M. Saragababic et al., MORPHOLOGICAL AND IMMUNOHISTOCHEMICAL CHARACTERISTICS OF AXIAL STRUCTURES IN THE TRANSITORY HUMAN TAIL, Annals of anatomy, 176(3), 1994, pp. 277-286
Ultrastructural relationships between the notochord and neighboring sp
inal cord were examined during the regression of the human tail. Also,
the presence of certain extracellular matrix components in the notoch
ord was immuno-histochemically analysed in the 4th to 12th week old em
bryos. At the early stages, a close apposition of the notochord to the
spinal cord exists in the entire tail region. The external surface of
both structures is covered with a continuous basal lamina. The narrow
tissue interspace contains interdigitating cell processes and both am
orphous and fibrillar extracellular matrix material. With advancing em
bryonic age, separation of the two structures occurs in craniocaudal d
irection and the widening interspace becomes occupied by mesenchymal c
ells. During tail regression and spinal cord retraction, the appearanc
e of large intercellular spaces and cell degeneration takes place in b
oth tissues. With age, the extracellular matrix of the notochord, pred
ominantly the perinotochordal sheath, increases in amount and antigeni
c complexity. While the intensity of laminin, collagen type IV and typ
e III expression rises continuously during the period examined, the ex
pression of fibronectin begins first at later stages, after the separa
tion of the notochord from the spinal cord. The possible developmental
significance of the described phenomena in the regression of the post
erior end of the human tail remains to be elucidated.