In the sea urchin embryo, another type of mesenchymal cell, secondary mesenchyme cells
(SMCs), potentially have an ability to become skeletogenic cells.
The main characteristics of this development are (1) incomplete cleavage that becomes holoblastic; (2) external migration of mesenchyme cells
, in the perivitelline space, from the animal to the vegetal pole during gastrulation; (3) hatching that occurs at the end of the gastrulation; (4) differentiation of the vestibule as soon as the end of gastrulation is attained; and (5) production of a juvenile directly from the gastrula without any larval stage.
METHODS: Ar and Esr1 mRNA levels were quantified in primary cultures of fetal mouse prostate mesenchyme cells
treated with [E.
Some of these embryos remained normal at the mid-blastula 2 stage (category 0), whereas others exhibited anomalies: inhibition of hatching, precocious appearance of mesenchyme cells
in the blastocele, and extrusion of some cells to the perivitelline space (Figure 7C, 8A).
The origin of spicule-forming cells in a 'primitive' sea urchin (Eucidaris trihuloides) which appears to lack primary mesenchyme cells
In larvae, epithelia of the future proboscis and proboscis sheath consisted of densely staining cells with underlying condensations of mesenchyme cells
Within 48 h of bisection, mesenchyme cells
with pseudopodia appeared at the site of bisection (Fig.
In these embryos, unlike the embryos of regular echinoids, secondary mesenchyme cells
did not seem to exert the force to pull up the archenteron toward the inner surface of the apical plate.
In the oocyte-free gonad portion, containing mainly collecting tubules and mantle mesenchyme cells
, only the 65-kDa fraction was detected.
The larval gut was filled with mesenchyme cells
, and opened posteriorly via the blastopore (Fig.
The sea urchin Brachyury gene (HpTa) is transiently expressed in the lineage of secondary mesenchyme cells
: first in the vegetal plate of the mesenchyme blastula, extending to the tip of the invaginating archenteron, and finally in the secondary mesenchyme cells
at the late-gastrula stage (16).