Cellular organization and appearance of differentiated structures in developing

stages of the parasitic platyhelminth Echinococcus granulosus.


Martinez C, Paredes R, Stock RP, Saralegui A, Andreu M, Cabezon C, Ehrlich R,

Galanti N.


Seccion Bioquimica, Facultad de Ciencias, Universidad de la Republica, Igua

4225, CP1400, Montevideo, Uruguay. clau@fcien.edu.uy


Echinococcus granulosus is the causative agent of hydatidosis, a major zoonoses

that affects humans and herbivorous domestic animals. The disease is caused by

the pressure exerted on viscera by hydatid cysts that are formed upon ingestion

of E. granulosus eggs excreted by canine. Protoscoleces, larval forms infective

to canine, develop asynchronously and clonally from the germinal layer (GL) of

hydatid cysts. In this report, we describe the cellular organization and the

appearance of differentiated structures both in nascent buds and developed

protoscoleces attached to the GL. Early protoscolex morphogenesis is a highly

complex and dynamic process starting from the constitution of a foramen in the

early bud, around which nuclei are distributed mainly at the lateral and apical

regions. Similarly, distribution of nuclei in mature protoscoleces is not

homogenous but underlies three cellular territories: the suckers, the rostellar

pad, and the body, that surrounds the foramen. Several nuclei are associated to

calcareous corpuscles (Cc), differentiated structures that are absent in the

earlier bud stages. The number of nuclei is similar from the grown, elongated

bud stage to the mature protoscolex attached to the GL, strongly suggesting that

there is no significant cellular proliferation during final protoscolex

development. The amount of DNA per nucleus is in the same range to the one

described for most other platyhelminthes. Our results point to a sequential

series of events involving cell proliferation, spatial cell organization, and

differentiation, starting in early buds at the GL of fertile hydatid cysts

leading to mature protoscoleces infective to canine.