Genetic polymorphisms at candidate genes affecting fat content and fatty acid composition in Modicana cows: effects on milk production traits in different feeding systems

Feeding greatly affects milk yield and composition. The research is highlighting the potential of genetic polymorphism at some loci to affect milk yield and quality traits. These loci can be up/down regulated depending on the production environment; therefore, we hypothesized that milk yield and composition could differ when cows with different genotype at SCD, DGAT1 and ABCG2 loci are reared in different feeding systems. The polymorphisms of SCD, DGAT1 and ABCG2 genes were investigated in Modicana breed. In all, three polymorphic sites, responsible for the genetic variation of quantitative trait loci and therefore defined quantitative trait nucleotides, were genotyped: the transition g.10329C>T in 5^th exon determines a substitution p.A293V in the SCD, the dinucleotide mutation g.10433-10434AA>GC in 8^th exon responsible for p.K232A substitution in the DGAT1 and the transition g.62569A>C in the 14^th exon responsible for p.Y581S substitution in the ABCG2 gene. In the sample of 165 Modicana cows, SCD and DGAT1 genes resulted polymorphic; the alleles g.10329T and g.10433-10434GC were the most frequent in SCD and DGAT1 (0.73 and 0.91) respectively, whereas ABCG2 locus was monomorphic for allele A (p.581Y). Sequencing analysis was carried out on 14 samples with different genotypes to confirm the results of the PCR-RFLP protocols. Based on the genotypes at SCD locus, 47 Modicana cows were selected for the nutritional trial: 24 cows in a semi-intensive farm, with 2 h/day grazing on natural pasture, and 23 cows in an extensive farm, with 8 h/day grazing on natural pasture. Monthly, milk yield and composition were evaluated and individual milk samples were analyzed for fatty acids composition by gas chromatography. No differences in milk yield, fat, protein, lactose, casein and urea were associated to SCD genotype. Feeding systems affected milk yield and composition. No significant genotype×feeding system interaction was observed for milk yield and composition. Fatty acids composition was significantly affected only by the feeding system. Significant interactions were found between SCD genotype and feeding system for six fatty acids: 4:0, 6:0, 8:0, 10:0, 12:0 and t11 18:1. We concluded that the feeding system was the factor that mostly affected milk production and composition; moreover, our results do not confirm what reported in literature as regard the effect of the SCD polymorphism on milk fatty acid composition. The high amount of pasture seemed to have resized the SCD polymorphism effects because of the different fatty acids composition of the diet.     

In vitro metabolism of flax lignans by ruminal and faecal microbiota of dairy cows

Aims: To determine the in vitro conversion of plant lignans from two flax products (hull and seed) into the mammalian lignans, enterolactone and enterodiol, by bovine ruminal and faecal microbiota. Methods and Results: Flax seeds and hulls were incubated in vitro over a 96-h time course with ruminal or faecal inoculum. Plant lignans in flax seeds and hulls averaged 9·2 and 32·0 nmol mg⁻¹, respectively. The highest net production of enterodiol at 72 and 96 h of incubation was obtained with flax hulls incubated with faecal microbiota. There was no difference in net production of enterodiol between flax products within the first 24 h of incubation. In general, net production of enterolactone over the 96-h time course was significantly higher for flax products incubated with ruminal than with faecal microbiota. Net production of enterolactone at 72 and 96 h of incubation was greater for flax hulls than flax seeds. Conclusions: Results of the present experiment suggest that, of the metabolites studied, the main mammalian lignan metabolite produced from flax hulls and seeds by ruminal microbiota is enterolactone while faecal microbiota leads mainly to the net production of enterodiol. Significance and Impact of the Study: This research will improve the understanding of the metabolic pathway of mammalian lignans in dairy cows, in order to enable targeted manipulation of their quantities in milk.     

Promoter variants at AP2 box region of Hsp70.1 affect thermal stress response and milk production traits in Frieswal cross bred cattle

Heat shock proteins (Hsp) are known to play major role in protection of cells from thermal stress. Nucleotide polymorphisms within the promoter of Hsp affect degree of expression and inducibility of Hsp mRNA. The present study aimed to investigate the effect of polymorphism within promoter region on the cellular expression of Hsp70.1 mRNA and association of identified polymorphisms with the physiological parameters during summer stress and milk production traits in dairy cattle. Two hundred Frieswal cows were genotyped using double PCR-RFLP to identify deletion of cytosine within the Hsp70.1 promoter AP2 box at base position 895. Homozygous wild type genotypes (CC) were found in lower frequency (39.29, n = 78) than heterozygous cytosine deletion mutant genotypes (C −) (60.71, n = 122). In the observed physiological parameters (rectal temperature, respiration rate and heat tolerance coefficient), cows that were homozygous wild types had better significant (P < 0.05) summer tolerance than the heterozygous deletion genotypes. Cytosine deletion mutation in the promoter region negatively affected (P < 0.01) the expression of Hsp70.1 mRNA in peripheral bovine mononuclear cells (PBMC) subjected to in vitro heat stress. Further association of observed polymorphism with the milk production traits was significant as the heterozygous cytosine deletion cows had lower total milk yield, peak yield, yield at 300 days, protein% (P < 0.01) and fat% (P < 0.05) than the native wild type promoter cows. The results from the present study suggest that the promoter region of bovine hsp70.1 gene is polymorphic and may be useful in selection of dairy cows for relatively better thermotolerance and higher milk production.     

The F279Y polymorphism of the <Emphasis Type="Italic">GHR</Emphasis> gene and its relation to milk production and somatic cell score in German Holstein dairy cattle

The bovine growth hormone receptor (GHR) gene has been identified as a strong positional and functional candidate gene influencing milk production. A non-synonymous single nucleotide polymorphism (SNP) in exon 8 leads to a phenylalanine to tyrosine amino acid substitution (F279Y) in the receptor. The aim of the study was to estimate the effects of the F279Y mutation on milk yield, fat, protein, casein, and lactose yield and content, as well as somatic cell score (SCS), in a German Holstein dairy cattle population. The analysis of 1,370 dairy cows confirmed a strong association of the F279Y polymorphism with milk yield, as well as with fat, protein, and casein contents. Furthermore, increasing effects on lactose yield and content for the 279Y allele were found. Even though the tyrosine variant occurred as the minor allele (16.5%), its substitution effects were 320 kg (305 d), 0.02 kg per day, and 0.07 kg per day for milk, casein, and lactose yields, respectively. The same allele had negative effects on fat, protein, and casein contents. Finally, the high-milk-yield tyrosine allele was also associated with lower SCS (p < 0.05). The data support the high potential of the F279Y polymorphism as a marker for the improvement of milk traits in selection programs.     

Multidrug transporter ABCG2/breast cancer resistance protein secretes riboflavin (vitamin B2) into milk

The multidrug transporter breast cancer resistance protein (BCRP/ABCG2) is strongly induced in the mammary gland during pregnancy and lactation. We here demonstrate that BCRP is responsible for pumping riboflavin (vitamin B(2)) into milk, thus supplying the young with this important nutrient. In Bcrp1(-/-) mice, milk secretion of riboflavin was reduced >60-fold compared to that in wild-type mice. Yet, under laboratory conditions, Bcrp1(-/-) pups showed no riboflavin deficiency due to concomitant milk secretion of its cofactor flavin adenine dinucleotide, which was not affected. Thus, two independent secretion mechanisms supply vitamin B(2) equivalents to milk. BCRP is the first active riboflavin efflux transporter identified in mammals and the first transporter shown to concentrate a vitamin into milk. BCRP activity elsewhere in the body protects against xenotoxins by reducing their absorption and mediating their excretion. Indeed, Bcrp1 activity increased excretion of riboflavin into the intestine and decreased its systemic availability in adult mice. Surprisingly, the paradoxical dual utilization of BCRP as a xenotoxin and a riboflavin pump is evolutionarily conserved among mammals as diverse as mice and humans. This study establishes the principle that an ABC transporter can transport a vitamin into milk and raises the possibility that other vitamins and nutrients are likewise secreted into milk by ABC transporters.     

Revisiting the quantitative trait loci for milk production traits on BTA6

A parallel association study was performed in two independent cattle populations based on 41 validated, targeted single nucleotide polymorphisms (SNPs) and four microsatellite markers to re-evaluate the multiple quantitative trait loci (QTL) architecture for milk performance on bovine chromosome 6 (BTA6). Two distinct QTL located in the vicinity of the middle region of BTA6, but differing unambiguously regarding their effects on milk composition and yield traits were validated in the German Holstein population. A highly significant association of the protein variant ABCG2 p.Tyr581Ser with milk composition traits reconfirmed the causative molecular relevance of the ABCG2 gene in QTL region 1, whereas in QTL region 2, significant and tentative associations between gene variants RW070 and RW023 (located in the promoter region and exon 9 of the PPARGC1A gene for milk yield traits) were detected. For the German Fleckvieh population, only RW023 showed a tentative association with milk yield traits, whereas those loci with significant effects in German Holsteins (ABCG2 p.Tyr581Ser, RW070) showed fixed alleles. Even though our new data highlight two variants in the PPARGC1A gene (RW023, RW070) in QTL region 2, based on the results of our study, currently no unequivocal conclusion about the causal background of this QTL affecting milk yield traits can be drawn. Notably, the German Holstein and Fleckvieh populations, known for their divergent degree of dairy type, differ substantially in their allele frequencies for the growth-associated NCAPG p.Ile442Met locus.     

AluI polymorphism of the bovine growth hormone (GH) gene, resumption of ovarian cyclicity, milk production and loss of body condition at the onset of lactation in dairy cows

Relationships among GH genotype (AluI polymorphism), parity, metritis and interval from calving to first ovulation, milk production and body condition score (BCS) loss were determined in dairy cows (n = 307) on four large-scale farms in Hungary. Cows with systemic signs of puerperal metritis or mastitis were excluded. Time of the first postpartum (PP) ovulation was obtained from milk progesterone profiles. Based on GH genotype determination, groups of leucine homozygous cows (n = 246) and valine allele carriers (n = 61) were formed. All animals became cyclic during the study period. The average interval to first ovulation was 27.6 ± 0.69-d PP (mean ± S.D.). Genotype had no effect on the commencement of ovarian cyclicity. First ovulation occurred sooner after calving in pluriparous than in primiparous cows. The greater BCS loss cows had during the first 30-d PP, the longer they took to resume cyclic ovarian function. The interval from calving to first ovulation was substantially affected by farm, but not by mild cases of puerperal metritis. Genotype was not related to cumulative 30-d milk yield or BCS loss after calving. Primiparous cows had lower milk yield than pluriparous ones. Cows with metritis lost more body condition than healthy individuals in the first month postpartum. We concluded that, under field conditions, AluI polymorphism of the bovine GH gene had no effect on the interval from calving to first ovulation and could not be directly related to differences in milk yield and to the extent of BCS loss during the first month after calving in Holstein-Friesian cows.     

Pten Regulates Development and Lactation in the Mammary Glands of Dairy Cows

Pten is a tumor suppressor gene regulating many cellular processes, including growth, adhesion, and apoptosis. In the aim of investigating the role of Pten during mammary gland development and lactation of dairy cows, we analyzed Pten expression levels in the mammary glands of dairy cows by using western blotting, immunohistochemistry, and quantitative polymerase chain reaction (qPCR) assays. Dairy cow mammary epithelial cells (DCMECs) were used to study the function of Pten in vitro. We determined concentrations of β-casein, triglyceride, and lactose in the culture medium following Pten overexpression and siRNA inhibition. To determine whether Pten affected DCMEC viability and proliferation, cells were analyzed by CASY-TT and flow cytometry. Genes involved in lactation-related signaling pathways were detected. Pten expression was also assessed by adding prolactin and glucose to cell cultures. When Pten was overexpressed, proliferation of DCMECs and concentrations for β-casein, triglyceride, and lactose were significantly decreased. Overexpression of Pten down-regulated expression of MAPK, CYCLIN D1, AKT, MTOR, S6K1, STAT5, SREBP1, PPARγ, PRLR, and GLUT1, but up-regulated 4EBP1 in DCMECs. The Pten siRNA inhibition experiments revealed results that opposed those from the gene overexpression experiments. Introduction of prolactin (PRL) increased secretion of β-casein, triglyceride, and lactose, but decreased Pten expression levels. Introduction of glucose also increased β-casein and triglyceride concentrations, but did not significantly alter Pten expression levels. The Pten mRNA and protein expression levels were decreased 0.3- and 0.4-fold in mammary glands of lactating cows producing high quality milk (milk protein >3.0%, milk fat >3.5%), compared with those cows producing low quality milk (milk protein <3.0%, milk fat <3.5%). In conclusion, Pten functions as an inhibitor during mammary gland development and lactation in dairy cows. It can down-regulate DCMECs secretion of β-casein, triglyceride, and lactose, and plays a critical role in lactation related signaling pathways.     

ABCG1 regulates pulmonary surfactant metabolism in mice and men

Idiopathic pulmonary alveolar proteinosis (PAP) is a rare lung disease characterized by accumulation of surfactant. Surfactant synthesis and secretion are restricted to epithelial type 2 (T2) pneumocytes (also called T2 cells). Clearance of surfactant is dependent upon T2 cells and macrophages. ABCG1 is highly expressed in both T2 cells and macrophages. ABCG1-deficient mice accumulate surfactant, lamellar body-loaded T2 cells, lipid-loaded macrophages, B-1 lymphocytes, and immunoglobulins, clearly demonstrating that ABCG1 has a critical role in pulmonary homeostasis. We identify a variant in the ABCG1 promoter in patients with PAP that results in impaired activation of ABCG1 by the liver X receptor α, suggesting that ABCG1 basal expression and/or induction in response to sterol/lipid loading is essential for normal lung function. We generated mice lacking ABCG1 specifically in either T2 cells or macrophages to determine the relative contribution of these cell types on surfactant lipid homeostasis. These results establish a critical role for T2 cell ABCG1 in controlling surfactant and overall lipid homeostasis in the lung and in the pathogenesis of human lung disease.     

Relations between divalent cation binding and ATPase activity in coupling factor from chloroplast.

Although 150 individual samples of milk from Italian water buffalo (Bubalus arnee) were examined by acid and alkaline gel electrophoresis, no polymorphism was observed for α-lactalbumin and β-lactoglobulin. After isolation and purification of these two proteins their amino acid compositions were determined and compared with those of the corresponding bovine proteins. The sequence alignments of 36 and 17 amino-acids from the N-terminal ends and 2 amino-acids from the C-terminal ends of buffalo α-lactalbumin and β-lactoglobulin, respectively, have been established. Our results indicate that buffalo α-lactalbumin differs from its cow B counterpart by a substitution Asn/Gly at position 17 and by another substitution, likely Glu/Gln or Asp/Asn, at an unknown position. Buffalo β-lactoglobulin is homologous to the bovine B variant. Three substitutions differentiate the two proteins: Ile/Leu and Val/Ile at positions 1 and 162 respectively; a further one, Gln/Ile, has not yet been located. According to these results the B variant of bovine β-lactoglobulin might be the wild type of the Bos genus.     

In vivo oocyte IGF-1 priming increases inner cell mass proliferation of in vitro-formed bovine blastocysts

Studies addressing the effects of supraphysiological levels of IGF-1 on oocyte developmental competence are relevant for unravelling conditions resulting in high bioavailability of IGF-1, such as the polycystic ovary syndrome (PCOS). This study investigated the effects of supraphysiological levels of IGF-1 during in vivo folliculogenesis on the morula-blastocyst transition in bovine embryos. Compacted morulae were non-surgically collected and frozen for subsequent mRNA expression analysis (IGF1R, IGBP3, TP53, AKT1, SLC2A1, SLC2A3, and SLC2A8), or underwent confocal microscopy analysis for protein localization (IGF1R and TP53), or were cultured in vitro for 24 h. In vitro-formed blastocysts were subjected to differential cell staining. The mRNA expression of SLC2A8 was higher in morulae collected from cows treated with IGF-1. Both IGF1R and TP53 protein were present in the plasma membrane and cytoplasm. IGF-1 treatment did not affect protein localization of both IGF1R and TP53. In vitro-formed blastocysts derived from morulae recovered from IGF-1-treated cows displayed a higher number of cells in the inner cell mass (ICM). Total cell number (TCN) of in vitro-formed blastocysts was not affected. A higher mean ICM/TCN proportion was observed in in vitro-formed blastocysts derived from morulae collected from cows treated with IGF-1. The percentage of in vitro-formed blastocysts displaying a low ICM/TCN proportion was decreased by IGF-1 treatment. In vitro-formed blastocysts with a high ICM/TCN proportion were only detected in IGF-1 treated cows. Results show that even a short in vivo exposure of oocytes to a supraphysiological IGF-1 microenvironment can increase ICM cell proliferation in vitro during the morula to blastocyst transition.     

The partial replacement of soyabean meal and rapeseed meal with feed grade urea or a slow-release urea and its effect on the performance, metabolism and digestibility in dairy cows

The objectives of the study were to determine the effect of the partial replacement of soyabean meal and rapeseed meal with feed grade urea or a slow-release urea on the performance, metabolism and whole-tract digestibility in mid-lactation dairy cows. Forty-two Holstein–Friesian dairy cows were allocated to one of three dietary treatments in each of three periods of 5 weeks duration in a Latin square design. Control (C) cows were offered a total mixed ration based on grass and maize silages and straight feeds that included 93 g/kg dry matter (DM) soyabean meal and 61 g/kg DM rapeseed meal. Cows that received either of the other two treatments were offered the same basal ration with the replacement of 28 g/kg DM soyabean and 19 g/kg DM rapeseed meal with either 5 g/kg DM feed grade urea (U) or 5.5 g/kg DM of the slow-release urea (S; Optigen^R; Alltech Inc., Kentucky, USA), with the content of maize silage increasing. There was no effect (P > 0.05) of dietary treatment on DM intake, which averaged 22.5 kg/day. Similarly, there was no effect (P > 0.05) of treatment on daily milk or milk fat yield but there was a trend (P = 0.09) for cows offered either of the diets containing urea to have a higher milk fat content (average of 40.1 g/kg for U and S v. 38.9 g/kg for C). Milk true protein concentration and yield were not affected by treatment (P > 0.05). Milk yield from forage and N efficiency (g milk N output/g N intake) were highest (P < 0.01) in cows when offered S and lowest in C, with cows receiving U having intermediate values. Cows offered S also tended to have the highest live weight gain (0.38 kg/day) followed by U (0.23 kg/day) and C (0.01 kg/day; P = 0.07). Plasma urea concentrations were higher (P < 0.05) at 2 and 4 h post feeding in cows when offered U and lowest in C, with animals receiving S having intermediate values. There was no effect (P > 0.05) of treatment on whole-tract digestibility. In conclusion, the partial replacement of soyabean meal and rapeseed meal with feed grade urea or a slow-release urea can be achieved without affecting milk performance or diet digestibility, with the efficiency of conversion of dietary N into milk being improved when the slow-release urea was fed.     

Mutations of the central tyrosines of putative cholesterol recognition amino acid consensus (CRAC) sequences modify folding,activity, and sterol-sensing of the human ABCG2 multidrug transporter

Human ABCG2 is a plasma membrane glycoprotein causing multidrug resistance in cancer. Membrane cholesterol and bile acids are efficient regulators of ABCG2 function, while the molecular nature of the sterol-sensing sites has not been elucidated. The cholesterol recognition amino acid consensus (CRAC, L/V-(X)_(1–5)-Y-(X)_(1–5)-R/K) sequence is one of the conserved motifs involved in cholesterol binding in several proteins. We have identified five potential CRAC motifs in the transmembrane domain of the human ABCG2 protein. In order to define their roles in sterol-sensing, the central tyrosines of these CRACs (Y413, 459, 469, 570 and 645) were mutated to S or F and the mutants were expressed both in insect and mammalian cells. We found that mutation in Y459 prevented protein expression; the Y469S and Y645S mutants lost their activity; while the Y570S, Y469F, and Y645F mutants retained function as well as cholesterol and bile acid sensitivity. We found that in the case of the Y413S mutant, drug transport was efficient, while modulation of the ATPase activity by cholesterol and bile acids was significantly altered. We suggest that the Y413 residue within a putative CRAC motif has a role in sterol-sensing and the ATPase/drug transport coupling in the ABCG2 multidrug transporter.     

Effects of duodenal infusion of free α-linolenic acid on the plasma and milk proteome of lactating dairy cows

This study is an exploratory analysis for understanding the effect of a duodenal infusion of an α-linolenic acid (LNA) on the plasma and milk proteome of lactating dairy cows. Four primiparous Holstein cows were fitted with duodenal cannulas and received 0, 100, 200, 300 and 400 g/day of LNA in a two-treatment crossover design. Blood and milk were collected for determination of protein composition by two-dimensional gel electrophoresis. Alteration of protein spots was detected and identified using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS). Plasma haptoglobin levels, and milk β-casein A2, α_s1-casein variant and albumin, did not differ in cows after infusion of 0, 100, 200 and 300 g/day of LNA, but were increased after the cows received duodenal infusion of 400 g/day of LNA. Western blot analysis of haptoglobin expression in plasma confirmed the alterations in protein expression seen using MS. This study demonstrated that infusion of high doses of LNA by duodenal cannula can result in metabolic stress within the bovine intestine and in changes in milk composition.     

In vitro and in vivo interaction of moxidectin with BCRP/ABCG2

The study characterizes the interaction between BCRP/ABCG2 and moxidectin by means of cellular transport, and pharmacokinetic studies in Bcrp1 (−/−) and wild-type mice. Milbemycin moxidectin ([³H]-moxidectin) was tested for its ability to be transported across MCDK-II epithelial monolayer cultures transfected with BCRP. In a second approach, accumulation assays by BCRP-expressing Xenopus laevis oocytes were carried out. Finally, pharmacokinetic studies were performed in order to establish the role of the transporter in milk secretion and tissue distribution. The efflux was negligible in polarized cells but moxidectin was efficiently transported in BCRP-expressing X. laevis oocytes. The transport was blocked by an acridone derivative, a novel BCRP inhibitor. Moxidectin secretion into breast milk was decreased in Bcrp1-knockout mice and the milk to plasma ratio was 2-fold higher in wild-type mice after i.v. administration. Drug accumulation in intestinal content, bile, and intestine was higher in wild-type mice but the plasma concentration was not different.Moxidectin is identified as a BCRP substrate since its Bcrp1-mediated secretion into breast milk and the involvement of Bcrp1 in intestinal and bile secretion has been demonstrated. This interaction has pharmacokinetic and toxicological consequences. The most important toxicological consequences of the interaction between BCRP and moxidectin may be related with the presence of drug residues in milk.     

Human milk protein production in xenografts of genetically engineered bovine mammary epithelial stem cells

Background

In the bovine species milk production is well known to correlate with mammary tissue mass. However, most advances in optimizing milk production relied on improvements of breeding and husbandry practices. A better understanding of the cells that generate bovine mammary tissue could facilitate important advances in milk production and have global economic impact. With this possibility in mind, we show that a mammary stem cell population can be functionally identified and isolated from the bovine mammary gland. We also demonstrate that this stem cell population may be a promising target for manipulating the composition of cow''s milk using gene transfer.

Methods and Findings

We show that the in vitro colony-forming cell assay for detecting normal primitive bipotent and lineage-restricted human mammary clonogenic progenitors are applicable to bovine mammary cells. Similarly, the ability of normal human mammary stem cells to regenerate functional bilayered structures in collagen gels placed under the kidney capsule of immunodeficient mice is shared by a subset of bovine mammary cells that lack aldehyde dehydrogenase activity. We also find that this activity is a distinguishing feature of luminal-restricted bovine progenitors. The regenerated structures recapitulate the organization of bovine mammary tissue, and milk could be readily detected in these structures when they were assessed by immunohistochemical analysis. Transplantation of the bovine cells transduced with a lentivirus encoding human β-CASEIN led to expression of the transgene and secretion of the product by their progeny regenerated in vivo.

Conclusions

These findings point to a common developmental hierarchy shared by human and bovine mammary glands, providing strong evidence of common mechanisms regulating the maintenance and differentiation of mammary stem cells from both species. These results highlight the potential of novel engineering and transplant strategies for a variety of commercial applications including the production of modified milk components for human consumption.     

Functional characterization of the S41Y (C2755A) polymorphism of tryptophan hydroxylase 2

Human TPH2 (hTPH2) catalyzes the rate‐limiting step in CNS serotonin biosynthesis. We characterized a single‐nucleotide polymorphism (C2755A) in the hTPH2 gene that substitutes tyrosine for serine at position 41 in the regulatory domain of the enzyme. This polymorphism is associated with bipolar disorder and peripartum depression in a Chinese population. Recombinant h TPH2 human proteins were expressed in bacteria and also stably expressed in PC12 cells. Following bacterial expression and purification, the tyrosine for serine substitution at position 41 (S41Y) polymorphic enzyme displayed increased V_max with unchanged K_m values. By contrast, enzyme stability was decreased in vitro from 32 min to 4 min (37°C) for the S41Y enzyme (as compared to the wild‐type enzyme). The S41Y polymorphism decreased cyclic AMP‐dependent protein kinase A‐mediated phosphorylation ~ 50% relative to wild‐type hTPH2, suggesting that the S41Y mutation may disrupt the post‐translational regulation of this enzyme. Transfected PC12 cells expressed hTPH2 mRNA, active protein, and synthesized and released serotonin. Paradoxically, while S41Y‐transfected PC12 cells expressed higher levels of hTPH2 than wild type, they synthesized less serotonin. These findings suggest a modified regulation of the S41Y gene variant leading to altered regulation and reduced neurotransmitter synthesis that may contribute to association of the polymorphism with bipolar disorder and depression.