Cloning and characterization of a second lamprey pituitary glycoprotein hormone, thyrostimulin (GpA2/GpB5).

A novel heterodimeric glycoprotein hormone (GpH) comprised of alpha (GpA2) and beta (GpB5) subunits was discovered in 2002 and called thyrostimulin for its ability to activate the TSH receptor in mammals, but its central function in vertebrates has not been firmly established. We report here the cloning and expression of lamprey (l)GpB5, and its ability to heterodimerize with lGpA2 to form a functional l-thyrostimulin. The full-length cDNA of lGpB5 encodes 174 amino acids with ten conserved cysteine residues and one glycosylation site that is conserved with other vertebrate GpB5 sequences.

Landmark discoveries in elucidating the origins of the hypothalamic-pituitary system from the perspective of a basal vertebrate, sea lamprey.

The hypothalamic-pituitary (HP) system, which is specific to vertebrates, is considered to be an evolutionary innovation that emerged prior to or during the differentiation of the ancestral jawless vertebrates (agnathans) leading to the neuroendocrine control of many complex functions. Along with hagfish, lampreys represent the oldest lineage of vertebrates, agnathans (jawless fish). This review will highlight our discoveries of the major components of the lamprey HP axis.

Co-localization of three gonadotropin-releasing hormone transcripts in larval, parasitic, and adult sea lamprey brains.

RNA expression of lamprey gonadotropin-releasing hormone (lGnRH)-I, -II, and -III was demonstrated in the brains of larval, parasitic phase and adult sea lampreys, Petromyzon marinus, using a highly sensitive triple-label in situ hybridization technique. In female larval lampreys, lGnRH-I and-II were co-expressed in the same neurons throughout the olfactory bulbs, preoptic area (POA), and rhombencephalon (hindbrain); lGnRH-I, -II and -III were triple co-expressed in the hypothalamus and in the paranuclear region of neuronal somas in the rhombencephalon. In female parasitic phase lampreys, lGnRH-I and -II were co-expressed in the POA, thalamus, and preoptico-neurohypophyseal tract (PNT); lGnRH-III was minimally triple co-expressed with lGnRH-I and -II in the hypothalamus.

A lamprey view on the origins of neuroendocrine regulation of the thyroid axis.

This mini review summarizes the current knowledge of the hypothalamic-pituitary-thyroid (HPT) endocrine system in lampreys, jawless vertebrates. Lampreys and hagfish are the only two extant members of the class of agnathans, the oldest lineage of vertebrates. The high conservation of the hypothalamic-pituitary-gonadal (HPG) axis in lampreys makes the lamprey model highly appropriate for comparative and evolutionary analyses.