Minimally invasive or non-invasive strategies include the analysis of blastocoel
fluid and spent culture media, both of which have demonstrated the presence of genetic material (11-14).
On day 5 of in vitro cultivation, resulting blastocysts were evaluated morphologically. Initially, they were assigned a numeric score (between 1 and 6) based on their degree of expansion, and hatching status: (1) early blastocyst (i.e., where the blastocoel
formed less than half of the volume of the embryo); (2) blastocyst, (where the blastocoel
formed more than half of the volume of the embryo); (3) full blastocyst, (where the blastocoel
completely filled the embryo); (4) expanded blastocyst, (where the blastocoel
volume was larger than that of the early embryo, and the zona had begun to thin); (5) hatching blastocyst, (where the TE had begun to herniate though the zona); and (6) hatched blastocyst, (where the blastocyst had completely escaped from the zona).
Blastocysts were categorized as Grade I; excellent or good quality blastocysts with blastocoele filling the entire blastocyst, compact inner cell mass (ICM), multicellular cohesive trophectoderm (TE) and oval shaped, Grade II; moderate quality blastocysts with normal ICM, but no optimal (fragmented or necrotic) TE, and Grade III; poor quality blas tocysts with very few cells or without ICM and with large vacuole instead of blastocoel
Because of the invariant cell fate in the Dendrobranchiata, a pair of future mesendodermal cells undergoes arrest, ingresses to a yolk-free blastocoel
, and organizes following gastrulation movements during later stages.
This shift is driven in part by the exponential increase in cell number from the morula to the blastocyst stage, and by the energy required to generate and maintain the blastocoel
(reviewed by ).
Metabolic characterization of the bovine blastocyst, inner cell mass, trophectoderm and blastocoel
At this stage a space was formed between yolk and blastoderm which is called blastocoel
. This stage of embryo is called blastula' (Figure -1 B).
Citrate stimulates fatty acid synthesis (8) and is a chelator of metal ions (e.g., Ca2+), a feature that may be of importance for maintaining junctional integrity and thus of importance for compaction and blastocoel
Developmental Stage Time(h or days) Oviposition 0 h First division 6 [+ or -] 1 h of cleavage Four-cell stage 8 h Eight-cell stage 11 h Morula 16 h Blastula, appearance of blastocoel
2 days Gastrula 2 days Motion of larvae by velar rudiment 3 days Early veliger stage, velum visible, viscera 4 days differentiated in stomach, left and right digestive diverticulum, shell color changed to purple Hatched 6 days No.
Even in larger embryo fossils estimated to contain 1,000 cells or more, the scientists did not observe a blastocoel
, a fluid-filled gap in the middle of the embryo and a common feature among modern animal embryos.
However, there was no sign of a blastocoel
, a fluid-filled hole in the centre which is a common feature of modern animal embryos.
Blastocyst--A sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel
), and a cluster of cells on the interior (the inner cell mass).