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Brief communication mtDNA variation in North Cameroon Lack of asian lineages and implications for back migration from Asia to sub-Saharan Africa.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 128:678 – 681 (2005)
Brief Communication: mtDNA Variation in North
Cameroon: Lack of Asian Lineages and Implications for
Back Migration From Asia to Sub-Saharan Africa
Valentina Coia,1 Giovanni Destro-Bisol,1* Fabio Verginelli,2 Cinzia Battaggia,1 Ilaria Boschi,3
Fulvio Cruciani,4 Gabriella Spedini,1 David Comas,5 and Francesc Calafell5
1
Department of Animal and Human Biology, University “La Sapienza,” 00185 Rome, Italy
Department of Oncology and Neurosciences, Section of Molecular Pathology, University “G. d’Annunzio,” and Center
for Research and Training on Cancer in Sub-Saharan Africa, University G. d’Annunzio Foundation,
66013 Chieti, Italy
3
Institute of Legal Medicine, Catholic University, 00168 Rome, Italy
4
Department of Genetics and Molecular Biology, University “La Sapienza,” 00185 Rome, Italy
5
Department de Ciències Experimentals i de la Salut, University “Pompeu Fabra,” 08003 Barcelona, Spain
2
KEY WORDS
mtDNA U6 haplogroup; Y-chromosome R1*-M173 haplogroup; Fulbe
ABSTRACT
The hypervariable region-1 and four nucleotide positions (10400, 10873, 12308, and 12705) of the
coding region of mitochondrial DNA (mtDNA) were analyzed in 441 individuals belonging to eight populations
(Daba, Fali, Fulbe, Mandara, Uldeme, Podokwo, Tali, and
Tupuri) from North Cameroon and four populations
(Bakaka, Bassa, Bamileke, and Ewondo) from South Cameroon. All mtDNAs were assigned to five haplogroups:
three sub-Saharan (L1, L2, and L3), one northern African
(U6), and one European (U5). Our results contrast with
the observed high frequencies of a Y-chromosome haplogroup of probable Asian origin (R1*-M173) in North Cameroon. As a first step toward a better understanding of the
evident discrepancy between mtDNA and Y-chromosome
data, we propose two contrasting scenarios. The first one,
here termed “migration and asymmetric admixture,” implies a back migration from Asia to North Cameroon of a
population group carrying the haplotype R1*-M173 at
high frequency, and an admixture process restricted to
migrant males. The second scenario, on the other hand,
temed “divergent drift,” implies that modern populations
of North Cameroon originated from a small population
group which migrated from Asia to Africa and in which,
through genetic drift, Y-chromosome haplotype R1*-M173
became predominant, whereas the Asian mtDNA haplogroups were lost. Am J Phys Anthropol 128:678 – 681,
2005. © 2005 Wiley-Liss, Inc.
In a recent study of 77 biallelic polymorphisms located
in the nonrecombining portion of the Y-chromosome, Cruciani et al. (2002) detected the haplotype R1*-M173 (YChromosome Consortium, 2002; Jobling and Tyler-Smith,
2003). It was found among six well-defined populations
from Cameroon (Fali, Tali, Uldeme, Fulbe, Daba, and
Ewondo), with the highest frequency in North Cameroon
(from 6.7% among the Tali to 95.2% among the Uldeme).
This finding has important implications for the peopling of
Africa, since it could signal an ancient back migration
from Asia (Cruciani et al., 2002). In fact, the haplotype
R1*-M173 harbors the derived allele at the M9 site, which
characterizes haplogroups K to R (Y-Chromosome Consortium, 2002; Jobling and Tyler-Smith, 2003) , all of nonAfrican origin (Underhill et al., 2001; Semino et al., 2000;
Wells et al., 2001; Cinnioglu et al., 2004; Luis et al., 2004).
Other lineages derived from the M9 superclade have not
been detected in sub-Saharan Africa, the only exception
being the haplotype K2 found among some sub-Saharan
populations (Cruciani et al., 2002; Luis et al., 2004). These
findings are difficult to reconcile with an African origin of
the R1*-M173 subclade, unless a considerable extinction
of lineages is assumed (Cruciani et al., 2002). Furthermore, according to present studies, the frequency of haplogroup R1*-M173 in Europe, the Middle East, and North
Africa seems to be substantially lower than in North Cam-
eroon (North Africa) (Bosch et al., 2001; Cruciani et al.,
2002; Cinnioglu et al., 2004; Luis et al., 2004; Arredi et al.,
2004). This makes it unlikely that the presence of R1*M173 in North Cameroon is due to recent gene flow from
neighboring regions.
Salas et al. (2002) suggested that the presence of the
haplotype R1*-M173 in northern Cameroon populations
could be due to recent gene flow from North Africa. These
authors maintained that the processes leading to the
present-day distribution of haplogroup R1*-M173 could
©
2005 WILEY-LISS, INC.
Grant sponsor: M.I.U.R.; Grant number: 2003054059; Grant sponsor: University of Rome “La Sapienza;” Grant number: G101819;
Grant sponsor: European Science Foundation; Grant number:
BFF2002-10206-E; Grant sponsor: Spanish Ministry of Science and
Technology; Grant number: BOS2001-0794.
*Correspondence to: Giovanni Destro-Bisol, Department of Animal
and Human Biology, University “La Sapienza,” P. le A. Moro 5, 00185
Rome, Italy. E-mail: destrobisol@uniroma1.it
Received 25 October 2003; accepted 29 June 2004.
DOI 10.1002/ajpa.20138
Published online 13 May 2005 in Wiley InterScience
(www.interscience.wiley.com).
mtDNA VARIATION IN NORTH CAMEROON
have followed the same route of the mtDNA haplogroup
U6, widespread among Berbers (Rando et al., 1998; Macaulay et al., 1999), which is thought to have arrived in
North Africa from the Near East between 20,000 –50,000
years ago. According to Salas et al. (2002), the Fulbe or
other pastoralists might have conveyed both mtDNA sequences belonging to the U6 and H haplogroups and the
haplotype R1*-M173 from Berbers to North Cameroon
populations. This hypothesis is based on the presence of
the Fulbe in North Cameroon and on the evidence that the
Fulbe who settled in Nigeria show signs of gene flow of
maternally transmitted characters from Berbers, namely
sequences belonging to the haplogroups U6 and H
(Watson et al., 1997).
As a logical development of the study by Cruciani et al.
(2002), we analyzed mtDNA variation in North Cameroon.
The present work is aimed at understanding whether the
presence of Y-chromosome haplotypes of Asian origin has
a counterpart in terms of maternally transmitted characters. It is also useful to test the role of the Fulbe from
Cameroon as possible carriers of maternal lineages from
Berbers to North Cameroon, since mtDNA data from this
area were not available to Salas et al. (2002).
MATERIALS AND METHODS
We analyzed mitochondrial variation in a total of 12
populations and 441 individuals from Cameroon. Informed consent was obtained from all donors. The sampling covers the eight populations from Cameroon studied
by Cruciani et al. (2002). In addition, we examined four
other populations: Mandara, Tupuri, and Podokwo from
North Cameroon, and Bassa from South Cameroon. For
information about the populations studied, readers are
referred to Table 2 and Figure 1 in Spedini et al. (1999).
Specimens collected in K3EDTA were maintained at 4°C
(for ⬍7 days) until their arrival at the Laboratory of Anthropology of the University of Rome “La Sapienza.”
Genomic DNA was extracted from blood by a standard
phenol-chloroform protocol (Gill et al., 1985). It was then
quantitated by direct comparison in agarose minigels.
We sequenced the hypervariable region-1 (HVR-1) from
np 16024 –16390 according to Vigilant et al. (1989), with
minor modifications. Each sequence was assigned to a
haplogroup according to the networks published by Salas
et al. (2002). A total of 102 haplotypes which could not be
unambiguously classified into L1, L2, or L3 haplogroups
on the basis of their HVR-1 sequence alone was further
analyzed for their variation at nucleotide positions 10400,
10873, 12308, and 12705 of the mtDNA coding region
which defines the almost exclusively non-African haplogroups M, N, R, and U. The SnapShot method (SNaPshot™ ddNTP Primer Extension Kit, Applied Biosystems)
was used to type those sites (Comas et al., 2004). The
samples assigned to haplogroup U6 were further investigated by a survey of the MnlI restriction site at np 11203,
whose presence is typical of the Ethiopian U6 mtDNAs,
and which distinguishes them from those of North Africa
(A. Torroni, unpublished data). Sequence data are available at the address: http://www.scienzemfn.
uniroma1.it/labantro/database.html.
RESULTS AND DISCUSSION
Five different haplogroups were found (Table 1): three
of sub-Saharan origin (L1, L2, and L3), one of European
origin (U5) (Richards et al., 2000), and one of North African origin (U6) (Rando et al., 1998; Macaulay et al., 1999).
679
Considering the overall sampling, the most frequent haplogroups were L3 (46.7%), L2 (26.5%), and L1 (25.2%),
which were observed in all 12 populations examined. All
sequences observed in South Cameroon belong to macrohaplogroup L. The non-African haplogroups U5 (0.9%) and
U6 (0.7%) were confined to North Cameroon, occurring
among the Fulbe and among the Podokwo and Uldeme,
respectively. All of the U6 mtDNAs lacked the MnlI site at
site 11203, which indicates that they do not belong to the
Ethiopian subclade of this haplogroup (A. Torroni, unpublished data).
We did not detect sequences belonging to haplogroups
currently found in Central and East Asia (superhaplogroups M (haplogroups M7–M10, C, D, E, and G), N (A,
N9, and Y), and R (R9, B, and F); Kivisild et al., 2002).
Therefore, according to our data, the processes leading to
the spread of Y chromosomes of Asian origin in North
Cameroon did not leave any detectable sign in terms of
maternally transmitted characters, at least if one considers the current mtDNA phylogeography of Asian populations. Certainly the lack of Asian sequences in our samples does not necessarily mean that such sequences are
absent from the populations. The probability of not finding
by chance a particular sequence that is present in a population at a frequency f in a sample of size N is given by ␣
⫽ (1 ⫺ f)N. Then for ␣ ⫽ 0.05 and an overall sample size of
441 chromosomes, we obtain a frequency value of 0.7%.
Considering only populations from North Cameroon,
where haplotype R1*-M173 is most frequent, the sample
size is 244 chromosomes, which leads to a maximum nondetectable frequency of 1.22%. Thus, with a 95% probability, it can be ruled out that Asian mtDNA lineages are
present in North Cameroon at frequencies over 1.22%,
whereas the Y-chromosome haplotype R1*-M173 is found
at frequencies of 7–95%, with an average of 39.5%.
Our study also points toward the existence of gene flow
from North Africa to North Cameroon. In fact, one of the
two U6 sequences found in northern Cameroon (in one
Podokwo and one Uldeme individual; HVR-1 transitions
at nucleotide positions 16172, 16219, and 16278 relative to
the Cambridge reference sequence; Anderson et al., 1991)
matches with sequences found among Berbers from Morocco, Mauritanians, West Saharans, and Canarians
(Rando et al., 1998, 1999; Brakez et al., 2001). The remaining U6 sequence (HVR-1 transitions at np 16172,
16219, and 16311), found in one Uldeme individual, is a
one-step neighbor of sequences found among Mauritanians, non-Berber Moroccans, and Wolof from Senegal
(Rando et al., 1998, 1999). These results suggest that the
U6 sequences found in the Podokwo and Uldeme could be
a signature of gene flow from North Africa. At the same
time, the presence of this mitochondrial haplogroup
among the population where R1*-M173 reaches its highest frequency (Uldeme) makes it worth testing the hypothesis that the Y-chromosomal haplogroup mentioned above
could have reached northern Cameroon starting from the
Near East, as suggested for U6 (Salas et al., 2002; Rando
et al., 1998; Macaulay et al., 1999). Even taking the abovementioned hypothesis for granted, a statistically significant difference between the frequency of R1*-M173 and
U6 in North Cameroon persists. In fact, U6 ranges from
0 –7% in North Cameroon, with an average frequency of
1.23%. These figures are much lower than those obtained
for the R1*-M173 in the same dataset (see above). Furthermore, the 95% confidence interval range of U6 for
North Cameroon is of 0 –2.6%, compared to 27.8 –52.4% for
R1*-M173 (recalculated from Cruciani et al., 2002). Fi-
2
4
2
5
2
2
2
10
29
15
15
4
7
6
3
10
34
9
27
13
25
16
21
2
15
14
6
24
21
6
2
7
6
2
4
7
20
15
4
15
5
5
12
11
5
5
8
11
4
5
10
2
6
11
5
5
12
For Bamileke and Ewondo, original data are reported in Destro Bisol et al. (2004). For other populations, sequence data are available at http://www.scienzemfn.uniromal.it/labantro/
database.html.
2
8
2
4
10
11
6
26
10
13
11
6
2
4
2
6
3
3
4
4
8
5
3
2
12
6
13
4
5
5
2
20
12
12
11
13
10
4
11
10
5
18
16
15
15
28
18
L3d
L3b
L3*
L2d
L2c
L2b
L2a
L2*
L1*
L1a
L1b
L1c
L1e
North Cameroon
Daba (20)
Fali (41)
Fulbe (34)
Mandara (37)
Podokwo (39)
Tali (20)
Tupuri (25)
Uldeme (28)
South Cameroon
Bakaka (50)
Bamileke (48)
Bassa (46)
Ewondo (53)
1
7
3
12
3
5
3
5
15
12
4
5
7
5
30
10
12
8
26
20
24
11
L3e
L3f
L3g
U5a
U
L3
Population
(no. of individuals)
Frequency of haplogroups (%)
L2
L1
nally, it is important to note that the high frequency of
R1*-M173 and the low frequency of U6 found in North
Cameroon contrast sharply with the low frequency of R1*M173 and the high frequency of U6 in North Africa (Bosch
et al., 2001; Cruciani et al., 2002; Cinnioglu et al., 2004;
Luis et al., 2004; Arredi et al., 2004; Salas et al., 2002).
Therefore, our study indicates a discrepancy between
Y-chromosomal and mitochondrial variation in North
Cameroon populations, either considering the current
phylogeography in Asia or assuming U6 to be the maternal counterpart of R1*-M173. This is not unexpected,
since the two genetic systems are transmitted independently. Previous studies showed that the phylogeography
of mtDNA and the Y chromosome may differ substantially
even in the same population. For instance, North Africans
and Near Eastern Arabs show a much larger maternal
than paternal sub-Saharan contribution (Plaza et al.,
2003; Richards et al., 2003).
We can imagine two extreme scenarios which could
explain difference which we have in the frequency of
“Asian” Y-chromosome and mtDNA lineages in North
Cameroon. In the first one, called “migration and asymmetric admixture,” a back migration from Asia to Africa
was conducted by groups carrying the Y-chromosome haplotype R1* -M173 at a high frequency. Such groups admixed with resident populations, but the admixture process involved only males of the migrant population. In the
second one, namely “divergent drift,” the present-day
North Cameroon populations originated from a small
group that migrated from Asia to Africa in which, through
genetic drift, Y-chromosome haplotype R1*-M173 became
the predominant Y-chromosome haplotype, whereas most,
if not all, Asian mtDNA lineages were lost. The lack of
robust information on movements of prehistoric populations to North Cameroon means that these scenarios must
be considered initial working hypotheses which need to be
supported by further data on Y-chromosomal and mitochondrial variation in Africa and Asia.
Finally, our results fail to support the hypothesis that
the Fulbe carried the U6 haplogroup into North Cameroon. In fact, the non-L sequences found in the Fulbe
from Cameroon differ substantially from those found
among the Berbers, since they belong to the U5 haplogroup (which has a very broad distribution in Eurasia).
The fact that the U5 Fulbe sequence (transitions at np
16189, 16192, 16270, and 16320) is a one-step derivative
of mtDNA types found in Moroccans (Brakez et al., 2001),
Saharawi, and Tunisians (Plaza et al., 2003) suggests that
this population had some genetic contact with North African populations. However, lacking a highly diagnostic
haplogroup such as U6, thought to be a Northwestern
African marker (Rando et al., 1998), our results do not
provide support to the role of the Fulbe from Cameroon as
U6 carriers to North Cameroon. Finally, the lack of the
two mtDNA haplogroups U6 and H in the Fulbe from
Cameroon already detected among the Fulbe from Nigeria
(Watson et al., 1997) provides evidence of a substantial
genetic heterogeneity among Fulbe populations from different areas. This feature is already noticeable in Y-chromosomal data (see Table 2 in Cruciani et al., 2002), where
the Fulbe from Burkina Faso lack completely haplogroup
R1*-M173. Such heterogeneity makes it difficult to apply
the results obtained for a Fulbe population of a certain
area to those settled in other areas.
U6
V. COIA ET AL.
TABLE 1. mtDNA haplogroup frequencies (%) in 12 populations from Cameroon1
680
mtDNA VARIATION IN NORTH CAMEROON
ACKNOWLEDGMENTS
We thank the blood donors whose availability made this
study possible. We are indebted to Rosaria Scozzari and
Cristian Capelli for their advice, and to Antonio Torroni
for sharing his unpublished data. This research was supported by grants from M.I.U.R. (Cofin Project “Dna e Biodemografia: Approccio Integrato allo Studio Della Mobilità
Umana,” grant 2003054059-005), the University of Rome
“La Sapienza” (Ricerche di Ateneo, contract grant
G101819) to G.D.B., the European Science Foundation
EUROCORES programme “The Origin of Man, Language
and Languages,” and the Spanish Ministry of Science and
Technology.
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