CHANGES IN LIPOPHOSPHOGLYCAN AND GENE-EXPRESSION ASSOCIATED WITH THE DEVELOPMENT OF LEISHMANIA-MAJOR IN PHLEBOTOMUS-PAPATASI

Stage-specific molecular and morphogenic markers were used to follow t he kinetics of appearance, number, and position of metacyclic promasti gotes developing during the course of L. major infection in a natural vector, Phlebotomzrs papatasi. Expression of surface lipophosphoglycan (LPG) on transformed promastigotes was delayed until the appearance o f nectomonad forms on day 3, and continued to be abundantly expressed by all promastigotes thereafter. An epitope associate with arabinose s ubstitution of LPG side-chain oligosaccharides, identified by its diff erential expression by metacyclics in vitro, was detected on the surfa ce of a low proportion of midgut promastigotes beginning on day 5, and on up to 60% of promatigotes on days 10 and 15. In contrast 100% of t he parasites egested from the mouthparts during forced feeding of 15 d ay infected flies stained strongly for this epitope. At each time-poin t, the surface expression of the modified LPG was restricted to morpho logically distinguished metacyclic forms. Ultrastructural study of the metacyclic surface revealed an approximate 2-fold increase in the thi ckness of the surface coat compared to nectomonad forms, suggesting el ongation of LPG as occurs during metacyclogenesis in vitro. A metacycl ic-associated transcript (MAT-1), another marker identified by its dif ferential expression in vitro, also showed selective expression by pro mastigotes in the fly, and was used in in situ hybridization studies t o demonstrate the positioning of metacyclics in the anterior gut.