Molecular evolution of growth hormone gene family in old world monkeys and hominoids

Growth hormone is a classic molecule in the study of the molecular clock hypothesis as it exhibits a relatively constant rate of evolution in most mammalian orders except primates and artiodactyls, where dramatically enhanced rate of evolution (25-50-fold) has been reported. The rapid evolution of primate growth hormone occurred after the divergence of tarsiers and simians, but before the separation of old world monkeys (OWM) from new world monkeys (NWM). Interestingly, this event of rapid sequence evolution coincided with multiple duplications of the growth hormone gene, suggesting gene duplication as a possible cause of the accelerated sequence evolution. Here we determined 21 different GH-like sequences from four species of OWM and hominoids. Combining with published sequences from OWM and hominoids, our analysis demonstrates that multiple gene duplications and several gene conversion events both occurred in the evolutionary history of this gene family in OWM/hominoids. The episode of recent duplications of CSH-like genes in gibbon is accompanied with rapid sequence evolution likely resulting from relaxation of purifying selection. GHN genes in both hominoids and OWM are under strong purifying selection. In contrast, CSH genes in both lineages are probably not. GHV genes in OWM and hominoids evolved at different evolutionary rates and underwent different selective constraints. Our results disclosed the complex history of the primate growth hormone gene family and raised intriguing questions on the consequences of these evolutionary events. © 2005 Elsevier B.V. All rights reserved.

Genetic differentiation in populations of the cestode Bothriocephalus acheilognathi (Cestoda, Pseudophyllidea) as revealed by eight microsatellite markers

The genetic structure of populations of the fish cestode, Bothriocephalus acheilognathi collected from Bailianhe Reservoir (BLH), Changshou (CSH) and Liangzi (LZH) Lakes was investigated by using 8 microsatellite loci. A total of 108 adult worms were genotyped at each of the 8 loci. For the 3 populations, the mean number of alleles per locus ranged from 2.38 to 5.5, and the mean expected heterozygosity ranged from 0.432 to 0.559. The average polymorphic information content (PIC) was from 0.384 to 0.492. The significant F-is values indicated non-random mating within LZH and BLH populations. On the other hand, when samples were further classified into subpopulations at the level of host fish species, no or little heterozygote deficiency was detected at most loci, showing that cross-fertilization, predominantly, but not exclusively, must have occurred within the subpopulations. Microsatellite markers also revealed an unexpected high level of genetic differentiation, as measured by R-st and N-m values or by deltau(2) genetic distance among subpopulations from different hosts. Factors influencing the population genetic structure and the parasite host specificity are discussed.

哺乳动物生长激素/泌乳刺激素基因超家族的分子进化研究

生长激素（Growthhormone，GH）和泌乳刺激素（Prolactin，PRL）基因具有相似的结构和功能，它们和其他一些相关基因组成了GH/PRL基因超家族。在大部分哺乳动物基因组中，GH和PRL都是单拷贝基因。但在灵长目动物中，PRL是单拷贝基因，GH基因却发生了串联重复事件，形成一个基因家族。而在啮齿目中则相反，GH是单拷贝的，PRL却发生了串联重复事件形成一个基因家族。用PCR、克隆、测序的方法，我们从7种灵长目动物中得到了35条GH－类似基因。系统发育分析的结果显示所有旧大陆猴／人猿超科（OWM/H）的GH一类似基因和所有新大陆猴（NWM）的GH-类似基因分别形成两个单系，提示新大陆猴的GH基因家族和旧大陆猴／人猿超科GH基因家族起源于独立的基因重复事件。我们的分析结果还提示在。H基因家族的进化历程中发生了多次基因重复和基因转换事件。此外，不同GH基因家族成员的进化速率和所受到的选择压力存在显著差异。GHN基因在人猿超科和旧大陆猴中进化速率都比较慢，且受到了很强的纯化选择的作用；而CSH基因在两个世系中进化速率都比较快而且可能受到近中性选择的作用；GHV的进化速率和选择压力在旧大陆猴和人猿超科之间存在显著差异。对于新大陆猴GH基因家族，我们发现3个主要的功能基因簇，有趣的是这3个基因簇分别受到了纯化选择、近中性选择和正选择3种不同类型的选择压力。进一步分析的结果显示GH基因家族的进化符合所谓"生一和一灭（Birth-and-death）"的进化模式，该模式以频繁的基因重复和假基因化为主要特征。啮齿目泌乳刺激素基因家族由多个结构相似、在染色体上串联排列的基因组成，创门主要在生殖过程中协调作用。我们利用生物信息学手段在大鼠中得到了两个新的家族成员。结合系统发育、基因转换分析及染色体相对位置的比较，我们认为啮齿目PRL基因家族中的PL-I和PL-II基因亚家族是在大、小鼠分歧之后由物种特异的基因重复事件形成的。此外，啮齿目PRL基因家族的进化历程较复杂，因为除了通常的5-外显子结构的基因外，该家族还包含6-外显子结构的基因，后者在前者的第2和第3外显子之间获得了一个额外的外显子。本研究中我们意外地发现这个外显子在两个基因簇中的起源方式并不相同。在groupA中，它来源于一段外源DNA的插入，而在groupB中则来源于原先的非编码序列。对同义替换和异义替换速率比较的结果显示，在这些获得额外外显子的基－因中纯化选择压力得到了放松。激素蛋白必须与其受体结合经过信号传导才能发挥其生物学功能，因此，研究激素和受体的协同进化就显得尤为重要。我们对哺乳动物泌乳刺激素基因和其受体（PRLR）基因进行了协同进化分析，结果发现哺乳动物PRLR的膜外区和膜内区显示出和PRL一致的"插曲"式的进化模式。皮耳森相关系数计算的结果说明PRLR的膜外区和PRL基因发生了协同进化，同时PRLR的两个功能区域：膜外区和膜内区之间也发生了协同进化。此外，我们还发现灵长目PRL基因也发生了和GH基因类似的"插曲"式的进化，而且快速进化可能是选择压力放松的结果。

A self-consistent field theory study on the morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers

By using a combinatorial screening method based on the self-consistent field theory, we investigate the equilibrium morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers in two dimensions. The triangle phase diagrams of both block copolymers are constructed by systematically varying the volume fractions of blocks A, B, and C. In this study, the interaction energies between species A, B, and C are set to be equal. Four different equilibrium morphologies are identified, i.e., the lamellar phase (LAM), the hexagonal lattice phase (HEX), the core-shell hexagonal lattice phase (CSH), and the two interpenetrating tetragonal lattice phase (TET2). For the linear ABCBA block copolymer, the reflection symmetry is observed in the phase diagram except for some special grid points, and most of grid points are occupied by LAM morphology. However, for the H-shaped (AB)(2)C(BA)(2) block copolymer, most of the grid points in the triangle phase diagram are occupied by CSH morphology, which is ascribed to the different chain architectures of the two block copolymers. These results may help in the design of block copolymers with different microstructures.

Comparing the morphology and phase diagram of H-shaped ABC block copolymers and linear ABC block copolymers

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymers, we have investigated the morphology of H-shaped ABC block copolymers (A(2)BC(2)) and compared them with those of the linear ABC block copolymers. By changing the ratios of the volume fractions of two A arms and two C arms, one can obtain block copolymers with different architectures ranging from linear block copolymer to H-shaped block copolymer. By systematically varying the volume fractions of block A, B, and C, the triangle phase diagrams of the H-shaped ABC block copolymer with equal interactions among the three species are constructed. In this study, we find four different morphologies ( lamellar phase ( LAM), hexagonal lattice phase ( HEX), core-shell hexagonal lattice phase (CSH), and two interpenetrating tetragonal lattice (TET2)). Furthermore, the order-order transitions driven by architectural change are discussed.