Blue gourami (Trichogaster trichopterus) gonadotropic beta subunits (I and II) cDNA sequences and expression during oogenesis

Abstract

We have cloned two cDNAs from the pituitary gland of blue gourami (Trichogaster trichopterus), coding for the subunits of the gonadotropin hormones GtH-I and GtH-II. The two cDNAs were sequenced and subjected to sequence analysis. We have found that the deduced amino acid sequences of both cDNAs were most similar to their striped bass counterparts. The GtH-I subunits of blue gourami and striped bass shared 73% of their residues, and the GtH-II subunits 84%. The cloning of the cDNAs ofGtH-I and GtH-II has enabled us to measure the expression of their respective mRNAs in the pituitaries of female blue gourami at different stages of the reproductive cycle. The highest levels of GtH-I and GtH-II mRNA were found in specimens classified as high vitellogenic and in females that were at the final stages of oocyte maturation.

Involvement of GnRH and Gonadotropin Genes in Oocyte Development of Blue Gourami Females (<i>Trichogaster trichopterus</i>)

“…The novelty of the findings by Wong and Zohar (2004) [8] is that oocytes also expressed these well-characterized gonadotropin subunits, which may serve as autocrine/paracrine factors participating in intraovarian communication. The level of gilthead seabream (Sparus aurata) pituitaries expressed FSH and LH transcripts at much higher levels than ovaries, similar to what was found in blue gourami [14]. The results of the current study support the hypothesis that the autocrine/paracrine of RnRH 1 and 3 may play a function in transferring the oocytes from PV to VIT in blue gourami and might act earlier than in the brain.…”

“…However, more detailed study is required to support this hypothesis. The highest levels of βFSH and βLH mRNA in the pituitary gland were found in blue gourami females during vitellogenesis and the final stages of oocyte maturation [14]. The level of mRNA of FSH and LH in the pituitary gland remained high in reproductive females during vitellogenesis and the final stages of oocyte maturation.…”

“…Therefore, vitellogenic oocytes should be found in the ovary of maturating and post-spawned blue gourami females [22]. A similar pattern of gene expression was found for LH [14]. The levels of its subunit transcript were undetectable in immature females, increased in low vitellogenic fish and showed a sharp increase during high vitellogenesis.…”

“…Three GnRH genes exist in teleost fish that are comprised of three systems: 1) the midbrain (MB)-GnRH system that produces the highly conserved GnRH2, also known as the chicken II GnRH form [4]- [6]; 2) the preoptic (POA)-GnRH system that produces a species-specific GnRH form, GnRH1, which serves as a hypophysiotropic regulator; and 3) the terminal nerve ganglia (TNg)-GnRH system, which produces GnRH3 (also known as salmon GnRH) [5] [6]. It is accepted in many teleost fish orders that the three GnRH genes [3] [5] exist and transcript in the hypothalamus, FSH and LH in the pituitary gland [7], however not much information has been published on autocrine and paracrine secretion of GnRH, FSH and LH from the gonads [8] [9]. GnRH plays an autocrine/paracrine regulatory role in mammalian and fish ovaries.…”

“…This fish serves as a useful model for studying the role of endocrine regulation on reproduction, since it is multi-spawning and male-dependent, having asynchronic ovary development [10]. Thus, each stage of its gonadal development can be controlled and examined separately in the laboratory [11]- [14]. The profiles of βFSH, βLH and GH secretion and gene expression, as well as the pattern of sex steroid secretion during gonadal development in male and female blue gourami, have been previously reported [15].…”