Drosophila GI tract as a model for gastro-intestinal physiology

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Drosophila GI tract as a model for gastro-intestinal

physiology

Sanmitha S Jujare

M S Ramaiah Institute of Technology

Guided by

Rajashekhar K Patil

Department of Applied Zoology, Mangalore University

1. Introduction

The gastrointestinal tract is one of the largest organ systems within human and other animals.

It plays a major role in digesting, absorbing nutrients, movement of bolus through the

gastrointestinal (GI) tract via peristalsis. In addition, the inner lining of the digestive tract

serves as the first line of defence against a wide range of pathogens.

At present, some of the major GI disorders like constipation and other motility related problems

are on rise. They are mainly due to intake of certain type of food or food groups (Lena Bohn,

et al., 2013). GI tract disorders also include increased acidity, gastro-oesophageal reflux,

heartburn and irritable bowel syndrome. To understand the physiological and molecular causes

of all these abnormalities, it is necessary to have good animal models. In the current study, I

investigated GI tracts of genetically amenable animal model Drosophila melanogaster to

explore its possible use in analysing different GI tract abnormalities.

Drosophila melanogaster has different advantages as a model organism. Approximately 60%

of a group of identified genes in a diverse set of human diseases have an analogous in

Drosophila. They are small and easy to handle. It could be easily anesthetized and manipulated

individually with unsophisticated equipment. They are sexually dimorphic, making it quite

easy to differentiate the sexes. Flies have a short generation time and do well at room

temperature. The care and culture of fruit flies is cheaper. The whole life cycle from egg to

adults in Drosophila takes only 10–11 days (Fig. 1).

Fig. 1. Life cycle of Drosophila melanogaster. It is of four major stages-egg, larva, pupa and

adult. The larval stage can be further classified into 1st, 2nd and 3rd instar stages. After 3rd

instar stage it undergoes major metamorphosis in the pupal stage before adults are enclosed.

In Drosophila melanogaster, the GI tract is segmented into an anterior neutral region, acid

secreting mid zone and a base secreting posterior region similar to humans. In human, the gut

is segmented into three regions: foregut, midgut and hindgut. The anterior segment is probably

absorptive, middle (short and narrow) segment are alternately absorptive and secretary while

re-absorption occurs in the posterior (long and wider) segment. Middle acidic region is

dependent on carbonic anhydrase catalysed H

pool. The acid or base secretion in the midgut

and in Malpighian tubule in insect is believed to be primarily driven by vacuolar or H

V-

ATPases. As in humans, the transport of H

, Cl

−

, K

and HCO3

–

is vital for acid generation in

Drosophila (Shubha Shanbhag et al., 2009). Many features of digestion and absorption appear

to be conserved between flies and mammals (Bruno Lemaitre et al., 2013). In the following

chart, the properties of GI tracts in Drosophila and humans are listed and compared.