Parasitic nematodes pose major human and veterinary health problems around the world. For the past 30 years, the parasitic nematode Ascaris suum has served as a model system for medically important helminths, such as filaria and hookworms. The early development of A. suum from embryo to 2nd-stage larvae takes place bathed in perivitelline fluid (PF) within an eggshell. However, little is known about the secretion of the PF, the regulation of its composition during development, or the molecular aspects of eggshell maintenance, even though these processes are critical for survival. The present study is designed to identify the major components of the PF and to characterize the pathway of their secretion from the larvae by exploiting the advantages inherent in the A. suum and Caenorhabditis elegans model systems. Changes in composition of the A. suum PF during development will be examined, and the roles of individual components in the hatching process assessed. Recently, the investigators have identified a developmentally regulated A. suum PF protein, As-p18, and have demonstrated that it exhibited almost identical patterns of expression with C. elegans LBP-1. Most significantly, LBP-1 appears to be secreted from hypodermal cells prior to the formation of the cuticle and the classical nematode excretory/secretory apparatus which only appears later in development. The present studies are designed to 1) characterize individual components of the PF, 2) clone, sequence and functionally express specific PF proteins to examine their potential roles in hatching of "eggshell" maintenance, 3) identify the cells responsible for the secretion of PF proteins either by immunolocalization with specific antisera or the identification of putative homologues in the C. elegans database and the use of the C. elegans transfection system, and 4) attempt to identify promoter elements responsible for the timing and specificity of expression. On a broad scale, the investigators intend to determine whether nematodes can be engineered to secrete specific proteins during specific stages in their life cycles.