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L. Carratu et al.
primary heat shock sensor (HSS) responsible for monitoring sudden
temperature variations is membrane-associated. Furthermore, we have
shown that modification of membrane fluid state and/or loss of bilayer
integrity, when the temperature exceeds the physiological range (during
heat shock), influences the level of expression of heat shock genes by
setting the temperature at which optimum heat shock response occurs [3].
Fish are ectotherms whose body temperature is determined by the water
temperature. Antarctic fish represent a particular class of poikilothermic
animals since they live in a very stable environment, and, therefore, are
more stenothermal than other fish species. Antarctic fish live in the
Southern Ocean at temperatures near the freezing point of sea water.
Furthermore, water temperature has been remarkably stable over the past
20 million years, exerting a strong and constant selective pressure on
biochemical as well as physiological mechanisms of adaptation of the
marine organisms. Antarctic fish can live at -1.9 °e, with seasonal
fluctuations of the order of only 0.2 °e [9,10]. Broadly speaking, two
classes of Antarctic fish can be distinguished based on their upper
acclimation temperature. This temperature, termed "ultimate incipient
lethal temperature," is 4-5 °e in the ice fish family (e.g. Chionodraco
hamatus) and around 12-14 °e in other Antarctic fish (e.g. Notothenia
rossii). Profound evolutionary changes have occurred in several enzymatic
and structural proteins of Antarctic fish that have allowed these organisms
to maintain roughly the same metabolic and locomotory activities of other
fish [2]. So far, very little is known on the mechanisms of regulation of
gene expression and how these have contributed to the adaptation to these
extreme temperatures.
The question that arose several years ago concerned the possibility that
stenothermal species may have lost the ability to respond to heat shock as a
result of the extreme environmental condition present in the waters of the
Antarctic Ocean [11]. To address this issue, we cloned hsp70 gene from
the Antarctic fish C. hamatus. This gene codes for the most conserved heat
shock protein throughout evolution, HSP70. Moreover, in the same species
a parallel project regarding the identification and analysis of expression of
f.,.9 -desaturase, whose product is involved in adaptation of membranes to
cold, is in progress in our lab. Understanding the regulation of the
expression of these two classes of genes in organisms such as Antarctic
fish living under the selective pressure of extreme climatic environments,
will give an insight into the molecular mechanisms of adaptation, while an
analysis of the gene structure will reveal how these sequences have
evolved in these organisms.
L. Carratu et al.
primary heat shock sensor (HSS) responsible for monitoring sudden
temperature variations is membrane-associated. Furthermore, we have
shown that modification of membrane fluid state and/or loss of bilayer
integrity, when the temperature exceeds the physiological range (during
heat shock), influences the level of expression of heat shock genes by
setting the temperature at which optimum heat shock response occurs [3].
Fish are ectotherms whose body temperature is determined by the water
temperature. Antarctic fish represent a particular class of poikilothermic
animals since they live in a very stable environment, and, therefore, are
more stenothermal than other fish species. Antarctic fish live in the
Southern Ocean at temperatures near the freezing point of sea water.
Furthermore, water temperature has been remarkably stable over the past
20 million years, exerting a strong and constant selective pressure on
biochemical as well as physiological mechanisms of adaptation of the
marine organisms. Antarctic fish can live at -1.9 °e, with seasonal
fluctuations of the order of only 0.2 °e [9,10]. Broadly speaking, two
classes of Antarctic fish can be distinguished based on their upper
acclimation temperature. This temperature, termed "ultimate incipient
lethal temperature," is 4-5 °e in the ice fish family (e.g. Chionodraco
hamatus) and around 12-14 °e in other Antarctic fish (e.g. Notothenia
rossii). Profound evolutionary changes have occurred in several enzymatic
and structural proteins of Antarctic fish that have allowed these organisms
to maintain roughly the same metabolic and locomotory activities of other
fish [2]. So far, very little is known on the mechanisms of regulation of
gene expression and how these have contributed to the adaptation to these
extreme temperatures.
The question that arose several years ago concerned the possibility that
stenothermal species may have lost the ability to respond to heat shock as a
result of the extreme environmental condition present in the waters of the
Antarctic Ocean [11]. To address this issue, we cloned hsp70 gene from
the Antarctic fish C. hamatus. This gene codes for the most conserved heat
shock protein throughout evolution, HSP70. Moreover, in the same species
a parallel project regarding the identification and analysis of expression of
f.,.9 -desaturase, whose product is involved in adaptation of membranes to
cold, is in progress in our lab. Understanding the regulation of the
expression of these two classes of genes in organisms such as Antarctic
fish living under the selective pressure of extreme climatic environments,
will give an insight into the molecular mechanisms of adaptation, while an
analysis of the gene structure will reveal how these sequences have
evolved in these organisms.