membranes of a fertile ovum, and the sperm-associated bodies were always present in these holes. Frequently observed in the vitelline membranes was a disk speculated to be a portion of the inner layer of the membrane partially affected by spermatozoa. However, neither sperm-associated bodies nor spermatozoa were observed there. It was suggested that the sperm-associated bodies assist fertile spermatozoa in binding the inner layer of the vitelline membrane and penetrating it.