Locational diversity of alpha satellite DNA and intergeneric hybridization aspects in the Nomascus and Hylobates genera of small apes

Abstract

Recently, we discovered that alpha satellite DNA has unique and genus-specific localizations on the chromosomes of small apes. This study describes the details of alpha satellite localization in the genera Nomascus and Hylobates and explores their usefulness in distinguishing parental genome sets in hybrids between these genera. Fluorescence in situ hybridization was used to establish diagnostic criteria of alpha satellite DNA markers in discriminating small ape genomes. In particular we established the genus specificity of alpha satellite distribution in three species of light-cheeked gibbons (Nomascus leucogenys, N. siki, and N. gabriellae) in comparison to that of Hylobates lar. Then we determined the localization of alpha satellite DNA in a hybrid individual which resulted from a cross between these two genera. In Nomascus the alpha satellite DNA blocks were located at the centromere, telomere, and four interstitial regions. In Hylobates detectable amounts of alpha satellite DNA were seen only at centromeric regions. The differences in alpha satellite DNA locations between Nomascus and Hylobates allowed us to easily distinguish the parental chromosomal sets in the genome of intergeneric hybrid individuals found in Thai and Japanese zoos. Our study illustrates how molecular cytogenetic markers can serve as diagnostic tools to identify the origin of individuals. These molecular tools can aid zoos, captive breeding programs and conservation efforts in managing small apes species. Discovering more information on alpha satellite distribution is also an opportunity to examine phylogenetic and evolutionary questions that are still controversial in small apes.

Figure 1. Karyotyping and chromosomal localization of alpha satellite DNA (AS) in three light-cheeked gibbon species.

A and B, Nomascus leucogenys (NLE) (female). C and D, N. siki (female) (NSI). E and F, N. gabriellae (male) (NGA). A), C), and E) DAPI-band (G-like band) reversed from the light fluorescence band of DAPI. B), D), and F) Localization of AS (red signal). The number in green is the chromosome number of the genus Nomascus. Chromosomes are classified with standard karyotypes as described previously . Numbers and letters with green underlines show the specific karyotype for the species. Numbers with red underlines indicates the chromosome with an interstitial band block in an arm. White arrowheads indicate the location of interstitial AS blocks.

Figure 2. Karyotyping and chromosome localization of AS in Hylobates lar, Conlar and Larcon.

A and B, Hylobates lar entelloides (male). C and D, Thai hybrid offspring between Hylobates lar (HLA) and Nomascus leucogenys (NLE) (female) (NLE/HLA, Conlar). E and F, Japanese hybrid offspring (female) (HLA/NLE, Larcon). A), C), and E) DAPI-band (G-like band) reversed from the light fluorescence band of DAPI. B), D), and F) Localization of AS (red signal). Numbers in orange are the chromosome number of the genus Hylobates. Chromosomes are classified with standard karyotypes as described previously (, for Hylobates; for Nomascus). Numbers and letters with orange and green underlines show specific karyotype for the species HLA and NLE, respectively. Numbers with red underlines indicate chromosomes with interstitial band blocks in an arm. White arrowheads indicate the location of interstitial AS blocks.

Figure 3. Chromosome paint analysis in light-cheeked gibbons.

Chromosome paint analysis was performed with human chromosome paint probes 9 (green), 14 (red), and 22 (yellow) on the chromosomes of light-cheeked gibbons (Nomascus). A) Nomascus leucogenys (NLE, female northern white-cheeked gibbon) with karyotype 1a-7b-22a. B) N. siki (NSI, female southern white-cheeked gibbon) with karyotype 1b-7b-22b. C) N. gabriellae (NGA, male tuff-cheeked gibbon) with karyotype 1b-7a-22b. D) Female hybrid offspring consisting of NLE and Hylobates lar (HLA, lar gibbon) with karyotypes 1a-7b-22a and 8c, respectively. The photograph in the inset shows the morphology of each individual. Numbers and letters show the chromosome number and karyotype, in green for Nomascus spp. and in orange for Hylobates lar. Classification of species was performed using karyotypes described by Couturier and Lernould .

Figure 4. Qualitative phylogenetic differences in the small ape.

The figure shows grouping of four genera of the small apes constructed by localization characteristics of AS. T, time period of transformation of the AS sequence to telomere regions. This topology was depicted with data from the present study and previous studies.