Dataset Information

Chromosomal rearrangements, phenotypic variation and modularity: a case study from a contact zone between house mouse Robertsonian races in Central Italy.

ABSTRACT: The Western European house mouse, Mus musculus domesticus, is well-known for the high frequency of Robertsonian fusions that have rapidly produced more than 50 karyotipic races, making it an ideal model for studying the mechanisms of chromosomal speciation. The mouse mandible is one of the traits studied most intensively to investigate the effect of Robertsonian fusions on phenotypic variation within and between populations. This complex bone structure has also been widely used to study the level of integration between different morphogenetic units. Here, with the aim of testing the effect of different karyotypic assets on the morphology of the mouse mandible and on its level of modularity, we performed morphometric analyses of mice from a contact area between two highly metacentric races in Central Italy. We found no difference in size, while the mandible shape was found to be different between the two Robertsonian races, even after accounting for the genetic relationships among individuals and geographic proximity. Our results support the existence of two modules that indicate a certain degree of evolutionary independence, but no difference in the strength of modularity between chromosomal races. Moreover, the ascending ramus showed more pronounced interpopulation/race phenotypic differences than the alveolar region, an effect that could be associated to their different polygenic architecture. This study suggests that chromosomal rearrangements play a role in the house mouse phenotypic divergence, and that the two modules of the mouse mandible are differentially affected by environmental factors and genetic makeup.

SUBMITTER: Franchini P

PROVIDER: S-EPMC4733104 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Chromosomal rearrangements, phenotypic variation and modularity: a case study from a contact zone between house mouse Robertsonian races in Central Italy.

Franchini Paolo P Colangelo Paolo P Meyer Axel A Fruciano Carmelo C

Ecology and evolution 20160130 5

The Western European house mouse, Mus musculus domesticus, is well-known for the high frequency of Robertsonian fusions that have rapidly produced more than 50 karyotipic races, making it an ideal model for studying the mechanisms of chromosomal speciation. The mouse mandible is one of the traits studied most intensively to investigate the effect of Robertsonian fusions on phenotypic variation within and between populations. This complex bone structure has also been widely used to study the leve ...[more]

PMID: 26855768

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Project description:BACKGROUND:Western house mice Mus musculus domesticus are among the most important mammalian model species for chromosomal speciation. Hybrids between chromosomal races of M. m. domesticus suffer various degrees of fertility reduction between full fertility and complete sterility, depending on the complexity of the chromosomal differences between the races. This complexity presents itself in hybrids as meiotic configurations of chromosome chains and rings, with longer configurations having a stronger impact on fertility. While hybrids with short configurations have been intensively studied, less work has been done on hybrids with very long configurations. In this study, we investigated laboratory-reared wild mice from two chromosomally very different races in Switzerland found in close proximity. Hybrids between these races form a meiotic chain of fifteen chromosomes. We performed a detailed analysis of male and female hybrid fertility, including three generations of female backcrosses to one of the parental races. We also tested for possible divergence of mate preference in females. RESULTS:While all male F1 hybrids were sterile with sperm counts of zero, 48% of female F1 hybrids produced offspring. Their litter sizes ranged from one to three which is significantly lower than the litter size of parental race females. When hybrid females were backcrossed to a parental race, half of the offspring resembled the parental race in karyotype and fertility, while the other half resembled the F1 hybrids. In the preference test, females of both races indicated a lack of a preference for males of their own karyotype. CONCLUSIONS:Although the fertility of the F1 hybrids was extremely low because of the complexity of the chromosomal differences between the races, reproductive isolation was not complete. As we did not find assortative female preferences, we expect that contact between these races would lead to the production of hybrids and that gene flow would occur eventually, as fertility can be restored fully after one backcross generation.

Project description:Mycoplasma bovis, an important pathogen of cattle, was recently shown to possess a family of phase- and size-variable membrane surface lipoprotein antigens (Vsps). These proteins spontaneously undergo noncoordinate phase variation between ON and OFF expression states, generating surface antigenic variation. In the present study, we show that the spontaneously high rate of Vsp phenotypic switching involves DNA rearrangements that occur at high frequency in the M. bovis chromosome. A 1.5-kb HindIII genomic fragment carrying the vspA gene from M. bovis PG45 was cloned and sequenced. The deduced VspA amino acid sequence revealed that 80% of the VspA molecule is composed of reiterated intragenic coding sequences, creating a periodic polypeptide structure. Four distinct internal regions of repetitive sequences in the form of in-tandem blocks extending from the N-terminal to the C-terminal portion of the Vsp product were identified. Southern blot analysis of phenotypically switched isogenic lineages representing ON or OFF phase states of Vsp products suggested that changes in the Vsp expression profile were associated with detectable changes at the DNA level. By using a synthetic oligonucleotide representing a sequence complementary to the repetitive vspA gene region as a probe, we could identify the vspA-bearing restriction fragment undergoing high-frequency reversible rearrangements during oscillating phase transition of vspA. The 1.5-kb HindIII fragment carrying the vspA gene (on state) rearranged and produced a 2.3-kb HindIII fragment (OFF state) and vice versa. Two newly discovered vsp genes (vspE and vspF) were localized on two HindIII fragments flanking the vsp gene upstream and downstream. Southern blot hybridization with vspE- and vspF-specific oligonucleotides as probes against genomic DNA of VspA phase variants showed that the organization and size of the fragments adjacent to the vspA gene remained unchanged during VspA ON-OFF switching. The mechanisms regulating the vsp genes are yet unknown; our findings suggest that a recombinative mechanism possibly involving DNA inversions, DNA insertion, or mobile genetic elements may play a role in generating the observed high-frequency DNA rearrangements.

Dataset Information

Chromosomal rearrangements, phenotypic variation and modularity: a case study from a contact zone between house mouse Robertsonian races in Central Italy.

Publications

Chromosomal rearrangements, phenotypic variation and modularity: a case study from a contact zone between house mouse Robertsonian races in Central Italy.

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