GREGARINE LAB

Purpose:

The purpose of this laboratory is to familiarize your self with one of the parasitic apicomplexins, The Gregarines. In this laboratory you will view slides of Monocystis agilis and Gregarina sp. in various stages of their development. By the end of this lab period you should be able to sketch and recognize the various stages involved in the life cycle of both these protists that we use as representative species for gregarines.

Introduction:

The Gregarines fall within the group Sporozoa, which means they use spores as a method of transfer. They are non-photosynthetic parasites that in general attack epithelial cells as hosts. They are unflagellated in most life stages, with the exception of the male gametes. They all also posses an apical complex, at the sporozoite stage, which earns them entry in to the group Apicomplexa. The Apical Complex is composed of secretory and cytoskeletal structures which are used to gain entry into the epithelial cells of the host. The Gregarines are divided into two groups based on their morphology during the first stage of infection (Trophozoite). The first group is the Cephaline Gregarines, in this group the cell is divided into 3 parts; the epimerite, protomerite and deuteromerite. The Acephaline Gregarines only have 2 parts; the protomerite and deuteromerite. In both groups the protomerite and deuteromerite are separated by a fibrous septum. Below is a figure explaining this relationship:

Figure 1: A figure detailing the relationship between the Cephaline and Acephaline gregarines.

Here are some Definitions that may help you in understanding this lab better:

Gamogony - The process where a gamont prouduces many gametes (ie. Gamete formation).

Sporogony - The process where a single zygote produces many spores or sporozoites.

Sporozoite - These are small cells that lie within a resistant spore and burst out when triggered.

Merogony - The process where one schizont produces a large number of merozoites (ie. increases number of infective cells).

Schizont - A trophozoite infecting a host cell.

Merozoite - Small cells which infect other host cells.

The Gregarines only undergo Gamogony and Sprogony but do not undergo Merogony. Another interesting fact about Gregarines is their movement in some stages. At the Trophozoite stage the surface is covered by deep longitudinal grooves (supported by cross-linked actin filaments). The trophozoite secretes a bed of visco-elastic slime and waves passing along the folds produces a gliding motion. This gliding motion is the movement synonomus with Gregarine motion.

Life Cycle:

The following is a general description (with a more detailed one to follow) of the life cycle of a Gregarine. Most of the development of this group of parasites occurs outside the host cell. We will start our cycle with the invading protist being ingested by the host organism. The Sporozoite is ingested by the host and invades an epithelial cell, in the gut (Gregarina sp.) or gametocyte (Monocystis agilis), of the organism. Once inside the cell the sporozoite transforms into a Trophozoite. The host cell then lyses releasing the Trophozoite. In the Cephaline gregarines the Trophozoite then attaches to the gut epithelium of the host while in the Acephaline gregarines the Trophozoite is released into the reproductive tract. At this stage two Trophozoites of complementary mating types associate with each other to form a Syzygy. Once a Syzygy has formed the Trophozoites are known as gamonts and are located within a Gamontocyst. The Gamontocyst is expelled via the feces in Gregarina sp. and with the gametes in Monocystis agilis. Next Gametogenesis occurs producing male and female gametes. The gametes form a zygote which undergoes 2 meiotic and 1 mitotic nuclear divisions. This is followed by Sporogenesis which results in eight Sporozoites which start the cycle once again.

The main focus of this lab will be the life cycle of Monocystis agilis.

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