Summer Research Fellowship Programme of India's Science Academies 2017
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.