Structure and function of a dual antagonist of the human growth hormone and prolactin receptors with site-specific PEG conjugates.

Human growth hormone (hGH) is a pituitary-derived endocrine protein that regulates several critical postnatal physiologic processes including growth, organ development, and metabolism. Following adulthood, GH is also a regulator of multiple pathologies like fibrosis, cancer, and diabetes. Therefore, there is a significant pharmaceutical interest in developing antagonists of hGH action. Currently, there is a single FDA-approved antagonist of the hGH receptor (hGHR) prescribed for treating patients with acromegaly and discovered in our laboratory almost 3 decades ago. Here, we present the first data on the structure and function of a new set of protein antagonists with the full range of hGH actions-dual antagonists of hGH binding to the GHR as well as that of hGH binding to the prolactin receptor. We describe the site-specific PEG conjugation, purification, and subsequent characterization using MALDI-TOF, size-exclusion chromatography, thermostability, and biochemical activity in terms of ELISA-based binding affinities with GHR and prolactin receptor. Moreover, these novel hGHR antagonists display distinct antagonism of GH-induced GHR intracellular signaling in vitro and marked reduction in hepatic insulin-like growth factor 1 output in vivo. Lastly, we observed potent anticancer biological efficacies of these novel hGHR antagonists against human cancer cell lines. In conclusion, we propose that these new GHR antagonists have potential for development towards multiple clinical applications related to GH-associated pathologies.

A novel peptide antagonist of the human growth hormone receptor.

Excess circulating human growth hormone (hGH) in vivo is linked to metabolic and growth disorders such as cancer, diabetes, and acromegaly. Consequently, there is considerable interest in developing antagonists of hGH action. Here, we present the design, synthesis, and characterization of a 16-residue peptide (site 1-binding helix [S1H]) that inhibits hGH-mediated STAT5 phosphorylation in cultured cells. S1H was designed as a direct sequence mimetic of the site 1 mini-helix (residues 36-51) of wild-type hGH and acts by inhibiting the interaction of hGH with the human growth hormone receptor (hGHR). In vitro studies indicated that S1H is stable in human serum and can adopt an α-helix in solution. Our results also show that S1H mitigates phosphorylation of STAT5 in cells co-treated with hGH, reducing intracellular STAT5 phosphorylation levels to those observed in untreated controls. Furthermore, S1H was found to attenuate the activity of the hGHR and the human prolactin receptor, suggesting that this peptide acts as an antagonist of both lactogenic and somatotrophic hGH actions. Finally, we used alanine scanning to determine how discrete amino acids within the S1H sequence contribute to its structural organization and biological activity. We observed a strong correlation between helical propensity and inhibitory effect, indicating that S1H-mediated antagonism of the hGHR is largely dependent on the ability for S1H to adopt an α-helix. Taken together, these results show that S1H not only acts as a novel peptide-based antagonist of the hGHR but can also be applied as a chemical tool to study the molecular nature of hGH-hGHR interactions.

GHR signalling: Receptor activation and degradation mechanisms.

Growth hormone (GH) actions via initiating cell signalling through the GH receptor (GHR) are important for many physiological processes, in addition to its well-known role in regulating growth. The activation of JAK-STAT signalling by GH is well characterized, however knowledge on GH activation of SRC family kinases (SFKs) is still limited. In this review we summarise the collective knowledge on the activation, regulation, and downstream signalling of GHR. We highlight studies on GH activation of SFKs and the important outcome of this signalling pathway with a focus on the different degradation mechanisms that can regulate GHR availability since this is an area that warrants further study considering its role in tumour progression.

Yeast recombinant production of intact human membrane proteins with long intrinsically disordered intracellular regions for structural studies.

Membrane proteins exist in lipid bilayers and mediate solute transport, signal transduction, cell-cell communication and energy conversion. Their activities are fundamental for life, which make them prominent subjects of study, but access to only a limited number of high-resolution structures complicates their mechanistic understanding. The absence of such structures relates mainly to difficulties in expressing and purifying high quality membrane protein samples in large quantities. An additional layer of complexity stems from the presence of intra- and/or extra-cellular domains constituted by unstructured intrinsically disordered regions (IDR), which can be hundreds of residues long. Although IDRs form key interaction hubs that facilitate biological processes, these are regularly removed to enable structural studies. To advance mechanistic insight into intact intrinsically disordered membrane proteins, we have developed a protocol for their purification. Using engineered yeast cells for optimized expression and purification, we have purified to homogeneity two very different human membrane proteins each with >300 residues long IDRs; the sodium proton exchanger 1 and the growth hormone receptor. Subsequent to their purification we have further explored their incorporation into membrane scaffolding protein nanodiscs, which will enable future structural studies.

Mechanism of homodimeric cytokine receptor activation and dysregulation by oncogenic mutations.

Homodimeric class I cytokine receptors are assumed to exist as preformed dimers that are activated by ligand-induced conformational changes. We quantified the dimerization of three prototypic class I cytokine receptors in the plasma membrane of living cells by single-molecule fluorescence microscopy. Spatial and spatiotemporal correlation of individual receptor subunits showed ligand-induced dimerization and revealed that the associated Janus kinase 2 (JAK2) dimerizes through its pseudokinase domain. Oncogenic receptor and hyperactive JAK2 mutants promoted ligand-independent dimerization, highlighting the formation of receptor dimers as the switch responsible for signal activation. Atomistic modeling and molecular dynamics simulations based on a detailed energetic analysis of the interactions involved in dimerization yielded a mechanistic blueprint for homodimeric class I cytokine receptor activation and its dysregulation by individual mutations.

GH and GHR gene cloning, expression and their associations with growth-related traits of the barbel chub (Squaliobarbus curriculus).

Growth hormone (ScGH) and growth hormone receptor (ScGHR) genes from the barbel chub (Squaliobarbus curriculus), in addition to their cDNAs, were cloned. The associations between their mRNA expression levels and growth-related traits were analysed, and the differences in the levels of expression of growth regulation-related genes between the largest and smallest individuals were compared. The full-length 1182-bp cDNA of ScGH contained a 633-bp open reading frame (ORF), and the length of the gene had 2492 bp. The full-length 2825-bp cDNA of ScGHRa contained a 1818-bp ORF, and the gene had 6970 bp. The full-length 2822-bp cDNA of ScGHRb contained a 1737-bp ORF, and the gene had 8149 bp. Quantitative real-time PCR revealed that ScGH was only expressed in the pituitary. ScGHRa was expressed predominantly in muscle, and the expression level of ScGHRb was the highest in the liver. The ScGHRa mRNA levels in the muscle were significantly negatively correlated with the caudal peduncle length. However, no correlation between growth-related traits and ScGH and ScGHRb expression levels were found. Pituitary ScGH, liver GHRb and liver insulin-like growth factor I (igf-1) expression levels were significantly higher in the largest individuals than those in the smallest S. curriculus individuals. Contrarily, the largest individuals had significantly lower expression levels of muscle igf-1 and liver myog than the smallest individuals. Overall, our results provide novel molecular information for growth-regulation study of S. curriculus.

Identification, characterization, and expressions profile analysis of growth hormone receptors (GHR1 and GHR2) in Hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus polyphekadion ♂).

Growth hormone is an essential hormone that plays essential roles in growth, metabolism, cellular differentiation, immunity and reproduction in fish, by means of the growth hormone receptors. The encoding cDNA growth hormone receptors (GHR1 and GHR2) were cloned and characterized from Hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus polyphekadion♂). Sequence analysis of the cloned GHR1 was observed as containing 2176, which comprised an ORF of 1842 bp, 5 UTR of 6 bp and 3 UTR of 328 bp, with 612 amino acids encoding proteins, while GHR2 was observed as containing 1824 bp that encompassed an ORF of 708 bp, 5 UTR of 48 bp and 3 UTR of 1068 bp with 235 amino acids encoding proteins. Relative mRNA expression of GHR1 and GHR2 in the liver and muscle was found to be highest respectively. Our findings provide vital statistics of GHRs likely to play a significant role in the growth of the fish.

Systematic profiling of clinical missence mutation effects on the intermolecular interaction between human growth hormone and its receptor in isolated growth hormone deficiency.

Isolated growth hormone deficiency (IGHD) is the most common pituitary hormone deficiency and can result from congenital or acquired causes. Among the known factors, genetic mutations in human growth hormone (hGH) remain the most frequent cause of IGHD, which influence the binding of hGH to its cognate receptor (hGHbp). Although previous studies have systematically investigated the residue importance at hGH-hGHbp complex interface, the molecular role of IGHD-associated residue mutations in the complex function still remains largely unexplored. Here, a total of 21 known hGH naturally-occurring missence mutations that have been clinically observed to be involved in IGHD disorder are collected and confirmed by original literature; they effects on the conformation, energetics and dynamics of hGH-hGHbp recognition and interaction are dissected at molecular level by using atomistic dynamics simulations, binding energy calculations and fluorescence spectroscopy assays. A systematic profile of hGH-hGHbp binding response to these clinical missence mutations is created, based on which it is revealed that (i) most mutations have appreciably unfavorable effect on the binding, which potentially destabilize the complex interaction, while only very few are predicted as moderate stabilizers for the complex system, and (ii) these disease-related mutations can locate either at complex interface or in hGH protein interior far away from the interface; both can influence the complex binding through either direct interaction or indirect allostericity. Two mutations, E100K (non-interface) and G146R (interface), are identified to address potent destabilization effect on hGH-hGHbp complex system; they can reduce the complex binding affinity by 8-fold (Kd changes from 0.76 to 5.9 nM) and 46-fold (Kd changes from 0.76 to 34.7 nM), respectively.

Structural insights into substrate recognition by the SOCS2 E3 ubiquitin ligase.

The suppressor of cytokine signaling 2 (SOCS2) acts as substrate recognition subunit of a Cullin5 E3 ubiquitin ligase complex. SOCS2 binds to phosphotyrosine-modified epitopes as degrons for ubiquitination and proteasomal degradation, yet the molecular basis of substrate recognition has remained elusive. Here, we report co-crystal structures of SOCS2-ElonginB-ElonginC in complex with phosphorylated peptides from substrates growth hormone receptor (GHR-pY595) and erythropoietin receptor (EpoR-pY426) at 1.98 Å and 2.69 Å, respectively. Both peptides bind in an extended conformation recapitulating the canonical SH2 domain-pY pose, but capture different conformations of the EF loop via specific hydrophobic interactions. The flexible BG loop is fully defined in the electron density, and does not contact the substrate degron directly. Cancer-associated SNPs located around the pY pocket weaken substrate-binding affinity in biophysical assays. Our findings reveal insights into substrate recognition and specificity by SOCS2, and provide a blueprint for small molecule ligand design.

Subdomain 2, Not the Transmembrane Domain, Determines the Dimerization Partner of Growth Hormone Receptor and Prolactin Receptor.

Growth hormone receptor (GHR) and prolactin (PRL) receptor (PRLR) are homologous transmembrane class I cytokine receptors. In humans, GH interacts with GHR homodimers or PRLR homodimers and PRL interacts with only PRLR homodimers to promote signaling. In human breast cancer cells endogenously expressing both receptors, GHR and PRLR specifically coimmunoprecipitate. We previously devised a split luciferase complementation assay to study GHR and PRLR assemblages. In this technique, firefly luciferase is split into two fragments (N- and C-terminal fragments of the luciferase), each without enzyme activity and tethered to the tails of two receptors. The fragments restore luciferase activity when brought close to each other by the receptors. Real-time ligand-induced complementation changes reflect the arrangement of receptors and indicate that GHR/PRLR is arranged as a heteromultimer comprised of GHR-GHR homodimers and PRLR-PRLR homodimers. We now dissect determinants for GHR and PRLR homodimerization versus heteroassociation. GHR and PRLR have extracellular domains comprised of the ligand-binding N-terminal subdomain 1 and a membrane-proximal subdomain 2 (S2), which fosters receptor-receptor contact. Based on previous studies of S2 versus the transmembrane domain (TMD) in GHR dimerization, we constructed GHR(PRLRS2), GHR(PRLRS2-TMD), and GHR(PRLRTMD), replacing GHR's S2 alone, S2 plus TMD, and TMD alone with PRLR's counterpart. We tested by complementation the ability of these chimeras and GHR or PRLR to homodimerize or heteroassociate. Comparing various combinations, we found GHR(PRLRS2) and GHR(PRLRS2-TMD) behaved as PRLR, whereas GHR(PRLRTMD) behaved as GHR regarding their dimerization partners. We conclude that S2 of GHR and PRLR, rather than their TMDs, determines their dimerization partner.

Structural and energetic study of cation-π-cation interactions in proteins.

Cation-π interactions of aromatic rings and positively charged groups are among the most important interactions in structural biology. The role and energetic characteristics of these interactions are well established. However, the occurrence of cation-π-cation interactions is an unexpected motif, which raises intriguing questions about its functional role in proteins. We present a statistical analysis of the occurrence, composition and geometrical preferences of cation-π-cation interactions identified in a set of non-redundant protein structures taken from the Protein Data Bank. Our results demonstrate that this structural motif is observed at a small, albeit non-negligible frequency in proteins, and suggest a preference to establish cation-π-cation motifs with Trp, followed by Tyr and Phe. Furthermore, we have found that cation-π-cation interactions tend to be highly conserved, which supports their structural or functional role. Finally, we have performed an energetic analysis of a representative subset of cation-π-cation complexes combining quantum-chemical and continuum solvation calculations. Our results point out that the protein environment can strongly screen the cation-cation repulsion, leading to an attractive interaction in 64% of the complexes analyzed. Together with the high degree of conservation observed, these results suggest a potential stabilizing role in the protein fold, as demonstrated recently for a miniature protein (Craven et al., J. Am. Chem. Soc. 2016, 138, 1543). From a computational point of view, the significant contribution of non-additive three-body terms challenges the suitability of standard additive force fields for describing cation-π-cation motifs in molecular simulations.

A long-acting GH receptor antagonist through fusion to GH binding protein.

Acromegaly is a human disease of growth hormone (GH) excess with considerable morbidity and increased mortality. Somatostatin analogues are first line medical treatment but the disease remains uncontrolled in up to 40% of patients. GH receptor (GHR) antagonist therapy is more effective but requires frequent high-dose injections. We have developed an alternative technology for generating a long acting potent GHR antagonist through translational fusion of a mutated GH linked to GH binding protein and tested three candidate molecules. All molecules had the amino acid change (G120R), creating a competitive GHR antagonist and we tested the hypothesis that an amino acid change in the GH binding domain (W104A) would increase biological activity. All were antagonists in bioassays. In rats all antagonists had terminal half-lives >20 hours. After subcutaneous administration in rabbits one variant displayed a terminal half-life of 40.5 hours. A single subcutaneous injection of the same variant in rabbits resulted in a 14% fall in IGF-I over 7 days. IN CONCLUSION: we provide proof of concept that a fusion of GHR antagonist to its binding protein generates a long acting GHR antagonist and we confirmed that introducing the W104A amino acid change in the GH binding domain enhances antagonist activity.

Fos-Zippered GH Receptor Cytosolic Tails Act as Jak2 Substrates and Signal Transducers.

Members of the Janus kinase (Jak) family initiate the majority of downstream signaling events of the cytokine receptor family. The prevailing principle is that the receptors act in dimers: 2 Jak2 molecules bind to the cytosolic tails of a cytokine receptor family member and initiate Jak-signal transducer and activator of transcription signaling upon a conformational change in the receptor complex, induced by the cognate cytokine. Due to the complexity of signaling complexes, there is a strong need for in vitro model systems. To investigate the molecular details of the Jak2 interaction with the GH receptor (GHR), we used cytosolic tails provided with leucine zippers derived from c-Fos to mimic the dimerized state of GHR. Expressed together with Jak2, fos-zippered tails, but not unzippered tails, were stabilized. In addition, the Jak-signal transducer and activator of transcription signaling pathway was activated by the fos-zippered tails. The stabilization depended also on α-helix rotation of the zippers. Fos-zippered GHR tails and Jak2, both purified from baculovirus-infected insect cells, interacted via box1 with a binding affinity of approximately 40nM. As expected, the Jak kinase inhibitor Ruxolitinib inhibited the stabilization but did not affect the c-Fos-zippered GHR tail-Jak2 interaction. Analysis by blue-native gel electrophoresis revealed high molecular-weight complexes containing both Jak2 and nonphosphorylated GHR tails, whereas Jak2-dissociated tails were highly phosphorylated and monomeric, implying that Jak2 detaches from its substrate upon phosphorylation.

Identification of Polymorphisms in the Rabbit Growth Hormone Receptor (GHR) Gene and Association with Finishing Weight in a Commercial Meat Rabbit Line.

A shortcut to identify DNA markers associated with economic traits is to use a candidate gene approach that is still useful in livestock species in which molecular tools and resources are not advanced or not well developed. Mutations in the growth hormone receptor (GHR) gene associated with production traits have been already described in several livestock species. For this reason GHR could be an interesting candidate gene in the rabbit. In this study we re-sequenced all exons and non-coding regions of the rabbit GHR gene in a panel of 10 different rabbits and identified 10 single nucleotide polymorphisms (SNPs). One of them (g.63453192C>G or c.106C>G), located in exon 3 was a missense mutation (p.L36V) substituting an amino acid in a highly conserved position across all mammals. This mutation was genotyped in 297 performance tested rabbits of a meat male line and association analysis showed that the investigated SNP was associated with weight at 70 days (P < 0.05). The most frequent genotype (GG) was in animals with higher weight at this age, suggesting that the high directional selection pressure toward this trait since the constitution of the genotyped line might have contributed to shape allele frequencies at this polymorphic site.

The role of protein "Stability patches" in molecular recognition: A case study of the human growth hormone-receptor complex.

Dynamic characteristics of protein surfaces are among the factors determining their functional properties, including their potential participation in protein-protein interactions. The presence of clusters of static residues-"stability patches" (SPs)-is a characteristic of protein surfaces involved in intermolecular recognition. The mechanism, by with SPs facilitate molecular recognition, however, remains unclear. Analyzing the surface dynamic properties of the growth hormone and of its high-affinity variant we demonstrated that reshaping of the SPs landscape may be among the factors accountable for the improved affinity of this variant to the receptor. We hypothesized that SPs facilitate molecular recognition by moderating the conformational entropy of the unbound state, diminishing enthalpy-entropy compensation upon binding, and by augmenting the favorable entropy of desolvation. SPs mapping emerges as a valuable tool for investigating the structural basis of the stability of protein complexes and for rationalizing experimental approaches, such as affinity maturation, aimed at improving it.

Intrinsically disordered cytoplasmic domains of two cytokine receptors mediate conserved interactions with membranes.

Class 1 cytokine receptors regulate essential biological processes through complex intracellular signalling networks. However, the structural platform for understanding their functions is currently incomplete as structure-function studies of the intracellular domains (ICDs) are critically lacking. The present study provides the first comprehensive structural characterization of any cytokine receptor ICD and demonstrates that the human prolactin (PRL) receptor (PRLR) and growth hormone receptor (GHR) ICDs are intrinsically disordered throughout their entire lengths. We show that they interact specifically with hallmark lipids of the inner plasma membrane leaflet through conserved motifs resembling immuno receptor tyrosine-based activation motifs (ITAMs). However, contrary to the observations made for ITAMs, lipid association of the PRLR and GHR ICDs was shown to be unaccompanied by changes in transient secondary structure and independent of tyrosine phosphorylation. The results of the present study provide a new structural platform for studying class 1 cytokine receptors and may implicate the membrane as an active component regulating intracellular signalling.

[Preparation of Transmembrane Fragments Growth Hormone Receptor GHR in a Cell-Free Expression System for Structural Studies].

Growth hormone somatotropin and its membrane receptor GHR, belonging to a superfamily of the type I receptors possessing tyrosine kinase activity, are involved in the intercellular signal transduction cascade and regulate a number of important physiological and pathological processes in humans. Binding with somatotropin triggers a transition of GHR between two alternative dimer states, resulting in an allosteric activation of JAK2 tyrosine kinase in the cell cytoplasm. Transmembrane domain of GHR directly involved in this complex conformational transition. It has presumably two dimerization interfaces corresponding to the "unliganded" and the active state of GHR. In order to study the molecular basis of biochemical signal transduction mechanism across the cell membrane, we have developed an efficient cell-free production system of a TM fragment of GHR, which contains its TM domain flanked by functionally important juxtamembrane regions (GHRtm residues 254-298). The developed system allows to obtain -1 mg per 1 ml of reaction mixture of 13C- and 15N-isotope-labeled protein for structural and dynamic studies of the GHR TM domain dimerization in the membrane-mimicking medium by high-resolution heteronuclear NMR spectroscopy.

Mechanism of activation of protein kinase JAK2 by the growth hormone receptor.

Signaling from JAK (Janus kinase) protein kinases to STAT (signal transducers and activators of transcription) transcription factors is key to many aspects of biology and medicine, yet the mechanism by which cytokine receptors initiate signaling is enigmatic. We present a complete mechanistic model for activation of receptor-bound JAK2, based on an archetypal cytokine receptor, the growth hormone receptor. For this, we used fluorescence resonance energy transfer to monitor positioning of the JAK2 binding motif in the receptor dimer, substitution of the receptor extracellular domains with Jun zippers to control the position of its transmembrane (TM) helices, atomistic modeling of TM helix movements, and docking of the crystal structures of the JAK2 kinase and its inhibitory pseudokinase domain with an opposing kinase-pseudokinase domain pair. Activation of the receptor dimer induced a separation of its JAK2 binding motifs, driven by a ligand-induced transition from a parallel TM helix pair to a left-handed crossover arrangement. This separation leads to removal of the pseudokinase domain from the kinase domain of the partner JAK2 and pairing of the two kinase domains, facilitating trans-activation. This model may well generalize to other class I cytokine receptors.

Genetic polymorphisms and protein structures in growth hormone, growth hormone receptor, ghrelin, insulin-like growth factor 1 and leptin in Mehraban sheep.

The somatotropic axis, the control system for growth hormone (GH) secretion and its endogenous factors involved in the regulation of metabolism and energy partitioning, has promising potentials for producing economically valuable traits in farm animals. Here we investigated single nucleotide polymorphisms (SNPs) of the genes of factors involved in the somatotropic axis for growth hormone (GH1), growth hormone receptor (GHR), ghrelin (GHRL), insulin-like growth factor 1 (IGF-I) and leptin (LEP), using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and DNA sequencing methods in 452 individual Mehraban sheep. A nonradioactive method to allow SSCP detection was used for genomic DNA and PCR amplification of six fragments: exons 4 and 5 of GH1; exon 10 of GH receptor (GHR); exon 1 of ghrelin (GHRL); exon 1 of insulin-like growth factor-I (IGF-I), and exon 3 of leptin (LEP). Polymorphisms were detected in five of the six PCR products. Two electrophoretic patterns were detected for GH1 exon 4. Five conformational patterns were detected for GH1 exon 5 and LEP exon 3, and three for IGF-I exon 1. Only GHR and GHRL were monomorphic. Changes in protein structures due to variable SNPs were also analyzed. The results suggest that Mehraban sheep, a major breed that is important for the animal industry in Middle East countries, has high genetic variability, opening interesting prospects for future selection programs and preservation strategies.

The co-existence of two growth hormone receptors and their differential expression profiles between female and male tongue sole (Cynoglossus semilaevis).

Growth hormone receptor (Ghr) is a single-transmembrane pass protein which is important in initiating the ability of growth hormone (Gh) to regulate development and somatic growth in vertebrates. In this study, molecular cloning, expression analysis of two different ghr genes (ghr1 and ghr2) in the tongue sole (Cynoglossus semilaevis) was conducted. As a result, the ghr1 and ghr2 cDNA sequences are 2364 bp and 3125 bp, each of which encodes a transmembrane protein of 633 and 561 amino acids (aa), respectively. Besides, the ghr1 gene includes nine exons and eight introns. The sex-specific tissue expression was analyzed by using 14 tissues from females, normal males and extra-large male adults. Both the ghr1 and ghr2 were predominantly expressed in the liver, and the ghr1 expression level in normal males was 1.6 and 1.4 times as much as those in females and extra-large males, while the ghr2 mRNA expression level in normal males was 1.1 and 1.2 times as much as those in females and extra-large males, respectively. Ontogenetic expression analysis at early life stages indicated that the ghr1 and ghr2 mRNAs were detected at all of the 35 sampling points (from oosphere to 410days-old). Furthermore, the sex differences in ghr mRNA expressions were also examined by using a full-sib family of C. semilaevis. Significantly higher levels of ghr1 mRNA were observed in males than in females at most stages of the sampling period (P<0.01). The ghr2 mRNA expression at most stages exhibited a significant sexual difference at each sampling point (P<0.01) without any variation trend related with the sexes during the whole sampling period.