Slides 77-88. Notes on Novel Ammonia Transporter Hiat1 and Ammonotelism

Novel Ammonia Transporter, Hiat1

(discovered by the CrabLab!)

  • Overview of Hiat1, a novel ammonia transporter discoverd by researchers at the CrabLab.

Expression Levels

  • Graphical Representation of Hiat1 Expression:

    • Y-Axis: Fold change in mRNA abundance.

    • X-Axis: Different tissues and acclimation times.

    • Tissues include:

    • Heart

    • Muscle

    • Hypodermal tissue

    • Gills: Ant.gland, Ant.gill, Post.gill

    • Cer. gang.

  • Findings:

    • Hiat1 is ubiquitously expressed across various tissues, indicating a fundamental role in ammonia transport.

Expression Changes

  • Expression Following Demand:

    • Expression changes according to the environmental ammonia levels over time.

  • Acclimation Time to High Ammonia:

    • The acclimation period is measured in hours, and a corresponding increase in mRNA abundance is observed, highlighted by the following data:

    • At 2 hours: Fold change = 2.5

    • At 4 hours: 2.3

    • At 6 hours: 2.0

    • At 12 hours: 1.5

  • Hemolymph Ammonia Changes:

    • Before acclimation, hemolymph ammonia shows considerable fluctuation as per the following data points:

    • 0 hours: 0

    • 24 hours: 2.5

    • Observations show a clear increase in hemolymph ammonia correlating strongly with mRNA abundance.

Transport Mechanism

  • Net Transport Mechanism:

    • Methylamine transport is outcompeted by NH4+NH_4^{+} and is sodium-dependent (Na+Na^{+}).

  • Knock-Down Studies in Zebrafish:

    • In Hiat1 knock-down zebrafish larvae, regional ammonia fluxes significantly reduce, demonstrating the vital role Hiat1 plays in ammonia transport.

Genetic Studies

  • Knock-Out Studies in Mice:

    • The loss of Hiat1 function leads to infertility characterized by globozoospermia.

    • Current unknowns include:

    • Hiat1's localization within the cell.

    • The specifics of its transport mechanism.

    • Suggested Function:

    • Acts as a housekeeping transporter to maintain low ammonia levels in both the cytoplasm and nucleoplasm.

Ammonia Transport Mechanisms

  • Combination of Transporters and Mechanisms:

    • Ammonia uptake or excretion typically involves a combination of various ammonia transporters or mechanisms to ensure efficiency in different environments.

Ammonotelism

  • Definition:

    • Ammonotelism refers to organisms that primarily excrete nitrogen in the form of ammonia.

Types of Ammonotelic Animals

Aquatic Invertebrates and Protozoa

  • Examples include:

    • Crustaceans

    • Tunicates

    • Snails

    • Mussels

    • Cephalopods

    • Protozoa: E.g., Paramecium

    • Porifera: E.g., sponges

    • Cnidaria: E.g., jellyfish

    • Polychaetes: Marine worms

    • Echinodermates: E.g., starfish

Aquatic Vertebrates

  • Examples include:

    • Trout (both marine and freshwater)

    • Lionfish

  • Important Note:

    • Elasmobranchs (sharks and rays) primarily excrete nitrogen in the form of urea, thus categorized as ureotelic, although exceptions exist.

Exceptions to Ammonotelism

  • Certain land-dwelling animals primarily excrete ammonia:

    • Common Woodlouse (Porcellio scaber) - Isopoda, Crustacea

    • Land Crab (Geograpsus grayi) - Decapoda, Crustacea; function unknown.

  • Blood Feeding Insects:

    • Examples include:

    • Aedes aegypti

    • Rhodnius prolixus

Conclusion

  • Understanding ammonia transport and excretion in different animals is essential for comprehending ecological adaptability and evolutionary biology.